Showing papers by "Abu Dhabi Company for Onshore Oil Operations published in 2003"

The Barremian-Aptian Evolution of The Eastern Arabian Carbonate Platform Margin (Northern Oman)

Abstract: Carbonate platform margins are sensitive recorders of changes in sea level and climate and can reveal the relative importance of global and regional controls on platform evolution. This paper focuses on the Barremian to Aptian interval (mid Cretaceous), which is known for climatic and environmental changes towards more intensified greenhouse conditions. The study area in the northern Oman mountains offers one of the very few locations where the Cretaceous carbonate margin of the Arabian Plate can be studied along continuous outcrops. Our detailed sedimentological and sequence stratigraphic model of the platform margin demonstrates how major environmental and ecological changes controlled the stratigraphic architecture. The Early Cretaceous platform margin shows high rates of progradation in Berriasian to Hauterivian times followed by lower rates and some aggradation in the Late Hauterivian to Barremian. High-energy bioclastic and oolitic sands were the dominant deposits at the margin. Turbidites were deposited at the slope and in the basin. The Early Aptian platform margin shows a marked change to purely aggradational geometries and a welldeveloped platform barrier that was formed mainly by microbial buildups. The sudden dominance in microbial activity led to cementation and stabilization of the margin and slope and, therefore, a decrease of downslope sediment transport by turbidites. In the Late Aptian, large parts of the Arabian craton were subaerially exposed and a fringing carbonate platform formed. Seven Barremian to Early Albian large-scale depositional sequences reflecting relative sea-level changes are identified on the basis of time lines constrained by physical correlation and biostratigraphy. The reconstruction of the margin geometries suggests that tectonic activity played an important role in the Early Aptian. This was most likely related to global plate reorganization that was accompanied by increased volcanic activity in many parts of the world. Along the northeastern Arabian platform the associated global changes in atmospheric and oceanic circulation are recorded with a change in platform-margin ecology from an ooid-bioclast dominated to a microbial dominated margin. Time-equivalent argillaceous deposits suggest an increase in rainfall and elevated input of nutrients onto the platform. This process contributed to the strongly diminished carbonate production by other organisms and favored microbial activity. The platform margin may thus represent a shallow-marine response to the Early Aptian global changes, commonly associated with an oceanic anoxic event in basinal environments.

Analyzing Reservoir Fluid Composition In-Situ in Real Time: Case Study in a Carbonate Reservoir

Abstract: Near-infrared (NIR) spectroscopy is used to provide in-situ quantitative characterization of reservoir fluids during wireline sampling using five representative composition groupings (C1, C2–C5, C6+, CO2, and water). This information is vital for the proper execution of wireline fluid sampling jobs. Time variances of fluid compositions, along with absolute compositions, give us important clues about the phase and contamination level of the capturing samples in real time. In addition, quantitative compositional analysis during wireline sampling provides immediate identification of the critical fluid issues, thereby enabling optimization of the sample acquisition program. Laboratory pressure-volume-temperature (PVT) analysis requires samples that are captured in single phase and are relatively free from mud filtrate contamination. Such information is essential for reservoir management and flow simulation modeling. This paper consists of three parts. The first part covers laboratory NIR spectroscopic study of petroleum fluids at elevated pressures and temperatures. This extensive database, coupled with principal components regression (PCR) technique, establishes the feasibility of such an in-situ compositional analysis. The second part reports shop test results on a downhole experimental prototype. The tool estimates density for each composition group for more than 10 live fluids at conditions simulating a petroleum reservoir. Typically, the measured mass fraction for each composition group agrees with the mass fraction acquired from PVT analysis within ±5% accuracy. The final part presents a field test case study conducted in an onshore carbonate reservoir in the United Arab Emirates (UAE). A gas injection pilot has been running for years, and a comprehensive monitoring program is in place. The first field trial of the subject technology in an observation well successfully identified the presence of injected gas, as determined by fluid compositions. This result was later found to be in good agreement with laboratory PVT analysis.