This paper presents a new workflow that combines the stochastic earth model and geomechanical analysis to assess the best geological landing intervals and geomechanical targeting zones in unconventional reservoirs before drilling and completion operations. The stochastic earth model uses geostatistical algorithms and multivariate analytics to create a shale quality index (QI) that identifies potential zones with a high probability of containing organic-rich, brittle shales with low effective shale water saturation. The geomechanical analysis uses the material point method (MPM) solid mechanics tools to assess the stress field in the fractured reservoir. This helps identify the best zones for hydraulic fracturing operations that can enable the development of a complex stimulated reservoir volume. The value of combining the two methods is illustrated in two generic areas (Areas A and B). Both areas have the same high shale QI but have different fracture sets characteristics. Area A has a broad range of fractures orientation and Area B has a uniform orientation. A sensitivity analysis highlighted the importance of shear fractures for deriving stress variability. Fractures oriented along and perpendicular to the maximum horizontal stress showed less impact. However, the final stress field was driven by the interaction between different fractures sets, when present. Geomechanical analysis of Area A indicated many zones of low-to-medium differential stress (DS) within high QI zones. However, Area B had a zone of high DS. Area A had a broader range of fracture orientation, which could result in more stress variability and possible connectivity of the induced fractures to the reservoir. These observations could affect the production of wells in similar areas. Therefore, the combined geomechanical and earth model analysis workflow is important to better understand shale reservoirs and adapt stimulation treatments according to local stress conditions related to the reservoir geology and geomechanics sweet spots. Thus, the integrated shale QI and geomechanical analysis can be used to design a fracturing operations strategy for wells to determine target stages.
The current low commodity prices present numerous challenges in the oil and gas industry, particularly in the unconventional reservoirs that have experienced tremendous growth in the past decade and still hold significant untapped potential. The positive aspect of the current downturn is the recognition that current hydraulic fracturing practices do not meet expectations, thus initiating new industry-wide efforts to optimize drilling and completion strategies in unconventional reservoirs.