CADE/CAODC DRILLING CONFERENCE October 20 & 22, 2003 Calgary, Alberta, Canada

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1 CADE/CAODC DRILLING CONFERENCE October 20 & 22, 2003 Calgary, Alberta, Canada Page 1 of 14 COPYRIGHT NOTATION: This paper was selected for presentation by the CADE/CAODC Drilling Conference Technical Committee, following a review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Technical Committee and do not necessarily reflect the position of any or all of the Conference sponsors. Permission to copy is restricted to just this abstract page. Illustrations may not be copied. The abstract should contain conspicuous acknowledgement of where and by whom the paper was presented. Further permission to copy may be requested from the CADE/CAODC Technical Chairman, 800, Avenue SW, Calgary, Alberta, Canada T2P 0M2. ABSTRACT: One of the results generated by the drilling process is the creation of drill cuttings or low gravity solids. There are detrimental effects of undesirable low gravity solids in drilling fluids. They include reduction in penetration rates, increased wellbore instability, potential for induced loss of circulation, decreased reservoir production as result of formation damage, increased drilling fluid and disposal costs, potential for differential sticking and others. Value can be added to operators drilling process by the effective and efficient use of solids control equipment, decanting centrifuges playing an important role. Often the centrifuge suppliers will emphasize the ability of their products by concentrating on only one characteristic of that particular machine such as the G-force, or the cut point or the feed rate or the variable speed, or the ability to provide a dry cake, etc. Because all these factors have an impact on economics, it is the authors opinion that a larger picture has to be reviewed and considered to determine centrifuges performance. This paper will present a quantitative/qualitative method of measuring decanting centrifuge performance as well as the centrifuge suppliers ability to interact with their equipment dynamically. The methodology is called Centrifuge Cost Analysis. It is a mathematical/statistical evaluation, which compares the theoretical and practical performance of different centrifuges. It also calculates the real cost of operating these machines.

2 Page 2 of 14 INTRODUCTION One of the results generated by the drilling process is the creation of drill cuttings or low gravity solids. There are detrimental effects of undesirable low gravity solids in drilling fluids. They include reduction in penetration rates, increased wellbore instability, potential for induced loss of circulation, decreased reservoir production as result of formation damage, increased drilling fluid and disposal costs, potential for differential sticking and others. Value can be added to operators drilling process by the effective and efficient use of solids control equipment, decanting centrifuges playing an important role. Often the centrifuge suppliers will emphasize the ability of their products by concentrating on only one characteristic of that particular machine such as the G-force, or the cut point or the feed rate or the variable speed, or the ability to provide a dry cake, etc. Because all these factors have an impact on economics, it is the authors opinion that a larger picture has to be reviewed and considered to determine centrifuges performance. This paper will present a quantitative/qualitative method of measuring decanting centrifuge performance as well as the centrifuge suppliers ability to interact with their equipment dynamically. The methodology is called Centrifuge Cost Analysis. It is a mathematical/statistical evaluation, which compares the theoretical and practical performance of different centrifuges. It also calculates the real cost of operating these machines. THE REALITY The centrifuging process often develops as follows: 1. Based on their experience, the centrifuge supplier in collaboration with the operator s representative chooses the number and sizes of centrifuges to be used. 2. The centrifuges are set up at well site. The centrifuge service provider sets the operating parameters of the machine. In the vast majority of cases, the initial settings of the centrifuge are kept the same throughout the duration of drilling. 3. Sometimes, the wellsite drilling foreman will direct the trim of centrifuge parameters based on his experience or the cake dryness. The so-called trim that can be controlled at the well site usually refers to feed rate, bowl RPM and pond depth. Fluid viscosity can also be controlled to some extent without defeating its other purposes (i.e. hole cleaning). 4. For onshore operations, the centrifuge supplier representative comes out to the wellsite once a week or second week to service the centrifuge, if required. 5. At the request of the operator, some centrifuge suppliers provide a retort test on centrifuge underflow to determine solids content (HGS and LGS) as well as oil content.

