Study Of Productivity Prediction Method For Horizontal Wells In Gas Reservoirs

In the 21st century, natural gas resources will be the main energy source in the world. Natural gas resources are rich in our country, and the natural gas industry is faced with unprecedented development opportunities as well. However, most of the natural gas formation in our country belongs to the middle and low permeability formation with obvious heterogeneity, low porosity and poor connectivity. It is difficult to exploit the formation effectively by using single vertical wells. In recent years, the results of horizontal wells development test for gas reservoirs are admirable. But now, there are few researches on the productivity analysis of horizontal wells in gas reservoirs. How to predict and evaluate the performance of horizontal wells in gas reservoirs accurately is one of key problems in efficient development of gas reservoirs. Therefore, the productivity prediction method for horizontal wells in gas reservoirs is developed in this paper, and the following work has been done:Firstly, the coupling model of gas reservoir percolation and wellbore flow for conventional horizontal wells is developed. The three dimensional percolation characteristic of horizontal wells is considered in the gas reservoir model, and the effect of pressure drop caused by the friction and the fluid inflow from gas reservoirs is considered in the wellbore model. The productivity prediction formula for conventional horizontal wells is provided, and influencing factors on the productivity are analyzed.Secondly, the coupling model of gas reservoir percolation, fracture percolation and wellbore flow for fractured horizontal wells is developed. The three dimensional percolation characteristic of fractured horizontal wells is considered in the gas reservoir model, the pressure drop in fracture is considered in the fracture model, and the effect of pressure drop caused by the friction and the fluid inflow from fractures is considered in the wellbore model. The productivity prediction formula for fractured horizontal wells is provided, and influencing factors on the productivity are analyzed.Thirdly, considering the heterogeneity of gas reservoirs, three dimensional percolation models of conventional horizontal wells and fractured horizontal wells are developed. The models are resolved by using finite element method, and the productivity prediction method of heterogeneous gas reservoirs is provided. Effects of heterogeneity on the productivity and the formation pressure are analyzed.Finally, cases of productivity prediction for horizontal wells in a certain deep gas reservoir of Song-Liao Basin are provided. The results show that the research method in this paper is in coincidence with the actual conditions of gas reservoirs, and it provides a new favorable method for productivity prediction of horizontal wells in gas reservoirs, and also provides necessary scientific basis for the development of gas reservoirs.