Reminder: January 12th, 2023 DGS Luncheon Presentation – Jonathan McKenna, Microseismic Inc.

Stress rotations and compounding pore-pressures from multiple well injections

Jonathan McKenna 

Abstract:

Multi-stage, multi-well completions cause pore-pressures to increase around each stage treated, compound from earlier offset treatment stages, then dissipate as the injected fluid leaks off into the rock formation. Local stress changes illuminated by microseismic focal mechanisms can be used to create maps of high and low pore-pressures which, in turn, can be used to guide a dynamic slurry propagation model and estimate fluid and proppant distribution from the injection.  Injected slurry volumes respond to these pore-pressure changes dependent upon lag time from previously treated stages.

An example is presented from a multi-stage, multi-well hydraulic stimulation in the Wolfcamp Formation located in Southeast New Mexico. In this location, previous researchers have identified that a normal-faulting stress regime exists with maximum horizontal stress (SH_max) oriented between N75°E and N83°E with intermediate horizontal stress anisotropy (Lund Snee and Zoback, 2017). Results from this study shows that SH_max=N80°E and stress anisotropy,ϕ=0.36 in the virgin stress state. During hydraulic stimulation horizontal stress anisotropy is reduced (ϕ=0.33) due to stress shadowing and SH_max rotates ~+/- 24°. Increased pore-pressures from previous treatments remain elevated for ~7 days confining fluid distribution to near the well on ensuing stages.  Sufficient pressure dissipates after leakoff providing opportunity for the fluid to propagate into previously opened fractures. Pore-pressure highs can be identified using microseismic hypocenters fitting an altered stress state which differs from events fitting the background unpressured virgin stress state. Since injected fluid migrates toward low pressures and away from highs, we suggest that virgin stress events can be used to guide injected slurry volumes including proppant.

Jon McKenna is a geological engineer at MicroSeismic, Inc. His work relies on microseismic measurements during hydraulic stimulation to quantify dynamic stress changes in the reservoir and develops accurate fracture models to simulate proppant placement and forecast production.  He holds a B.S. and a M.S. from the University of Georgia in Geology and Geophysics and a Ph.D. from the Colorado School of Mines in Geological Engineering.  He has over 20 years of engineering geology experience.