Impact of Hydraulic Fracture Permeability on Oil Production

Oil and gas production from tight formations or shales has become possible due to technological advancements in horizontal drilling and hydraulic fracturing. Proppants such as sand mixed with fracturing fluids are pumped at high pressures to crack the reservoir formation rock creating hydraulic fractures. The effectiveness of a fracturing job is measured by the dimensions of the fracture and ease of hydrocarbon flow within the fracture, i.e. the fracture permeability. Since hydraulic fractures connect the wellbore to the formation, economic production for any well is highly dependent on how conductive these fractures are. The objective of this study is to investigate the impact of hydraulic fracture permeability on oil and gas production performance in terms of fluid rate and recovery. Five reservoir fluids (two volatile oils, two gas-condensates and one dry gas case) are tested in a 100 nD permeability reservoir with two operating bottomhole pressures of 1000 psia and 3000 psia. The flow rates and recovery for most fluids increase with fracture permeability up to 1000 mD. We found that fractures with a permeability above 1000 mD act as infinitely conductive to fluids leading to no further improvements in rates and recovery. However, recovery is not always proportional to fracture permeability. For the cases of volatile oils and condensates, a crossover in recovery is observed where the production is higher for low fracture permeability compared to higher permeability fractures. Rates are very high for higher fracture permeability cases, but rates drop sharply (80% of initial rate in 1 year). Rates for lower fracture permeability cases are not as high, but do not decline as sharply either. In some instances, lower fracture permeabilities outperform higher fracture permeability cases in terms of cumulative production. Although higher fracture permeability is essential for high flow rates, higher pressure drop near fractures causes gas to come out of oil solution, eventually dominating the multiphase flow and suppressing liquid rate. A similar phenomenon also happens for volatile and condensate fluids. An optimal fracture permeability is necessary to extract the maximum amount of oil or gas. The type of fluid, operating bottom hole pressure and reservoir permeability are the main factors to determine the optimum fracture permeability.