Rheology of drilling fluids in slim well designs

Thesis

Rheology of drilling fluids in slim

well designs

Study of the rheology of drilling fluids

as function of temperature, pressure

and composition

Nederlandse Aardolie Maatschappij B.V.

Sophia Sadi

Avans Hogeschool University of Applied Sciences

Chemical Engineering

Thesis

Rheology of drilling fluids in slim

well designs

Study of the rheology of drilling fluids as

function of temperature, pressure and

composition

Graduate: Sophia Sadi

sophia.sadi@shell.com ss.sadi@student.avans.nl

Institution: Avans Hogeschool University of Applied Sciences

Address: Lovensdijkstraat, Breda

Internship coördinator: Martin Bode m.bode@avans.nl

Supervisor: Benno de Vries

b.devries1@avans.nl

Company name: NAM (Nederlandse Aardolie Maatschappij)

Address: Schepersmaat 2, Assen

Mentor: Gert Lammers

gert.lammers@shell.com

Function: Team leader WE Design

Department: Well engineering

Supervisor: Hans van Velzen

Function: Senior Production Chemist

Department: Production Chemistry

Graduation period: 15-04-2013/ 06-09-2013

Version: 2.0

Foreword

As part of the program Chemical Engineering at Avans University of Applied Sciences in Breda, the 4th _{grade students are expected to}

complete the program with a graduation internship. The duration of this internship is five months. The students have the opportunity to search for a company that connects to the study. My preference went to the

Nederlandse Aardolie Maatschappij (NAM) because I am interested in one of the main activities of this company, namely the production of oil and gas. Planning a well and the drilling process itself is a complex technical process which I want to deepen myself into. It is also an innovative company that develops new techniques to work more cost effective, energy efficient and environmentally friendly. Through this internship, I do not only want to finished my thesis successfully, but also discover what the tasks of the various disciplines are within the NAM. My thanks go to my supervisor Hans van Velzen, my mentor Gert Lammers and the other Well Fluids team colleagues Peter Rijnen and Auke Pollema who support me with this project.

Place: Schepersmaat 2, Assen Date: 06-09-2013

Author: Sophia Sadi

Table of Contents

Foreword...3

Summary...6

1. Introduction...9

2. Fundamentals for determining the rheology of drilling fluids...13

2.1 Drilling fluids...13

2.2 Drilling fluid rheology...13

2.3 Definition of viscosity...13

2.4 Newtonian and Non- Newtonian fluids [1]_...14

2.5 Rheological models...14

2.5.1 Bingham Plastic Model...15

2.5.2 Power Law model [2]_...16

2.5.3 Herschel Buckley model...17

3. Fundamentals for predicting the pressure drop...18

3.1 Equivalent circulating density...18

3.2 Temperature and pressure effects on drilling fluid rheology...21

3.2.1 Predicted plastic viscosity and yield point by IDM...21

3.2.2 Predicted plastic viscosity by Politte [3]_...22

3.2.3 Predicted yield point by Politte [3]_...23

3.2.4 Discussion of plastic viscosity and yield point from Guzman-Andrade...23

4. Materials and Methods...25

4.1 Materials...25

4.2 Methods...29

5. Results and findings...30

5.1 Available rheology data...30

5.2 Rheological model...31

5.3 Bingham parameters as function of temperature and pressure...31

5.4 Comparison of the predicted en measured plastic viscosities...37

5.5 Comparison of the predicted and measured yield point...39

Conclusions...44

Recommendations...45

References...46

List of figures...48

List of explanatory words...51

List of abbreviations...53

Appendix I. Drilling fluid functions...54

Appendix II. Criteria for selecting a drilling fluid...55

Appendix III. Integrated Data Model (IDM)...57

Appendix IV. Fann 70/75 viscometer...59

Appendix V. Available and required rheology data...60

Appendix VI. Measured and predicted plastic viscosity and yield point values by Politte...61

Appendix VII. Measured and predicted plastic viscosity and yield point values by IDM...65

Appendix VIII. Duplicate measurements of the plastic viscosity and yield point...68

Appendix IX. Triplicate measurements of the plastic viscosity and yield point...69

Summary

Beside the Groningen gas field, there are about four hundred smaller gas fields discovered in the Netherlands. One of the challenges for the

Nederlandse Aardolie Maatschappij (NAM) is to take these smaller gas fields into production. To do this cost effective the need has been

recognized to drill smaller and therefore cheaper wells. When using smaller bore holes new challenges have to be overcome such as pressure losses by pipe friction, cutting transport, correction pipe rotation and large flow area reduction. During the planning phase the NAM uses the Integrated Data model (IDM) to identify these issues/concerns. A drilling fluid is a complex mixture of various types of base fluids and chemical compounds that must remain stable under various temperatures and pressures conditions in the well. When the NAM drilled some wells with the smaller borehole diameter they noticed higher pressures than IDM predicted. A potential problem identified by the Production Chemistry Well Fluids Team could be the rheology of drilling fluids under down hole conditions (small annuli, high temperature- high pressure). Incorrect prediction of pressure drop (for example due to improper rheology prediction) can cause several problems; the pressure cannot be controlled anymore.

The purpose of this project is to design a method or datasheet so that the rheological behaviour of drilling fluids and therefore the

pressure loss can be predicted more realistic.

First a literature study was performed to learn more about drilling fluids and the rheology of drilling fluids. The rheology behaviour of a drilling fluid can be described with: 1) Bingham Plastic model, 2) Power Law model and/or 3) Herschel-Buckley model.

Afterwards required measuring equipment was inventoried. Out of the inventory it was clear that the equipment required for rheology

measurements under down hole conditions was unavailable in NAM laboratory in Assen. The next step was measuring the rheology as

Model 800 viscometer by OFITE. Several mud systems have been measured. Rheology data under high pressure- high temperature conditions were obtained from colleagues from Shell laboratory in

Aberdeen and Norway and from the mud supplier Halliburton. Models to translate rheology data into down hole conditions have been found in the literature (IDM and Politte). Predicted values obtained with these models have been compared with the measured data available.

Out of this project it is concluded that:

1. At the moment realistic rheology data is not available for down hole conditions. With the datasets obtained in this project it is not

possible to make a datasheet or correlation with which a good prediction of rheological behaviour down hole can be made and therefore pressure drop prediction. To obtain more rheology data at down hole conditions a measuring tool is required. The Fann 70/75 viscometer seems to be the most suitable one.

2. The best model to describe a drilling fluid behaviour is the

Herschel- Buckley model because it describes the flow behaviour of most drilling fluids. When dealing with shear rates higher than 100 rpm, the Bingham Plastic model is the most practical to use. The model can be described by two parameters: plastic viscosity and yield point. These parameters are well understood by Well

Engineers and Mud Engineers in the office and in the field.

3. Plastic viscosity and yield point are both temperature, pressure and composition dependant.

4. In 21% of the cases the predicted plastic viscosity values calculated by making used of the equations as used in IDM don’t

correspondent with the measured values when the difference is less than ten. 53% of the predicted yield point values don’t correspondent with the measured values when the difference is less than three. When the temperature decreases starting at 20°C, the deviation for the plastic viscosity lies between 37 and 41. In extremely conditions (-1°C/138 bar and 5°C/159 bar) the deviation gets higher than 300. At a condition of 8°C and atmospheric

pressure the deviation for the measured and predicted plastic viscosity value is 92.