3 Page 3 of 14 THE PROBLEMS Based on the above process, the authors identified a number of issues that are common throughout the industry: 1. Choosing the right size and number of centrifuges is somewhat of an educated guess. 2. The centrifuges are not treated as dynamic machines. The fit-all initial settings will not provide the best solids removal when some of the working conditions change (i.e. change in penetration rates, change in lithology, change in pump output, change in drilling fluid type and/or drilling fluid characteristics, etc.). 3. Changing the centrifuging parameters according to the dryer the cake, the better or the bigger the pile, the better is just wrong. 4. Servicing/ trimming the centrifuge at certain times without having a monitoring program of their efficiency in place is again somewhat of an educated guess. 5. For oil based muds, oil content on cuttings is only one parameter of assessing the centrifuge performance and should not be considered alone. There are a number of questions that operators try to find answers to: How many centrifuges do I need?, What size?, How do I know that I get the best benefit for the buck? THE IDEA Centrifuging efficiency can be defined in many ways, depending on the centrifuging objectives. One of the better theoretical definitions is The separation efficiency of a centrifuge can be described as the ratio of solids to surface area discarded versus the solids to surface area presented to the centrifuge. However, in economical terms, the situation is not that easy. A broader picture has to be reviewed, one that takes into consideration not only the theoretical and practical performance of the machine but also the cost effectiveness of solids removal, the environmental impact of the waste generated as well as the cost of the fluid lost on cuttings. Energy consumption costs and the impact on drilling fluids buy-back costs should also be taken into consideration. When determining the effectiveness of solids control equipment and in particular the centrifuges, the collection of certain data is required. The example shown in this paper will clarify the details. To understand the overall solids control efficiency, a mass balance needs to be performed. Through such process, the total amount of rock drilled and its disposition through the surface system can be determined (i.e. % solids removed by shakers, % solids removed by centrifuges, % solids removed by dump-and-dilute technique, % solids retained in the mud from the total solids generated through drilling process). This is a laborious process that requires 24-hr/day monitoring of the circulating system. Previous solids control studies performed using the mass balance technique have indicated that in a lot of areas the centrifuges work share (% solids removed by centrifuges) can be quite high. Therefore, a simpler evaluation system had to be found for centrifuges only. Centrifuge Cost Analysis has been developed as a process to mitigate all these issues. A computer software program was built to analyze raw data and produce meaningful graphics that could be interpreted in a qualitative way. The objectives achieved by using this process are: 1. Evaluate performance of different types of centrifuges. 2. Evaluate centrifuge suppliers ability to provide effective and efficient centrifuging. 3. Determine the cost effective centrifuge capacity (number and size) required for a typical well in a particular field. 4. Determine the best performance parameters within the testing conditions.

4 THE THEORY Page 4 of 14 The Stokes Law governs the centrifuge decanting ability: Vs = Φ p 2 * (ρ p ρ f ) * G / (18 * µ) Where: Vs particle slip velocity, (m/s) Φ p particle diameter, (m) ρ p particle density, (kg/m 3 ) ρ f fluid density, (kg/m 3 ) G G-force, (m/s 2 ) µ fluid viscosity, (Poise) As such, the following parameters will influence centrifuge performance: a. Particle settling velocity is proportional to the G-force. The G-force is obtained from a combination of centrifuge bowl RPM and bowl diameter. Therefore, both of these parameters will affect centrifuge performance. While a high G-force is desirable, it may limit machine performance in some aspects. Usually a higher G-force is obtained by increasing the bowl RPM. However, when that happens, the difference between centrifuge bowl RPM and conveyer (or scroll) RPM, known as scroll differential increases. In this case, an agitated pond more often than not generates a turbulent flow, discouraging solids from settling. A reduced processed flow rate is often the outcome. b. Particle settling velocity is inversely proportional to fluid viscosity. Therefore, the lower the fluid viscosity, the higher the particle settling velocity. From a solids separation viewpoint, a low viscosity of the drilling fluid is desirable. c. Cake dryness is often wrongly viewed as a good centrifuge performance due to less liquid associated with separated solids. The bowl RPM and the length of dry beach (the length of the conic bowl section found above the pond and influenced by the pond depth) can influence the cake dryness. In experimental particle size distribution tests, dry cakes have proved to be formed of coarser solids, thus carrying the penalty of less efficient separation especially for the fine LGS. d. The pond depth (which is an expression of the volume of the fluid retained inside the bowl at any given time) is a parameter that influences the fluid residence time as well as the dry beach length. An increase in pond depth will generate an increase in fluid residence time therefore, an increase in solids separation. However, an increase in pond depth will generate a decrease in processed flow rate due to potential flooding of the machine. e. Intake flow rate capacity can be controlled with an intake line valve. Maximum flow rate is determined by the height of the cake (underflow) discharge port. The highest flow rate processed can be obtained at the shallowest pond depth, usually at the expense of separation efficiency. Refer to Appendix A Decanting Centrifuge Schematics. Another very important aspect of centrifuging efficiency is the particle size distribution of the drilling fluid processed. Maximum solids are removed by processing large flow rates when the particle size distribution is coarse. As this distribution becomes finer through the drilling process, the separation efficiency has to be increased by using lower feed rates and/or deeper pond depths.

