The article is devoted to analysis drilling results at BU212 and BU213-1 deposits of Vostochno-Messoyakhskoe field. These deposits are composed by deep-water fans of lower Neokomian clinoform complex. Srednemessoyakhsky Swell had a huge impact to lateral paleo-transport directions of sediments. It was a kind of barrier helped to generate a sediment wedge that has affected on sediment flow direction. BU212 and BU213-1 deposits differ from analogue Achimov formation in neighbor oilfields by relatively high properties: average value of porosity coefficient varies from 16.5 to 19.5 %, while permeability may reach from 3.6·10-3 up to 46·10-3 μm2. Comparison of well lithology interpretation with simultaneous inversion results has showed that P-wave impedance cube matches well data best of other calculated elastic parameters. Therefore, this cube is used in geological model for net volume cube calculation. Due to seismic data resolution, calculated acoustic impedance shows only the tendency of reservoir distribution. There is a risk to estimate net volume incorrectly in the case of layer thinning and interference with underlying bed. For instance, section of one of the wells, drilled in proximal part of fan and channel, testifies that impedance matches well log interpretation data: you can clearly determine the borders of distributary channel and fan on seismic section. At the same time another well, drilled in distal part of the fan, has revealed the section with significantly higher compartmentalization and lower NTG, despite the fact that seismic data in this zone are characterized by the same values of acoustic impedance as in the proximal zone. In this case, optimal drilling strategy and well construction were chosen owing to sedimentary process understanding. Regarding formation are characterized by anomalous high pressure, therefore elastic parameters behavior in overpressured reservoir conditions should be taken into account. In this state acoustic impedance decreases within argillaceous rocks as well as in the reservoir. This feature makes geological interpretation of inversion results more complicated and ambiguous. According to analysis of Achimov formation at Vostochno-Messoyakhskoe field such a dramatic decrease of impedance down to reservoir values might be caused by decompaction in conjunction with gas presence in clay pores. To avoid misinterpretation of argillaceous formation as reservoir units, complex geological and geophysical analysis should be conducted including petro-elastic modelling and precise seismic and geological model with potential reservoir area determination.
References
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