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Study On The Formation Mechanism And Exploration Target Of Jurassic Subtle Gas Reservoir In Western Sichuan Basin

Posted on:2008-05-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:W L ZhangFull Text:PDF
GTID:1100360215969343Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
Subtle oil and gas reservoir exploration is a problem at present. In view of thegeological feature of the Jurassic subtle gas reservoir in western Sichuan province, this papersystematically studied the hydrocarbon generative capacity of source rock, the dynamics andconducting conditions of secondary hydrocarbon migration, and hydrocarbon accumulation andformation mechanism based on hydrocarbon organic geochemistry, reservoir formation dynamics,seismic stratigraphy, sequence stratigraphy and subtle oil and gas reservoir exploration theory. Italso summarized the main control factors for the formation of gas reservoir and its basicdistribution laws. The prominent characteristic of this study was the cross and mixing ofmultidisciplinary, multi-fields and multi-levels. New results and understandings were achieved asthe following:Based on source rock organic geochemistry feature analysis and the hydrocarbongenerative capacity simulation, it was pointed out that in western Sichuan provincemost Jurassic stratigraphy can not generate hydrocarbon except the low hydrocarbongenerative capacity of Ziliujing Member in local area. The gas source was mainlyfrom the underlying coal system layer of upper Triassic. Gas source correlationresearch showed that natural gas in Jurassic reservoir was mainly generated from No.in Xujiahe Member.Through typical gas reservoir analysis, it was summarized that in the southernarea of western Sichuan province the sedimentation and diageneses were the maincontrol factors for Jurassic subtle gas reservoir with lithologic traps andlithologic~structural combination traps. The sedimentation controlled the spatialdistribution and the thickness of sand body, sand granularity and feldspar content, etc.,while corrosion and fracture decided the developing degree of porosity andpermeability of effective reservoirs.Based on the systematic study on fluid potential, fluid pressure, hydrocarbon generation and conducting conditions, it was pointed out that the upper Triassic hydrocarbon in the southern area of western Sichuan province migrated v ertically and laterally through conducting systems as sand layer and fractures.Natural gas in the upper Triassic erupted vertically into the Jurassic reserves along the fracture system, while on the lateral the region was controlled by fluid potential so gas migrated and accumulated southeastward to the high partswith low potential. Subtle gas reservoir formation pattern was set up on the basis of comprehensive analysis on reservoir formation mechanism.Based on the field outcrops, coring observation and well logging data, andsequence stratigraphy principle, this paper systematically studied the sequenceframework of Jurassic in this area. On this basis high resolution sequence stratigraphyresearch was carried out for the first time on Jurassic Shaximiao Member inDaxingxi~Mingshan region in the favorable target zone, and summarized the verticaland horizontal distribution laws of the reserves. It also predicted the favorable zonefor reservoir distribution.Combined the methods of natural gammar inversion, velocity inversion withporosity reversion, 38 seismic lines, totally 805.16km, was specially processed, andcomprehensive prediction on reservoir distribution was carried out. Also the planeand section distribution feature of Shaximiao Member reservoir was made clear. Onthis basis the advanced Freca fracture prediction software was used for prediction andanalysis on fracture developing region to decide the recent favorable explorationtarget.
Keywords/Search Tags:western Sichuan basin, Jurassic, subtle gas reservoir fluid pressures compartment, reservoir formation mechanism, gas released from water, pressures drop and expansion
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