Experimental Set-up for Formation Damage Testing

The design of apparata for testing of reservoir core samples with fluids varies with specific objectives and applications. Typical testing systems include core holders, fluid reservoirs, pumps, flow meters, sample collectors, control systems for temperature, pressure or flow, and data acquisition systems. The degree of sophistication of the design of the core testing apparatus depends on the requirements of particular testing conditions and expectations. High quality and specific purpose laboratory core testing facilities can be designed, constructed, and operated for various research, development, and service activities. Ready-made systems are also available in the market.

The schematic drawing given in this article indicates that primitive core testing systems consist of a core holder, a pressure transducer controlling the pressure difference across the core, an annulus pump to apply an overburden pressure over the rubber slieve containing the core plug, a reservoir containing the testing fluid such as a drilling mud or filtrate, a displacement pump to pump the testing fluid into the core plug, and an effluent fluid collection container, such as a test tube. There is no temperature control on this system. It operates at ambient laboratory conditions.

The schematic drawing given in the image and shows the elements of a typical overbalanced core testing apparatus. This system has been designed for core testing at a near-in-situ temperature and stress conditions, although other features are similar to that of the primitive system shown in this article. The elements of a typical underbalanced core testing apparatus, which also operates at near-in situ temperature and stress conditions.

Special Purpose Core Holders

Core flood tests can be conducted in one-dimensional linear and radial modes show a schematic of typical radial flow models. Radial models

File:Current reservoir condition fluid leak-off evaluation system.png File:Underbalanced reservoir condition fluid leak-off evaluation system.png File:Systems for horizontal wellbore studies.png File:Continued.png

better represent the effect of the converging or diverging flows in the near-wellbore formation. However, linear models are preferred for convenience in testing and preparation of core samples.

The majority of the core flow tests facilitate horizontal core plugs because the application of Darcy's law for horizontal flow does not include the gravity term and the analytical derivations used for interpretation of the experimental data is simplified. This approach provides reasonable accuracy for single-phase fluids flowing through small diameter core plugs. However, when multi-phase fluid systems with significantly different properties and paniculate suspensions are flown through the core plugs, an uneven distribution of fluids and/or suspended particles can occur over the cross-sectional areas of cores. This phenomenon complicates the solution of the equations necessary for interpretation of the experimental data. In particular, errors arise because, frequently, the transport phenomena occurring in core plugs are described as being onedimensional along the cores. In order to alleviate this problem, it is more convenient to conduct core flow tests using vertical core plugs.

Consequently, the gravity term is included in Darcy's law, but errors associated with uneven distribution of fluid properties over the cross-sectional area of the core plugs are avoided. Therefore, Cernansky and Siroky (1985) used a vertical core holder. The dimensions of the core plugs are mportant parameters and should be carefully selected to extract meaningful data. Typically 1 to 2 in (2.54 to 5.08 cm) diameter and 1 to 4 in (2.54 to 10.58 cm) long cores are used. The aspect ratio of a core plug is defined by the diameter-to-length ratio. Small diameter cores introduce more boundary effects near the cylindrical surface covered by the rubber slieve. This, in turn, introduces errors in model-assisted data interpretation and analysis when onedimensional models are used, as frequently practiced in many applications for computational convenience and simplification purposes.

On the other hand, short cores do not allow for sufficient distance for investigation of the effect of the precipitation and dissolution processes and depth of invasion (Fambrough and Newhouse, 1993; Gadiyar and Civan, 1992; Doane et al., 1999). Longer cores are required for measurement of sectional or spatial porosity and permeability alteration. As described by Doane et al. (1999), a number of special purpose core holders have been designed.

This type of system is usually used with small core plugs. It only yields core response, integrated over the core length. on sectional permeability alteration over the core length. Especially, core holders designed for tomographic analysis using sophisticated techniques, such as NMR, Cat-scan, etc., may provide additional internal data. However, it is not always possible to obtain sufficiently long core plugs. In this case, several core plugs of the same diameter can be placed into a long core holder to construct a long core (20-40 cm long) and capillary contact membranes are placed between the core plugs to maintain capillary continuity (Doane et al., 1999).

