George A. Cooper

Inactive and Former Projects

Interests

  • Drilling simulation

  • Novel drilling methods

  • Drill bit design

  • Directionjal drilling

  • Drilling for environmental investigation

  • Borehole stability

 

Drilling Simulation

Computer simulation of drilling operations is valuable in training Drilling Engineers and in predicting and optimizing Field Drilling Operations.

For some years we have been developing a PC based Drilling Simulator that can be used both for training and for planning and optimizing field operations.

 

The Simulator

The simulator is built around a drilling mechanics model that predicts the rate of penetration and rate of wear of a drill bit as a function of the bit, the rock being drilled and the set of operating parameters.

Over time, we have added more features to the program, so that it is now possible to carry out the following operations:

  • Drilling
  • Hydraulics optimization
  • Directional Drilling
  • Dealing with kicks and losses
  • Handling hole stability problems
  • Logging
  • Casing and Cementing

The program is accompanied by about fifty specialized exercises that illustrate all of the above features.

 

Simulating Field Operations

Most recently, we have developed a capability to run simulations of real world operations. This started with our deveopling a routine that allows the importation of real field data via a LAS (Log, ASCII Standard) file.

We are now developing methods that allow the simulator to be tuned to conditions in a specific field. Once tuned, the simulator may be used to optimize drilling operations in the current well, or predict performance in an adjacent offset well.

 

 

For More Information:

  • See Drilling Simulator

     

    Publications

  • 1) "An Interactive Simulator for Teaching and Research"
    G A Cooper, A G Cooper and G Bihn
    SPE Paper 30213, presented at the 10th Petroleum Computer Conference, Houston, TX 11 - 14 June 1995.

    This paper describes the Payzone C Drilling Simulator

    2)"Integrated Petroleum Engineering Simulation and Decision Making Teaching Program"
    G A Cooper, J F Mota and A G Cooper
    SPE Paper 36660, presented at the SPE 71st Annual Technical Conference and Exhibition, Denver, 6 Oct 1996.

    This paper describes the use of the simulator in developing an integrated "Capstone Petroleum Engineering Course" that brings together all of the different subjects that a typical university undergraduate studies in a program on Petroleum Engineering. The course follows the process of discovery and evaluation of an oilfield. Fifteen topics cover the history of the process, starting with the seismic survey, and continue via the planning and drilling of the wildcat, and the design of drill pipe strings, casing, cementing, and logging operations. This is followed by the interpretation of well tests, the evaluation of PVT properties, the estimation of the size of the reservoir, and the volumes of oil and gas in place. Finally the students carry out an economic analysis to establish whether the field can be exploited economically. The Payzone simulator is used in many but not all of the exercises.

    3)"Novel Training Simulator Integrates Disciplines"
    G A Cooper, J F Mota and A G Cooper
    Petroleum Engineer International, 70, 1, 89 - 95 Jan 1997

    This paper has a more popular description of the Payzone C simulator and its use in the "Capstone Petroleum Engineering Course".

    4)"The use of a Drilling Simulator to Optimize a Well Drilling Plan"
    A A Abouzeid and G A Cooper
    Presented at the Geothermal Resources Council 2001 Annual meeting,
    26 - 29 August 2001, San Diego, California.

    Overall, the paper shows how the simulator may be used to help in the planning of future wells if information is available from offset wells.
    Method :
    LAS files from an offset well were imported and used to build a lithology.
    The simulator was adjusted to reproduce the drilling performance observed in the offset well.
    The well was re-drilled to see if a better set of operating conditions could be specified.
    It was found that the offset well had been drilled with optimum hydraulics, but in a future well better results might be obtained by increasing rotary speed while reducing weight on bit.
    It might also be advantageous to use a milled tooth or PDC bit in place of the tungsten carbide insert bits that had been used in the offset well.

    5) "A proposal for the real-time measurement of tooth wear"
    G A Cooper
    To be presented at the Geothermal Resources Council 2002 Annual meeting,
    22 - 25 September 2002, Reno, Nevada.

    The paper suggests how the drilling mechanics algorithms in a drilling simulator may be used in real time to determine bit tooth wear.

    Now that MWD measurements are available to determine rock properties at or near the bit, it becomes possible to use two methods to infer the strength of the rock being penetrated. The first is by geophysical methods, typically involving some combination of the sonic, natural gamma ray and possibly other measurements. The second is by inverting the drilling mechanics calculations that are at the heart of a typical drilling simulator so that, instead of determining rate of penetration from a known rock strength, one infers the rock strength from the rop.

