Towards Effective Resolution of Borehole Stability Issues in Koshayskaya Suite while Drilling Horizontal Sidetracks in Samotlor
- Andrey B. Kharitonov (Halliburton) | Svetlana Pogorelova (Halliburton) | Evgeny Vladimirovich Tikhonov (Halliburton) | Sergey Sergeev (TNK-BP) | Sergey Andriadi (TNK-BP)
- Document ID
- Society of Petroleum Engineers
- SPE Russian Oil and Gas Exploration and Production Technical Conference and Exhibition, 16-18 October, Moscow, Russia
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 1.2.2 Geomechanics, 4.3.3 Aspaltenes, 1.11 Drilling Fluids and Materials, 6.5.4 Naturally Occurring Radioactive Materials, 1.6 Drilling Operations, 4.3.1 Hydrates, 5.1 Reservoir Characterisation, 6.5.3 Waste Management, 4.2.3 Materials and Corrosion
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The development of the AV1 (1-2) reservoir of the Samotlor field is a priority because it accounts for 37% of the recoverable reserves of the deposit. Horizontal wells were proposed for this reservoir to help ensure satisfactory production figures. The primary problem associated with the drilling of horizontal wells by sidetracking is the necessity of opening the interval of unstable mudstone in the Koshayskaya suite, which is the overlapping impermeable seam AV1 (1-2). In the recent past, successful sidetracking in an extended interval of Koshayskaya clay exposed at an angle of more than 70º was considered to be a difficult task, and despite many attempts, this has not been achieved. In 2011, while drilling one of the wells using standard KCL/Polymer, an attempt was made to drill such a well. Initially, an additional inhibitor, asphalthene (a stabilizer of shales), was also added to the existing drilling mud used in sidetracking, but because of a more complex profile of traversing the Koshayskaya shale, various complications developed during drilling, precluding a trouble-free drilling process. The goal was set to solve this problem. After in-depth laboratory studies involving cuttings and cores collected during the drilling, the use of an additional reagent, a shale stabilizer, which includes a mixture of asphaltenes, gilsonite, and polyglycols with various cloud points was proposed for the existing drilling solution system. This system enabled the drilling of 32 wells with a complex profile. It also significantly reduced the construction time required for each well.
This study was performed on the results of 32 wells drilled. Adverse geo-physical characteristics of the AV1+2 reservoir included complex geological structure, low thicknesses, low permeability and productivity, and a high degree of heterogeneity and of initial water saturation. In addition, a gas cap is present; despite significant oil reserves (more than 900 million tons of C1 category) the reservoir has not been part of a commercial development.
For economic reasons, the development of the AV1+2 reservoir is impossible without the use of transit wells of the underlying productive horizons and without the study of geological structures and analyses of reserves in the underlying layers. The exploration and establishment of an effective technology for developing the complex reservoir is impossible without a detailed study of the geological structure and without summarizing the experiences of various development methods of the AV1+2 reservoir.
The problem of ensuring stability of argillaceous sections is critical in the construction of oil and gas wells. Time spent on addressing complications of rock deformation represents 25% of the total drilling time. In addition, the negative effects of clay slurry dispersion cause process complications, chemical cost overruns, increased volumes of technological drilling waste, and increased waste disposal costs. Hydration and the development of hydration stresses on the walls of the wells made up of argillaceous rocks can be prevented if the liquid phase of the drilling mud is a non-polar fluid, the large molecules of which cannot access the inner surface of the sliding grid minerals. The adsorption of such molecules (usually monomolecular) occurs only on the outer surface.
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