Stratigraphic Analysis of Microseismic Signatures During Hydraulic Stimulation

ABSTRACT: This paper presents a novel workflow to enhance the interpretation of microseismic events by comparing the temporal evolution of the microseismic cloud between adjacent stages from two different wells. The stratigraphic properties of identified rock layers along with changes within the local stress field distribution may determine the propagation path and aperture of the hydraulic fracture. Hydraulic fractures however are largely aseismic, and thus microseismic signatures surrounding the hydraulic fracture may indicate important damage-zone fracture formation. A comparison of each microseismic event with the local rock stratigraphy of the hypocenter determined regions where rock composition and larger formation layers influenced the microseismic signals of events. This analysis allowed for classification of microseismic events by formation layers and can elicit different in-situ stress states during hydraulic stimulation. Principal Component Analysis of each formation microseismic cloud can quickly show dominating stresses in the microseismic signals. The changes in the microseismic cloud between the first and second stimulated wells during a zipper fracture stimulation shows the significant changes in formation stress from one well to another in a multi-well system. 1. INTRODUCTION The Hydraulic Fracture Test Site (HFTS-1) is a Public-Private partnership funded by the United States Department of Energy (DOE) with various industry and academic partners to expand our knowledge of the hydraulic stimulation of unconventional reservoirs. In the project 11 horizontal wells were drilled with over 400 stimulation stages completed with advanced monitoring deployed in multiple wells. The test site is located in the West Texas Permian (Midland) Basin targeting the upper and middle Wolfcamp formations. A total of 183 m (600 ft.) of core was recovered from a slanted investigation well drilled after stimulation to determine the extent of fracture propagation and proppant transport (Ciezobka et al., 2018; Courtier et al., 2017).