Towards Effective Resolution of Borehole Stability Issues in Koshayskaya Suite while Drilling Horizontal Sidetracks in Samotlor

Kharitonov, Andrey B. (Halliburton) | Pogorelova, Svetlana (Halliburton) | Tikhonov, Evgeny Vladimirovich (Halliburton) | Sergeev, Sergey (TNK-BP) | Andriadi, Sergey (TNK-BP)


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.