5 THE EXAMPLE Page 5 of 14 Q Max Solutions Inc. has worked together with a number of oil and gas operators in North and South America on Centrifuge Cost Analysis studies. Here are the processes involved as well as an example of such study. The objectives of the project are as follows: 1. Evaluate the performance of minimum two different types of centrifuges. 2. Evaluate centrifuge suppliers ability to provide effective and efficient centrifuging. 3. Determine the cost-effective centrifuge capacity (number and size) required for a typical well in the field, usually drilled with Invert - Oil Based Mud. 4. Determine the best performance centrifuge parameters within testing condition and acquire information that will be useful in establishing centrifuging parameters for optimum performance on future wells. On project kick-off meetings between representatives of Q Max Solutions Inc., the oil and gas operator and the centrifuge suppliers, the following procedures are agreed upon: Select one well for the project purposes. The well should be representative for the type of drilling in a particular field and drilled with Invert-OBM fluid. Determine the test period of time. Due to the amount of work involved, it should be spread over a period of 1 1 ½ months. Determine the persons to jointly co-ordinate the project, formed of both the operator s and Q Max Solutions representatives. Acknowledge that Q Max Solutions Inc. provides the methodology, the laboratory facility and performs the required tests. Although the lab tests are quantitative, they are interpreted in a qualitative/comparison basis. The operator installs monitoring equipment on centrifuges as per Q Max Solutions requirements. Information is gathered as per Appendix B Data Collection Form. Sample methodology is developed so that a consistent method is used. Appropriate sample frequency is predetermined and agreed upon. Q Max representative collects the samples in the presence of operator and centrifuge suppliers representatives. The centrifuge suppliers set-up their equipment and perform adjustments without operator or Q Max representatives interference. The agreed upon requirements are that centrifuges should be set on the same stand, at the same height, feed from the same shaker tank and discharge into the same suction tank. The equipment suppliers are to be provided with test results only through the operator representative, in real time, as they are developed. The information gathered is computed and analyzed by Q Max Solutions Inc. as per Appendix C Technical Evaluation / Software. The authors generate a mathematical/statistical evaluation and comparison study of the centrifuges and present the conclusions to the operator. THE CONCLUSIONS DRAWN ARE GROUPED IN: Equipment technical performance Equipment economical performance Equipment suppliers performance Cost effective centrifuge capacity Best performance parameters In this paper s example, based on the processed data that generated Appendix D Technical Evaluation / Graphics, the authors determined the following: In average, Centrifuge A processed ~93% of its proposed theoretical feed rate (800 l/min). It removed ~21% of the total solids generated through the drilling process and discharged ~5,190 kg/day waste out of which ~1.45 m 3 /day was Invert-OBM attached to solids. The areal removal rate was ~91,160 m 3 /hr.