    However, the estimate of rock strength derived from the drilling response is affected by the state of wear of the bit teeth. If no allowance is made for tooth wear, then the estimate of rock strength will gradually rise as the teeth wear (since the rop drops under constant operating conditions). By comparing the log-derived and rop-derived estimates of rock strength it then becomes possible to deduce the state of wear of the bit teeth from the difference between the two estimates.

    The proposal is tested against synthetic (but not field) drilling data and shown to give good results.

Drilling on Mars

Drilling on Mars will be done at low temperatures and in near vacuum. These conditions pose problems for the cooling of the cutting teeth and for the removal of the cuttings. We are investigating both of these questions.

This new project is aimed at investigating some critical issues involved in the search for water and evidence of life on Mars. We shall have to drill holes into the surface of the planet and remove samples for analysis. Because of the low temperature and near vacuum of the Martian surface, we shall not be able to have a gas or liquid medium in the hole to cool the bit and remove the cuttings. It looks likely that the cuttings will be removed by mechanical means, for example by auger. We are investigating the basic mechanics of how augers work, and how they may be optimized for Martian conditions.

We expect the drill bit teeth to be made of diamond. Because there will be no fluid flow around the bit to cool it, we can expect that the diamond bit teeth may be significantly heated. On the other hand, the ambient temperature will be very low, and the absence of oxygen in the Martian atmosphere will protect the diamond from oxidation. This is known to be a significant contributor to the wear of diamond drilling bits under Earth conditions.

We shall investigate how diamond drilling tools behave under low temperature, near vacuum conditions with a view to recommending suitable tools and operating conditions for Martian conditions.

 

For More Information:

contact graduate student Kris Zacny

Cryogenic Drilling

The basic concept of cryogenic drilling is to use low-temperature nitrogen gas to freeze the ground being drilled. This stabilizes the hole walls and also prevents fluids moving ito or out of the hole.

The invention is a method for drilling in loose, unconsolidated ground, typically sandy soils that are characteristic of many hazardous waste sites, by injecting very cold nitrogen, as gas or liquid, through the drill pipe and out of nozzles at the bit. The cold gas stream performs the usual function of blowing the drilled cuttings out of the borehole. This has two important functions. The first is to stabilize the soil around the hole, which prevents the collapse of the walls before a supporting casing can be placed in the hole. The second is to freeze water and any liquid pollutants in place, thereby preventing the spread of pollution away from or along the borehole, and making possible a more accurate measurement of any pollutants that may be present.

Full scale Cryogenic drilling field tests have been performed at Lawrence Berkeley Laboratory.

 

For More Information:

  • Simon, Rafael and G. A. Cooper. (1994). "Use of Cryogenic Fluids for Environmental Drilling in Unconsolidated Formations". ASME Energy Sources Technology Conference - Drilling Technology, New Orleans, LA, 23-26 Jan., 1994. pps. 199-206

     

  • Cooper, G.A. and Rafael Simon (1995). "Field Test of the Cryogenic Drilling Method for Environmental Well Installation". ASME Energy Sources Technology Conference - Drilling Technology, Houston, TX, 31 Jan-2 Feb., 1995. pps.57-66

     

  • R D Simon and G A Cooper "Cryogenic Drilling: a new method for environmental remediation" Ground Water Monitoring and Remediation, Summer 1996, pp 79 - 85.

     

  • P Cavagnaro, R D Simon and G A Cooper "A successful borehole drilled by cryogenic drilling in an unconsoolidated soil with boulders" Presented at the 1997 Energy Week Symposium, Houston, TX, 28 - 30 Jan 1997.

     

  • G A Cooper "Cryogenic Drilling: a new method for accessing and sampling unconsolidated soils" Geodrilling International, 5, No. 6 (August) pp. 12-16, 1997.

     

The Wear of Diamond Rock Cutting Tools

 

We have carried out numerous studies of the ways in which diamonds wear or are broken when used in rock-drilling operations

We have been working for several years on understanding the way in which bit cutter teeth are worn as they cut rocks. Most often we have worked on natural or synthetic diamond materials, of several types. These studies have not only aimed at understanding the way in which the cutter materials wear, but also at designing processes that reduce wear (by the use of electro-osmosis, for example, see "Applications of Electro-Osmosis in preventing bit balling" or working to develop new cutter designs that are either wear-resistant or wear-tolerant (see "The Long-Life Drill Bit )"

Our work has covered a number of areas, ranging from comparisons of the wear mechanisms of cutters under field and laboratory conditions to investigations of the underlying wear and failure mechanisms of the cutter materials themselves. These have included work on residual stresses, fracture, fatigue and other failure mechanisms. The list of publications below will give an idea of the subjects investigated.

