Productivity Evaluation Of Horizontal Wells In Volcanic Gas Reservoirs

As a new exploration and development field, volcanic rock gas resources are abundant and have a broad prospect. At present, the proved geologic reserves are more than hundreds of billions of cubic meters in China which has the largest volcanic rock gas reserves in the world. Facing rapid growth in national energy demand, the development of volcanic rock gas reservoirs will be of great significance for ensuring national energy security, optimizing the energy structure and improving the environment.Compared with conventional gas reservoirs in sandstone formation, volcanic rock gas reservoirs developed a complex storage-percolation modes, which include pore, cavity and fracture. There are no suitable percolation mathematical models and productivity prediction methods for volcanic rock gas reservoir with the complex multiple media for the poor reservoirs property and complex percolation mechanism. With the combination of modern fluid mechanics in porous medium, reservoir engineering, well test analysis, mathematical physics, computer programming and other subjects knowledge, in the conditions of different media, we make a series of researches on unstable seepage theory, well test analysis methods of horizontal well and fracturing horizontal well in volcanic rock gas reservoir, providing a theoretical basis for volcanic rock gas development.The main works accomplished in this article are as follows:(1)Based on the extensive research on domestic and foreign literature, the volcanic rock gas reservoir characteristics, micro-flow characteristics, output characteristics, methods of productivity evaluation within horizontal and fractured horizontal wells are summarized.(2)Starting from the seepage principle of volcanic rock gas reservoir, considering the effect of wellbore storage and skin effect, an unstable flow mathematical model of horizontal well in fracture-pore media volcanic rock gas reservoir has been established. Solving the model with LAPLACE transform and FOURIER transform, we can obtain the LAPLACE space solution under different outer boundary conditions. At last, we draw the productivity feature curves, divide the phases of productivity feature curves and analyze the effects of various parameters on the curve shape.(3)An unstable productivity model of finite conductivity fracturing horizontal well in fracture-pore media shale gas reservoir has been established. The cracks discrete mechanism has been introduced in the model. Solving the seepage model with semi-analytical method, we draw the productivity feature curves, divide the phases of productivity feature curves and analyze the effects of various parameters on the curve shape.(4)An unstable productivity model of infinite conductivity fracturing horizontal well which consider the flow resistance of artificial crack in fracture-pore media volcanic rock gas reservoir has been established. Solving the seepage model with semi-analytical method, we draw the productivity feature curves and divide the phases of productivity feature curves.(5)The real well test data are analyzed by well test models of volcanic rock reservoirs which are established in this article. The results verify the proposed well test interpretation theory and its applicability.