Multi-stage Fracturing Capacity Prediction For Shale Gas Horizontal Wells

Multi-stage fracturing technology has already been widely used in developing low-permeability hydrocarbon reservoirs such as shale gas reservoir.The permeability of shale gas reservoirs is usually in a very low level.And there is a large amount of micro-fractures in the matrix of shale gas reservoirs.What is more,there are many kinds of occurrence states of shale gas such as absorbed state and free state.With a view to the characteristics of the gas reservoirs and the multi-stage fracturing technology,predicting the post-frac production performance correctly is a subject which has a research value.The generally used methods of production predicting are analytic method and the numerical method.(1)According to the geologic feature and the flow mechanism,this paper establishes a three-dimensional and two phase differential equation of infiltration.With the comparison between the dual-porosity media and the triple-porosity media,a pseudo triple-porosity media is established.(2)With the differential equation,discrete difference linear equations are establishied.In consideration of the characteristics of the distribution of the fractures,the grids are divided in a reasonable way to form a seven diagonal matrix equation set.And considering the characteristic that the permeability of the man-made fracture is much higher than the permeability of the natural fracture,the permeability of the former is handled according to its flow conductivity.(3)Considering the convergence and the stability of the equation set,this paper uses the Successive Over Relaxation method and theImplict Pressure-Explicit Saturation method to solve the equation set.The data of each layer will be updated while the time step increasing.(4)Based on the seven diagonal matrix equation set and the solving methods,a numerical simulator is developed with Visual Basic 6.0 for the shale gas reservoir.The dynamic curve of the productivity will be shown when the user input the parameters.(5)This paper analyzes the relationship between different parameters and the production and the relationship between different parameters and the pressure.And the results are interpreted with the theories of the geologic feature and the flow mechanism.