The Role of Proppant Mesh Size on Stimulation Effectiveness

Abstract

Abstract

There is an inherent understanding that effective stimulations in shales depend on a recipe consisting of different mesh sized proppants injected under a variable pressure regime resulting in an interconnected network of open fractures that increase permeability in the reservoir and thereby production. To evaluate the effectiveness of this process, microseismic monitoring is often used to describe the overall frac dimension and orientation. However, by utilizing multi-array multi-well geophone distributions around the potential frac volume, additional information can be attained on individual fractures (Seismic Moment Tensor Inversion) including their orientations (strike/dip), failure mode (shear versus tensile or shear-tensile failure exhibiting opening or closure components), and fracture dimensions. As a result, we can explicitly examine the development and growth of the fracture network during any point of the injection cycle and further be able to determine the role of proppant and pressure on the development of the fracture network.

In this study we examine a series of different stages recorded during a zippered stimulation of a shale play in North America. The injection program included an initial increase in pressure followed by the addition of 100-mesh proppant and a subsequent change to 30/50 mesh proppant prior to the end of the stage. Typically, we observe an initial increase in pressure activated fractures with a broad range of failure mechanisms including, shear, shear-tensile opening and closure. The introduction of 100-mesh proppant results in vertical and sub-vertical fracturing whereas switching to 30/50 mesh proppant leads to a significantly higher concentration of events with shear-opening mechanisms and sub-horizontal fractures. There is also an apparent rotation in the sub-vertical failures that can be related to the changing local dynamic stress field overprinting the regional stresses. At the conclusion of the stimulation, a higher proportion of closures occur as distal stresses due to the injection relax. Generally, similar results were observed for the various stages of the injection program when injecting into virgin rock. However, depending on the overlap between stages, the injection program could be considered as less effective, as closure dominated the observed failure processes. Based on our investigation, we suggest that careful thought into mesh size may definitively improve stimulation effectiveness.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016