A VALID APPROACH TO CORRECT CAPILLARY PRESSURE CURVES- A CASE STUDY OF BEREA AND TIGHT GAS SANDS

摘要

Capillary pressure data have been used over the years to estimate important petrophysical parameters that are being employed to predict hydrocarbon reserves. However, little or no attention is given to the accuracy of the capillary pressure curves obtained from the mercury injection technique. Primary drainage capillary pressure data are crucial to determining the percentage of water saturation, irreducible water saturation above the original oil-water contact or gas-water contact, thickness of the transition zone, and the hydrocarbon-in-place, Honarpour et al. [1]. A laboratory study was carried out to evaluate the importance of applying corrections to the capillary pressure data from mercury injection method. This paper evaluates the effects of blank and modified blank corrections on the capillary pressure curves from tight gas and Berea core samples. The tight gas samples are from the East Texas and North Louisiana formations. The capillary pressure curves were measured by means of high-pressure mercury injection (HPMI), using an Autopore IV instrument, which measures up to 60,000 psia. Blank correction was applied to the curves developed from the samples. In order to incorporate the compressibility of the core samples, a modified blank correction approach was developed and applied, and the differences of the two corrections were studied. Six core samples, comprising three Berea and three tight gas sands, were analyzed. This study suggests that the effect of both correction methods is minimal on tight gas samples, but significant on Berea samples. The modified blank correction method gives more accurate corrections to capillary pressure curves obtained from high porous rocks like Berea, and hence more accurate estimates of water saturation and resource-in-place, because it incorporates the compressibility of reservoir rocks.