As emphasized by Doane et al. (1999), small diameter core plugs are not sufficient for testing of heterogeneous porous rocks. Therefore, full

File:Cross-flow fluid leak-off evaluation system.png File:Core holder design for fractured core.png

diameter core plugs have been used to alleviate this problem. But, Doane et al. (1999) warn, full diameter core plugs would not be representative when significant anisotropy exists between the horizontal and vertical permeability, such as in typical carbonate formations. For the latter case, they recommend the core holder arrangement shown in this article. In this system, the two opposing side surfaces of the core plugs are flattened by facing off and the fluid is flown over the side surface by means of a specially designed sleeve. This provides larger surfaces exposed to fluid to include the effect of the heterogeneous features of the core plugs.

Obtaining and testing representative samples of fractured formations are difficult (Doane et al., 1999). Actual core samples containing natural fractures are preferred, but they are often difficult to obtain because core samples are usually poorly consolidated and may not include natural fractures (Doane et al., 1999). Then, a hydraulic fracturing apparatus can be used to prepare artificially fractured core plugs.

References

Amaefule, J. O., Ajufo, A., Peterson, E., & Durst, K., "Understanding Formation Damage Processes," SPE 16232 paper, SPE Production Operations Symposium, Oklahoma City, Oklahoma, 1987.

Amaefule, J. O., Kersey, D. G., Norman, D. L., & Shannon, P. M., "Advances in Formation Damage Assessment and Control Strategies," CIM 88-39-65 paper, 39th Annual Technical Meeting of Petroleum Society of CIM and Canadian Gas Processors Association, June 12- 16, 1988, Calgary, Alberta, 16 p.

Amyx, J. W., Bass Jr., D. M., & Whiting, R. L., Petroleum Reservoir Engineering, Physical Properties, R.L. McGraw-Hill, 1960, New York, 610 p.

Bennion, D. B., & Thomas, F. B., "Underbalanced Drilling of Horizontal Wells: Does it Really Eliminate Formation Damage?," SPE 27352 paper, SPE Formation Damage Control Symposium, February 1994, Lafayette, LA.

Cernansky, A., & Siroky, R., "Deep-bed Filtration on Filament Layers on Particle polydispersed in Liquids," Int. Chem. Eng., Vol. 25, No. 2, 1985, pp. 364-375.

Civan, F., "A Generalized Model for Formation Damage by Rock-Fluid Interactions and Particulate Processes," SPE 21183 paper, SPE 1990 Latin American Petroleum Engineering Conference, October 14-19, 1990, Rio de Janeiro, Brazil, l i p .

Civan, F, "Evaluation and Comparison of the Formation Damage Models," SPE 23787 paper, SPE International Symposium on Formation Damage Control, February 26-27, 1992, Lafayette, Louisiana, pp. 219-236.

Civan, F, Predictability of Formation Damage: An Assessment Study and Generalized Models, Final Report, U.S. DOE Contract No. DE-AC22- 90-BC14658, April 1994.

Civan, F., "A Multi-Phase Mud Filtrate Invasion and Well Bore Filter Cake Formation Model," SPE 28709 paper, SPE International Petroleum Conference & Exhibition of Mexico, October 10-13, 1994, Veracruz, Mexico, pp. 399-412.

Civan, F., "A Multi-Purpose Formation Damage Model," SPE 31101 paper, SPE Formation Damage Symposium, Lafayette, Louisiana, February 14-15, 1996, pp. 311-326.

Delclaud, J., "Laboratory Measurement of the Residual Gas Saturation," in Worthington, P. F. & Longeron, D. (Eds.), Advances in Core Evaluation //, Proceedings of the Second Society of Core Analysts, European Core Analysis Symposium, London, UK, pp. 431-451, 1991.

