“Temperature and Poroelasticity
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by
Tobias Orlander
Abstract
Current rock physical and geomechanical models are unable to handle conditions found in High Pressure and High Temperature oil and gas reservoirs with high regional overpressures and hence model updates are needed. In order to improve models we need knowledge of strength and stiffness properties of the sedimentary rocks constituting the HPHT reservoirs at high temperature. We also need an understanding of how the effective stress field responds to changes in pore pressure. The knowledge required for model updating is obtained from state of the art theory of poroelasticity and experimental data collected from dedicated rock testing under HPHT conditions. The effective stress field is controlled by the effective stress coefficient which is a fundamental parameter in poroelasticity, often denoted as Biot’s coefficient. Conflicting definitions of Biot’s coefficient have been published, but it is observed to be stress dependent, pore fluid dependent, nonlinearly temperature dependent and a number of authors disregard it for the failure case while applying it for the stress–strain build-up. This leaves an inconsistent picture of a highly relevant rock property and with dwindling exploitation of conventional oil and gas resources and a worldwide trend towards HPHT reservoirs, the need for a fully descriptive theory of poroelasticity capable of describing the effective stress fields under HPHT conditions is crucial in order to secure: safe drilling during operations, well life and drilling operations with a narrow drilling window.