Fracturing Treatment/Geometry Optimization and Post-frac Performance Evaluation in a Tight Gas Reservoir

Abstract

Abstract Unconventional gas resources, tight gas in particular, complements other major sources of hydrocarbon which if exploited effectively can play a significant role in meeting today’s energy challenges faced by Pakistan. The production of these major resources poses many economical challenges, which could be overcome by the astute use of available resources and technological efficacy. Hydraulic fracturing is an essential stimulation technique for the economic development of tight gas reservoirs. Mostly, fracture jobs are designed based on the maximum achievable treatment sizes which can result in wider fracture width, greater height, and longer half length. The ultimate aim is to achieve maximum deliverability. This approach is not versatile because the treatment parameters and fracture geometries are not sensitized. As a result, the treatment sizes and geometries are not the optimized ones. A better approach is to determine the best compromise between the resources available and the productivity enhancement achieved i.e., optimizing the fracturing treatment and geometry both physically and economically. Once the optimum balance is found, the next step is to establish the operational parameters (e.g. Pump Rate, Net Pressure, etc.). This paper discusses the process to achieve the optimum fracturing treatment and geometry design and compares the actual field results obtained with those predicted. The analytical Pseudo-3D model has been used for the simulation of fracture propagation and optimization of parameters. The post-frac performance of the reservoir is predicted using both analytical and numerical methods (Using numerical reservoir simulator). In order to validate the analytical and numerical models, the actual fracturing results from the field (fracture dimensions and deliverability) have been compared with those predicted by the model. The same fracturing treatment parameters that were used in the actual job execution have been used in the model validation process. Once the model is validated, the difference between the optimized treatment parameters and that used in the actual executed job has been highlighted; these differences emphasize the value of using the optimization process defined in this paper to achieve the best possible deliverability in an economically efficient manner. The paper presents a systematic approach towards the optimization process of the fracturing treatment and geometry for tight gas reservoirs, which in turn influence the post fracturing deliverability results. The sensitivity analysis points out the parameters to which the fracture deliverability is most sensitive. The determination of such parameters and hence the fracture geometries remains a big challenge for tight gas reservoirs and industry remains committed to developing a thorough understanding of tight sands behavior.