Demir, I., "Formation Water Chemistry and Modeling Fluid-Rock Interaction for Improved Oil Recovery in Aux Vases and Cypress Formations," Illinois Basin, Illinois Petroleum Series 148, Department of Natural Resources, Illinois State Geological Survey, 1995, 60 p.

Deo, M., Tariq, S., & Halleck, P. J., "Linear and Radial Flow Targets for Characterizing Downhole Flow in Perforations," SPE 16896 paper, 62nd Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, September 27-30, 1987, Dallas, Texas, pp. 181-188.

Doane, R. D., Bennion, D. B., Thomas, F. W., "Special Core Analysis Designed to Minimize Formation Damage Associated with Vertical/Horizontal Drilling Applications, " J. Canadian Petroleum Technology, Vol. 38, No. 5, May 1999, pp. 35-45.

Egbogah, E. O., "An Effective Mechanism for Fines Movement Control in Petroleum Reservoirs, "CIM 84-35-16 paper, 35th annual Technical Meeting of the Petroleum Society of CIM, June 10-13, 1984, Calgary, Canada.

Eickmeier, J. R., & Raimey Jr., H. J., "Wellbore Temperature and Heat Losses During Production or Injection Operations, " 7016 paper, Proceedings of the 21st Annual Technical Meeting, Calgary, Canada, may 1970, Canadian Institute of Mining.

Fambrough, J. D., & Newhouse, D. P., "A Comparison of Short-Core and Long-Core Acid Flow Testing for Matrix Acidizing Design, " SPE 26186 paper, SPE Gas Technology Symposium, June 28-30, 1993, Calgary, Canada, pp. 491-502.

Forchheimer, P., Hydraulik, L. Ed. Teubner, Leipzing and Berlin, Ch. 15, 1914, pp. 116-118.

Gabriel, G. A., & Inamdar, G. R., "An Experimental Investigation of Fines Migration in Porous Media, " SPE 12168 paper, SPE Annual Technical Conference and Exhibition, September 5-8, 1983, San Francisco, California.

Gadiyar, B., & Civan, F., "Acidization Induced Formation Damage-Experimental and Modeling Studies, " SPE 27400 paper, SPE Formation Damage Control Symposium, February 9-10, 1994, Lafayette, Louisiana, pp. 549-460.

Gruesbeck, C., & collins, R. E., "Entrainment and Deposition of Fine Particles in Porous Media, " SPEJ, December 1982, pp. 847-856.

Haggerty, D. J., & Seyler, B., "Investigation of Formation Damage from Mud Cleanout Acids and Injection Waters in Aux Vases Sandstone Reservoirs, " Illionois Petroleum Series 152, Department of Natural Resources, Illionois State Geological Survey, 1997, 40 p.

ISGS Oil and Gas Section, "Improved and Enhanced Oil Recovery Through Reservoir Characterization: Standard Operating and QA/QC Procedures," Illionois State Geological Survey, Open File Series 1993-13, 184 p.

Keelan, D., & Amaefule, J. O., "Rock-Water Reaction: Formation Damage,: Laboratory Methods, Part 5, pp. @49-257, in Development Geology Reference Manual, Methods 10, 1993, edited by D. Morton-Thompson and A. M. Woods. 548 p. AAPG Publication, Tulsa, Oklahoma.

Keelan, D. K., & Koepf, E. H., "The Role of Cores and Core Analysis in Evaluation of Formation Damage," JPT, May 1977, pp. 482-490.

Kersey, D. G., "The Role of Petrographic Analysis in the Design of Nondamaging Drilling, Completion, and Stimulation Programs," SPE 14089 paper, SPE International Meeting on Petroleum Engineering, Beijing, March 17-20, 1986.