6 Page 6 of 14 In average, Centrifuge B processed ~58% of its proposed theoretical feed rate (900 l/min). It removed ~19% of the total solids generated through the drilling process and discharged ~5,020 kg/day waste out of which ~1.59 m 3 /day was fluid attached to solids. The areal removal rate was ~94,670 m 3 /hr. The particles size distribution of the solids presented to the machines, discarded by the machines and left by the machines in the system was analyzed. It is important to know that although different particle diameters [D(v,0.1) 10% of the sample is below this diameter, D(v,0.5) - 50% of the sample is below this diameter and D(v,0.9) - 90% of the sample is below this diameter] in the particle size distribution are recorded, these numbers, as well as the cut points, are not considered alone. Interpretation is based rather, on the solids specific area, which encompasses all the solids present. The bigger the specific area, the finer the particle size distribution. A centrifuge that generates a bigger areal removal rate discards finer solids. However, there is a trade-off: Due to their bigger surface area, finer solids contain more attached fluid, therefore, a higher fluid removal rate is encountered as well as a larger waste volume. Of course, the associated costs are higher as well. Based on the findings in the Appendix E Centrifuge Cost Analysis, the following was determined: Three Centrifuges A would be required to process the amount of solids remaining in the mud after the shakers cut. The operating costs of these machines would amount to ~CAN 3, $/day. This includes rental costs, disposal costs and lost fluid costs. Three Centrifuges B would be required to process the amount of solids remaining in the mud after the shakers cut. The operating costs of these machines would amount to ~CAN 4, $/day. This includes rental costs, disposal costs and lost fluid costs. Therefore, it is more economical to run three Centrifuges A than three Centrifuges B. Had Centrifuge B operated at the same 93% of its proposed theoretical feed rate and maintained the same efficiency at that rate, the economics may have changed as follows: In average, the Centrifuge B would process ~93% of its proposed theoretical feed rate (900 l/min). It would remove ~28.4% of the total solids generated through the drilling process and would create ~8,050 kg/day waste out of which ~2.55 m 3 /day would be fluid attached to solids. Two Centrifuges B would be required to process the amount of solids remaining in the mud after shakers cut. The operating costs of these machines would amount to ~CAN 4, $/day. This includes rental costs, disposal costs and lost fluid costs. With regards to centrifuge suppliers performance, the following was determined: As agreed upon in the project kick-off meeting, suppliers performed adjustments to their machines to their best ability and without outside interference. This ability is reflected by the consistency in the trend-line generated from Charts #3 through #8 in the Appendix D. Supplier A s performance seemed to be more consistent than Supplier B s. Charts #1 and #2 in the Appendix D suggest that Centrifuge B should, in theory, outperform Centrifuge A. However, Chart #3 suggests that Centrifuge B was consistently run only at about half of its theoretical capabilities.

7 Page 7 of 14 As seen in Chart #3 - Appendix D, Centrifuge A processed 93% of its proposed theoretical feed rate, which is acceptable in the authors opinion. By processing only 58% of its proposed theoretical feed rate, Centrifuge B s performance was not acceptable in the authors opinion. Therefore, Supplier A seemed to understand the dynamics of their machine better and more consistently than Supplier B. THE BENEFITS The benefits of this type of analysis are threefold in nature: 1. Evaluating centrifuge efficiency in real time as well as the ability of their suppliers to operate them in dynamic conditions; 2. Determining the total cost of running these machines and, 3. Estimating the required centrifuging capacity, operating parameters and associated costs for a typical well in a particular field. Evaluation of centrifuge efficiency allows the operator to determine if the centrifuge is functioning properly and where changes can be made to increase efficiency. Pre and post-change comparison of centrifuge manipulation allows the centrifuge supplier to tune his machines for optimal efficiency under variable conditions. As demonstrated in this paper, cost includes more than just machine day rate. The cost of waste processing is an important aspect in the economic evolution and is greatly influenced by centrifuge operating parameters. In a more detailed look, the influence on drilling fluid buy-back cost can also be considered. A proper economic study should potentially reduce operating costs and generate realistic estimates on optimum performance. GENERAL RECOMMENDATIONS Since centrifuges are dynamic machines, their performance depends on many factors. The type of drilling fluid used, the characteristics of such fluid, the lithological composition of the formations drilled, the bit design and last but not least the centrifuges parameters will influence their performance. Therefore, it is quite difficult to make general practical recommendations. As a process, when optimization of the cost efficiency of centrifuging in a certain field is required, the authors recommend that a comprehensive study such as the one described in this paper be undertaken. Otherwise, the following suggestions may be considered in choosing the right machines for the job: a. The same G-force can be generated by larger centrifuges that run at a lower bowl RPM or by smaller

