Optimal Design of Nonuniform Multiple Transverse Fractures for Horizontal Wells in Tight Gas Reservoirs

摘要

A new comprehensive approach for designing the optimal nonuniform multiple stage/cluster transverse fractures intercepting horizontal wellbores is proposed. The proposed approach relies on the Genetic Algorithm (GA) method. Its aim is to optimize nonuniform transverse fracture spacing, number of fracture stages and clusters, nonuniform half length of fracture and fracture conductivity in order to achieve maximum net present value (NPV). The advantages of this method include: 1) The automated and comprehensive process makes it easier and more precise to find the optimum design than most previous works. 2) The design is based on a new configuration of nonuniform transverse fractures in a horizontal well. 3) The optimization of cluster spacing considers the effect of stress shadowing (Nicolas P. Roussel 2011) e.g. the opening of a fracture causes a reorientation of stresses in its neighborhood affecting negatively the efficiency of treatment. 4) It is based on NPV maximization, not just the initial production rate and cumulative production. 5) The procedure concerning well productivity also considers the effect of non-Darcy flow. A field example in Sulige gas field is presented to demonstrate the application of our method for optimal design of multiple patterned transverse vertical hydraulic fractures intercepting horizontal wellbores. It is showed that this approach enable operators to achieve maximum reservoir productivity and NPV. The multi-stage and multi-cluster per stage fracture treatments in horizontal wells have proven successful in tight gas recovery, by creating a large stimulated reservoir volume (SRV). In order to avoid sub-optimum fracture design relying on historical databases of hydraulic fracturing and personal experience, this new systematic method considers various factors affecting the optimal fracture spacing and length, and thus helps to get close to the optimal fracture pattern.