Increased Production Through Microseismic Monitoring of Hydraulic Fracturing Over a Multiwell Program

Abstract

Abstract Surface based microseismic monitoring enabled an E & P company to optimize their hydraulic fracture treatments. This case study covers a six well program, consisting of 25 stages with 84 hours of continuous microseismic monitoring. The first part of the program consisted of stimulations in three vertical wells. This part of the program provided information indicating fracture orientation and lateral extent of the asymmetrical hydraulic fractures. This was then used to design optimal spacing and fracture design of the stimulations in the remaining three horizontal wells. The common fracture azimuths are 320º +/- 10º and 40º +/- 8º. More complex multi-stage stimulations in the horizontal wells showed microseismic activity growing before the proppant injection with a significant fracture half length. However, microseismic activity occurred near the wellbore during the mid and late portion of the proppant injections indicating the bulk of the proppant load was delivered near the wellbore. High initial post-stimulation production with a rapid decline was observed, supporting this interpretation. This led to the redesign of the fracpack treatment using smaller proppant sizes resulting in larger fractures and more productive wells. We also estimated a stimulated reservoir volume for each stage. The data were then combined into a table for reference, along with aerial extents of activity for the six wells. The microseismic activity then increased with more optimized treatments. We show that generally the production of each well is proportional to the stimulated volume. These results have given the operator an insight to the fracture orientation, and fracture effectiveness of 25 individual hydraulic fracture treatments. Introduction Micrsoseismic monitoring can be a valuable tool to characterize fracture networks, their geometries and effectiveness. Early in a multi-well program, determining the fracture azimuth and geometries of fractures can give great insight to the treatment efficiency, and provide information that can positively impact future treatments. Retrospectively, case histories and production matching can also strengthen the validity of the data. We present here six individual wells in the same locale consisting of 25 treatment stages, with a target depth of 13000 feet. Over the course of these treatments differing methodologies were tried and tested. This paper will focus on two areas: proppant types and placement and stimulated reservoir volume. The common method of microseismic monitoring employs one or more down hole arrays of geophones and uses P and S wave arrival times to locate events. Another approach, which is the method presented in this paper, is placing a large array at the surface, using a migration routine to locate events (Figure 1). As a result of hydraulically fracturing the reservoir, tensile and shear failures of the formation release energy which can be detected from an array specifically designed to capture small micro-earthquakes.