Simulation Study On Development Mechanism Of Carbonate Gas Reservoir In Sinian Formation Of Gaoshiti Structure

The reservoir in the study area is a fracture-vug carbonate reservoir controlled by karstification. The typical characteristics of the reservoir are that the size of vugs is different and the distribution of the fractures is complex, so that the heterogeneity of the reservoir is strong; Unlike the conventional clastic rock reservoir, the genesis of the reservoir is relatively complicated. Therefore, there is no mature developmental model can be taken advantage for the reservoir, and how to choose the modeling method of fracture-vug type carbonate reservoir is relatively difficult. With less well point data, predicting the spatial distribution of the reservoir, and establishing a geological model conformed to the law of reservoir distribution is one of the key issues, which are needed to be resolved for the development of gas reservoir at present.According to field outcrop section, core, conventional logging and imaging logging characteristics, the reservoir can be divided into four types: I- inter- breccias vug configuration, II-porosity vug configuration, III- grape lace vug configuration, IVfracture-vug configuration. Different configuration types reflect the heterogeneity of the reservoir. Based on the above consideration, according to the existing geological static data, and aiming at the characteristics of Gaoshiti carbonate reservoir formed in Sinian system, this paper done an exploratory study about the geological modeling of fracture-vug carbonate reservoir. Drawing lessons from clastic sedimentary facies-controlled modeling ideas, the distribution of reservoir configurations was applied to the modeling of reservoir’s physical parameters as a constraint condition.In addition, for the fracture-vug carbonate reservoirs possess multiple medium, which will have an effect on fluid percolation. In order to establish the numerical simulation model with multiple medium as a preparation for the simulation study on development mechanism of the gas reservoir, this article also made an exploratory study about the triple medium’s properties modeling of matrix- fracture-vug. Firstly, utilizing conventional small plunger property data to acquire the contribution of matrix porosity and permeability,which be used to model the properties of matrix based on the existing reservoir property model. Then, utilizing the fracture parameter data from logging to acquire the contribution of fracture porosity and permeability, to get the property model of fractures. Finally, deducting the contribution of matrix and fracture porosity and permeability, to get the property model of vugs.In order to avoid the blindness of adjusting the permeability around the wells during history matching, and ensure the reliability of the numerical simulation model, with studying of the steady state instead of transient state method and the production data, this paper created the method that was deployed and used in low permeability gas reservoir of Gaoshiti Structure for the first time. With this method, the permeability in the control radius of GS3 well is 0.47×10-3μm2.According to the result of geological modeling and calculation of permeability around gas wells, here we built a triple porosity numerical modeling model of matrix-fracture-vug, then producing history of gas wells have been matching.On this basis, Though the simulation of influence over different proration productions for Z2dn2, perforating level and height of water avoidance to productivity, the results of the reasonable parameter for the stable GS1 gas well production more than 20 years include: 15×104m3/d of the rational production, 86.5m~ 98.1m of the height of water avoidance, 30%~50% of the perforating level and 25.93% of the reserve recovery degree.Though the simulation study of the GS3 well reasonable allocation for Z2dn4,the results of the parameter for the stable gas well production with 20 years include: 30×104m3/d of the rational production, 34.2% of the reserve recovery degree. The results of the parameter for the stable gas well production with 15 years include: 40×104m3/d of the rational production, 42.36% of the reserve recovery degree.By simulating of influence over different reservoir renovation scope of GS3 well to productivity, the reservoir renovation length and width should be reached 45 m and 15 m or more; permeability Multiple proportions of reservoir renovation scope inside and outside should reach more than 5 times.