Study On Reservoir - Forming Characteristics Of Chang 6 Oil - Bearing Layer In Anbian - Xin'an Area Of ​​Ordos Basin

Anbian-Xin’anbian region is located in the middle western of Yishan Slope, which is the secondary structural elements of Ordos Basin, Chang6formation is the main exploration strata in this area, lots of reservoir in scale have been found, but the hydrocarbon enrichment in different blocks of different layers of the study area has significant differences. In this paper, on the basis of the achievements of predecessors, with petroleum geology, the modern theory of hydrocarbon accumulation as the foundation, hydrocarbon accumulation conditions and hydrocarbon enrichment reason for the difference were comprehensively analyzed by using a large number of test data, then the accumulation model was established and the main controlling factors of hydrocarbon accumulation was summarized, to provide a good guidance for exploration and development of oil and gas in the next step.In this paper, by using reservoir geology, sedimentary petrology, logging geology and other theories and methods, the reservoir characteristics and the distribution features of sand body in study area were analyzed and studied comprehensively. The results showed that" the rock types of Chang6formation in study area are mainly gray fine-grained feldspar sandstone and lithic feldspar sandstone, the reservoir space are mainly intergranular pore and feldspar dissolved pore, in addition to a small amount of fracture developed. The porosity of Chang6formation are mainly distributed in the range of6%to18%and the main distribution of permeability are in the range of less than0.1to3×10-3μm2. In the vertical, the physical properties of Chang63was the worst, followed by Chang62, Chang61was the best; The physical properties of Anbian area was better than that of Xin’ anbian area on the plane. The sand body of Chang61was most developed and had large thickness, the lateral stability of sand body was good along the direction of source; followed by Chang62, the scale of sand body is less than that of Chang61, there were several sets of sand body superimposition, in part of the region also had a certain degree of connectivity; the scale of sand body of Chang63was the smallest and its lateral connectivity was the worst.The current exploration results indicate that the hydrocarbon accumulation were rich in Chang63,Chang62and Chang61in Xin’anbian region, while in Anbian area only Chang61was relatively enriched, Chang62and Chang63basically had no oil and gas show. Through the oil and source correlation pointed out Chang6crude oil in study area were mainly from the underlying Chang7source rocks long supplying, Chang6mudstone had limited contribution for accumulation; through Chang7mudstone distribution map we can conclude that Chang7mudstone was developed in Xin’anbian area, while in Anbian area was not developed; the main driving force for hydrocarbon accumulation is abnormally high pressure produced by mudstone undercompaction and hydrocarbon generation; the fracture was more developed in Xin’anbian area, while in Anbian area was not developed. In conclusion, the hydrocarbon accumulation in Xin’anbian area was the result of the hydrocarbon generated by the underlying Chang7source rock migrating vertically to Chang6formation, the fractures are the key to hydrocarbon accumulation in Xin’ anbian area. While hydrocarbon accumulation in Anbian area was the result of crude oil in Chang61of Xin’anbian migrating laterally to Chang61of Anbian, sand connectivity, physical properties and monoclinic structure are the key to hydrocarbon accumulation in Anbian area. In summary, the main controlling factors on hydrocarbon accumulation in study area are mainly in the following aspects" the distribution of source rocks, the distribution of fracture, reservoir properties, the distribution of sand body and monoclinic structure.