 

For More Information:

  • Zhong Liu & G A Cooper "An analysis of field-worn TSD cutting elements". Proceedings of the ASME Energy Sources Technology Conference, Houston, TX, 26 - 29 Jan 1992.

     

  • Tze-Pin Lin, Michael Hood, George A Cooper and Xiaohong Li "Wear and Failure Mechanisms of polycrystalline diamond compact bits" Wear, 156, pp 133 - 150, 15 July 1992.

     

  • Tze-Pin Lin, George A Cooper and Michael Hood "Fatigue test on polycrystalline diamond compacts" Mats Sci and Eng. A, 163, 23 - 31, May 1993.

     

  • T P Lin, M Hood, G A Cooper and R H Smith "Residual stresses in polycrystalline diamond compacts" J Amer Ceram Soc. 77, 6, 1562 - 1568, June 1994.

     

  • G A Cooper, Z Liu and M Yang "Wear of thermally stable diamond during rock cutting" Energy-sources Technology Conference and Exhibition, New Orleans, LA 23 - 26 Jan 1994. Also published in Trans. ASME 116, 4, pp 268 - 272 Dec 1994.

     

  • G A Cooper, M Yang, J Cohen and P A Westcott "Comparison of the performance of thermally stable diamonds when operating as single cutters with their behavior when mounted on field drill bits" Energy-sources Technology Conference and Exhibition, New Orleans, LA 23 - 26 Jan 1994. Also published in Journal of Energy Resources Technology, 116, Dec 1994, pp 273 - 277.

     

  • T P Lin, G A Cooper and M Hood, "Fracture toughness tests on polycrystalline diamond compacts using the double torsion test" J Materials Science 29, 4750 - 4756, 1994.

     

  • P R Hariharan, A H Hale and G A Cooper "Reduction of bit or tool wear using electro-osmosis" Presented at the 1997 Energy Week Symposium, Houston, TX, 28 - 30 Jan 1997.

     

  • Joseph Lee and George A Cooper "An investigation of the relative wear resistance of polycrysytalline diamond and polycrystalline cubic boron nitride when cutting cement containing iron pyrites" Berkeley Scientific, 1 , 2, pp 59 - 63, Spring 1997.

     

  • P R Hariharan, A H Hale and G A Cooper "Further evidence of reduction in tool wear by electro-osmosis in various rocks" Presented at the SPE 1997 Western Region Meeting, Long Beach, CA 25 - 27 June 1997.

     

  • P R Hariharan, A H Hale and G A Cooper, "Decrease in coefficient of friction between rock and metal by electro osmosis" Presented at the 1998 Energy Technology Conference and Exhibition, Houston, TX 2 - 4 Feb 1998.

     

Applications of Electro-Osmosis in Reducing Bit Balling and Wear

 

Application of a few volts negative potential to a drill bit causes water to be liberated at the bit-clay interface. This reduces the tendency of clay to stick to the bit (bit balling). The lubricating effect of the water film also reduces wear of the bit.

Electro-Osmosis is the process whereby, when a block of a clay or clay-containing material e.g. a shale, is subjected to an electric potential, water migrates towards the negative electrode. Simultaneously, the region near the anode is dried.

We have applied this phenomenon to develop a method of reducing Bit-balling when drilling shales and clays (described below), and also to help in running and setting casings. (See "The Application of Electro-Osmosis in Running and Setting Casings").

 

Preventing Bit-Balling when drilling in shales and clays

Bit balling is the phenomenon that occurs when sticky clay or ground up shale lodges between the teeth of a drill bit and prevents the bit from drilling. Often the flow of flushing fluid is stopped, which can lead to a loss of cooling and resultant overheating of the bit. The stickiness of the cuttings generally results from the absorption of water by the rock debris, and so one way of reducing bit balling is to drill using oil or oil-water emulsions as the drilling fluid. Other chemicals, including polymers or solutions containing potassium ions are sometimes effective. Overall, however, these chemical additives are potentially harmful to the environment, and so it has become more and more difficult to get permission to drill with oil-based or chemically-treated muds.

