Haggerty and Seyler (1997) conducted an extensive laboratory investigation of formation damage by mud cleanout acids and injection waters in Aux Vases sandstone reservoirs. They determined that typical Aux Vases reservoir formation is "a poorly cemented, soft, friable, fine-grained sandstone with pores lined with diagenetic clay minerals. The diagenetic clay mineral suite in Aux Vases reservoirs is a closely intergrown mixture of mixed-layered illite/smetite, chlorite, and illite. No kaolinite was found in the Aux Vases reservoir rocks sampled." They recommended that injection waters should be as saline as the formation brines and a properly formulated mud cleanout acid should be used to reduce formation damage.

Petrographic Analyses

Seyler (1998) conducted an extensive petrographical analyses of the core samples obtained from Aux Vases reservoirs. Seyler (1998) examined over 150 thin sections.

The petrographical analyses conducted included:

1. Standard optical microscopy using thin sections. For this purpose, they stained the thin sections with potassium ferricyanide and alizarine red to distinguish and detect the carbonate phases. Petro

graphical characteristics and attributes, such as grain composition and size, cementing agents, porosity types, and reservoir quality were determined.

2. X-ray diffraction analysis (XRD). The XRD analyses determined the type and semi-quantitative composition of the minerals present in the samples.

3. Scanning electron microscopy (SEM) with energy dispersive x-ray microbeam (EDX) analysis, referred to as the SEM/EDX analysis.

For this purpose, the samples were sputter-coated with gold and palladium. The SEM analyses identified the pore-lining minerals and the EDX analysis determined the elemental composition.

The analyses of the individual core samples are presented by Haggerty and Seyler (1997). They concluded that Aux Vases formation core samples contained 65-90% quartz, 3-15% feldspar, 0-15% calcite and 2-7% clay minerals.

Haggerty and Seyler (1997) determined that calcite is the primary porefilling mineral. They described the observed three types of pore filling calcite as: "In relative order of abundance, they are

1 patchy cement filling intergranular porosity;

2 framework grains such as marine fossil fragments, ooids, and pelloids; and

3 minute, late-stage euhedral crystals on diagenetic clay minerals that coat framework grains and line pores.

" Haggerty and Seyler (1997) describe the pore-lining minerals to be, "in descending order of abundance, dominantly diagenetic clay minerals, calcite, partially dissolved feldspars, solid hydrocarbons, anatase, barium-rich celestite, and traces of dolomite." Haggerty and Seyler (1997) observed that "Pores in Aux Vases sandstone reservoirs are lined with, and may be bridged by, diagenetic clay minerals that consist of an intimately intergrown mixture of mixed-layered illite/smectite, chlorite, and illite. Although clay minerals constitute only 2-7% of the bulk mineral content, SEM analysis indicates that clay minerals coat more than 95% of pore surfaces.

Therefore, an understanding of the composition and response of these diagenetic clay minerals to injected fluids is of utmost importance when selecting drilling muds and stimulation methods." "Chlorite identified by XRD and SEM/EDX analyses in Aux Vases samples is typically not iron-rich, but contains approximately equal amounts of iron and magnesium." "Reservoirs containing chlorite rich in iron may be more susceptible to formation damage than those containing other varieties of chlorite because they may form insoluble iron oxides or iron hydroxides." Haggerty and Seyler (1997) report that the mixed-layered illite/montmorillinite (smectite) varieties are the only water sensitive, expandable clay minerals they found in the Aux Vases core samples.

Focus and Design of Experimental Studies

The primary objective of the studies by Haggerty and Seyler (1997) is the Experimental Investigation of Formation Damage by

1 mud cleanout acids and

2 injection waters in Aux Vases sandstone reservoirs.

Haggerty and Seyler (1997) describe that: "Development of sandstone reservoirs in the Illinois Basin typically includes these steps:

1. Drilling with freshwater mud;

2. Perforating the potential reservoir zone, if casing is used, or open hole completions with casing cemented above the producing zone;

3. Preflushing with 15% hydrochloric acid (HCL) or mud cleanout acid (MCA) to remove drilling mud;

4. Cleaning out perforations or the well bore with MCA;

5. Initial swabbing to retrieve stimulation fluids and induce oil flow toward the wellbore;

6. Hydraulic fracturing using a freshwater gelled pad and sand propant;

7. Final swabbing during the production test.

In an effort to simulate the field practice in the laboratory investigations, Haggerty and Seyler (1997) state that: "The experiments focused on five objectives:

1. Determine how MCA containing 15% HCL with additives, typically used during completion and/or stimulation, affects pore-lining minerals and the permeability of Aux Vases reservoir rocks by conducting dynamic, constant rate injection coreflood experiments;

2. Investigate how 15% HCL and MCA affects crude oil from Aux Vases reservoirs by conducting compatibility experiments;

3. Examine how exposure to fluids of various salinities affects permeability in samples of Aux Vases reservoirs by conducting coreflood experiments;

4. Investigate the effects of long-term contact of 15% HCL and MCA with pore-lining minerals in reservoir samples by conducting static soak experiments;

5. Compare XRD analyses of the bulk mineralogy and SEM/EDX analyses of pore-lining minerals with flood results to identify minerals that would be most affected by fluids commonly used during drilling, completion, and stimulation of Aux Vases reservoirs.

Therefore, Haggerty and Seyler (1997) carried out five sets of bench experiments, with the specific objectives described in this article. The direct contact experiments have been conducted to determine the effect of the acids on the physical properties of crude oil. In the coreflood tests, they continuously injected excessive amounts (25 to 50 pore volumes) of fluid during coreflood experiments. Therefore, Haggerty and Seyler (1997) state that their coreflood experiments most closely represent the completely flushed reservoir zones and, under these conditions, the precipitates cannot deposit and cause formation damage in porous media, within the time scale of the convective flow. The acid soak experiments served for the purpose of observing the long-term effects of reactions in unflushed and incompletely flushed zones.


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.