Research On Non-liner Percolation Mechanism And Productivity Models Of Gas Well In Volcanic Rock 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 sandsonte formation, volcanic rock gas reservoirs developed a multiple media including pore, fracture and vug. 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 study of the volcanic rock gas reservoir XuShen, researches on the storage-percolation patterns and nonlinear percolation mechanism have been done in this paper. Combined with the production dynamic data, mathematical models based on the nonlinear percolation mechanism in different storage-percolation modes in volcanic rock gas reservoirs have been established. The development optimization methods of volcanic rock gas reservoirs have been formed. These all provide theory foundation for the efficient development of the volcanic rock gas reserviors.The main findings are as follows:(1) According to the organic combination of different types of reservoir space and throat, the storage-percolation patterns can be divided into two types:pore and pore-fracture.5 storage-percolation patterns as follows pore type,intergranular pore type, fracture-pore type,fracture-intergranular pore type and fracture-emposieu type are proposed. Fracture-emposieu and fracture-pore patterns have better storage-percolation ability.(2)Experiment show that there are 3 flow states in volcanic rock gas reservoirs:turbulent flow, transition flow and slip flow. The flow state determining criterion for gas percolation has been built.The study reveal the non-liner percolation mechanism, such as slippage effect, turbulent flow effect, threshold pressure effect and stress sensitivity effect. The concept model for gas supply mechanism in different production stages is developed with reference to dynamic production data.(3)Based on the storage-percolation patterns and the non-liner percolation mechanism, the dynamic characteristics of gas well production of volcanic rock gas reservoirs in different storage-percolation patterns are revealed with the analysis of dynamic production data. The gas well dynamic reserve estimate models and methods, which are suitable for volcanic rock gas reservoirs, are established. The reliability of dynamic reserve estimate results are thus enhanced.(4) Based on the non-liner percolation mechanism and the production patterns, focus on the consideration of storage-percolation patterns of pore type, intergranular pore type, and fracture-pore type, the production prediction models in vertical wells, horizontal wells, fractured vertical wells, and fractured horizontal wells are built respectively. The influence of slippage effect, threshold pressure effect, and stress sensitivity effect on the volcanic rock gas production is evaluated.The research results have been applied in the development of volcanic rock gas reservoirs in China, providing theory basis for the dynamic analysis and productivity evaluation of volcanic rock gas reservoirs.