Research On The Diagenesis And Porosity Evolution Of Gas Reservoirs In Gypsum And Salt Rock Layers In Dongying Depression

The exploratory development of hydrocarbon is becoming more and more difficult,and it's field is also spreaded from shallow layer to deep zone and from conventionreservoir to complex reservoir. The deep gas reservoir in north actic region of DongyingDepression is researched in this paper. Because the diagenetic evolution of these gluteniteis complicated with burial deep, and there are gypsum and salt rock layers in this area, sothe predication of glutenite reservoir is very difficult. It is significant for generalization ofgas clasolite valid reservoirs in gypsum and salt bed sets distribution axiom and directionof exploration activity to research on the diagenesis and porosity evolution of gasreservoirs in gypsum and salt rock layers.In combination with core observation, logging data and regional geological settings,the characteristics of diagenesis and porosity evolution of gas reservoirs (major glutenitewith buried depth of over 3500m) in gypsum and salt bed sets in this area are studied here,by the following reservoir testing techniques such as thin section analysis, scanningelectron microscope, mercury penetration, X-ray diffraction, inclusion filling testing andfractional analysis. (1)The characteristics of reservoir diagenesis in studied area are asfollows: Part of primary intergranular pores are reserved for local reservoir uncompactionaffecting by upper gypsum and salt rock layers; Feldspar, calcite and quartz are dissolved;Hydrite mineral exist; It is general that Oil emplaces and asphalt fills pore. And fluidproperty in porosity has transformed from alkalinity formerly to acidity accompanied bythe injection of hydrocarbons. (2)Three reservoir types are divided by accumulating spacetype, whose pore evolution characteristics are then quantitatively studied respectively.Diagenesis affects pore evolution obviously:â… reservoir, whose primary accumulatingspace is emposieu, undergoes stronger compaction. The subsequent acid liquid increasereservoir porosity.â…¡reservoir, whose primary accumulating space is emposieu andfenestra, undergoes weaker compaction, and saves a great deal of fenestra. Because earlystronger alkalescence weaken subsequent acid, it undergoes weaker denudation.â…¢reservoir, whose primary accumulating space is cranny, undergoes strong compaction andcalcite cements densely. The subsequent acid liquid enters reservoir to improve it's physical property difficutly. (3)Gas reservoirs in gypsum and salt rock layers in studiedarea is poor in physical properties which is characterized by low porosity and lowpermeability. It's storage is major affected by sedimentation and diagenesis reconstructuin.Thereinto, sedimentation is base of reservoir, while diagenesis is a master factor.