Study On The Law Of Decreasing Capacity Of Horizontal Well In Puguang Gas Field

Puguang Gas Field is located in Xuanhan of Sicuan Province, and is the gas source of Sichuan to East Gas Transmission in China. Due to the strong heterogeneity and the effect of edge-bottom water, the development of gas field is of high difficulty. Because of the wide use of horizontal well, the productivity analysis and decreasing characteristics analysis of horizontal well are of critical importance.Based on the reservoir properties and development characteristics of Puguang gas field, theory of gas reservoir engineering and percolation mechanics are applied, and percolation model and wellbore coupling model are established. Then the productivity analysis and the study of production decline law have been done according to the model. This paper has done some research on the following aspects:1) After deep analysis of the reservoir properties and development characteristics of Puguang gas field, the percolation models can be classified into three types by analyzing the well-testing characteristic curves, namely two homogeneous compound gas reservoir, three-section radial compound gas reservoir, and dual-media gas reservoirs.2) Based on the percolation physical models, percolation mathematical models of the horizontal wells are established. After that, this paper solved the mathematical models and analyzed the seepage law of all the models.3) Integrated coupling simulation model of "gas reservoir-horizontal wellbore-nozzle" is established. The influences of wellbore coarse degree, formation heterogeneity, damage degree and permeability are all discussed. By analyzing the production data of14horizontal wells in Puguang gas reservoir, single well reserves and skin factor, formation permeability and pressure were derived.4) Considering the effects of edge water invasion, this paper presents a forecasting method of water breakthrough time based on streamline method. According to the migration rate of gas-water interface of water invading region, the breakthrough time is derived by inversion method and the influential factors like length of horizontal well, water phase saturation, viscosity of water phase and gas phase are all considered.5) On the basis of production performance analysis of the wells, the production decline law is analyzed from respective aspects:time production decline, pressure production decline, and recovery production decline. This paper found that pressure production decline method could better represent the production decline characteristics of the gas reservoir. Besides, the production decline rate and pressure decline law are also analyzed.