5. In 38% of the cases the predicted plastic viscosity values calculated by making used of Politte’s equations don’t correspond with the measured values when the difference is less than ten. 67% of the predicted yield point values don’t correspondent with the measured values when the difference is less than three. When the

temperature decreases starting at 20°C, the deviation for the plastic viscosity lies between 14 and 19. In extremely conditions (-1°C/138 bar and 5°C/159 bar) the deviation gets equal or higher than 70.

6. No correlation was found in the literature where composition of drilling fluids is taken into account.

Based on this project the following recommendations are made:

1. To be able to build a database or correlation for every mud system rheology data should be measured. First the temperature should be varied where pressure and composition (density) should keep

constant. And secondly the pressure should be varied where

temperature and composition should be kept constant. And at least the composition should be varied where the pressure and

temperature should be kept constant.

To obtain realistic rheology data under down hole conditions it is strongly recommended to purchase or rent the Fann 70/75

viscometer or source out to mud contractors who can measure the rheology at the required conditions (temperature range

between110- 160°C and pressure range 400-600bar).

2. Based on the comparison of the predicted rheology parameters calculated by IDM and the measured rheology parameters, the calculations in IDM should be check. If the rheology values calculated from equations used in IDM are more in line with the

measured rheology values, there is a certainty that the predicted pressure losses are more reliable.

3. The low end rheology (3 to 50 sec-1_{) can have a strong influence on}

the circulating pressure in the annulus, thus on ECD. If for the whole shear rates range a model have to be chosen than the recommended model to use is the Herschel- Buckley model.

1. Introduction

Background

This graduation internship took place at the Nederlandse Aardolie

Maatschappij, also known as the NAM. The project was performed by the Well Fluids team department under the guidance of Mr. Hans van Velzen. This team is part of the Production Chemistry department. This

background information describes who the NAM is, how Well Fluids team is part of this business and the relationship between the project and the organization which it operates.

The Nederlandse Aardolie Maatschappij

In 1943 Shell Exploration Company Netherlands found an oil field at Schoonebeek. After World War II Shell and Esso decided to join a capital injection into a new company that has to engage in the exploration and production of oil in the Dutch territory: The Nederlandse Aardolie Maatschappij, also called NAM. The NAM was founded on September 19th _{1947. The Shell Company has taken the executive tasks. Today the}

NAM has 1700 employees. The NAM is a joint venture of Shell and ExxonMobil. Each company is 50% shareholder. The daily management lies with the CEO Bart van de Leemput. The headquarter of the NAM is in Assen; in addition the NAM has also offices in Hoogezand and Den Helder.

The main activities of the NAM are: - Detection of oil and gas fields.

- Drilling of production and exploration wells. - Winning and sale of oil and/or gas.

- Cleaning up after completion of the above activities.

From company to department in which the graduation project took place.

The Well Fluids team is part of the Production Chemistry (PC) department. PC is on itself a division of Production Services. The manager of Production Services reports directly to the CEO.

The Production Chemistry organization in the Netherlands consists of five teams:

- Well Fluids team – service provider to Well Engineering and Well Construction.

- Laboratory – performs all chemical analyzes for the NAM. - Process Chemistry Onshore – service provider for Onshore-

production.

- Process Chemistry Offshore – service provider for Offshore- production.

- Chemical Management - controls information of chemicals and permits.

Well Fluids team

The Well Fluids team consists of three Shell/NAM employees. The team delivers its production chemistry support to well structures and well maintenance department. This work is done by providing chemical- technical support along with drilling fluids and cementing contractors. The drilling fluids contract lies now with the firm Halliburton Baroid and cement contract lies with Schlumberger. The relevant services of the Well Fluids team are:

- Making of drilling fluids and cement programs for drilling/ or maintenance of wells.

- Maximum production with minimal formation damage by appropriate choice of fluids.

- Cement integrity throughout the lifecycle of a well.

- Daily PC operational support for drilling and maintenance of wells. - Giving expert PC advice when planning and maintaining wells. - Giving support at well- related chemical permits.

- Contract management (drilling fluids and cement related contracts).

Annulus 10mm

Annulus 10mm

Motivation

The Groningen gas field is the biggest gas field onshore in Europe. This field is located in the Northwest German Basin extending over The Netherlands and Germany. Beside this big gas field there are about four hundred smaller gas fields in the Netherlands. The NAM contributes about 75% of the gas production in The Netherlands. Early 70’s the government decided that the priority of gas winning has to be won from the small gas fields. This was called the small- field’s policy. The idea behinds this is to buffer gas from the Groningen gas field for longer availability for the future. The NAM is continuously developing new techniques to work more cost effectively, energy efficient and

environmentally friendly. Those techniques allow the company to take smaller gas fields into production and get more gas of the existing fields. One of these new techniques is drilling and production from smaller borehole diameters. Those wells are called slim well designs or ultra slim well designs. The purpose is to exploit economically profitable.

Unlike big bore wells, many issues/concerns can occur when drilling with smaller borehole diameters as lifting up the cuttings in the annulus, well bore stability, cleaning of the bit and differential mud pressures and temperatures in the annulus. Although drilling fluids are complex mixtures of various types of base fluids and chemical compounds it must remain stable under various temperatures and pressures

conditions in the well. There are software tools (IDM = Integrated Data Model is one of them) that can predict pressure loss by pipe friction, cutting transport, correction pipe rotation and large flow area reduction during the planning of a well.

After the NAM drilled some slim wells, they noticed that the pressure was higher than predicted. In an earlier investigation into

higher than predicted pressures for slim well design it was observed that these were partially cause by the large

Flow area reduction of 50% Flow area reduction of 50% Annulus 20mm Annulus 20mm Annulus 10mm Annulus 10mm

annular flow area reduction (FAR) when circulating the 3.5’’ cemented completion.

The FAR over connections in the narrow annuli over 3.5’’-5’’ liner section can be 40% or more. In figure 1 an illustration of the FAR in narrow annulus is given. For normal sized wells is this less than 20%. The large annular FAR was taken into another study where Well Hydraulics

software updates were discussed. After the study was done IDM was updated by taken the correction for large annular flow area reductions into the model. For well engineering the problem was solved. The in IDM Software calculated pressures were brought more in line with the

measured pressures in the field.

Figure1. Flow area reduction in slim well designs.

Another potential problem identified by the Production Chemistry Well Fluids Team for the founded higher pressure could be the rheology of drilling fluids. When the flow area in de annulus gets smaller, more

pressure is exerted on the system while circulating the fluid. As the fluid is circulated in the wellbore, heat from the formation flows into the wellbore this causes an increase in fluids temperature. Drilling fluids rheology is pressure and temperature dependant so the rheology behaviour changes. This can cause pressure drop/pressure losses that can result in formation damage that further in the process may entail consequences such as uncontrolled gas production or the unavailability to drill/produce these wells. IDM requires real rheology data in order to get a good prediction of the pressure drop. A good pressure drop

prediction is important because this can overcome formation damage. IDM is a database developed by Shells for Wells department. This software requires detailed input data of the well such as the casing scheme, drill string, directional data, formation data, mud data etc. By using good detailed data, engineers can improve well planning.

The end result is important for the engineers who are responsible for the planning of a well. By building a catalog of standard liquid

descriptions in IDM, engineers can easily retrieve data. In this way profits can be achieved because each engineer can sort out the correct input data (pressure, temperature, drilling mud etc) when planning a well.

Purpose

The purpose of this graduation is to design a method or datasheet so that the rheological behaviour of drilling fluids and therefore the pressure loss can predict better. Hereby correlations should be established between the rheological data of the drilling fluid, the pressure and temperature.

