Investigating Microseismic Responses and Interaction Between Offset Hydraulic Fracture Treatments During Horizontal Well Completions

Abstract

Observations of microseismic data collected during hydraulic fracturing treatments in horizontal wells often show variations in the numbers of events and/or the locations of the events that cannot be attributed to differences in the treatment schedule, local variations in geology, or rock properties. These variations might be related to induced stresses from previously completed hydraulic fracturing treatments in the same well or in nearby offset wells. The responses to local changes in stress can be difficult to visualize. A method to identify and evaluate the possible influences of induced stress using seismic moment is proposed. Seismic moment is a measure of the intensity of the energy release that is detected as a microseismic event. Moment values can be related to the strains resulting from the deformation that produced the microseismic event. A simple summation of the moment values provides a measurement of the total deformation associated with the microseismic events and is used to compare the microseismic responses of offset fracturing treatments. The cumulative moment responses can be compared to both the separation between consecutive stimulation treatments and the intervening time between those treatments. Two case histories are used to illustrate the observed responses. The first example highlights the effect that resting time between stimulation treatments in a single well has on the microseismic response. The second example examines the contemporaneous completion of multiple wells on a single drilling pad. The initial results presented in this paper show that microseismic responses can be affected by both the time between stimulation treatments and the distance separating offset fracturing treatments even though there appears to be little difference in the external dimensions of the event clouds. The evaluation technique used minimizes monitor well bias when the monitoring tools are deployed in nearby wells. Cumulative moment-based responses therefore provide an analytical tool that can be used to evaluate microseismic responses during hydraulic fracturing treatments that incorporates the characteristics of the microseismic events.

A Validation Assessment of Microseismic Monitoring

“…Diversion is an application where microseismic monitoring is used to determine if fracturing could be forced into regions that perhaps would not otherwise be fracturable because of stress, rock properties, shadowing, entrance conditions, or a number of other possible factors (Waters et al 2009b;Downie et al 2013;Viswanathan et al 2014;Gutierrez et al 2015;Krenger et al 2015;Diakhate et al 2015). Diversion could be applied in both refractured wells and in original stimulations.…”