An alternative approach is to use electro-osmosis. If a negative potential of a few (2 - 10) volts is applied to the drill bit when drilling in shales, the film of water that is generated at the bit - clay interface effectively prevents the shale cuttings from sticking to the bit. We have investigated this behavior thouroughly, and checked the influence of changing voltage and current, the effects of drilling with different types of bits, and of using pure water or different muds for removing the cuttings. We have also investigated the optimum placement of the counter electrode (the anode) that accepts the return current.

Under the correct conditions, we have found that bit balling may be prevented, and the rate of penetrsation of the bit may be doubled.

Based on these laboratory experiments, we have carried out field tests that confirm that similar improvements may be obtained under field conditions.

 

Reducing Friction and Wear

We have also found that the film of water that is generated at the clay-cathode interface acts not only to prevent clay from sticking to the metal surface, but also functions as a lubricant. The coefficient of friction is thus reduced, and so is the rate of wear of the metal surface if it is being rubbed against the clay. We therefore expect that if the entire Bottom Hole Assembly is charged negatively, friction and wear of these elements will be reduced. This may be of particular interest when drilling in highly deviated wells when it is important to transfer the weight of the BHA to the bit to cause it to advance.

 

For More Information:

  • Sanjit Roy and G A Cooper "The effect of electro-osmosis on the indentation of clays" Proceedings of the the 32nd US Rock Mechanics Symposium, Norman, OK, 10 - 12 July 1991. Published in "Rock mechanics as a multidisciplinary science" ed Roegiers, Balkema, Rotterdam, 1991. pp 335 - 344.

     

  • Sanjit Roy and G A Cooper " Prevention of bit-balling in shales - some preliminary results" IADC Paper 23870, Proceedings of the SPE/IADC Drilling conference, New Orleans LA, 18 - 21 Feb 1992. pp 259 - 268. Also publ. in SPE Drilling and Completion, Sept 1993

     

  • Sanjit Roy and G A Cooper "Studies on stability of a simulated borehole in compacted clay". Proceedings of the 33rd U S Symposium on rock mechanics, Santa Fe NM 3 - 5 June 1992. ed J R Tillerson and W R Wawersik, Balkema, Rotterdam, 1992. pp 355 - 364.

     

  • G A Cooper and Sanjit Roy "Reduction of bit-balling in PDC and roller cone bits by use of a negative electric potential" SPE 1994 Western Regional Meeting, Long Beach California, 23 - 25 March 1994.

     

  • P R Hariharan, A H Hale and G A Cooper "A new test method for measurement of bit/stabilizer balling phenomenon in the laboratory and its prevention using electro-osmosis. Presenterd at the 1996 SPE Eastern Region Meeting, Columbus, Ohio, 23 - 25 October 1996.

     

  • A J Dick and G A Cooper, "Optimization of drill string electrode geometry for bit balling prevention by electro-osmosis" Presented at the 1997 Energy Week Symposium, Houston, TX, 28 - 30 Jan 1997.

     

  • P R Hariharan, A H Hale and G A Cooper "Reduction of bit or tool wear using electro-osmosis" Presented at the 1997 Energy Week Symposium, Houston, TX, 28 - 30 Jan 1997.

     

  • P R Hariharan, A H Hale and G A Cooper "Further evidence of reduction in tool wear by electro-osmosis in various rocks" Presented at the SPE 1997 Western Region Meeting, Long Beach, CA 25 - 27 June 1997.

     

  • A J Dick and G A Cooper "Field tests of electro-osmosis to reduce bit balling" Presented at the 1998 Energy Technology Conference and Exhibition, Houston, TX 2 - 4 Feb 1998.

     

  • P R Hariharan, A H Hale and G A Cooper, "Decrease in coefficient of friction between rock and metal by electro osmosis" Presented at the 1998 Energy Technology Conference and Exhibition, Houston, TX 2 - 4 Feb 1998.

     

  • Peringandoor R Hariharan, George A Cooper and Arthur H Hale "Further experiments with electro-osmosis on reducing bit balling in shales" Presented at the 1998 Energy Technology Conference and Exhibition, Houston, TX 2 - 4 Feb 1998.


Application of Electro-Osmosis in Running and Setting Casings

 

Application of an electric field across a clay-casing interface causes either lubrication of the interface or drying of the clay, depending on polarity. If the former, the casing may be run in more easily. If the latter, weak soils with poor bearing capacity can be strengthened.

