Study On Carbonate Reserovir Predication In West Sichuan Depression

The oil & gas exploration of carbonate rocks in Tarim, Erdos and Sichuan basins has made important progress in these years so the exploration and study of carbonate rock reservoirs regains attention from the world. This also increases the pace of discovering marine facies gas field in west Sichuan depression. There is much 2D and 3D seismic data about west Sichuan area, but most of them targets in middle and shallow formation and the drilling data are especially scarce. The study on the conditions of oil & gas generation, accumulation and migration is comparatively little and the exploration & research is in the primary phase. This study is conducted by the thoughts of combining the geology and seismic, the macroscopic and the microscopic, the spots and the areas, and the study progress plus the dynamic exploration. On the base of the former study and the information from the new practice about 2D seismic activities, exploration wells, study wells, this dissertation conducted compound research on the structure, sedimentary facies and reservoir formation, expecting to find advantageous reservoir stratum and the distribution laws to guide the exploration work on the carbonate rock depressions in west Sichuan marine Facies. The study area locates in west Sichuan Basin from Longmen Mount. in the west, Guangyuan, Wangcang in the north, Danling, Ziyang in the east and Qionglai in the south with total area about 20000km2. The study formation is between Permian and the Middle to Lower Triassic. According to the study work designed by this dissertation, many study work on the formation, sedimentation, structure and the reservoir prognosis & evaluation have been done and the comparison of formations, section observation, interpretation of drilling and seismic data study have been took to analyze the characteristics of structure evolvement and sedimentation, predicting the traits and distribution of advantageous reservoir and the following achievements have been made:1. On the base of former researchers, improved the marine carbonate rock formation distribution plan by comparing the study area and the adjacent formations.2. The evolving pattern of marine carbonate rock sedimentation from Permian to Middle & Lower Triassic in west Sichuan has been built according to the area sedimentary conditions, drilling, outcrop sections, seismic data and the analysis of sedimentary characteristics in this area. Two main sedimentary system have been evolved in west Sichuan depression: one is the slope sedimentary system, mainly distributes in the Qixia Formation and Maokou Formaion in Permian, the other is rimmed platform sedimentary system and located in the Upper Permian to the Triassic.3. Advantageous sedimentary facies distribution of Permian and Triassic in west Sichuan depression has been depicted by the technology of seismic facies analysis. The platform rimmed facies of late Permian-Feixianguan locates in Hanwang-Jiangyou-Bazhong areas, the Jialingjiang-Leikoupo rimmed platform facies locates in the east of Jiuding Mount, which is on the west side of Yangzi, Majiaoba-Mianyang-Deyang-Pengzhou-Dayi areas.4. Based on the model analysis and started from the seismic reflection structure, combining the velocity analysis results, seismic property analysis and spectrum imaging analysis will be the mainly effective technology combination of predicting carbonate rock reservoir in west Sichuan. The seismic facies analysis shows that four reflection structures has the features of platform margin shoal facies and intra-platform facies which include"low frequency, weak amplitude, inter chaos, mound seismic reflection configuration","low frequency, weak amplitude, mound and forest seismic reflection configuration","middle frequency, middle-strong amplitude, interrupted seismic reflection configuration","low frequency, middle-strong amplitude, stacked seismic reflection configuration". The properties as seismic reflection intensity and the energy frequency scanning etc. have a good depiction of the rock characteristics. The velocity analysis took the shoal reservoir as"bright spot"reflection property and had the inter reflection structure traits of progressive (or regressive) type and the mound overlay.5. The study shows that the reservoir mainly belongs to the low porosity and low permeability and the pore structure is mainly characterized by middle-small pore. The advantageous reservoirs mainly distribute in the second and third section of Leikoupo Phase, followed by the second section of Jialingjiang Phase and the third Feixianguan Formation. The best petrophysical properties will be in the oolitic dolomite or middle-fine crystal dolomite. The best pore type is the denudation pores.6. The II-IV type of comparatively good or middle reservoir mainly formed in the west Sichuan marine carbonate rock formation of Permian-Middle/Lower Triassic, and most of them evolved on the platform rimmed facies, located in the middle and north section of west Sichuan. Considering the formations, the comparatively poor or poor reservoir of III-IV type evolved in the Qixia and Maokou Formation of Permian in this area and Feixianguan, Jialingjiang and Leikoupo formation of middle-lower Triassic evolved the II-IV type of comparatively rich or poor reservoirs.