Utilizing Microseismic Scanlines to Characterize the Fracture State in Unconventional Reservoirs

Abstract

Hydraulic fracture stimulations generally result in microseismicity that is associated with the activation of pre-existing fractures or in the generation of new fractures. Typically, the event distribution provides a sense of where fracturing is occurring and the extent of fracturing away from the treatment zone. However, by utilizing a multi-array multi-well distribution of sensors, a more complete descriptive image of the individual fractures can be obtained, including the type of failure (eg., tensile, shear, or shear-tensile), fracture azimuth and dip, as well as the relative dimensions (assuming a penny-shaped crack). These fractures, in essence, define the discrete fracture network that has been activated as a result of the stimulation program. These data offer a unique approach to characterizing the rock mass fracture state. One approach we have considered is the adaptation of traditional scanlines utilized in rock mechanics applications. Scanlines are an effective systematic approach that considers the location and number of discontinuities that intersect the scanline. In order to effectively apply this approach to microseismic data, consideration had to be made of the event location errors for placement along scanlines perpendicular to the treatment zone at points of perforation. Much like setting a scanline at a rock face, additional quantifiable estimates of fracture curvature and roughness were defined. Additional estimates of discontinuity aperture were obtained based on the calculated tensile component of failure and corrections for angular differences between fractures obliquely oriented to scanlines. Utilizing this approach, we were able to define the relative uniformity of rock mass structure with similar fracturing properties. As well, we have been able to characterize the degree of uniformity with position from the perforation intervals. Our observations suggest that a change in fracture spacing and type is indicative of changes in rock mass response to the stimulation and can therefore be used to classify the varying fracture state of the reservoir. Data from these analyses provide further constraint or input on the development of geomechanical and reservoir models.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016