It is critical to identify optimum well spacing to develop cost-effective full field development plans for tight gas reservoirs. Accurate prediction of well performance is a major challenge that arises during the development of such reservoirs. Understanding well performance is needed for both well design and depletion planning. Almost all wells in tight gas fields are hydraulically fractured. We have investigated methods of simulating hydraulic fractures using coarse grids since explicitly gridding these fractures can easily lead to an impractical number of grid blocks for large, full field models with many and complex wells.
We have developed practical solutions for accurately representing both flowing and shut-in performance of hydraulically fractured vertical wells and multiply fractured horizontal wells in full-field models. We have validated these approximations in trials with actual field examples.
We found it necessary to enable wellbore cross-flow in the simulator for coarse grid field-scale models to more accurately simulate observed shut-in pressures. We also found differences in pressure distribution results of finite difference simulation between models using a pressure formulation vs. those using a pseudo-pressure formulation when simulating tight gas reservoirs under certain conditions.
In summary, the existing commercial reservoir simulation tools can be adapted to model challenging tight gas depletion scenarios and optimize well spacing. However, care must be taken to ensure that the models are properly constructed and results frequently checked for consistency.