Research On Diagenetic Facies Of The 2^th Member Of Xu Jiahe Formation In The Xin Chang Structural Belt

The deeply buried 2nd member of Xujiahe formation in the Xinchang structural belt developed a tight sandstone reservoir with extraordinary low porosity and permeability and strong heterogeneity.The diagenesis,which, combined with diagenetic environment and products, can be characterized integratedly by diagenetic facies, has remarkable effects on the reservoir development and is the key factor in controlling the reservoir quality.Based on the core and thin section observation and description, with the use of SEM, EMPA, XRD, CL and geothermometry from fluid inclusions, this thesis described the lithology and mineralogy, investigated the diagenetic history and porosity/permeability evolution, and summarized the diagenetic facies and their reservoir properties of the 2nd member of Xujiahe formation.Logging data are very useful materials in reservoir study, but they were seldom used in digenetic facies investigation to date. By means of analyzing the responses of different logging data to certain diagenetic facies, the most sensitive ones were screened out to construct the logging interpretation models of diagenetic facies. On the basis of these models coupled with the data of mud logs gas shows, well log interpretation and gas production test, the comprehensive discretion criteria of different diagenesis facies were established.Vertically continuous diagenetic facies of a number of wells were studied with the help of established criteria and further horizontal-well correlation of diagenetic facies were performed, which revealed the spatial distribution of diagenetic facies of the 2nd member of Xujiahe formation.At last, the controlling factors of those diagenetic facies advantageous to reservoir development were discussed.The major conclusions are as follows:The reservoir of the 2nd member of Xujiahe formation consists primarily of lithic sandstone,lithic quartz sandstone and feldspar lithic sandstone.Three sub members of the stratum show a certain degree of petrological differences.The sandstones underwent a complex diagenetic history. Destructive diageneses include compaction, carbonate and siliceous cementation while constructive diageneses include dissolution and fracturing. Chlorite rim formation and initial carbonate and siliceous cementation can be looked as reservoir quality retention processes.Though the sandstones,taken as a whole,are in the middle diagenetic phase B, each submember experienced different history of diagenetic evolution.Compaction is the most important process in the sandstone porosity loss, and the carbonate and siliceous cementation further reinforced the densification of the sandstones.The main types of the diagenetic facies include compaction facies, corrosion facies,carbonate cementation facies, siliceous cementation facies, grain rimming Chlorite facies, fracturing facies, corrosion-compaction facies, corrosion-cementation facies, and cemention-compaction facies.The diagenetic facies advantageous to the development of the high-quality reservoir include grain rimming chlorite facies,fracturing facies and corrosion facies. Siliceous cementation and corrosion-compaction facies are the less advantageous diagenetic facies.The main controlling factors for the diagenetic facies formation are lithology, sedimentary micro-facies and the degree of sandstone fracturing.