Pore volume compressibility controls formation compaction, surface subsidence, and stress redistributions during petroleum production. Its measurement is also essential for reserve estimation, production forecasting and history matching, permeability estimation, etc. The uniaxial strain stress path is generally considered as the most representative stress path at a field scale for many petroleum-related processes, as it normally approximates the underground boundary conditions thought to be active during hydrocarbon production or fluid disposal operations. However, uniaxial strain pore volume compressibility is rarely measured on cores mainly due to equipment and time constraints as well as procedural difficulties. With the development of advanced hydraulic fracturing technologies, shale/tight oil/gas reservoirs have become a viable source of energy. The test as reported in this paper is intended to measure the pore volume compressibility of an intact black shale sample provided by an oil company under a uniaxial strain condition with a stress relaxation loading condition. 380 hours (about 16 days) have been spent for the full loading-unloading process with the pore fluid depletion test as the unloading process took about 8 days. Two approaches have been used to interpret the pore volume change. In the first approach, the pore volume change is based on the rock bulk volume change as measured by strain gauges, using the Biot's coefficient to bind the rock bulk volume measurement with the produced oil volume. In the second approach, the pore volume change is directly based on the produced oil volume with a correction based on a specific oil volume correction test. The agreement between the theoretical horizontal stress path based on the rock properties and the actual horizontal stress path followed during the test indicates that this test has been properly conducted.
Rock poro-mechanical properties are key to reliable assessment of the formation deformation response to pore pressure changes, which can have a critical impact on production and field development. Pore volume compressibility (PVC), defined as the relative change in pore volume with a change in pore pressure is of fundamental importance in material balance calculations and water/compaction drive performance studies (e.g., Galloway and Burbey; 2011; Ong et al., 2001). Pore volume compressibility measurements and calculations are essential for reserve estimation, production forecasting and history matching, etc. (e.g., Schutjens and Heidug, 2012).