Fracturing in Tight Gas Reservoirs: Application of Special-Core-Analysis Methods To Investigate Formation-Damage Mechanisms

Abstract

Summary Gas-well productivity in tight reservoirs is greatly impeded by fracturing-fluid interactions with the formation. New simulators introduce formation-damage mechanisms to calculate gas-well productivity. However, equations describing formation damage must be supported by experimental data obtained in conditions representative of fracturing operations. The purpose of this work is to derive absolute-permeability and multiphase-flow damages upon return gas permeability after core invasion by a fracturing fluid by methods used in the Special Core Analysis Laboratory (SCAL). The core permeability is in the microdarcy range with significant illitic content. Absolute-permeability damages caused by fracturing-fluid filtration and water sensitivity are measured. Water-saturation profiles recorded by X-ray in two-phase-flow experiments are interpreted. The methodology of interpretation provides the petrophysical data specific to the rock/fluid system: absolute permeability, relative permeability damage caused by hysteresis, and capillary pressure. In addition, simulations are presented for the evaluation of the effect of various operational parameters, such as pressure drawdown, on gas productivity. It is shown that permeability hysteresis is the determinant factor to explain low gas recoveries at short term. In the long term, the natural cleanup is very slow. The results, derived from a real rock/fluid system, are used to provide recommendations for improving backflow procedures. This methodology can be applied to any case of damage caused by the alteration of rock/fluid properties.