The temperature and pressure effects on drilling fluids rheology have been investigated by literature research, measurements in the laboratory, discussions with colleagues and rheology data provided by colleagues from Aberdeen, Norway and mud contractor Halliburton.

Study organization

This thesis is composed of 5 chapters, which gives the introduction in chapter one, chapter 2 gives the fundamentals for determining the rheology of drilling fluids. The fundamentals for predicting the pressure drop can be read in chapter 3. The materials and methods that were used to obtain the rheological parameters values are given in chapter 4 and in chapter 5 the results and findings. Based on this project conclusions and recommendations were made. Most of the theoretical information and figures in this report can be find back in the reference list and list of figures. The following lists are the list of explanatory words and list of abbreviations. At least this thesis concludes appendixes I to IX.

2. Fundamentals for determining the rheology of

drilling fluids

The rheological properties of drilling fluids are important in the

calculation of circulating hydraulics, hole cleaning efficiency and barite sag. This chapter describes what drilling fluids are, the rheology of drilling fluids and how they are characterized.

2.1 Drilling fluids

Now a day’s not only vertical wells are drilled, but also horizontals. The objective of a drilling operation is to drill, evaluate and complete a well that will produce oil or gas efficiently. Not every reservoir is the same so the drilling fluid or also called mud has to be customized to suit the drilling process and reservoir conditions. Drilling fluids perform

numerous functions to help make this possible. In appendix I the drilling fluid functions [2] _{are described. Drilling mud is a suspension of solids in a}

liquid phase [14]_{. The liquid phase can be water based or oil based with}

various chemical additives. The amount and type of these additives are based on the formations to be drilled. Most drilling fluids are

pseudoplastic. Based on several criteria a mud selection can be made. The criteria for selecting a mud are given in appendix II.

2.2 Drilling fluid rheology

Rheology is the study of how drilling fluids deforms and flows [2]_{. One of}

the most influential rheological properties of a drilling fluid is its

viscosity. In the oilfield the term plastic viscosity and yield point are used to describe the rheological properties. The determination of drilling fluid rheological parameters are important for circulation hydraulics

calculations, hole cleaning efficiency, and prediction of barite sag in oil wells.

2.3 Definition of viscosity

Viscosity is a measure of the resistance of a fluid to deform under shear stress [2] _{and it is defined as the ratio of shear stress to shear rate. This}

defines how the fluid will flow. In equation 2.1 the formula [2] _{is given. The}

relationship between shear stress and shear rate is explained in figure [2]

2. The two fluid layers A and B are moving past each other when a force is applied. When a fluid is flowing, an existing force in the fluid opposes the flow. This force is known as the shear stress (τ) and it is measured as a force per unit area (see equation 2.2). The rate at which one layer is moving past the next layer is called the shear rate (ϒ) and it is therefore a velocity gradient. Equation 2.3 gives the formula [2]_.

Viscosity (µ) = shear stress (τ )

shear rate (ϒ ) (2.1) τ = F_A (2.2) ϒ (sec-1_{) =} V 2−V 1 d (2.3)

Figure2. Shear rate and shear stress.

2.4 Newtonian and Non- Newtonian fluids

Fluids for which the shear stress is directly proportional to the shear rate are called Newtonian. This results in a constant viscosity independently the flow of the fluid. Sir Isaac Newton discovered that the viscosity of those fluids changes only when the temperature and pressures changes.

When the applied shear rate and the resulting shear stress is not directly proportional, the fluid is called non- Newtonian. Most drilling fluids are non-Newtonian. Non-Newtonian fluids can be further classified in

pseudo-plastics (shear thinning) and dilatants (shear thickening). The fluid is pseudo-plastic when the viscosity decreases with increasing shear rate and dilatants when the viscosity increases with increasing shear rate.

2.5 Rheological models

The flow behaviour of drilling fluids can be described by using rheological models. A rheological model is a description of the

relationship between the shear rate and shear stress. The three most used models in the oil and gas industry are 1) The Bingham Plastic model, 2) The Power Law model and 3) The Herschel Buckley model.

2.5.1 Bingham Plastic Model

The Bingham Plastic model [2]

describes a fluid which required a force to initiate flow. That force is known as the yield point. After the force exceeded the fluid exhibits a constant viscosity with increasing shear rate. The slope of the line is called the plastic viscosity. From the Bingham

Plastic model two parameters can

be calculated; the yield point and the plastic viscosity.

Figure 3.Bingham Plastic values at Θ600 and Θ300.

In general these parameters are determined with the standardized model 800 viscometer by OFITE from shear rates at 511s-1 _{and 1022s}-1_{. This}

model characterizes fluids in the high shear rates range. The shear stress at a certain shear rate can be calculated using equation 2.4. Figure 3 illustrates the Bingham Plastic model. With equation 2.5 and 2.6 the plastic viscosity and yield point values can be calculated (when using the model 800 viscometer by OFITE).

τ =τ₀+µ_p∗ϒ (2.4)

τ = Shear stress [lb/100 ft2_]

τ0 = Yield point or shear stress at zero shear rate [lb/100 ft2]

µp = Plastic viscosity [cP]

ϒ = Shear rate [sec-1_]

PV = θ600 – θ300 (2.5)

PV = Plastic viscosity [cP]

Θ600 = Reading value from the viscometer at 600 rpm Θ300 = Reading value from the viscometer at 300 rpm

YP = θ300 – PV (2.6)

YP = Yield point [lb/100 ft2_]

Θ300 = Reading value from the viscometer at 300 rpm

2.5.2 Power Law model [2]

The Power law model is used to describe the flow behaviour of shear thinning fluids. In this model no stress is required to initiate flow (see figure 5). This model describes a fluid for which the viscosity decreases when shear rate increases. The shear stress at a certain shear rate can be calculated from equation 2.7. K is the consistency index which gives the viscosity of the fluid at a shear rate of 1 sec-1_{. The Power Law n index}

indicates a degree of non-Newtonian behaviour. n < 1 the fluid is shear thinning

n = 1 the fluid is Newtonian n > 1 the fluid is shear thickening

Figure 4 shows the Power Law model for different types of fluids. The constants n and K can be calculated from viscometer data measured with the model 800 viscometer at speeds of 300 and 600 rpm. With equation 2.8 and 2.9 the Power law index n and the consistency index K can be calculated.

τ =K∗ϒn _(2.7)

τ = Shear stress [lb/100 ft2] ϒ = shear rate [sec-1]

K = Consistency index [lb.sec-1_{/100 ft}2_]

n = (logτ 2_{τ 1})/(logϒ 2

ϒ 1)

(2.8)

K = τ 1

ϒ 1n (2.9)

τ1 = mud viscometer reading at lower shear rate (300 RPM) τ2 = mud viscometer reading at higher shear rate (600 RPM) ϒ1 = mud viscometer RPM at lower shear rate (300 RPM) ϒ2 = mud viscometer RPM at higher shear rate (600 RPM)

Figure 4.Effect of Power Law index “n” on fluid behaviour. Figure 5.Power Law model.

2.5.3 Herschel Buckley model

Another model that describes a drilling fluid behaviour is the Herschel Buckley model or modified Power law model. This model describes the flow behaviour as the Power Law model including the shear stress that is required to initiate flow. The shear stress can be calculated from

equation 2.10. τ = τ0 + K*ϒn

(2.10)

τ = shear stress [lb/100 ft2_]

τ0 = Yield point or shear stress at zero shear rate [lb/100 ft2]

ϒ = shear rate [sec-1_]

K = Consistency index [lb.sec-1_{/100 ft}2_]

n = Power Law index [-]

The differences of flow behaviour for the three models are shown in figure 6. The initiated force from the

between the Bingham Plastic model, which is highest, and the Power Law, which is the lowest.

