Multiple Packer Techniques for In Situ Stress Measurement in Hard Soils-Soft Rocks

Abstract

Caprock Integrity analysis is the most critical stage in any thermal enhanced oil recovery (EOR) project. One of the primary input data for conducting a reservoir-geomechanical analysis to assess the mechanical and hydraulic integrity of the caprock is the in situ stress state within the caprock. Among the methods that have been developed for in situ stress measurements, micro-hydraulic fracturing has been extensively applied by the petroleum industry. A common technique to carry out stress tests in impermeable and weak rocks like clay shale is to combine sleeve fracturing with the micro- fracturing test. The initial sleeve fracturing stage is intended to avoid premature initiation of a fracture at the packer level. Interpretation of data using this method, however, reveals illogical magnitudes of the minimum stress in hard soil-soft rock such as clay shales, at least for tests conducted in northeastern Alberta. Two micro-hydraulic fracturing tests conducted in two different projects: one shallow SAGD project and one CSS project, are analyzed in this research. Comprehensive analyses and characterization of Clearwater clay shale completed and through the use of an inverse analysis technique, constitutive parameters for a modified Cam Clay model were selected. For the CSS project, the paucity of laboratory data on the clay shales of the Joli Fou Formation required the development of a unique tool for calibration and optimization of its geomechanical properties. The rate of excess pore pressure development or drainage conditions during the sleeve fracturing test have been studied to better understand how permeabilities and loading rate influence packer-induced stresses during sleeve fracturing test. This research also includes the evaluation of the pressure transmissibility of the packer elements both analytically and numerically during hydraulic fracturing test and the optimal pressure regarding the relevant internal pressure to maintain an efficient seal to prevent leakage and unsuccessful test ` iii introduced. Fluid-structure interaction analyses using a co-simulation technique was conducted to evaluate the principal stress components of caprock in both SAGD and CSS projects. Finally, the main source issue of unreliable micro hydraulic fracturing test data conducted in hard soil- soft rock diagnosed using the simulation of the fracture mechanism, XFEM technique and the analyses gained from the fracture behavior studies provided valuable insight into the modified suggested method.