ISRM Suggested Method for Uniaxial-Strain Compressibility Testing for Reservoir Geomechanics

Excerpt

Rock hydromechanically coupled properties are key parameters needed for an accurate understanding of the formation deformation response to pore-pressure changes in rocks and sands. They can have a critical impact on both the economics and the containment risks associated with fluid withdrawal or injection operations, particularly in the petroleum industry (where, e.g., reservoir compaction and subsidence impacts can be many millions of US dollars). Pore-volume and bulk-volume compressibility are needed in reservoir modeling and compaction/subsidence computations. Those parameters are functions of intrinsic hydromechanical properties, but more importantly they are stress-path dependent. The uniaxial-strain (zero-lateral-strain) stress path is often considered the most representative stress path at a field scale for many petroleum-related recovery processes, as it normally approximates the underground boundary conditions thought to be active during hydrocarbon recovery or fluid injection disposal operations. Figure 1 illustrates the deformation differences between hydrostatic, differential, and uniaxial-strain compression on a homogeneous and isotropic material. The uniaxial-strain compressibility can vary over several orders of magnitude, and in addition it can be constant or highly variable (varying by over two orders of magnitude) with stress, all depending on the character of the material (Jones et al. 1987; Crawford et al. 2011), which highlights the importance of accurately determining the compressibility. This document presents suggested methods (SMs) for conducting uniaxial-strain compressibility measurements, for which no widely accepted standard or SM is currently available. It has been developed by a group of petroleum geomechanics practitioners from industry and academia with experience in these measurements and a commitment to help improve their standardization and quality.

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