Productivity Analysis Research On Staged-fracturing Horizontal Wells In Shale Gas Reservoir

The feature of shale gas reservoir has characteristics of minimal porosity, extremely low permeability, generally deeper formation and poorer physical properties, so shale gas must go through hydraulic fracturing in order to obtain a higher production capacity. Development of shale gas by using horizontal well fracturing measure has become a trend in shale gas development all over the world,but the interaction of the desorption, diffusion and seepage exists in in shale gas reservoir and it has the unique seepage characteristics, and productivity analysis is more complex.After a lot of survey and study on correlated documents, this paper summarizes the reservoir characteristics and properties of the shale gas reservoirs and research progress on productivity analysis, introduces the characteristics and properties of shale gas reserviors,the storage of shale gas and the mechanisms of the migration and output. Considering the special coexistence of adsorbed gas and free gas in shale gas reservoir, a mathematical transient flow model incorporating gas desorption function was established based on dual porosity gas reservoir model. The analytical point source solution of shale gas reservoir was solved in Laplace space, and the bottom-hole pressure of multi-stage fractured of single crack and multiple cracks with constant rate was obtained by superposition. The results show that a large portion of gas production comes from desorbed gas. When gas desorption in shale matrix is considered, lower draw down pressure is required to achieve constant production rate for those fractured horizontal wells, it takes longer time for the pressure front reaching boundary, and the pressure derivative curve shows more obvious groove. If the fractured well is produced under constant bottom hole pressure condition, higher gas production rate and lower decline rate can be achieved. The results also show that the bigger the Langmuir absorption volume is, the slower the pressure front propagates, and the deeper the groove shows on the pressure derivative curve. And the Langmuir absorption pressure impact must be analyzed with both matrix pressure and Langmuir adsorption isotherm curve. Furthermore according to the literature of the characteristics of shale gas reservoir in the area of Weiyuan-Changning Sichuang of the lower Silurian Longmaxi formation, establishing the combinated model of the shale gas reservoir and fractured zone, considering the Langmuir adsorption isotherms, Knudsen diffusion process,the slippage effect, the included angle alpha of the artificial fractures and the horizontal wellbore and the crack interference, the author established the productivity prediction model of shale gas reservoir of fractured horizontal well, gave the basic idea to solve the model, simulated in the area and got the optimal parameters of the horizontal well. Finally we summarize and analyze the influencing factors of shale gas well productivity in the aspects of development and geological properties. Furthermore, we used the method of orthogonal experiment and selected four factors to do 25 groups of orthogonal test. The range calculation shows that the weight of the permeability of matrix and half length of artificial fractures is heavier and the weight of the fracture interval and the gas adsorption ratio is lighter. Comparing with A.Kalantari-Dahaghi`s sensitive parameters influence on shale gas production situation analysis table, the reliability of the productivity prediction model is verified. It has certain guiding significance in exploitation of shale gas.