The Water-rock Interaction Mechanism Of The Relatively Higher Quality Sandstone Reservoirs Formation In The Fourth Member Of Xujiahe Formation, Xiaoquan-FengGu Area

Xiaoquan-FengGu area deep xujiahe formation have some geological conditions ofproduce the large and medium-sized gas field, it is also the hot spots for prospect the deepnatural gas in Western sichuan depression. But since it restricted by some difficult problemsof ultra-deep, super compactedness, fractured, heterogeneity etc., it is extremely hard toexploration and development. In many of the difficult geological problems, one of the keyproblem is the formation mechanism and development situation of the relatively higherquality reservoirs, and the diagenesis is the most important factor in many factors of controlthe high quality reservoirs, it directly affects the microscopic pore structure of the reservoir,and decided the porosity conditions of the sandstone.The thesis mainly for the study of the water-rock interaction mechanism in the reservoirdiagenetic process Xiaoquan-FengGu area, Through analysis the petrologic characteristicsand physical characteristics of sandstone reservoir, combined with the main diagenetic type inthis area, discussed the formation factors of the water-rock interaction in the relatively highquality reservoirs of research area. Through further analysis of the cause of relatively highquality reservoirs in the study area, established geological model for the prediction ofrelatively high quality-reservoir in Xiaoquan-FengGu area.The reservoir rock mainly type in the fourth member of Xujiahe formation in the studyarea are lithic sandstone, lithic quartz-sandstone and feldspar lithic sandstone, debris feldsparsandstone, feldspar sandstone, quartz sandstone and feldspar quartz sandstone. The lithicsandstone and lithic quartz-sandstone had93.09%of all rocks, and the rich in feldsparsandstone represents only about6.24%of the rock. So highly debris and poor feldspar is themain features of the particles of the sandstone skeleton in the study area. The secondaryporosity is the main reservoir space type in the study area, accounting for86.83%of the totalporosity, primary pores is10.08%, and the fracture pores and unclassified just3.09%.Arcosic dissolution is the main cause for the formation of secondary porosity in the study area.The mainly diagenesis types of the study area are compaction, pressure solution, allkinds of cemented filling action of authigenic mineral and dissolution. The mainlyprecipitation of authigenic minerals is the carbonate mineral, silicon, the next is theautogenetic clay mineral and so on. Through the research of the main water-rock interactionmechanism of the diagenetic process in the study area, the main authigenic minerals of thefourth member of Xujiahe formation of the research area are carbonate minerals (calcite,dolomite), quartz, kaolinite, illite and chlorite. Carbonate cementation is the most importantauthigenic mineral in xujiahe formation, the feature of carbon and oxygen isotope show thatthe dissolution of the feldspar and the transformation of the clay minerals is the main originabout carbonate cement in the study area. the distribution of kaolinite must be basic isdistributed in the upper section of the fourth member of Xujiahe formation, a few will berelation to the middle section. Autochlorite in the fourth member of Xujiahe is lower.Through the analysis of the formation water, the fourth member of Xujiahe formationhave obvious freshwater background, the lower feldspar content about the chemicalcharacteristic of formation water in the fourth member of Xujiahe formation have significantinfluence. Overall, excepting the buried factors, the water-rock interaction mechanism ofdiagenetic process is the important reasons lead to the differences between the strata ioncontent and isotope in the fourth and second member of Xujiahe formation.Through the thermodynamic analysis thinks that the temperature is the main factors ofinfluence feldspar dissolution; The amphodelite has the lower Gibbs free energy increment,and it more likely to occur dissolution at low temperature, potassic feldspar is one of the moststable feldspar type. Through the precipitation mechanism research of autogenetic claymineral in the study area thinks, it is the lower ratio of K+/H+activity and enough places forK+migration (adjacent thin layer of mudstone) is the main reasons of kaolinite can bepreserved on top of the fourth member of Xujiahe formation.The uniform temperature analyzed of the inclusions in the autoquartz and overgrowthquartz that: The main origins of the siliceous cement in connection with the silicon of therelease of the dissolved feldspar minerals in the fourth member of Xujiahe formation of thestudy area. The transformation of clay minerals provide some silicon, the pressolution of thehigher sandstone content in clastic quartz may be another way for the silicon source.Through the diagenetic factors of relatively high quality reservoirs analysis in the studyarea, Compaction and cementation is the main destructive diagenesis of the reservoir in thestudy area, and the compaction is the most important factors; Different grain composition ofthe rock skeleton impact on the relatively high quality reservoirs in the study area isdifference; Carbonate cementation is the first important destructive diagenetic cement in the fourth member of Xujiahe formation of the study area, it has a significant katogene forreservoir; The dissolition, especially the arcosic dissolition is the main constructive diagenesisin the fourth member of Xujiahe formation of the study area.