Figure 6.Rheological models.

3. Fundamentals for predicting the pressure drop

Pressure losses can be predicted by making use of hydraulic behaviour prediction tools. The NAM uses the application IDM MoDrill to predict pressure losses while drilling in the planning phase of a well. This program simulates advanced drill string hydraulics and mechanics. To get a broader picture about IDM and the MoDrill application [10,11]

reference is made to appendix III. The IDM tool works optimal when planning a normal well, but when planning a slim hole well it is unknown if the predicted pressures are correct (in the field higher pressures have been observed than predicted). Accurate prediction of down hole drilling fluids rheology is important for hydraulics optimization and hole-

cleaning capabilities and can help to predict these pressures with a

higher accuracy. Rheological properties of drilling fluids may be different at down hole conditions than at measured conditions (50°C and

atmospheric). Evaluations of the effects of temperature and pressure on wellbore hydraulics are needed. As the well depth increases, the

temperature and pressure also increases. This chapter will discuss the equivalent circulating density and temperature/pressure effect on drilling fluid rheology.

3.1 Equivalent circulating density

The equivalent circulating density (ECD) of a drilling fluid is defined as the sum of the hydrostatic head or hydrostatic pressure of the fluid column, and the pressure loss in the

annulus due to fluid flow [5]_{. It is}

expressed as a density term at the point of interest. ECD is the outcome of the hydraulic calculations (in NAM IDM is used for this). The combination of mud weight pressures and frictional forces has to be below the fracture point of the

weakest formation and above the highest pore pressure that is expected (see figure 7). When the pressure exceeds the strength of a formation, it may result in a fracture and loss of drilling fluid. ECD can be calculated using equation 3.11 Figure 7.Balancing formation pressure. ECD = ρ + _{0.00981∗TVD}P (3.11) 26

ECD = Equivalent circulating density [kg/m3_]

ρ = mud density [kg/m3] TVD = True vertical depth [m] P = Annular pressure loss (kPa) Modeling ECD

Pressure losses in slim-hole drilling are higher than for conventional wells because of the very narrow annulus between the drill string and the borehole wall in slim wells. Parameters that are relevant in the ECD calculations [6] _{are shown in figure 8.}

Description of ECD calculation from picture 8:

- Rheology and density are temperature and pressure dependant.

- Viscosity of a drilling fluid is a function of shear rate and shear stress.

- Hydraulic diameter and circulation rate determine the shear rate and together with the viscosity and friction factor (Reynolds number) the frictional pressure drops in the annulus.

- When added the above point to the static density, the ECD at each point can be calculated.

Figure 8.Parameters that are relevant in ECD calculations.

The low end rheology (3 to 50 sec-1_{) can have a strong influence on the}

circulating pressure in the annulus, thus on ECD. In table 3.1 the shear rate range at a specific location in the circulating system is given. This table also shows the drilling fluid performance in a circulating system that is related to the speeds of the Model 800 viscometer by OFITE. Table 3.1: Relationship between equivalent shear rate of the viscometer and shear rate ranges in a circulating system.

28 Viscometer RPM Equivalent shear rate [sec-1_] 3 5.11 6 10.22 30 51.09 60 102.18 100 170 200 341 300 511 600 1022 Circulating system Location Shear rate

range [sec-1_] Tanks 1-5 Annulus 10- 500 Pipe 100- 700 Collar 700- 3000 Nozzles 10.000-100.000

3.2 Temperature and pressure effects on drilling fluid

rheology

In IDM software tool the drilling fluid rheology is corrected for

temperature and pressure. In the open literature two other methods have been found to predict the temperature and pressure effects on drilling fluid rheology. These are from 1) Mark D. Politte and 2) Guzman-Andrade. This paragraph contains information of how fluid rheology can predicted according to IDM, Politte and Guzman-Andrade.

3.2.1 Predicted plastic viscosity and yield point by IDM

The pressure losses can be predicted by putting the fluid properties into IDM. The input parameters for the fluid properties are given in figure 9.The input data requires rheology data which are measured at API standards conditions. For the viscosity law input, the Bingham plastic model, Power Law or Herschel- Buckley model can be chosen. For the fluid rheology the input parameters in figure 10 can be chosen. For more IDM information this report refers to appendix III. For the users of the tool it is not know what temperature and pressure correction model IDM used. The temperature and pressure corrections made by IDM were investigated by comparing the predicted with measured rheology data

(see chapter 5).

Figure 9.Input parameters of the fluid properties in IDM.

Figure 10.Input parameters for fluid rheology.

3.2.2 Predicted plastic viscosity by Politte [3]

Politte investigated the effect of temperature and pressure on drilling fluid rheology and reported his results in SPE paper 13458. To estimate the flow behaviour of drilling fluids under high temperature- high

pressure conditions, Politte uses the Bingham Plastic parameters. Politte proposed to calculate the theoretical plastic viscosity from equation 3.12. Before this calculation can be made, equation 3.13 and 3.14 should be calculated. Equation 3.13 gives the density formula that is needed in equation 3.14 which calculate the base oil viscosity at the temperature and pressure conditions of interest.

PVT,P = PV0* µT,P/µ0

(3.12)

PVT,P = plastic viscosity at the conditions of interest

PV0 = PV of the drilling fluid at reference conditions

(µ0) = base oil viscosity at the reference conditions [cP]

µ T,P = base oil viscosity at the temperature and pressure conditions of

interest [cP] ρ = A2 + B2PT + C2P + D2P2 + E2T + F2T2 (3.13) ρ = density [lb/gal] µ = P (TP)C1 10(A1 +B1T + D1TP + E1P + F1δ + G1/ρ) (3.14) 1000≤ P ≥ 15000 75≤ T ≥ 300 µ = viscosity [cP] T = Temperature [°F] P = Pressure [psi] A1 = -23.1888 A2 = 0.8807 B1 = -0.00148 B2 = 1.5235* 10 -9 C1 = -0.9501 C2 = 1.2806* 10 -6

D1 = -1.9776* 10-8 D2 = 1.0719 * 10-10 E1 = 3.3416* 10-5 E2 = -0.00036 F1 = 14.6767 F2 = -5.1670* 10-8 G1 = 10.9973

3.2.3 Predicted yield point by Politte [3]

Politte also calculate the theoretical value of yield point under high

temperature- high pressure conditions. He concluded that the yield point is not a strong function of pressure, and become less as temperature increases. Because of the chemical and particles effects that have to be considered, the temperature effects on yield point are hard to predict. He provides equation 3.15 for the prediction of yield point of the drilling fluid at the temperature and pressure of interest.

YP = YP0 ¿ A 3+B 3 T −1 +C 3T−2 A 3+B 3 T 0−1+C 3T 0−2 (3.15) 90 ≤ T ≥ 300

YP = yield point of the drilling fluid at the temperature of interest [lb/100 ft2_]

YP0 = yield point at the reference conditions [lb/100 ft2]

T = Temperature [°F]

A3 = -0.186 B3 = 145.054 C3 = -3410.322

The predictions as proposed by Politte have been compared with measured data. This will be discussed in chapter 5.

