Numerical Simulation on the Influence of Natural Fractures on the Productivity of Parent and Child Wells Considering Frac Hits

Abstract

Abstract The commercial extraction of shale gas has led to frequent fracture hits, significantly affecting the ultimate recovery rate of the reservoirs. The objective is to analyze how natural fractures impact the production of parent and child wells considering fracture hits through a more comprehensive fluid-solid coupling productivity model, providing a reference for adjusting construction parameters during the production process. Firstly, a multi-scale quadruple-medium model considering organic matter, inorganic matter, natural fractures, and artificial fractures is established based on the theory of poroelasticity and fluid-solid coupling. This model integrates shale gas multiple flow regimes, gas adsorption/desorption, and stress sensitivity. The COMSOL is utilized to numerically solve the model and its accuracy is verified with field production data. Subsequently, a dual-well numerical model is established to analyze how the characteristics of natural fractures, including length, aperture, density, roughness, and dominant orientation, impact the productivity of parent and child wells during shale gas development. In scenarios involving frac hits, the production rate of the parent well initially experiences a temporary increase followed by a decline, which is higher than in scenarios without frac hits. Over time, however, the production rates under both conditions-frac hits and no frac hits-tend to converge. In the early stage of child well production, due to frac hits, its rate is lower than the production rate of the parent well, and the cumulative production decreases. The length, density, and aperture of natural fractures are positively correlated with the degree of interference, while the dip and roughness of natural fractures are negatively correlated with the degree of interference. The impact of natural fracture occurrence on the degree of interwell interference is ranked as density>length>dip>opening>roughness. Among them, the impact of natural fracture roughness on production is minimal. When the roughness coefficient changes by 20%, the change rate of production in the parent and child well are only 0.003%, which can be basically ignored. A more comprehensive and accurate quadruple-medium fluid-solid coupling productivity model for shale reservoir is establised. The effect laws of natural fracture occurrences on the productivity variation of parent and child wells considering fracture hits are analyzed. The research findings can guide the prediction of shale gas productivity and the dynamic adjustment of production parameters.