Easy oil has gone and now the focus of exploration and development in China has shifted to tight reservoirs deemed technically challenging. One of the key challenges in tight reservoirs is how to place and land horizontal wells in sweet spots (with high reservoir quality and completion quality) and how to stage-fracture these wells efficiently to produce these tight reservoirs economically.
The paper presents a new 3D reservoir geomechanics workflow that has been applied to a tight gas reservoir in western China. The reservoir is very deep (up to 4500m) and the production rates from the wells are very low. Some hydraulic fracturing had been conducted for vertical exploration wells but the post-fracturing production rates were still not satisfactory. The best chance to produce this tight reservoir is to place horizontal wells in the areas with the best reservoir quality and completion quality and carry out optimized multistage hydraulic fracturing. To this end, a 3D full field geomechanics model was constructed through integration of seismic data, geological structure, core data and log data. This 3D geomechanics model enables a 3D identification of the high completion quality (high fracturability) zones in the reservoir and subsequently placement of a new horizontal well. A 1D mechanical model was then extracted along the planned trajectory from the 3D geomechanics model. Based on the 1D geomechanics model, optimization of the stage-fracturing design was conducted to obtain the optimal number of stages, optimum fracture half length and optimum staging.