3.2.4 Discussion of plastic viscosity and yield point from Guzman-Andrade

In a study performed byJ.V. Fisk and D.E. Jamison [16] _{they concluded that}

the physical properties of drilling fluids were controlled by using additives that absorb liquid and disperse into the liquid phase of the mud. They concluded that the physical properties for WBM changes with increasing temperature because WBM contains bentonite clay. For OBM there are not large changes in the physical properties of the drilling fluids with increasing temperature. They uses a formula that was founded by Guzman- Andrade for predicting the temperature and pressure effects on plastic viscosity for oil based fluids. The Guzman- Andrade formula is given in equation 3.16. C1, M1 and M2 are constants that were

determined by the least- squares analysis of data obtained with a dynamic HPHT system.

µ

=

µ

exp (

p

(3.16)

µ

µ

P = Pressure of the fluid for the viscosity in question T = Temperature of the fluid for the viscosity in question

C1 = 0.15 M1 = 0.02 M2= 222

Based on the measurements in the study and predicted values by Guzman Andrade the author concluded that the change in PV with temperature is more dependent on the base oil than the additives in the fluids and that the changes are not greatly dependent on pressure. For the YP changes the author observed that the temperature effects can be attributed to an increase in kinetic energy of the particles in the fluid.

The solid/liquid interactions were overcome by the increase in the total energy of the fluid which allows fluid particles to flow more freely.

Because this model can only predict the plastic viscosity (not the yield point), no further attention has been given to this model.

4. Materials and Methods

This chapter outlines the methods that were used to measure the

rheology of drilling fluids as function of temperature and pressure. First the materials that have contributed to the research are summed.

4.1 Materials

All materials that supported the research are listed in this paragraph. The materials that were used are different mud systems and equipments to determine the rheology of drilling fluids. The mud systems that were used to determine the rheology are the same as the mud systems used by the NAM. The supplier of the mud systems are Halliburton Baroid and M-I Swaco. Besides for the mud systems from Halliburton and M-M-I Swaco, rheology calculations were also made for mud systems that are not used in the Netherlands but in Aberdeen and Norway. The rheology of those mud systems were measured under high pressure and high temperature conditions in the laboratory of Shell in Aberdeen and Norway.

Mud systems from Halliburton Baroid

- OBM Enviromul 1.39sg

- OBM Enviromul 1.40sg

- OBM Enviromul 1.50sg

- OBM Enviromul 1.63sg Mud systems from M-I Swaco

- KCL polymer 1.23sg

- KCL polymer 1.50sg

Mud systems from Aberdeen and Norway

- WBM 1.20sg

- OBM 1.20sg

- OBM 1.08sg

Equipment

- Model 800 viscometer by OFITE [7]

This model viscometer is used to determine the rheology of fluids under various temperature ranges and atmospheric pressure. The model 800 is an 8 speed viscometer with 3, 6, 30, 60, 100, 200, 300 and 600 rpm. This model

viscometer is an alternative of the Fann 35 viscometer that is also used for laboratory rheology measurements under API

standards. The model 800

viscometer determines the shear rate/ shear stress ratio as know as the flow characteristics of oils and drilling fluids over various temperature and time ranges at

atmospheric pressure. The Model 800 viscometer by OFITE is shown in figure 11. This figure includes the corresponding parts (rotor, splash guard, bob, sleeve and platform).

Figure 11.Model 800 viscometer by OFITE

The following steps have to be taken when measuring the viscosity:

- Mix the sample on the “STIR” setting for 10 seconds while heating or cooling the fluid.

- Monitor the temperature with a thermometer.

- Continue to mix the sample until it reaches the target temperature.

- Rotate the knob to one of the speed settings. On the right side of figure 10 the speed selector knob is given. The button lies at the top of the Model 800 viscometer.

- Record the reading and the temperature when the dial reading stabilizes. On the left side of figure 12 the dial reading can be seen.

Figure 12.The top view of the Model 800 viscometer.

With the readings from the Model 800 viscometer the following equations that accounts for the rheology of drilling fluids can be calculated:

1) Plastic viscosity in centipoises (cP) = 600 RPM reading – 300 RPM reading

2) Yield point in pounds/100 square feet (lb/100 ft2_{) = 300 rpm – plastic}

viscosity

3) Apparent viscosity (cP) = 600 RPM reading /2

After every measurement the viscometer must be cleaned by first removing the sleeve from the rotor and then remove the bob. After the bob is removed, the splash guard can be removed and the bob shaft can wiped down. All the removed parts can be cleaned with soap and water and dry sophistically.

These speeds of the Model 800 viscometer by OFITE are related to the drilling fluid performance in a circulating system9_{. Table 3.1 in the}

previous chapter outlines this relationship.

- Hamilton Beach mixer [8]

The Hamilton Beach mixer is used in the laboratory to mix or shear drilling fluids in a homogeneous fluid. Most drilling fluids contain a base liquid and additives that must be dissolved mechanically dispersed into a homogeneous mixture. This mixer confirms to the API

Specification 13A and is applied with the API recommended mud impeller blade for mixing

WBM and OBM. In figure 13 the Hamilton Beach mixer is shown.

F

Figure 13.Hamilton Beach mixer.

- OFITE Universal Heat cup [15]

Cup heaters are designed for controlling the temperature of

drilling fluids when measuring the readings with a viscometer. The fluid can be heat-up till a maximum

temperature of 93°C is reached. When the pilot light turns on, the set

temperature is reached. It takes about 15 minutes to heat- up. The drilling fluid has to be put in a stainless steel

cup and then in the cup heater as shown in figure 14.

Figure 14.OFITE Universal Heat cup.

- Fluke 52 kj Thermometer

The mud temperature was controlled with the Fluke thermometer model 51 kj,

shown in figure 15. The readouts are in °C. The fluid temperature was measured by

putting the thermocouple into the stainless steel cup when it is filled with mud.

Figure 15.Fluke

thermometer model 51 kj.

Note:

This study needed rheology data under high pressures and high temperatures. For the high temperature and high pressure

measurements a Fann 70/75 viscometer is required. Because of the unavailability of the equipment in the laboratory of NAM in Assen, a

description of the equipment is not taken in this chapter. For a description of the Fann 70/75 viscometer see appendix IV.

4.2 Methods

In this paragraph the performed procedure for measuring the rheology of Enviromul 1.39sg, 1.51sg and 1.63sg is described. First the viscometer readings have to be measured.

Measuring viscometer readings 1. Shake the mud monster.

2. Decant the mud into the Hamilton Beach mixer cup till the fill line is reached.

3. Mix the mud for 10 minutes with the Hamilton Beach mixer. 4. Decant into the viscometer cup till the fill line is reached. 5. Heat the mud till the temperature of interest.

6. Place the cup under the viscometer and confirm it so that the sleeve of the viscometer is immersed in de mud monster till the fill line is reached.

7. Adjust the speed to 600 rpm. 8. Write down the reading.

9. Repeat step 7 and 8 for the other 7 speed dials. Calculate the viscosity

- Calculate ϒ [sec-1_{] by multiplying the rpm with 1.703}

- Calculate τ [lb/100 f2_{] by multiplying the viscometer reading with}

1.0678

- Calculate the viscosity [cP] for each shear rate with equation 2.1. Calculate the plastic viscosity and yield point.

- Calculate PV [cP] with equation 2.5.

- Calculate YP [lb/100 ft2_{] with equation 2.6.}

5. Results and findings

Using the method describe in chapter 4 and the provided data from

colleagues, the rheology data for the mud systems are given in paragraph 5.1. For these mud systems a rheological model was chosen to describe their flow behaviour (see paragraph 5.2) With the parameters of the chosen model a comparison has been made between the measured

rheology values and the predicted rheology values by making used of the equations used in IDM and the equations from Politte (see equations in chapter 2 and 3).

