Carbonate reservoir rocks are estimated to contain approximately half of the worlds discovered hydrocarbon reserves. While such rocks have been relentlessly studied by petroleum geologists for many decades to understand the controls of sedimentology, sequence stratigraphy and diagenetic overprints on reservoir quality, less emphasis has been given to quantifying how the mechanical compaction of these calcareous sediments resulting from production-driven effective stress changes can impact porosity/permeability response. To better comprehend the potential stress-sensitivity of carbonate reservoir rocks, we have utilized geomechanics testing of analog limestones and dolomites with widely varying initial porosity and permeability magnitudes to directly observe the influence of lithology (microstructure and pore type) and stress path (hydrostatic versus uniaxial) on compaction-driven pore volume reduction and permeability loss in the laboratory. We quantify relative storage and transport stress-sensitivity using exponential pore volume and transmissibility multipliers relating, respectively, porosity change to pressure difference and permeability change to void ratio difference, and observe distinct trends between multiplier-magnitudes and complementary characterization data. These results represent valuable quantitative analog data that can be used to inform selection of appropriate multiplier magnitudes for replicating carbonate stress sensitivity in numerical models, for example when no subsurface core is available to directly quantify such effects in the laboratory.

1. INTRODUCTION

Carbonate reservoir rocks exhibit a range of porosity and permeability values that result from depositional and diagenetic processes. Although numerous researchers have studied the controls on porosity and permeability in carbonates, less attention has focused on the mechanical response of these rocks including their geomechanical properties (e.g.; Yale et al, 1993; Yale & Crawford, 1998). Given the impact that the carbonate pore system has on factors including porosity, permeability, and hydrocarbon displacement (e.g. Fullmer et al, 2019), we evaluate how the variation in pore types from a number of carbonate settings influences their mechanical properties. Recent work on quantifying the distribution of carbonate pore types has demonstrated how the relative abundance of pore types can vary (Buono et al, 2019). We suspect this variation in pore type distribution may impact how carbonate rocks respond to varying effective stress changes resulting from subsurface stimulation and production.

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