Research On The Geological And Engineering Sweet Spot Index Of Shale Gas

Many scholars use the organic carbon content of the shale,the shale thickness and distribution of the area and other indicators,to select the sweet spot for the exploration and development of shale gas.Many breakthroughs has been achieved based on horizontal wells and multi-stage fracturing technology.However the production of some wells is still low,and falls fast in the test area.Therefore,this paper selects the factors,affecting the development of shale gas,and establishes the shale gas geological and engineering sweet spot index system and evaluation method.The production of shale gas needs the flow path from pore to well bottom,including three stages: flowing from pore to micro-fractures,from micro-fracture to hydraulic fractures and from hydraulic fractures to the well bottom.Wherein the organic abundance,micro-fracture,Water saturation,Shale fracability are the key factors controlling the process of production.Abundance of organic matter not only affects the hydrocarbon strength,physical and chemical properties of shale,elasticity,fracture characteristics,but also affects the organic matter pore and adsorbed gas content.The higher abundance of organic matter,the stronger hydrocarbon generation and the more TOC content of shale gas reservoir are.Considering the water saturation,adsorption model was established in the clay nano-tube pores.The results showed that effect of the moisture content on the adsorption capacity is significant.Considering the water saturation,apparent permeability model in the clay nano-tube pores was established.In the case that the reservoir water saturation is 20%,gas flow capacity will be reduced by 10% compared with the case that the reservoir water saturation is 0.Taking into account that the presence of wall water film in the micro-fractures,the solid-gas,gas-liquid adsorption model were established used to evaluate the shale gas adsorption capacity.Taking into account the presence of water in the micro-fractures,the storage capacity of the reservoir natural micro-fractures are evaluated,the ratio of microcracks adsorbed gas and free gas is about 0.09%.Micro-fractures almost contain entirely free gas.The effects of natural fracture porosity on the shale gas production capacity by numerical simulation methods.AS the fracture porosity is 0.03 down to 0.005,the cumulative gas production decrease approximately 11.8%.The shale brittleness,fracture toughness,natural weak surface,fracturing fluid properties,and time-impendence were chosen as shale fracability comprehensive evaluation index and methods.The reservoir parameters and hydraulic fractures were analyzed by CMG.The numbers of hydraulic fracture and the fracture conductivity have important influence on the gas production capacityFinally,combined with geological factors and engineering factors,sixteen indexes for shale gas development sweet spot are chosen to evaluate the shale gas reservoirs,aimed at improving the successful rate of shale gas development in China.