8 Page 8 of 14 centrifuges that run at high RPM. The larger centrifuges seem to produce better performance, both technically and economically. b. Without knowing the solids generation rate and the solids removal rate, the number of required centrifuges may be chosen based on their feed rate. If the sum of the centrifuges feed rates equals the pump output, there is a good chance that solids will be removed in the first pass and not retained in the system to be circulated and damaged beyond the cut point of the centrifuges. c. Installing an in-line flow meter on the centrifuge feed line is always recommended. The flow meter measures the centrifuge s actual feed rate and is inexpensive. Past studies found that a centrifuge can process as low as 30% of its proposed theoretical feed rate. d. Adjusting the centrifuge parameters using the dryness of the cake or the volume of the underflow as reference is not recommended. e. Install centrifuges just above the rig tanks. Allow an easy slope for the overflow line to discharge into the tanks so it will prevent centrifuge flooding. f. Feed centrifuge from the bottom of the shaker tank and discharge overflow into the suction tank, if possible, below the mud line to prevent mud foaming. g. Maintain the mud viscosity as low as possible without jeopardizing its other objectives. h. Connect the centrifuges feed pumps to the shaker tank and the centrifuges intake to the feed pumps using the shortest, largest diameter lines, so that centrifuges feed rates will not be affected by unnecessary pressure drops in these lines. i. Ensure that feed pumps have the ability to feed the centrifuges at their maximum operating capacity. j. Have centrifuges regularly inspected, serviced and adjusted by competent personnel. NOMENCLATURE Feed Rate, (m 3 /hr) Theoretical Cut Point, (µm) Area ¾ Solids Removal Rate, (kg/hr) - refers to the centrifuge intake flow rate - refers to the smallest theoretical particle diameter removed by the centrifuge within certain test parameters - refers to the surface area of an imaginary settling tank with the same decanting ability as the centrifuge running with the liquid set at ¾ of the bowl inside radius - refers to the mass of solids removed by the centrifuge per hour of operating Solids Generation Rate, (kg/hr) - refers to the mass of solids generated per hour at the bit through the drilling process Solids Feed Rate, (kg/hr) - refers to the mass of solids present in the Feed Rate

9 Page 9 of 14 Areal Removal Rate, (m 2 /hr) Fluid Removal Rate, (m 3 /hr) - refers to the surface area of the solids removed per hour by the centrifuge - refers to the volume of liquid attached to the solids removed per hour by the centrifuge ACKNOWLEDGEMENTS The authors extend their thanks to Mr. Bill Hans and Mr. Al Gutheil of Q Max Solutions for their mentoring, to Mrs. Flori Baltoiu of Q Max Solutions for the excellent lab work, to the operators and the centrifuge suppliers from past studies for their co-operation and to Q Max Solutions field personnel for their continuous support. APPENDIX A DECANTING CENTRIFUGE SCHEMATICS

10 Page 10 of 14 APPENDIX B DATA COLLECTION FORM

11 Page 11 of 14 APPENDIX C TECHNICAL EVALUATION / SOFTWARE

12 Page 12 of 14 APPENDIX D TECHNICAL EVALUATION / GRAPHICS

13 Page 13 of 14 APPENDIX D TECHNICAL EVALUATION / GRAPHICS

14 Page 14 of 14 APPENDIX E CENTRIFUGE COST ANALYSIS