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A New Method for Conformance and Compression Corrections of Mercury Injection Capillary Pressure and Its Application in Petrophysical Evaluation of Mudrocks


Mercury injection capillary pressure (MICP) is a commonly-used technique for measurement of porosity, pore throat size distribution, and injection pressure vs. mercury saturation for many types of rocks. The latter two are correlated to and can be used to estimate permeability. Problems for MICP application in mudrocks are associated with two types of system errors: conformance and compression effects. These two sources of error are well-recognized, but quantitative analysis of the two sources of error is lacking, and standard procedures to correct them do not exist.

In this study, a new method for conformance and compression corrections was developed, and permeability was estimated based on the corrected MICP data. The method was applied to five Eagle Ford Shale samples. Conformance correction is based on comparison of mercury injection volume vs. pressure curves between epoxy-coated and uncoated block samples. An epoxy with high compressive strength was used for sample coating. Bulk compressibility of the samples was measured using the epoxy-coated samples in MICP. Compression correction is based on the calculation of compression before and after mercury intrusion at each pressure step in the MICP experiment. Solid-phase and pore compressions were defined and quantified. Compression corrections on porosity, pore throat size distribution, and injection pressure vs. mercury saturation were performed. Results show that compression effect, although regarded as one of the major sources of error, is generally insignificant with compressibility values for the samples in a level of 1E-7 psi-1. Conformance effect and correction is more important for porosity and permeability estimation. MICP-based porosity results were compared to helium porosity. Permeability was estimated based on the corrected MICP saturation curve and a regression-type equation from literature. Estimated permeability values are comparable with the laboratory measured values for Eagle Ford Shale samples. Because intact core plug samples are not required in MICP experiment as in the pulse/pressure decay method, the corrected MICP-based method can serve as an easier and faster way for permeability evaluation of mudrock samples.