Research On Well Testing Theory Of Fractured Horizontal Wells For Shale Gas Reservoirs

The present percolation theory study of shale gas reservoirs falls behind development practice because of the widely-distributed natural fractures in shale reservoir,complicated storage and transport mechanisms of shale gas as well as various secondary fractures shapes resulting from staged fracturing.On the basis of abundant literature reviews,this paper,taking the effects of secondary fractures on fluid flow into account,carries out a well testing theory research on fractured horizontal well for shale gas reservoir by semi-analytical method after coupling multiple transport mechanisms.First,two kinds of shale gas reservoir fractured horizontal well mathematical models are established,namely,orthogonal line fracture network and tree-like branching fracture network.Then,line-source solutions considering multiple transport mechanisms including adsorption-desorption,diffusion and seepage are derived by analytical algorithm.For the fluid flow in fractures,numerical algorithm is adopted for infinite conductivity fractures and finite conductivity fractures respectively.Next,bottom-hole pressure response is obtained by coupling flowing equations of reservoir and fractures.Typical well testing curves are plotted,and influencing factors and flow distribution features are analyzed.Finally,the reliability of the proposed model is validated by a filed case study.Based on the above study,the following conclusions are obtained:(1)Steady and non-steady mathematical models for shale gas reservoir coupling multiple transport mechanisms are derived,and continuous line-source solutions at different flow patterns and different boundary conditions are obtained by analytical algorithm.(2)Orthogonal line network model and tree-like branching network model for fractured horizontal well are established.Bottom-hole pressure response for infinite conductivity fractures are derived by semi-analytical method,and typical well testing curves are also plotted.The features of secondary fractures are analyzed according to the changing slope of pseudo-pressure derivative curves.(3)For finite conductivity fractures,flowing equation is solved by finite difference method through analyzing flow distributions at fracture nodes,and bottom-hole pressure response is obtained.(4)Influencing factors analysis are carried out to characteristic parameters representing secondary fractures intensity like group number,angle and half length,etc.The flow distribution features are discussed and the reliability of the proposed model is validated by a field case study.The findings of this paper will provide a theoretical foundation for guiding shale gas reservoirs high-efficient development.