DEA-113 – Drilling Gumbo Shale – A Study of Environmentally Acceptable Muds to eliminate shale hydration and related borehold problems

DEA-113     Drilling Gumbo Shale – A Study of Environmentally Acceptable Muds to eliminate shale hydration and related borehold problems     OGS Associates

Status report of an active DEA Project

DEA Project Number: DEA-113
Project Title: Environmentally Suitable Fluids for Drilling Gumbo Shale
Contractor: OGS Laboratory, Inc. 15730 Park Row, Suite 500 Houston, Texas 77084 Phone: 281-599-1300 Fax: 281-599-1326
World Wide Web Site:
Startup Date: August, 1997
Scope of Work: The use of water-base fluids for drilling the young shales in the Gulf of Mexico has created problems which have gone unresolved for decades. These shales are termed gumbo because of the bit-balling, balling of bottom-hole assemblies, plugging of flowlines and blinding of shale shaker screens that can be observed, often leading rigsite personnel to believe that a wet, soft shale formation is being drilled. A recent core of the notorious gumbo shale in West Delta Block 109, cut using a synthetic-base mud at a depth of 4,100 ft, has shown how erroneous that conception is. The Pleistocene shale has a moisture content of only 12% and a penetrometer hardness of 99. (This can be compared to older Oligocene shale from 5,800 ft in the North Sea Central Graben which had a moisture of 15% and a penetrometer hardness of only 50.) Obviously gumbo problems result from hydration of the shale when drilled with a water-base mud. The weakening of the shale then results in high torque, drag, fill, stuck pipe and poor cementing. These problems can be avoided by use of a hydrocarbon-base mud (diesel, mineral oil, synthetic) but discharge of cuttings from such muds is prohibited within the three-mile limit and there is concern about extension of such prohibitions to other Gulf of Mexico operations. Over the years many types of water-base muds have been used with very little success in combating gumbo shale problems. The lack of success can be attributed in part to misleading results of laboratory studies exposing unconfined, unstressed specimens of weathered shale to the muds being studied. A major artifact is air in the shale pore spaces creating capillary forces that are not present when drilling water-saturated shale at depth. Now, for the first time, preserved shale core and the necessary laboratory equipment and procedures are available to determine whether or not a water-base mud will actually prevent hydration and weakening of a typical Gulf of Mexico gumbo shale. The OGS Downhole Simulation Cell (DSC) equipment developed under DEA-22 has been modified in the Gas Research Institute (GRI) project “Effects of Drilling Fluid/Shale Interactions on Borehole Stability” to permit measurement of water transport from drilling fluid into shale or from shale to drilling fluid, and to determine the resulting effect on the strength of the shale. Only solids-free drilling fluids have been tested in the GRI research. This proposed DEA-#113 project will study complete drilling muds having rheology, gel strength, and filtration control suitable for typical Gulf of Mexico drilling operations. A shale specimen will be restored to the in situ temperature, vertical stress, horizontal stress and pore pressure estimated for the shale as cored. The shale will then be drilled with the mud to be studied. Each DSC test will measure the rate of water transport into or out of the shale. At the end of the exposure period the borehole pressure will be reduced incrementally to observe for borehole failure and obtain a measure of effect of the mud on the relative stability of the shale. Upon removal from the DSC the shale specimen will be photographed and examined as to moisture, penetrometer hardness, borehole condition and type of failure, if any. Module 1 of the proposed project will include tests of certain muds to permit correlation with field performance. A DSC test will be made of a synthetic-base mud representative of that used to obtain the core and now being used successfully for drilling. Another reference system will be a potassium hydroxide/lime mud representative of water-base systems previously used when experiencing gumbo problems. Each sponsoring company will have the option of selecting a mud system to be tested as part of Module 1. It is anticipated that these selections will include many of the newer water-base muds (such as polyglycol, terpene, formate, silicate and methyl glucoside systems) that have been proposed for combating shale problems in the Gulf of Mexico. Module 2 will be based on the results of Module 1. Mud systems found to prevent water entry and weakening of the shale will be tested further to investigate operating limits and optimize cost/performance. The test selection will be made by a group composed of a representative of each Sponsor. The deliverables will give a performance comparison of the candidate mud systems under the best simulation of downhole conditions available to the Industry. Guidelines will also be provided for formulation and maintenance of successful systems to obtain optimum cost/performance.  For additional information, please contact either Jay P. Simpson, O’Brien-Goins-Simpson & Associates, Inc., Telephone 713-2760-1192 Fax 713-270-4105 or Harry L. Dearing, OGS Laboratory Telephone 713-266-3173 Fax 713-266-6491.
Current Status: The final report for Phase I of DEA-113 has been sent to the Participants’ Representatives. The packet included a bound copy of the DEA-113 report as well as well as a bound copy of the related Gas Research Institute report. A final review meeting for Phase I of DEA 113 has been scheduled for Tuesday August 21 at 9AM at the Houston Engineering and Scientific Society (HESS), 5430 Westheimer, Houston, TX. The meeting will provide a summary review of the test results and a discussion of additional studies that could be conducted in a Phase 2 extension of DEA-113.
Projected Completion Date: August 2001
Project Cost: $455,000
Participants: Amoco Production Company, Arco E&P Technology, Baker Hughes Inteq, Baroid Drilling Fluids, Chevron Petroleum Technology, Exxon Production Research Company, Gas Reserch Institute, M-I Drilling Fluids, L.L.C., Mobil E&P Technology, Schlumberger Technology Corporation, Shell E&P Technology, Texaco E&P Technology, Unocal Technical & Operations Support, Newpark Drilling Fluids, PQ Corporation.
Cost per Participant: $35,000
Comments: Additional sponsors could result in extension of the scope of the work and the time for completion.

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