5.1 Available rheology data

An overview of the available rheology data measured under various temperatures and pressure ranges is given in this paragraph (see table 5.2). The data from mud systems 1, 2, 3, 5 and 6 were obtained by measurements performed in laboratory of NAM in Assen and the data of mud systems 7, 8, 9 and 10 were provided by colleagues from the

laboratory of Shell in Aberdeen and Norway. Mud system 4 has been provided by Halliburton (preferred supplier NAM).

Table 5.2: Overview of the rheology data at various temperature and pressure ranges.

Mud system Temperature [°C] Pressure

[bar] 1 Enviromul 1.39sg 20, 30, 40, 50, 60 70, 80 atmospheric 2 Enviromul 1.51sg 20, 30, 40, 50, 60 70, 80 atmospheric 3 Enviromul 1.63sg 20, 30, 40, 50, 60 atmospheric

70, 80 4 Enviromul 1.40sg 50 atmospheric 5 KCL polymer 1.23sg 20 50 atmospheric 6 KCL polymer 1.50sg 20 50 atmospheric 7 WBM 1.20sg -1, 8, 49, 85, 121 Atmospheric, 138, 517, 1034 8 OBM 1.20sg -1, 8, 49, 85, 121 Atmospheric, 138, 517, 1034 9 OBM 1.08sg 5, 45, 49, 66 Atmospheric, 159, 248, 324 10 OBM 2.03sg 50, 100, 160 Atmospheric, 100, 200, 300, 450, 600, 750, 820, 950 The available rheology data measured at certain temperature and pressure ranges and the rheology data at required conditions were plotted in a table (see appendix V). Out of the table it can be seen that rheology data at required conditions is not available. The required

temperature range to measure the rheology of drilling fluids in slim wells lies between 110°C and 150°C. The pressure range lies between 400 and 600 bar.

5.2 Rheological model

In order to characterize the flow behaviour of drilling fluids under

various pressure and temperature conditions the Bingham Plastic model has been chosen. This model was used because it generates realistic rheology values when the shear rates are above 100 rpm. Another reason why chosen for this model is because of its non-complexity calculations and it is the most practical to use. Furthermore these parameters are well understood by mud engineers working in the oil and gas industry. If

for the whole shear rates range a model have to be chosen than the recommended model to use is Herschel- Buckley model.

5.3 Bingham parameters as function of temperature and

pressure

In this paragraph the effect of temperature and pressure on the Bingham Plastic parameters, PV and YP are discussed. For the temperature effect the mud systems 1, 2 and 3 were taken into account and mud systems 9 and 10 for the pressure effect. The mud numbers applies to table 5.2. The PV and YP values that were used for creating the graphs are given in appendix VI. The measurements of mud systems 1, 2 and 3 were

performed trice. See appendix VIII for the duplicate and appendix IX for the triplicate measurements of the plastic viscosity and yield point. Discussion of plastic viscosity for mud systems 1, 2 and 3 as function of temperature

Mud system 1, 2 and 3 are the same mud systems with different

densities. The PV was measured with the OFITE model 800 viscometer under different temperature ranges and atmospheric pressure to see what the temperature effect is. At a temperature till 80°C the viscosity of the mud was measured. The effect of temperature on plastic viscosity for mud system 1, 2 and 3 is given in figure 16.

Figure 16.Temperature effect on plastic viscosity for OBM- Enviromul 1.39sg, 1.51sg and 1.63sg.

Out of the graph in figure 16 it can be seen that 1) the plastic viscosity of all mud systems decreases when the temperature increases and 2) the plastic viscosity increases when the density increases.

Discussion of yield point for mud systems 1, 2 and 3 as function of temperature

The YP for these mud systems were measured with the OFITE model 800 viscometer under different temperature ranges and atmospheric

pressure to see what the temperature effect is. The maximum

temperature at which the mud was measured was 80°C. The effect of temperature on yield point for mud system 1, 2 and 3 is given in figure 17.

Figure 17.Temperature effect on yield point for OBM- Enviromul 1.39sg, 1.51sg and 1.63sg.

Out of the graph in figure 17 it can be seen that 1) there is no regularity in the yield point values for the three mud systems when the temperature increases and 2) the same effect occurs as in point one when density increases.

Discussion of plastic viscosity for mud system 9 as function of pressure and temperature

OBM 1.08sg was chosen to describe the effect of pressure at one temperature range. This mud system was chosen because of all the available rheology data, this was the only mud system where the

pressure effect at one temperature range could be describe and also. Out of this graph the temperature effect also can be seen. The pressure and temperature effect on plastic viscosity for mud system 9 is given in figure 18. The mud was measured at:

- 5°C at atmospheric pressure

- 45°C at 248 bar.

- 49°C at atmospheric pressure, 159, 248 and 324 bar.

Figure 18.Pressure and temperature effect on plastic viscosity for OBM 1.08sg.

Figure 18 shows that the PV increases when the pressure increases at 49°C. It can also be seen that the PV increases/decreases when the temperature decreases/increases

Discussion of plastic viscosity for mud system 10 as function of pressure The pressure effect on plastic viscosity for OBM 2.03sg is given in the graph shown in figure 19. This mud system was measured at:

- 50°C at atmospheric pressure, 100 bar and 200 bar.

- 100°C at 300, 450 and 600 bar.

- 160°C at pressure of 750, 820 and 950 bar.

Figure 19.Pressure effect on plastic viscosity for OBM 2.03sg.

Out of figure 19 it can be seen that 1) the PV increases when the pressure increases and 2) the PV decreases when temperature and pressure increases at the same time.

Discussion of yield point for mud system 9 as function of pressure and temperature

The pressure and temperature effect on yield point for mud system 9 is given in figure 20. The mud system was measured at:

- 5°C at atmospheric pressure

- 45°C at 248 bar.

- 49°C at atmospheric pressure, 159, 248 and 324 bar.

Figure 20.Pressure and temperature effect on yield point for OBM 1.08sg.

Figure 20 shows that the YP at 49°C increases when pressures increases, but shows a rapid increase when the pressure increases from 248 bar to 324 bar. It also can be seen that the YP increases when temperature decreases and decreases when temperature increases.

Discussion of yield point for mud system 10 as function of pressure The pressure effect on yield point for OBM 2.03sg is given in the graph shown in figure 21. This mud system was measured at:

- 50°C at atmospheric pressure, 100 bar and 200 bar.

- 100°C at 300, 450 and 600 bar.

- 160°C at pressure of 750, 820 and 950 bar.

Figure 21.Pressure and temperature effect on yield point for OBM 2.03sg.

Out of figure 21 it can be seen that 1) from the measurements that were taken at 50°C, the YP increases when pressure increases 2) from the measurements that were taken at 100°C, YP stays stable and 3) from the measurements that were taken at 160°C, the YP increases from 750 bar till 820 bar and remain stable from 820 bar till 950 bar.

5.4 Comparison of the predicted en measured plastic

viscosities

In this paragraph the measured and predicted plastic viscosity values will be compared and discussed. The predicted values were obtained by

making used of equations used in IDM (see equations in reference 4) and equations from Politte (see equations in chapter 3 for the plastic

viscosity). The measured values were obtained from the equations given in chapter 2. The graphs were made from the measured and predicted values given in appendix VI and VII.

