The Stimulation Efficiency Of Horizontal Well With Complex Fracture-Networks In Tight And Low Permeability Gas Reservoirs

Due to features of tight and low permeability gas reservoirs including low porosity, low permeability, poor connectivity and strong flow resistance, it is essential to stimulate reservoirs with some intense and large-scale fracturing technologies such as complex-fracturing leads to fracture networks. But the basic principles of fluid flow and optimaztion of horizontal well with fracture-networks in tight and low permeability gas reservoirs are still not known completely. Firstly, based on theory of fluid flow in tight and low permeability gas reservoirs, this thesis established analytical complex-linear flow model coupled with threshold pressure gradient, stress sensitivity and features of secondary fractures, which was verified by field data and numerical simulation data. And we obtained the analysis of transient pressure and its affected factors. Secondly, this thesis built typical conceptual horizontal wells with single fracture & fracture network model with numerical simulation methods in tight and low permeability gas reservoirs and found the main fators affect on those stimulation efficiencies, then finished the optimization plates of fractured horizontal wells with single-fractures under different reservoir conditions. Thirdly, the thesis put forward classification criterions of different reservoirs based on field datas and established three types of different geologic gas reservoir model, then finished the optimizal design and predication of stimulated efficiency of horizontal wells with single fractures & fracture-networks.The results show that the fluid flow of horizontal wells with fracture-networks could be divided into three stages including wellbore storage and transient flow, linear flow inside main fracture, radial flow around fracture networks and formation pseudo-steady flow. And with the increase of wellbore storage coefficient, the wellbore storage and transient flow could override the linear flow inside main fracture and radial flow around fracture networks. The impact of formation stress-sensitivity on horizontal well productivity of fracture networks is larger than that of formation starting-pressure. The sequence of different geologic fators affecting on the productivity of multiply-fractured horizontal wells with single-fracture is basically consistent woth those on stimulation efficiency of horizontal wells with fracture-networks. The sequence of fracture affecting on horizontal well with fracture-networks shows, fracturing stage > horizontal well length > network length > fracture distance > main fracture conductivity > secondary fracture distance > secondary fracture conductivity > distribution pattern of fracture-networks. As for three types of Sulige tight and low permeability gas reservoirs, the worse performs gas reservoir, the stronger is intensity of complex fracturing. The worse perform reservoir conditions, the more obvious show stimulation efficiency of horizontal wells with fracture network. The increasing multiple of horizontal wells productivity with fracture-networks in three types of reservoirs are about 1.37, 1.57 and 1.69 respectively. Finally, this study testifies the accuracy of numerical complex fracturing models and optimization results with the example of one block in gas fileds. The results provide theoretical references to the understanding of fluid flow, optimization design and promotion of complex fracturing technology in tight and low permeability gas reservoirs.