Fabrication and petrophysical characterization of artificial carbonate rocks with multiscale porosity sintered in a CO2 atmosphere

Abstract

Carbonate rock samples are used in research related to enhanced oil recovery, acid stimulation, calibration of well-logging tools, and validation of numerical petrophysical simulations. However, natural carbonates samples are extremely heterogeneous and have limited availability, compromising experimental analyses. Furthermore, the previous attempts to fabricate synthetic rock replicas were unable to produce samples with pure calcium carbonate composition and multiscale porosity. This paper presents the fabrication of artificial rock with pure calcite composition. Calcite powder was compacted with a pore former (ammonium bicarbonate) and sintered at 850 °C with CO2 atmosphere to avoid the decomposition of the CaCO3. Five groups of samples were produced: partially sintered, sintered with 5, 10, and 20% of the large porogen, and with 20% of the small porogen. The artificial rocks were characterized through X-ray diffraction, porosimetry, X-ray microtomography, scanning electron microscopy, mercury injection, permeability, nuclear magnetic resonance, mechanical compression, and acidizing core flooding experiments. The results revealed that the artificial rocks have a controlled bimodal porosity, with large pores induced by the pore formers (83–211 μm) and nanometric intrinsic pores and fractures. In addition, the samples presented a high mechanical resistance (40 to 126 MPa), similar to natural rocks, and could withstand water immersion and even the core flooding tests. The main drawback was the low permeability (0.05–0.06 mD) achieved, an aspect to be improved in future works. The reported methodology is a significant advance because it allows independently tuning the porosity and pore size distribution, controlling the resultant petrophysical properties in a reproducible way without compromising the chemical constitution, enabling several applications in research.