The overall objective of this research effort is to gain knowledge that will be useful for efficient recovery of both hydraulic fracturing water and hydrocarbon fluids in stimulated unconventional reservoirs through an enhanced understanding of the influences of gravity and capillarity in fractures.
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA 94720
A preliminary assessment indicates that water losses could be reduced by about 50% by stimulating fractures primarily above horizontal wells in order to facilitate drainage and recovery of the working fluid. Given the immiscibility of water with hydrocarbon fluids of interest (natural gas and light oil), improved water recovery through optimized gravity drainage is expected to improve reservoir productivity.
In order to advance our understanding of processes controlling water and gas recovery, this research will progress through three stages. First, the interactions between matrix permeability, fracturing fluid viscosity, shut-in time, and gas pressure will be experimentally explored to obtain practical scaling relations for describing gas counter-flow. Next, through laboratory experiments on gravity drainage of water from synthetic fractured rocks, empirical scaling relations for the dependence of water drainage on fracture aperture, fracture wettability, interfacial tension, and fluid viscosities and densities will be developed. In the third and final phase of work, scaling analyses will be completed for estimating water and hydrocarbon recovery under different directional fracturing and shut-in scenarios, thereby helping guide design of more efficient hydraulic fracturing.
The study will provide insights needed to improve water-based fracturing fluid flowback from unconventional reservoirs, thereby improving hydrocarbon recovery. Following hydraulic fracturing and shut-in, very high capillary pressures (Pc, on the order of 1 MPa or 150 psi) are required to initiate desaturation and permit counter-flow of gas [Tokunaga et al., 2017]. This fact, combined with the higher density of water relative to gas, implies that removal of water from fractures generated below horizontal wells will likely not occur, especially when long shut-in periods are employed. Conversely, water in stimulated fractures overlying horizontal wells are gravity-drainable back through perforations for removal. The complexity of immiscible fluid displacement from fractures of variable aperture and wettability warrants this systematic experimental investigation of gravity drainage for developing practical scaling relations that can help inform development of optimal reservoir stimulation strategies.
Work is ongoing to complete the imbibition experiments initiated during 2021 and to complete manuscript preparation using previously collected and anticipated data. The manuscript will address experiments on water imbibition into shales and sandstones with and without surfactant addition.