(295c) 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.