Estimating Cementation Factor (m) for Carbonates Using Borehole Images and Logs

Abstract

Abstract Carbonate reservoirs account for 60% of today's hydrocarbon production. Several giant carbonate fields in the Middle East are expected to be the dominant source of hydrocarbon production through the current century. Therefore, understanding carbonate reservoirs and producing them efficiently have become industry priorities and are likely to remain so. In order to assess a possible hydrocarbon reservoir, hydrocarbon saturation needs to be determined with good accuracy. In 1942 Archie published a formula to estimate water saturation in reservoirs. In case of carbonates, the saturations computed by the formula are not always correct. The factors complicating the role of the formula are known as Archie Exponents, namely, porosity exponent (m, also known as cementation factor) and saturation exponent (n). Both exponents tend to vary quite often in the carbonate reservoirs. With the exception of cores, no reliable and well established techniques exist today that can give a good estimate of these exponents. Estimating cementation exponent (m, porosity exponent) from the well logs is the main objective of this paper. The technique addressed in it is based on the assumption that the amount and pattern of cementation, caused by diagenesis, in carbonates is one of the factors controlling the value of m. Therefore in order to estimate it for carbonates, the cementation in them should be quantified. It was achieved through integration of electrical borehole images and petrophysical logs with the cores. The data on cementation was then used to estimate 'm' as a continuous curve for carbonate reservoirs. The technique provides a unique way, which incorporates textural part of carbonates, to estimate cementation factor (m) for carbonates. It has been applied to carbonates of the Middle East and Europe with good results, which were verified by the core data and production results.