Microseismic depletion delineation

Abstract

Hess Corporation performed an extensive data collection project in 2011 designed to investigate infill well spacing in the Williston Basin. Using combined microseismic and pressure data collected from six observation wells and the original depleted horizontal wellbore, we identified the potential for using microseismic data to monitor the extent of depletion in unconventional reservoirs. We propose broader use of this surveillance process, which we call microseismic depletion delineation. We recommend pumping pressurized fluids into, or in the vicinity of, a well that has been on production while simultaneously monitoring for microseismic events as a means to discover the optimal spacing for development wells. Our measurements revealed that depletion over a two-and-a-half year period puts the reservoir in a critically stressed state. By repressurizing the depleted wellbore to a level below the minimum horizontal stress, we promoted shear events that revealed the location of the connected, permeable fractures that delineate the depleted part of the subsurface. We considered alternative interpretations for the nonuniform depletion that we mapped along the length of this Middle Bakken well, including completion fluid diversion by faults and wellbore sloughing occluding the production string. We conclude that this procedure has application to shale plays in much the same way that 4D seismic monitoring is used as a production surveillance tool for conventional reservoirs.

Laboratory experiments simulating poroelastic stress changes associated with depletion and injection in low‐porosity sedimentary rocks

“…The hydrocarbons of the Middle Bakken formation are significantly overpressured with a pore pressure gradient of 0.7 psi/foot, or P p ≈ 48 MPa at the coring depth. Dohmen et al [2014] reported that the pore pressure gradients in the overlying Lodgepole and underlying Three Forks formation are slightly below and above that of the Middle Bakken, respectively (by~452.4 Pa/m).…”

“…According to previous studies in the region [ Dohmen et al , ; Yang and Zoback , ] and surrounding region [ Wang and Zeng , ], we construe that the initial stress conditions in situ has a stress gradient of S V / S H max / S h min = ~ 1.05/0.95/0.8 psi/foot (or 23.8/21.5/18.1 MPa/km). This yields a mean stress ( S mean = ( S H max + S h min + S V )/3) of 9450 psi (≈65 MPa) at the depth of ~10,000 feet (≈3 km) where the cores were extracted.…”

“…This amounts to a pore pressure range of 15 to 55 MPa in possible depletion and injection scenarios. The horizontal stress coupled with pore pressure and changed accordingly within a range of ~20 MPa, as indicated by measurements [ Dohmen et al , ]. These inferred magnitudes of in situ stress and pore pressure as well as potential changes to these values set realistic bounds for our laboratory experimental simulation (see section 3.3).…”

Integrating Microseismic, Geomechanics, Hydraulic Fracture Modeling, and Reservoir Simulation to Characterize Parent Well Depletion and Infill Well Performance in the Bakken

“…A Microseismic Depletion Delineation (MDD) was performed on the H1 before the new well fracturing operations. The objective of the MDD was to gain an understanding of the drainage area of a produced well by pressurizing the wellbore and hydraulic fractures that had previously been depleted (Dohmen et al, 2013(Dohmen et al, , 2014. Before the MDD operation, a pressure gauge was installed on the H1 to record bottomhole pressure (BHP) during the MDD operation and H2, H3, and H4 hydraulic fracture treatments.…”

Single-well moment tensor inversion of tensile microseismic events

“…Moment tensors estimated from microseismic data recorded to monitor hydraulic-fracturing operations usefully complement the event hypocenters, a standard deliverable of microseismic surveys. Even though computing moment tensors is more difficult, labori-ous, and noise prone, than computing event hypocenters, practitioners are willing to undertake the task to find out details of the rupture process, helping them better understand the geomechanical behavior of unconventional reservoirs during their stimulation and production (e.g., Baig and Urbancic, 2010;Dohmen et al, 2014;Yang and Zoback, 2014;Staněk et al, 2015).…”