Analyzing pressure interference between fractured wells in unconventional reservoirs




Seth, Puneet

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In conventional reservoirs, pressure transient analysis has been well studied and is based on hydraulic diffusion in the reservoir. In such high permeability reservoirs, pressure interference tests have been widely used to gather information about inter-well communication and reservoir permeability in the vicinity of the tested wells. However, in unconventional ultra-low permeability reservoirs (100 nD - 1μD), hydraulic diffusion through the reservoir matrix is negligible, instead poroelastic deformation of the rock dominates the pressure transient response. This renders traditional pressure interference analyses and well testing techniques ineffective in unconventional reservoirs. Horizontal wells drilled in unconventional reservoirs are hydraulically fractured during multiple stages of injection to increase the surface area available for production of hydrocarbons from these reservoirs, and similar to conventional reservoirs, pressure interference is often observed between fractured wells drilled in close proximity in unconventional reservoirs. However, unlike conventional reservoirs, pressure interference between fractured wells in unconventional reservoirs is not well understood. In this research, pressure interference between fractured wells in unconventional reservoirs is analyzed by developing numerical simulation models and investigating field data to understand the mechanisms that result in pressure communication between fractured wells, both during stimulation and production. Additionally, pressure interference analysis has been applied as a fracture diagnostics technique to investigate real field scenarios at multiple locations (Hydraulic Fracturing Test Site #1, DJ Basin and Permian Basin). A 3-D, fully-coupled geomechanical model that can simulate fracture propagation from the treatment well while monitoring pressure changes inside a compliant fracture in a nearby offset well has been developed. Numerical simulations and field data analyses show that in unconventional reservoirs, pressure interference between fractured wells is caused either by reservoir stress alterations during hydraulic fracture propagation, or high-permeability fracture connections (hydraulic communication) between the wells. The application of pressure interference analysis to diagnose inter-well communication during production and as a fracture diagnostics tool during stimulation to estimate fracture geometry, SRV permeability, diagnose diversion effectiveness and stimulation efficiency is demonstrated. Compared to other techniques such as micro-seismic monitoring and fiber optics that are expensive and require additional equipment, pressure interference analysis is presented as a novel and inexpensive tool that enables fracture diagnostics during both production and stimulation in unconventional reservoirs


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