Toru Terabayashi

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

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.

Gas-oil ratio of live crude oils determined by near-infrared spectroscopy

12 The Gas-Oil Ratio (GOR) of crude oil has a tremendous impact on the processes used for oil production from subsurface formations. Determination of GOR thus becomes of central importance to oil operating companies. Here, it is shown that near-infrared (NIR) spectral measurements on single- phase crude oils (with dissolved gas) can be used to obtain a reliable estimate of the GOR. Furthermore, the NIR measurement is shown to be compatible with process flow streams at elevated temperatures and pressures.