Diagenesis Of The Devonian Donghetang Formation Reservoir In The Bachu Area, Tarim Basin

The Donghetang reservoir in west Bachu area had good oil and gas shows, it was low oil yield and belonged to low porosity, low permeability tight reservoir. According to regional geological data, drilling and logging data, a lot of rock thin section, scanning electron microscope, cathodoluminescence, and X-ray diffraction test data etc., and combining previous research results, the paper detailedly research diagenesis types and feature, diagenesis stage, diagenetic sequence, porosity evolution, guided by sedimentology and reservoir geology. Following work is diagenetic classification, and seriously analyzes the influence of diagenesis on reservoir and the relationship between diagenetic facies and reservoir physical property.In the research area, there developed three types of sandstone, including lithic quartz sandstone, quartz sandstone and lithic sandstone, which mainly were lithic quartz sandstone. The lower Donghetang reservoir was mainly lithic quartz sandstone, and the upper Donghetang reservoir was mainly quartz sandstone. The debris granularity was mainly medium to fined grained and fined grained, its granule separation was medium to fined.The roundness was primarily subangular, followed by subroundrd to subangular. Textural maturity was medium. Porosity and permeability were correlation, Donghetang reservoir belong to pore type reservoir.Donghetang reservoir has experienced six kinds of diagenesis. The compaction destruction degree of original pore was greater than the cementation, both were the main reasons for the reservoir density. Cementation had two stage siliceous cementation, two stage calcite cementation and clay mineral cementation. Metasomatism was that calcite mainly replace detrital grain, which had little influence on reservoir property. Dissolution grew three stage, which was key to improve the reservoir property. Dissolution object covered feldspar, lithic, quartz and calcareous cement. Fracturing formed structural fracture and diagenetic fracture. Hydrocarbon injection grew three stage. Both fracturing and hydrocarbon injection had a positive effect on reservoir physical property. Diagenetic stage of Donghetang formation was divided into Medium-term A-B. The paper quantitatively analyses pore evolution of Donghetang formation, including lower Donghetang reservoir from 33.8% to 8.03%, and upper Donghetang reservoir from 35.76% to 6.38%.This thesis, through different diagenesis, diagenetic strength and asphalt filling, has put forward seven kinds of diagenetic facies, including medium compaction medium cementation strong dissolution facies (?), medium compaction medium cementation medium dissolution facies (?), medium compaction medium cementation weak dissolution facies (?), strong compaction medium cementation weak dissolution facies (?), weak compaction strong cementation weak dissolution facies (?), medium compaction strong cementation weak dissolution facies (?) and asphalt filling facies. ?-? facies are favorable facies, that have well physical property. ?-? facies are destructive facies, that have poor physical property. Using the log data of neutron logging, density logging, acoustic logging, gamma-ray logging, and base on k-nearest neighbor classification method, the continuous logging diagenetic facies automatically recognize Donghetang formation in research area. On this basis, the favorable diagenetic facies(?-? facies) of Donghetang formation are primarily distributed on northwest Bachu area whose porosity is well. Both favorable diagenetic facies and porosity distribution have good matching relationship. In contrast, the favorable diagenetic facies of the lower Donghetang reservoir is more development than the upper Donghetang reservoir.