Controlling Factors Analysis And Evaluation Study On The Upper Triassic Oil And Gas Reservoir In Western Sichuan Basin

The reservoir of Xujiahe formation of the Upper Triassic clastic reservoir is one of the key stratum series in the western Sichuan foreland basin. Due to the pay formation was buried deeply and depressed for a long time, it is the reservoir with low porosity , low permeability and heterogeneous, which is very hard to explore. Therefore, it is necessary to make research into Xujiahe formation of the Upper Triassic reservoir characteristics.Based on the theories and technologies of sedimentology, reservoir geology, petrology, geochemistry and reservoir evaluation, researches are carried out on several aspects such as reservoir petrologic characteristics, reservoir sandbody genesis types and distribution characteristics, diagenesis type, reservoir pore types and evolution, physical property characteristics and its controlling factors. The results are as follows:(1) By the thin section observation, the analysis of the scanning electron microscope and the electron microprobe, it is thought reasonable that quartz direct dissolution exist in west Sichuan foreland basin of the Upper Triassic formation. The paper not only pointed out the area of quartz dissolution, analyzed the origion of alkaline fluid and the order of acidic and alkaline dissolution, but also quanized the effect of the alkaline dissolution to the reservoir characteristics.(2) By combination of diagenetic facies study with regional structural movement, depositional environment, fluid characteristics and provenance property, the paper proposed the effective study method of reservoir diagenetic facies. The diagenetic single factor of reservoirs was analyzed in the western Sichuan foreland basin of the Upper Triassic. This paper determined the comprehensive diagenetic facies by superimposing the single factor diagenetic facies. The relationship of diagenetic facies and reservoir physical property was established. The reservoir of the Upper Triassic in the western Sichuan foreland basin can be divided into six kinds of single diagenetic facies and eleven kinds of comprehensive diagenetic facies. The mainly diagenetic facies which effect the reservoir characteristics include lining chlorite facies, dissolution facies, fracture facies, compaction-pressolution facies, quartz secondary enlargement facies and carbonate cementation facies.(3) Based on the comprehensive analysis on the influence of structure, sequence– sedmient and diagenesis, worked out the chief controlling factors of reservoir property in different foreland structure: in thrust belts structure fracture were chief factor, in fore-deep fracture and diagenesis were necessary, in fore-slope the kinds of sand body were important,which were controled by sequence– sedmient and diagenesis, in fore-bulge sequence and sedmient were chief factors. The high quality reservoir mainly developed in fore-slope and fore-bulge belt.(4) In the end, the clastic reservoir evaluation and prediction were performed in the different tectonic zones and different sequences of the Upper Triassic in the western Sichuan foreland basin on the base of sedimentary facies distribution, diagenesis facies, reservoir evolution mode, pore and permeability distribution ichnographies. SequenceⅡLST high quality reservoirs developed in Anyue, Nanchong, Tongnan and Moxi structure, SequenceⅢLST high quality reservoirs developed in Bajiaochang, Xichong, Tongnan and Moxi structure. Good reservoirs developed in delta front subfacies, with the kind of diagenetic facies series of compaction-lining chlorite-dissolution-fracture facies.