Discussion of the measured PV and predicted PV by making used of the calculations used in IDM

The measured and predicted PV values were plotted in a graph (see figure 22). The line trough the origin indicates the one to one ratio between the measured and predicted PV. This indicates that how closer the points are of the line, how accurate the calculations are. Out of figure 22 it can be seen that most of the predicted PV values from the mud systems correspondent with the measured values, except in cases where the temperature is lower than 20°C. The two points which deviates far from the line, were measured at -1C°, 5C° and 8C°.

Figure22. Measured and predicted plastic viscosity by IDM.

A total of 43 measured and predicted PV values were plotted in the graph. The difference between the measured and predicted PV values was calculated. Out of the 43 differential values, 34 values had a deviation less than 10 and 27 values had a deviation less than 5. Deviation less than 10 PV units:

(34/43) * 100 = 79%

Deviation less than 5 PV units: (27/43) * 100 = 63%

Discussion of the measured PV and predicted PV by Politte

The measured and predicted PV values were plotted in a graph (see figure 23). The line trough the origin also indicates the one to one ratio between the measured and predicted PV. Out of figure 23 it can be seen that the predicted values correspondent with the measured values, except in cases where the temperature is lower than 20°C and for WBM. The three points which deviates far from the line, were measured at -1C°/138 bar and 5C°/159bar.

Figure 23.Measured and predicted plastic viscosity by Politte.

A total of 42 measured and predicted PV values were plotted in the graph. The difference between the measured and predicted PV values

was calculated. Out of the 42 differential values, 26 values had a deviation less than 10 and 21 values had a deviation less than 5. Deviation less than 10 PV units:

(26/42) * 100 = 62%

Deviation less than 5 PV units: (21/42) * 100 = 50%

5.5 Comparison of the predicted and measured yield

point

In this paragraph the measured and predicted yield point values will be compared and discussed. The predicted values were obtained by making used of the equations used in IDM (see equations in reference 4) and equations from Politte (see equations in chapter 3 for the yield point). The measured values were obtained from the equations given in chapter 2. The graphs were made from the measured and predicted values given in appendix VI and VII.

Discussion of the measured YP and predicted YP by IDM

In figure 24 the measured and predicted YP values are given. The line through the origin indicates the one to one ratio for the measured and predicted values. Figure 24 shows that the measured and predicted values deviate far from each other, except for OBM 2.03sg.

Figure 24.Measured and predicted yield point by IDM.

A total of 43 measured and predicted YP values were plotted in the graph. The difference between these 43 measured and predicted YP values were calculated. Out of the 43 differential values, 26 values had a deviation less than 5 and 20 values had a deviation less than 3.

Deviation less than 5 YP units: (26/43) * 100 = 60%

Deviation less than 3 YP units: (20/43) * 100 = 47%

Discussion of the measured YP and predicted YP by Politte

The measured and predicted YP values were plotted in the graph shown in figure 25. The line through the origin gives a one on one ratio for the measured and predicted values. The graph shows that the measured and predicted values also differ very much from each other, except for OBM 1.39sg, OBM 1.51sg and OBM 1.63sg

Figure 25.Measured and predicted yield point by Politte.

A total of 42 measured and predicted YP values were plotted in the graph. The difference between the measured and predicted YP values was calculated. Out of the 42 differential values, 23 values had a deviation less than 5 and 14 values had a deviation less than 3. Deviation less than 5 YP units:

(23/42) * 100 = 55%

Deviation less than 3 YP units:

(14/42) * 100 = 33%

5.6 Effect of composition on drilling fluid rheology

To show the effect of composition on drilling fluid rheology, two graphs were made that contains all the available mud systems that were

measured at 50°C and atmospheric pressure. The plastic viscosity and yield point were compared as function of composition. In figure 26 the effects of composition on plastic viscosity is shown and in figure 27 the effect of composition on yield point. This criterion was taken into the study because in IDM the composition effects are not taken into account. Discussion of plastic viscosity as function of composition

The plastic viscosity values for all mud systems have been plotted in a graph shown in figure 26.

This graph shows that the plastic viscosity values for all mud systems are different and is therefore a function of composition as well for OBM and WBM systems.

0 5 10 15 20 25 30 35 40

Plastic viscosity of different mud systems at 50°C and atmospheric pressure

OBM Enviromul 1.39 sg OBM Enviromul 1.51 sg OBM Enviromul 1.63 sg OBM Enviromul 1.40 sg WBM KCl Polymer 1.23 sg WBM KCl Polymer1.50 sg WBM 1.2 sg OBM 1.2 sg OBM 1.08 sg OBM 2.03 sg Plastic viscosity [cP] M u d s ys te m

Although the densities of OBM Enviromul 1.39sg and OBM Enviromul 1.40sg are close to each other, the PV values differ much. In contrast to OBM 1.63sg, the PV value of OBM Enviromul 1.39sg is almost the same as OBM Enviromul 1.63sg. The rheology of OBM 1.40sg was obtained by the mud supplier itself (Halliburton) and the rheology of OBM Enviromul 1.39sg. 1.51sg and 1.63sg were obtained by measurements in the NAM laboratory in Assen. Those three mud systems were taken from the mud plant. The big difference in PV value could be the fact that OBM

Enviromul 1.40sg was a mixture of new and return mud. Recycle mud contains more solid particles (drilled particles) than new mud. The

different PV values of the mud systems in figure 26 shows that every fluid can have specific rheology behaviour most probably caused by the type and concentration of chemical additives. This statement also applies for the yield point.

Discussion of yield point as function of composition

The same mud systems and temperature- pressure conditions were used as for the effect of composition on plastic viscosity. The yield point values for all mud systems have been plotted in a graph shown in figure 27. This figure shows that the yield point values for all mud systems are not the same and is therefore a function of composition.

0 5 10 15 20 25 30 35

Yield point of different mud systems at 50°C and atmospheric pressure

OBM Enviromul 1.39 sg OBM Enviromul 1.51 sg OBM Enviromul 1.63 sg OBM Enviromul 1.40 sg WBM KCl Polymer 1.23 sg WBM KCl Polymer1.50 sg WBM 1.2 sg OBM 1.2 sg OBM 1.08 sg OBM 2.03 sg Yield point [lb/100ft^2] M u d s ys te m

Conclusions

The purpose of this project was to design a method or datasheet so that the rheological behaviour of drilling fluids and therefore the pressure loss can predict better. The temperature and pressure effects on drilling fluids rheology have been investigated by literature research,

measurements in the laboratory, discussions with colleagues and

rheology data provided by colleagues from Aberdeen, Norway and mud contractor Halliburton.

Based on the work the following conclusions are made:

7. At the moment realistic rheology data is not available for down hole conditions. With the datasets obtained in this project it is not

possible to make a datasheet or correlation with which a good prediction of rheological behaviour down hole can be made and therefore pressure drop prediction. To obtain more rheology data at down hole conditions a measuring tool is required. The Fann 70/75 viscometer seems to be the most suitable one.

8. The best model to describe a drilling fluid behaviour is the

Herschel- Buckley model because it describes the flow behaviour of most drilling fluids. When dealing with shear rates higher than 100 rpm, the Bingham Plastic model is the most practical to use. The model can be described by two parameters: plastic viscosity and yield point. These parameters are well understood by Well

Engineers and Mud Engineers in the office and in the field.

