Simulation Study On Fracturing Capacity Of Horizontal Well In Multi - Scale Shale Gas Reservoir

With the endlessly progress and development of the exploration and exploitation technology, the unconventional shale gas has become an import resource, which can succeed the conventional oil and gas resource. At present, shale gas has been successfully developed in North America, the production of which gets an explosive growth and hasreached2700×108m3in2014. Studies have shown that China has rich shale gas resource which accounts for22%of the world’s totals. However the shale gas development is still in the initial stage, so it is necessary to carry out the relative research to improve the independent development level.Different from the traditional gas reservoirs, the pore scale of shale reservoir ranges from a few nanometers to several hundred nanometers, and shale gas has complex flow patterns, which includes viscous flow, slip flow, transition flow and molecular flow. Because of the low-porosity and low permeability properties, it has to take the staged fracturing technology for horizontal wells to stimulate shale reservoir, eventually to get economic production. Expansion of hydraulic fracture in shale reservoirs presents a different characteristic, that is, a fracture network system that contains self-standing shear fracture away from wellbore and proppant-supporting fracture near wellbore will form during large-scale hydraulic fracturing. Based on the above characteristics of shale reservoirs, a study of gas flow behavior is conducted in consideration of diffusion, adsorption, desorption and slip. In addition, based on the gas flow characteristics in microscopic and macroscopic, a productivity mathematical model of the fractured horizontal well in shale reservoir is established, which takes the distribution state of self-standing shear fracture and proppant-supporting fracture into consideration. Finally, the production capacity of shale gas is simulated and analyzed. The important findings are as follows:(1) In consideration of low porosity and low permeability characteristics of shale reservoirs, the unified equation of apparent permeability about viscous flow, slip flow, transition flow and free flow of molecular is set up, which combines the different effects of different flow regimes. And then the microscopic flow model of shale gas is established.(2) Based on the microscopic flow in shale matrix system, a two-dimensional single-phase flow model is established and solved by the numerical method, in which the impact of proppant-supporting fractures and self-standing fractures and the adsorption and desorption phenomena of shale gas are taken into consideration. And then the numerical calculation procedure of shale gas production is compiled on visual basic6.0.(3) Based on this numerical calculation procedure, the relevant parameters affecting the production capacity of the fractured horizontal well in shale reservoirs are comprehensively analyzed, in eluding the number of hydraulic fractures, fracture conductivity, fracture length, formation permeability, pore radius, bottomhole pressure, Langmuir volume and Langmuir pressure.