Realistic Fracture Conductivity Calculation Using Well Performance Data in Saudi Arabian Deep Gas Reservoirs

Abstract

The actual fracture conductivity contributing to gas flow after a proppant treatment is usually much lower than what is reported in the laboratory tests. This is because the ideal conductivity values can be impaired by numerous factors in the reservoir conditions – from high unconfined compressive strength to condensate yield – that cannot be fully captured in the laboratory measurements. Although there are many publications in the literature discussing this issue and software in the industry that predict certain percentage decreases in conductivity due to various reasons, these results are usually specific to certain reservoirs, formations, and laboratory tests and cannot be extrapolated or used for all reservoirs. To understand and compute actual conductivity values in Saudi Arabian gas reservoirs stimulated by proppant fracturing, a new workflow is proposed. The workflow involves using all available data to first calculate the actual fracture geometry using a mass balance and pressure matching. Subsequently, fracture conductivity is computed from another standard method, such as the Cinco-Ley correlation; and using industry software to estimate realistic conductivity values at static and dynamic conditions using closure pressure, actual well performance, and bottomhole flow pressure measurements. A range of fracture conductivity is computed during initial and later periods by matching the well performance data. The calculations show the fracture conductivity achieved after a fracture treatment at reservoir conditions and also how the values change during the production period of a well. Later, correlations relating to productivity increases with reservoir rock and pumping properties can be used to optimize fracture treatments such that a high rate can be maintained after a fracture treatment.