Preliminary Study on the Practical Implementation of Anisotropic Shale's Pore Pressure Response

ABSTRACT: Shale plays a crucial role as the overburden rock of most conventional oil and gas fields, as well as carbon capture and storage sites. Therefore, understanding its geomechanial response is vital for ensuring safe operations. Shale rocks exhibit strong elastic anisotropy due to the presence of highly anisotropic clay minerals and its alignment, which significantly impacts geomechanical responses. For example, in anisotropic materials, Skempton's B parameter needs to be generalized to a second-order tensor, as it greatly influences the undrained induced pore presure caused by drill-out. Accurate prediction of undrained induced pore pressure requires knowledge of the components of the generalized Skempton's B tensor. However, due to the cost and complexity of core measurements, the generalized Skempton's B tensor is not typically measured in the field. To address this issue, a preliminary study was conducted to estimate the generalized Skempton's B tensor of shale using exsiting core measurment results. The generalized Skempton's B tensor was estimated using anisotropic poroelasticity, taking into account the measured undrained rock stiffess, measured porosity, estimated fluid bulk modulus, and assumed grain bulk modulus. The estimated components of the generalized Skempton's B tensor were compared with the measured values to evalute the effecitiveness of this approach. 1. INTRODUCTION Shale plays a crucial role as the overburden rock of most conventional oil and gas fields, as well as in Carbon Capture and Storage (CCS) sites. Therefore, understanding its geomechanical response is vital for ensuring safe drilling and operations. Shale rocks exhibit strong elastic anisotropy (e.g., Vernik and Nur, 1992; Wang, 2002; Szewczyk et al., 2018; Lozovyi and Bauer, 2019) due to the presence of highly anisotropic clay minerals and their alignment. Additionally, Skempton's B parameter needs to be generalized to a second-order tensor, as demonstrated by existing core measurements (e.g., Lozovyi and Bauer, 2019; Holt et al., 2018). This has significant implications for the estimation of undrained induced pore pressure in shales.