Application of uniaxial strain boundary condition as stress path to measure mechanical and petrophysical properties is critical in estimation of reservoir compaction/ subsidence, estimation of recoverable resource via compaction drive, change in reservoir producibility and finally, to calibrate 4D seismic. The drop in demand in hydrocarbon resources, coupled with operating at low-price environment will continue to constrain laboratory measurement. This warrants for optimally utilizing the available core material and acquire of multiple datasets from limited material and testing occurrence. However, the available space inside a typical rock mechanics cell is limited, as radial deformation transducer, a key to establish uniaxial strain boundary condition, need to be placed at the center of the sample. This paper reports results of an experimental study aimed at finding a viable alternative that permits maintaining uniaxial strain boundary condition without using radial deformation transducer. The amount of pore fluid expelled/injected during simulated depletion/re-injection sequence is studied and its applicability to replicate uniaxial strain condition is explored. Results indicate that the change in porosity, uniaxial compaction and pore volume compressibility coefficient measured using the new technique show excellent agreement with that measured utilizing conventional method, i.e., radial deformation transducer. In addition, the measured variation in sample diameter is found to be well within the acceptable limit of experimental error.

1. Introduction

Knowledge of insitu stress and pore pressure and how they change during the geological and production time scale is a topic of interest for decades. Stress and pore pressure change during hydrocarbon extraction and resulting rock deformation has consequences that can be tied back to a dollar value because of lost time and/or lost production. Understanding of geomechanical and petrophysical properties of reservoirs that are soon to be exploited or already producing thus warrants for in-depth characterization effort. Although interpretation of geophysical data takes a significant share of these efforts, direct measurement performed on core materials extracted from subsurface always plays a key role. However, obtaining whole core for every new development/ project can be costly and requires time. Optimum utilization of core material is hence more important than ever in the current operational environment. One solution to this problem is acquiring sidewall plugs and conducting measurements (Mitra et al., 2016; Govindarajan et al., 2019). Another option is obtaining multiple measurements from single experiment while obeying the underlying physics behind the measurements. The latter not only helps optimum utilization of core materials but also allows to integrate and reconcile various geomechanical and petrophysical properties as the uncertainty owing to rock heterogeneity is avoided and the stress path for measurement remains the same. However, realization of such experimental program requires using multiple transducers in a single experiment. This subsequently brings in the challenges of accommodating each of them in the tight annular space inside the test vessel. For example, estimation of permeability change across the sample while maintaining uniaxial strain boundary condition requires strain gauges/radial transducer which in turn interferes with the plumbing used for fluid flow. Another area of concern is testing at high temperature environment, typical for deepwater operation, steam-flood or geothermal wells. At elevated temperature, the performance of radial transducers suffers significantly. Utilizing uniaxial strain stress path at elevated temperature can thus be challenging.

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