9. Plastic viscosity and yield point are both temperature, pressure and composition dependant.

10. In 21% of the cases the predicted plastic viscosity values calculated by making used of the equations as used in IDM don’t correspondent with the measured values when the difference is less than ten. 53% of the predicted yield point values don’t

correspondent with the measured values when the difference is less than three. When the temperature decreases starting at 20°C, the deviation for the plastic viscosity lies between 37 and 41. In extremely conditions (-1°C/138 bar and 5°C/159 bar) the deviation gets higher than 300. At a condition of 8°C and atmospheric

pressure the deviation for the measured and predicted plastic viscosity value is 92.

11. In 38% of the cases the predicted plastic viscosity values calculated by making used of Politte’s equations don’t correspond with the measured values when the difference is less than ten. 67% of the predicted yield point values don’t correspondent with the measured values when the difference is less than three. When the temperature decreases starting at 20°C, the deviation for the plastic viscosity lies between 14 and 19. In extremely conditions (-1°C/138 bar and 5°C/159 bar) the deviation gets equal or higher than 70.

12. No correlation was found in the literature where composition of drilling fluids is taken into account.

Recommendations

Based on this project the following recommendations are made:

4. To be able to build a database or correlation for every mud system rheology data should be measured. First the temperature should be varied where pressure and composition (density) should keep

constant. And secondly the pressure should be varied where

temperature and composition should be kept constant. And at least the composition should be varied where the pressure and

To obtain realistic rheology data under down hole conditions it is strongly recommended to purchase or rent the Fann 70/75

viscometer or source out to mud contractors who can measure the rheology at the required conditions (temperature range

between110- 160°C and pressure range 400-600bar).

5. Based on the comparison of the predicted rheology parameters calculated by IDM and the measured rheology parameters, the calculations in IDM should be check. If the rheology values calculated from equations used in IDM are more in line with the measured rheology values, there is a certainty that the predicted pressure losses are more reliable.

6. The low end rheology (3 to 50 sec-1_{) can have a strong influence on}

the circulating pressure in the annulus, thus on ECD. If for the whole shear rates range a model have to be chosen than the recommended model to use is the Herschel- Buckley model.

References

[1] American Petroleum Institute (2010). I and Hydraulics of Oil-well

Fluids: API recommended practice 13D. Sixth edition

Washington DC: API Publishing Services

[2] M-I SWACO (1998). Drilling Fluids Engineering Manual. Revision No: A-0

[3] Politte, M.D. (1985). Invert Oil Mud I as a function of Temperature

and Pressure

New Orleans, Louisiana: Amoco Production Co.

[4] Calculations IDM SIEP 97-5372 MoDrill Extensions and Enhancements; Appendix A.

[5] Shell Wiki. Equivalent circulating density.

http://www.wiki.shell.com/wiki/index.php/Equivalent_circulating_density Consulted August 8th ₂₀₁₃

[6] Narayan Singh, S., Jong, S.H. ECD Modeling in Slim Hole: To

compare accuracy of ECD modeling between IDM and WellPlan in slim hole application.

[7] Windows Internet Explorer. Model 800 Viscometer. http://www.ofite.com/instructions/130-10.pdf

Consulted August 8th ₂₀₁₃

[8] Products/Global Drilling Products. Mixers-Hamilton Beach. http://www.globaldrillingproducts.com/en/products/fann-laboratory-equipment/oil-well-cement-testing/blenders-and-mixers.html

Consulted August 9th ₂₀₁₃

[9]IDF Technical Manual: The Advanced Technology of International

Drilling Fluids 1988.

Aberdeen: International Drilling Fluids Limited of IDF House.

[10] Using IDM

http://www.shell.com/pt/business_units/techit/subsurfacesoftware/platfor m/well_delivery/using_idm.html

[11] MoDrill: Integrated Hydraulics & Mechanics IDM Well Engineering Applications (2013).

Shell Exploration & Production [12] Worldwide Baroid Laboratories

http://www.hrheologyton.com/public/bar/contents/Brochures/Web/H0551 4.pdf

Consulted August 12th ₂₀₁₃

[13] Laboratory Facilities – GEO Drilling Fluids

http://www.geodf.com/index.cfm/fuseaction/Pages.Page/id/306 Consulted August 12th ₂₀₁₃

[14] Suhascaryo Nur, Nawangsidi Dody, handayani Sri Rejeki. (2005).

Laboratory Study of High Temperature Additive to I Properties of Drilling Mud under Dynamic Conditions.

Indonesia: UPN Veteran

[15] Recipientes de Calentamiento y Termovasos – Lhoil http://www.lhoildemexico.com.mx/thermocups.html Consulted August 16th ₂₀₁₃

[16] Fisk J.V, Jamison D.E. Physical Properties of Drilling Fluids at High

Temperatures and Pressures.

Baroid Drilling Fluids

List of figures

Figu re

Reference 1 Flow area reduction in

slim well designs. 2 Shear rate and shear

stress.

M-I SWACO (1998). Drilling Fluids Engineering Manual. Revision No: A-0 3 Bingham Plastic values

at θ600 and θ300.

M-I SWACO (1998). Drilling Fluids Engineering Manual. Revision No: A-0 4 Effect of Power Law

index “n” on fluid behavior.

M-I SWACO (1998). Drilling Fluids Engineering Manual. Revision No: A-0 5 Power Law model. M-I SWACO (1998). Drilling Fluids

Engineering Manual. Revision No: A-0 6 Rheological models M-I SWACO (1998). Drilling Fluids

Engineering Manual. Revision No: A-0 7 Balancing formation

pressure.

http://www.wiki.shell.com/wiki/index.ph p/Equivalent_circulating_density

8 Parameters that are relevant in ECD calculations.

Narayan Singh, S., Jong, S.H. ECD

Modeling in Slim Hole: To compare accuracy of ECD modeling between IDM and WellPlan in slim hole

application.

9 Input parameters of the fluid properties in IDM. 10 Input parameters for

fluid rheology

11 Model 800 viscometer by OFITE.

http://www.ofite.com/instructions/130-10.pdf

12 The top view of the model 800 viscometer.

http://www.ofite.com/instructions/130-10.pdf

n/allibu/fann-laboratory-equipment/oil-6 well-cement-testing/blenders-and-mixers.html 14 OFITE Universal Heating cup. http://www.lhoildemexico.com.mx/therm ocups.html 15 Fluke thermometer model 51 kj. http://www.ebay.com/itm/Fluke-51-K-J- 1604-9V-6F-22-9V-006P-Thermometer-/190868329070 16 Temperature effect on

plastic viscosity for OBM-Enviromul 1.39sg, 1.51sg and 1.63sg. 17 Temperature effect on

yield point for OBM-Enviromul 1.39sg, 1.51sg and 1.63sg. 18 Pressure and

temperature effect on plastic viscosity for OBM 1.08sg.

19 Pressure effect on plastic viscosity for OBM 2.03sg.

20 Pressure and

temperature effect on yield point for OBM 1.08sg.

21 Pressure and

temperature effect on yield point for OBM 2.03sg. 22 Measured and predicted plastic viscosity by IDM. 23 Measured and 66

predicted plastic viscosity by Politte. 24 Measured and

predicted yield point by IDM.

25 Measured and

predicted yield point by Poiltte.

26 Effect of composition on plastic viscosity. 27 Effect of composition

on yield point.

28 Drilling fluid functions. ] M-I SWACO (1998). Drilling Fluids Engineering Manual. Revision No: A-0 29 IDM MoDrill input

parameters.

30 FANN 70 viscometer. http://www.hrheologyton.com/public/bar /contents/Brochures/Web/H05514.pdf 31 FANN 75 viscometer. http://www.geodf.com/index.cfm/fuseact