Integration of High-Resolution CT-Scan and Minipermeameter Measurements With Wireline Logs To Correlate Thin, High Permeable Zones

Abstract

The characteristic vertical variation in petrophysical properties across thin (0.6-1.5m) reservoir units was determined at 5 cm intervals from CT-scan and minipermeameter measurements of core samples from the Upper Cretaceous UA-SB sandstone at Patrick Draw Field, Wyoming and the Pennsylvanian Bartlesville sandstone of Oklahoma. This information was used to determine their expected responses on wireline logs. The correlation with this data of a highly permeable interval at the base of the producing shoreline sandstone (UA-5B) indicated that the distribution of this interval significantly affected waterflood production from the field. Introduction The most productive of the shoreline barrier island reservoirs at Patrick Draw field, Wyoming, is the Upper Cretaceous UA-SB sandstone, which produces from both high-permeability (consisting of the tidal inlet, tidal channel, and tidal delta facies) and low-permeability (consisting of tidal creek, tidal flat, swamp, and lagoonal facies) rocks. Within the high-permeability facies, there are low-permeability intervals resulting from detrital clay, carbonate and clay cementation, and also zones with permeabilities as high as 400-500 mD compared to an average permeability of 20-40 mD for the rest of the sandstone. The high-permeability streaks are predominantly from the tidal channel facies and are believed to be an important source of heterogeneity contributing to poor waterflood recovery from certain parts of the field. For optimum planning of waterflood projects, techniques are needed to map the distribution of the highly permeable streaks from wireline logs. To determine the expected log responses of these streaks, the vertical variation in petrophysical properties across these zones was obtained from CT-scan and minipermeameter measurements of one outcrop and three subsurface cores from the Patrick Draw Field. In addition, two more cores from the Pennsylvanian Bartlesville sandstone obtained from a roadcut near the city of Claremore, Oklahoma, were also studied. The Bartlesville (bluejacket) sandstone was deposited in a delta plain setting at the location of the study. For the purposes of this investigation, only cores from the fluvial channel-fill facies were examined. In a general way, the channel-fill facies of the Bartlesville sandstone can be used to gain some insights into the tidal channel deposits from Patrick Draw Field. All cores were described in detail for vertical distribution of lithology, mineralogy, grain size, sedimentary structures, etc. The characteristic vertical variation of petrophysical properties within and at the bounding surfaces of each producing facies was studied to determine if highly permeable zones could be identified and correlated on logs from the diagnostic changes in petrophysical properties. Measurements of Porosity and Permeability Distributions A minipermeameter (initially calibrated with permeability measurements on standard core plugs) was used to measure permeability of the core samples at every 5 cm depth interval. These measurements gave good estimates of permeability within about 1-2 cm3 of rock for average rock types. The CT density gave an accurate measure of bulk densities over about 50 cm3 of rock volume. P. 973^