Vuggy carbonates, such as the reef facies of the Arun limestone, require modification of standard core analysis procedures. The key problem is that when large, wellconnected vugs are present, coring fluid and laboratory materials can enter the pore spaces. When the core is cut the whole coring fluid, not just filtrate, enters those pore spaces connected by large pore throats. The Arun limestone was so deeply invaded during coring that in some cases vugs in the center of 3.5 inch diameter cores were filled with mud solids. Standard core cleaning techniques cannot remove these mud solids. Mud solids invasion and the efficiency of cleaning techniques were evaluated by X-ray CAT scanning the cores. In the laboratory, mercury and all types of jacketing materials also invade the pores. Because mercury enters large vugs, bulk volume was determined by direct measurement of the sample dimensions with calipers. To avoid errors in pore compressibility measurements, due to intrusion into surface pores of material used to jacket samples, a new technique was developed to measure pore compressibility of vuggy samples. In general, all core analysis procedures should be carefully evaluated before application to vuggy formations. Many assumptions fail when vugs are present. The best procedures for vuggy carbonates may not be the methods of choice for other types of rocks.

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