Electro-Osmosis is the process whereby, when a block of a clay or clay-containing material e.g. a shale, is subjected to an electric potential, water migrates towards the negative electrode. Simultaneously, the region near the anode is dried.

We have applied this phenomenon to develop a method of reducing Bit-balling when drilling shales and clays (see "Reducing Bit-Balling )", and also to help in running and setting casings.

 

The Casing Problem

Difficulties arise when setting the first (Structural or Surface) casing in very soft subsea sediments. The sediments down to the first hundred feet or so can be very weak and it can be difficult to get the surrounding soils to provide enough support to prevent the casing from collapsing. The difficulties can be increased if the casing is jetted into place because the jetting process may wash out a much larger diameter of hole than will accommodate the casing, making a good strong contact between the casing and surrounding soil even more difficult to achieve. On the other hand, pile-driving the casing is more expensive as it requires the operation of a pile driving hammer. Finally, the presence of shallow, overpressured sands can cause substantial flows of salt water up along the outside of the casing that can give rise to difficulties in placing and curing the cement.

Our approach has been to use electro-osmosis in two applications. First, if the casing is made negatively charged, the liberation of water at the casing-soil interface should provide lubrication that will enable the casing to be jetted-in more easily, and second, but more importantly, if the casing polarity is changed to positive when the casing is in place, water will be repelled from the vicinity of the casing. This drying effect on the soil around the casing will cause the soil to become stronger and it will therefore provide greater support to the casing.

We have carried out many laboratory tests to show that this concept works, and we have developed design guidelines that give the voltage, current and time required to achieve certain bearing capacities in different soils. Overall, it appears that significant and sufficient increases in soil bearing strength may be achieved by this process at modest costs and over time scales that do not slow down the normal process of drilling a typical offshore well.

For More Information:

  • R. Wrixon and G A Cooper "In situ casing consolidation by electrokinetic methods" Presented at the 72nd SPE Annual Technical Conference and Exhibition, San Antonio, TX 1997.
    • Also published in shortened form in the Jour. of Petr. Technology, 50, 2, pp 51 - 53, February 1998.
  • R Wrixon and G A Cooper "Theoretical and practical guidelines for using electrokinetics to improve casing support in soft marine sediments" SPE/IADC Paper 39299, Presented at the 1998 SPE / IADC Drilling Conference, Dallas TX 3-6 March 1998.

The Long-Life Drill Bit

 

The project aims to make a drill bit whose teeth retain a constant sharpness in spite of wear. Such a bit will maintain a constant rate of penetration and will be self-repairing if damaged.

The idea of the Long-Life Drill Bit is to recognize that since wear of the drill bit is inevitable, the designer of drill bits should make this a part of his design. Until the present, drill bits have been designed to drill as well as possible when new, but it is accepted that the performance of the bit will decrease steadily as the bit tooth height and sharpness are lost. This progressive loss of performance meeans that the driller has to alter the operating parameters continually as the bit run continues, usually by increasing weight-on-bit. It also means that interpretation schemes that use values of torque and rate of penetration to determine the properties of the rocks being penetrated have difficulty in distinguishing changes in the hardness of the rock from changes in the state of wear of the bit. For both of these reasons, it would be useful to have a drill bit whose sharpness and cutting behavior do not change as the bit wears.

Our idea is therefore to make a bit whose sharpness, i.e. the shape of the cutting edges, does not change as the bit wears. This is done by making the teeth of a composite of hard and soft materials so that as the tooth wears, instead of developing the usual wear flat, a profile is developed that maintains a sharp cutting edge. If the composite teeth are in addition made in the form of parallel-sided slabs, the same cutting profile will be maintained regardless of the amount of material that has been worn off the teeth. Hence the bit performance will be constant from the beginning of drilling until the teeth are entirely worn away.

An additional consequence is that if the bit teeth are broken by some accidental overload, continued drilling will re-sharpen the teeth back to their equilibrium profile.

We have carried out tests on model drill bits in the laboratory that have demonstrated that the principle works. Actual performance depends on the choice of materials for the composite cutter teeth and the type of rock being drilled. Overall, we have seen better performance in soft rocks and rocks that are somewhat granular, for example sandstones. Drilling in hard, very fine grained rocks is more difficult.

 

For More Information:

  • L Restorick and G A Cooper "Preliminary experiments on a long life drill bit" Presented at the 1997 Energy Week Symposium, Houston, TX, 28 - 30 Jan 1997.