Publications

Carbonate reservoirs in the Ujung Pangkah field demonstrate a high degree of heterogeneity in terms of rock properties. Representative sampling of conventional core in both full diameter (FD) and plugged samples is an important step in getting reliable routine and special core analysis (SCA) results. A good combination of FD and plug samples is necessary to address potential issues with sampling scale, and at the same time to understand more about the degree of reservoir heterogeneity.Very complete and rigorous core analyses were performed on both FD and plug samples in recent work. The core analyses included routine porosity and permeability measurements, various SCA capillary pressure and electrical properties, wettability tests, relative permeability and NMR measurements. Permeability measurements on FD samples at any given porosity are generally higher than those on plug samples with lower rock quality. Measurements of electrical properties (cementation exponent m and saturation exponent n) from FD samples demonstrate a much narrower range of measurements than those from plug samples. Brooks Corey capillary pressure analysis using the porous plate technique on FD samples also provides a much better understanding of the relationship between Irreducible Water Saturation (Swir) and capillary entry pressure (Pe), with Reservoir Quality Index (RQI) compared to the same data from core plugs. This phenomenon is commonly seen in carbonate rocks. One of the common reasons for this discrepancy, other than their intrinsic heterogeneity, is the different degree in alteration and invasion by drilling mud particles.The value of investment in conducting core analyses on FD samples is high in carbonate rocks, not only due to degree of heterogeneity, but also because FD samples are required for correcting and calibrating plug samples in wells without FD samples, which provide much more accurate and representative reservoir rock properties. While having these advantages, FD sample core analyses normally take much longer and are more expensive than for plug samples.