Transverse Fracturing of Horizontal Well - A Unified Fracture Design to Stimulate Tight Gas Sands

摘要

Unconventional tight gas reservoirs offer an enormous opportunity towards fulfilling our energy demand, and hence, they have been subject to significant R&D activities these days. Although the tight gas sands may not be a major focus today in UAE, their potential, however, must be recognized; for, UAE has several deep tight reservoirs that need to be fully exploited for their gas reserves. For such reservoirs the conventional approach of simply fracturing the formation to stimulate the horizontal well is inadequate. This is because most currently available commercial software may lack proper optimization tools in them with several key parameters and realistic constraints. Even the systematic design methods for fracture treatment parameters with constraints are not well presented in the literature. There are optimal number of transverse fractures and optimum treatment parameters when real field constraints and economic aspects are considered. An integrated model to optimize multistage transverse fractures has been developed to maximize gas production and net present value (NPV) with minimum treatment cost. Model couples both the industry experience and unified fracturing design parameters based on hydraulic fracture mechanics. Unified fracturing design defines the optimal compromise between the fracture width and fracture length for a given mass of proppant. Model integrates unified fracture geometry, reservoir in-situ parameters, treatment parameters at every stage, realistic design constraints, and production and economic modules. The integrated model has been successfully applied to a hypothetical deeper and tight gas sands to demonstrate its merits. A simple analytical approach has been used for evaluating and optimizing the productivity. The design indicates a significant incremental production. Effect of mass of proppant on production rate and NPV is also presented. Authors are working further to couple this integrated model with an optimization algorithm (genetic and polytope) to optimize the treatment parameters globally. This model could also be used to study the potential of the deep UAE offshore tight gas sands.