Interpretation of Microseismicity Resulting from Gel and Water Fracturing of Tight Gas Reservoirs

Abstract

We provide a comparative analysis of the spatiotemporal dynamics of hydraulic fracturing-induced microseismicity resulting from gel and water treatments. We show that the growth of a hydraulic fracture and its corresponding microseismic event cloud can be described by a model which combines geometry-and diffusion-controlled processes. It allows estimation of important parameters of fracture and reservoir from microseismic data, and contributes to a better understanding of related physical processes. We further develop an approach based on this model and apply it to data from hydraulic fracturing experiments in the Cotton Valley tight gas reservoir. The treatments were performed with different parameters such as the type of treatment fluid, the injection flow rate, the total volume of fluid and of proppant. In case of a gelbased fracturing, the spatio-temporal evolution of induced microseismicity shows signatures of fracture volume growth, fracturing fluid loss, as well as diffusion of the injection pressure. In contrast, in a water-based fracturing the volume creation growth and the diffusion controlled growth are not clearly separated from each other in the space-time diagram of the induced event cloud. Still, using the approach presented here, the interpretation of induced seismicity for the gel and the water treatments resulted in similar estimates of geometrical characteristics of the fractures and hydraulic properties of the reservoir. The observed difference in the permeability of the particular hydraulic fractures is probably caused by the different volume of pumped proppant.

Features of CO2 fracturing deduced from acoustic emission and microscopy in laboratory experiments

“…In actual reservoirs, Baria and Green [] in geothermal field and Warpinski et al [] and Dinske et al [] in tight gas reservoirs made comparative analyses of microseismicity induced by HF using viscous fluid and water. Baria and Green [] and Dinske et al [] could not show clear difference between the two fluids, while Warpinski et al [] showed that slickwater fracturing extends a much larger area further in three dimensions than gel fracturing, which is consistent with the findings from our laboratory experiments. In actual field operations of HF, weak planes, such as preexisting cracks, sedimentary planes and defects in strata, may behave in a similar manner to grain boundary in the granite specimens.…”

Dual Seismic Migration Velocities in Seismic Swarms

“…To ensure such an activity during days to months, a driving mechanism is required. It could be pressure diffusion, as such swarms are induced by reservoir (injection and impoundment) activities (Deichmann & Giardini, 2009; Diehl et al., 2017; Dinske et al., 2010; Ellsworth, 2013; Lengliné et al., 2017). The similarity between induced and natural swarms suggests that even natural swarms are driven by transient episodes of fluid flow at depth.…”

Predicting permeability and gas production of hydraulically fractured tight sands from microseismic data

“…The state of affairs has changed with the development of a technique for estimating the in situ formation permeability from microseismic data ͑Shapiro et al, 2006;Dinske et al, 2009;. This technique, called the r ‫מ‬ t method, derives the permeability from the rate of growth of a microseismic cloud by measuring the changes in distances r between the recorded microseismic events and a fluid injector with time t. Here, we apply the r ‫מ‬ t method to data acquired during hydraulic treatments of nine stages in wells Vible 1-11D and 8-11D, and of eleven stages in wells Warbonnet 7-5D and 8-5D, owned and operated by Shell in the tightgas Pinedale Field, Wyoming, U.S.A. We also introduce and test an alternative technique that estimates the same formation permeability by inverting the diffusion equation.…”