Measuring Porosity and Permeability From Drill Cuttings

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 111286, "Advances in Measuring Porosity and Permeability From Drill Cuttings," by R. Lenormand, SPE, IFP, and O. Fonta, Geopetrol, prepared for the 2007 SPE/EAGE Reservoir Characterization and Simulation Conference, Abu Dhabi, UAE, 28-31 October. The paper has not been peer reviewed. Drill cuttings can provide quick and useful information for reservoir characterization, especially when cores are not available. Several petrophysical properties can be determined from cuttings: porosity, permeability, and transverse-relaxation-time (T2) nuclear-magnetic-resonance (NMR) distributions (related directly to the pore-size distribution). Results are presented for porosity and permeability measurements on cuttings with diameters of approximately 0.5 mm and for a field test. Introduction Early determination of rock petrophysical properties is needed during the reservoir-characterization process because it affects estimates of reserves (porosity and saturation) and of well deliverability (permeability). Generally, well logs provide a good estimate of porosity and saturations along the wellbore, but permeability is more difficult to obtain. Cuttings are used routinely by mud loggers to build the "master log" of the geological description of the drilled formation. Hydrocarbon indices are determined from cuttings to identify the reservoir levels. Although rock-cutting material comes directly from the reservoir, few applications of porosity and permeability characterization are reported in the literature. The full-length paper details the methods used for porosity and permeability determinations from cuttings and presents results from tests on crushed cores. The main result is accurate determination of porosities for 0.5-mm-diameter cuttings for permeability of less than 1 md. The porosities and T2 NMR data measured on real cuttings from a well in the Paris basin are presented and compared to log results. Porosity Measurement on Cuttings The methods for measuring porosity on cuttings are the same as those for cores when the cutting size is larger than 3 mm. For smaller cuttings (most cases), the best results are obtained by use of a centrifuge or a porous plate to remove the interstitial liquid with a controlled capillary pressure. Porosities were measured to within 1 to 2 p.u., even for flat cuttings with diameters of approximately 1 mm and thickness of 0.5 mm collected during the field case. Improved Methods. To improve measurement accuracy for cutting sizes down to 0.5 mm, most of the existing methods were tested. A porous-plate method provided the most consistent results and is detailed in the full-length paper. The saturated cuttings are placed in a tube set on its end on the porous plate. Vacuum is applied through the plate to remove interstitial liquid and partially desaturate the plate. Then, the porous plate pulls the remaining interstitial liquid with a controlled capillary pressure. When the excess water is removed, the cuttings no longer stick together and move freely like dry samples.