Optimization of multi-stage fracturing horizontal wells is with great significance in shale oil and gas reservoir production to enhance the gas recovery. The stimulated reservoir volume (SRV) is an important factor for fracturing horizontal well design and gas reservoir development. However, very few research has studied horizontal well optimization considering the effect of SRV. This paper proposes a mathematical model for SRV estimation during hydraulic fracturing. The model couples both rock and fluid mechanic effects. The displacement discontinuity method (DDM) is adopted to calculate the formation stress field. Then a natural fracture failure criterion based on formation pressure and stress fields is used to estimate the SRV. Additionally, a stress dependent permeability (SDP) algorithm is applied to estimate permeability change within the SRV region. Based on SRV and SDP models, an automatic optimization framework is established, with the net present value (NPV) employed as the optimization objective function, in which the overall cost and the ultimate income are involved simultaneously. A Modified-PSO algorithm is proposed and adopted to realize the optimization process, which can significantly reduce the calculation time while maintaining the accuracy of the result. In the end, two cases with shale gas reservoirs are presented, and different types of hydraulic fracturing wells are optimized to validate this optimization framework. Parameters including hydraulic fracturing spacing and half-length, well spacing and well length are optimized to achieve the optimum well design. The optimization results are compared and discussed, which show that this approach can contribute to obtaining the optimal shale gas recovery and provide a new insight into hydraulic fracturing well design under the effect of SRV.
- Displacement discontinuity method
- Fracturing optimization
- Modified-PSO algorithm
- SRV estimation
- Stress dependent permeability