Abstract
Field development planning requires a proper understanding of layer permeability in order to predict production rates. Experience with horizontal production wells in the Pokurskaya formation of the Messoyakhskoye field showed systematically lower flow rates from the B sands versus the C layers even though their petrophysical properties appear similar. It was proposed that differing permeability anisotropy between the layers might be the cause and an upcoming well in the field offered the ability to test this hypothesis. A logging program that included Vertical Interference Tests (VIT) with a Wireline Formation Tester tool (WFT) and advanced petrophysical logs, 3D resistivity, NMR and dielectric scanner was run to estimate the the kv/kh ratio pointwise with VIT and extrapolate these measurements through the entire section.
VIT tests were done at several depths with a dual-packer for the fluid withdrawing and a pressure probe for pressure monitoring. Estimated anisotropy coefficient varies mainly from 0.02 to 0.07 but with both higher and significantly lower values at some depths, which indicate extremely limited connectivity in some intervals. In general, the kv/kh ratio is significantly lower in the upper interval of the PK1-3 formation versus its lower interval. The triaxial induction logging shown the anisotropy of the reservoir electrical properties (Rv> Rh), caused by thin interbedding of the sandy fraction rocks with the interlayers of clays and siltstones, which are several times lower than the resolution of standard logging methods. Similarly, interlayering of thin sand and silty rock types, which have different absolute permeabilities, causes anisotropy of the formation permeability. It is possible to estimate the permeability of the macroanisotropic formation along and across the bedding knowing the water-retaining capacity as well as the laminated sand fraction coefficient. The VIT and the logging results are consistent enough. The VIT test results are the reference measurements while the 3D induction logging results are used for interpolation and extrapolation of these direct measurements through the entire interval and in wells without VIT tests including horizontal wells.
The subsequent analysis showed a significant anisotropy of permeability in the Pokurskaya formation, which varies along the interval of the formation and, probably, laterally. This must be taken into account when calculating the flow rates of the well. The complex of studies makes it possible to perform an express estimation of the permeability anisotropy in the pilot wells in order to select the optimal interval for horizontal wells landing.
