In many cases, the production prediction at the fracture design stage and later from the post-fracture pressure-matching exercise is never realized. The underperformance of fracture treatments is often attributed either to formation damage, proppant crushing and embedment, or to the poor reservoir quality despite a reasonably good reservoir property indicator from all sources including the pressure decline in a mini-fracture test. Based on several case studies, this paper highlights a number of issues that were found responsible for underperformance of fracture treatments. The understanding and mitigation of these issues require the application of comprehensive geomechanics.
For each case, a comprehensive geomechanical model was built for the field, characterizing the depth profiles of all three stresses, rock mechanical properties and the direction of the horizontal stresses by integrating available data from various sources including drilling and logging data, laboratory rock test data and mini-fracture test data. The contrasts in stress and rock mechanical properties among various lithologies along the well path were created based on fundamental geomechanical principles. The hydraulic fracture growth was simulated as per the pressure-matching practice for each treatment carried out. The production condition was applied to the simulated propped fracture to predict the production and compare it with the actual production data where available.
Issues that were found responsible for lower-than-expected production include (1) out-of-zone fracture growth that could not be predicted using the oversimplified geomechanics; (2) poor connection between wellbores and fractures for unfavorably oriented wells; (3) non-optimum perforation intervals that caused non-optimum fracture growth and near-perforation low conductivity; (4) malpractices in treatment execution that resulted in disconnected fractures with the perforations; and (5) suboptimal treatments for reservoir conditions. Appropriate mitigation strategies were recommended for wells in production, and increased productions were reported where the recommendations were implemented. One significant observation is that several oversimplified techniques currently used in the industry create significantly different stress contrast profiles than that was found based on fundamental physics of geomechanics, though all these profiles could be calibrated with the same closure pressure from a mini-fracture test. The use of such inaccurate stress contrast profiles is primarily responsible for unrealistic fracture and production predictions.