鄂尔多斯盆地富县地区长7段深水重力流沉积及勘探意义OA

[Objective]The Chang 7 member of the Triassic Yanchang Formation in the Ordos Basin mainly developed semi-deep lake-deep lake subfacies;deep-water gravity flow deposits are widely developed.This study aimed to clarify its sedimentary characteristics and distribution rules which can indicate the direction of oil and gas exploration.[Methods]Taking the Chang 7 member in the Fuxian area of the southeastern basin as the research object,based on the fine description,grain size analysis and logging data of centimeter-level cores from 13 coring wells,the types and characteristics,distribution law and evolution model of gravity flow deposits in the Chang 7 member were clarified.Combined with oil and production test data,the control effect of gravity flows on reservoir distribution was analyzed.[Results]The results show that the Chang 7 member in the Fuxian area mainly developed three types of gravity flow sedimentary microfacies:sliding-slump,sandy debris flow,and turbidity current deposition.The sliding-slump deposits are characterized by the development of enclave bedding,crumpled deformation structures,and syn-depositional stepped small faults and sliding surfaces and are dominated by mixed deposits of sandstone and mud-stone.Sandy debris flow deposits have developed thick massive sandstone,mudstone tearing debris,and mud-encapsulated gravel structure.The thickness of single sand body is 0.3-3.5 m,and the cumulative thickness can reach more than 10 m.Turbidity current deposits have developed flame-like structures,groove molds,other bottom mold structures,and incomplete Bouma sequences.Sand bodies are small in scale and limited in development.The thickness of single sand bodies is several centimeters to tens of centimeters.The Chang 7 member is divided into six typical logging facies combinations and 11 lithofacies types.The grain size probability accumulation curve is charac-terized by"one-stage suspension"and a"wide arch".Most of the data in the C-M diagram are parallel to the C=M baseline.[Conclusions]Among the three kinds of gravity flow sedimentary microfacies in the Chang 7 member,the sandy debris flow has the largest scale of development,accounting for approximately 80%,and the drilling frequency is 60%,making it the most favorable reservoir.Sliding-slump and turbidity current deposits account for approximate-ly 10%.The formation mechanism of the gravity flow in the Chang 7 member is a variety of effects of underwater slope break zones,volcanos,and earthquakes.The development scale of deep-water gravity flow deposits is large,and it forms a good"source-reservoir-cap"combination configuration with source rocks vertically,creating conditions for the near-source accumulation of tight oil.On the plane,the Chang 73 sub-member mainly developed turbidity current deposits,and the Chang 72 and Chang 71 sub-members mainly developed sandy debris flow and turbidity current de-posits.The sandy debris flow sand body has a high oil level,mainly oil immersion and oil spots.In the sandy debris flow development area,the industrial oil flow wells account for 21%of the total number of test wells,making it the key target area for the next exploration.