Khilar, K. C, & Fogler, H. S., "Water Sensitivity of Sandstones," SPEJ, February 1983, pp. 55-64.

Kia, S. F., Fogler, H. S., & Reed, M. G., "Effect of Salt Composition on Clay Release in Berea Sandstones," SPE 16254, February 1987.

Kyte, J. R., & Rapoport, L. A., "Linear Waterflood Behavior and End Effects in Water-Wet Porous Media," Transactions of the American Institute of Mining, Metallurgy and Petroleum Engineers, Vol. 213, 1958, pp. 423-426.

Levorsen, A. I., Geology of Petroleum (2nd ed.), W.H. Freeman & Company, 1967, San Francisco, California, 409 p.

Marshall, D. S., Gray, R., & Byrne, M., "Development of a Recommended Practice for Formation Damage Testing," SPE 38154 paper, SPE European Formation Damage Conference, June 2-3, 1997, The Hague, The Netherlands, pp. 103-113.

Masikevich, J., & Bennion, D. B., "Fluid Design to Meet Reservoir Issues —A Process," /. Canadian Petroleum Technology, Vol. 38, No. 5, May 1999, pp. 61-71.

Miranda, R. M., & Underdown, D. R., "Laboratory Measurement of Critical Rate: A Novel Approach for Quantifying Fines Migration Problems," SPE 25432 paper, SPE Production Operations Symposium, March 21-23, 1993, Oklahoma City, Oklahoma, pp. 271-286.

Mungan, N., "Discussion of An Overview of Formation Damage," JPT, Vol. 41, No. 11, November 1989, p. 1224.

Piot, B. M., & Perthuis, H. G., "Matrix Acidizing of Sandstones," in M. J. Economides & K. G. Nolle (eds.), Reservoir Stimulation (2nd ed.), Prentice-Hall, Englewood Cliffs, New Jersey, 1989, pp. 14.1-6.

Porter, K. E., "An Overview of Formation Damage," JPT, Vol. 41, No. 88,1989, pp. 780-786.

Prada, A., Civan, F., & Dalrymple, E. D., "Evaluation of Gelation Systems for Conformance Control," Paper SPE 59322, SPE Permian Basin Oil & Gas Recovery Conference held in Midland, TX, March 21-23, 2000, 15 p.

Saleh, S. T., Rustam, R., El-Rabaa, W., & Islam, M. R., "Formation Damage Study with a Horizontal Wellbore Model," /. of Petroleum Science and Engineering, Vol. 17, No. 1/2, 1997, pp. 87-99.

Selby, R. J., "Flow of Fines and Sand Production in Unconsolidated Porous Media," Masters thesis, The University of Alberta, 1987, 212 p.

Seyler, B., "Geologic and Engineering Controls on Aux Vases Sandstone Reservoirs i« "^ ' Field, Illinois—A Comprehensive Study of a Well-Managed Oil Field," Illinois Petro eum Series 153, 1998, Department of Natural Resources, Illinois State Geological Survey, 79 p.

Sharma, M. M., & Yortsos, Y. C., "Fines Migration in Porous Media," AIChE J., Vol. 33, No. 10, 1987, pp. 1654-1662.

Thomas, R. L., Saxon, A., & Milne, A. W., "The Use of Coiled Tubing During Matrix Acidizing of Carbonate Reservoirs Completed in Horizontal Deviated, and Vertical Wells," \SPE Production & Facilities, August 1998, pp. 147-162.

Wojtanowicz, A. K., Krilov, Z., & Larglinais, J. P., "Experimental Determination of Formation Damage Trans, of the ASME, Journal of Energy Resources Technology, Vol. 110, 1988, pp. 34-42.

Wojtanowicz, A. K., Krilov, Z., & Langlirjais, J. P., "Study on the Effect of Pore Blocking Mechanisms on Formation Damage," SPE 16233 paper, Society of Petroleum Engineers 5 Oklahoma City, Oklahoma, pp. 449-463.