Subsurface Fracture and Stress Determination using In-situ Full Azimuth Seismic data and Orthorhombic Imaging and Inversion

Abstract

High density full azimuth seismic data acquisition may record data revealing information about sub-surface fracture and stress orientation and intensity. This information is useful for prospecting and developing unconventional and tight reservoirs. Current methods to recover reliable fracture information based on azimuth sectoring with offset vector tiling (OVT) are often not sampled sufficiently in azimuth to accurately recover in-situ stresses and fractures. Furthermore, gathers constructed from offset vector tile methods organize data based on surface acquisition parameters. These solutions are often compromised by complex overburdens and complex geology. Orthorhombic velocity modeling, imaging, and inversion for fracture properties provide key alternative technologies to recover natural fractures. However, the determination of orthorhombic parameters is challenging and requires special methods to obtain in-situ azimuths with rich sampling. Additionally, proper orthorhombic imaging and inversion in the depth migration domains require interval parameters rather than simple effective parameters. In this paper, we present methodology where the entire process of orthorhombic imaging and characterization is carried out in the Local Angle Domain (LAD), a domain that describes subsurface image points by two polar angle systems that capture full azimuth reflectivity and full azimuth directivity. The data parameters are measured in-situ over all reflection angles and azimuths making data more relevant for further analysis (e.g. inversion for fracture properties). In order to build an orthorhombic velocity model for imaging and fracture characterization, other workflow steps are essential to ensuring a more stable and reliable outcome. These processes include shallow velocity modeling, surface noise attenuation and data regularization for low fold acquisitions. This paper will also cover the orthorhombic imaging and inversion procedures, and other processing steps that are pre-requisite for a successful outcome. Advantages of imaging and characterization in the local angle domain are central to the workflow and will also be covered in this paper. The resulting fracture/stress maps are consistent with the geology of the area and observations in the well.

AAPG Datapages/Search and Discovery Article #90372 © 2020 AAPG Pacific Section Convention, 2020 Vision: Producing the Future, Mandalay Beach, Oxnard, CA, April 4-8, 2020 (Cancelled)