TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNear-infrared (NIR) spectroscopy is used to provide in-situ quantitative characterization of reservoir fluids during wireline sampling using five representative composition groupings (C 1 , C 2 -C 5 , C 6+ , CO 2 , 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.

Reservoir screening studies were carried out on all of ADCO’s reservoirs to determine their applicability for Underbalanced Drilling (UBD). These studies resulted in a prioritization of potential UBD candidates. The primary business benefits of UBD were determined as follows: –reduction of formation damage ○Productivity Improvement Factors (PIFs) much greater than 1 were determined in many cases;○potential elimination of complicated (and expensive) stimulation jobs.–dynamic reservoir characterization ○improved understanding of geological architecture/flow units and hence the potential for more accurate and reliable reservoir models;○improved completion designs. Some of the secondary benefits of UBD that were identified beforehand included Rate of Penetration (ROP) improvements while drilling and improved rig performance. In one field, it was demonstrated that the PIFs per well resulting from UBD would enable fewer wells to be used to develop the field by optimization of the horizontal well length and hence a significant reduction in capital expenditure. From these studies, two fields were selected to carry out initial trials. This paper describes the lessons learnt from the planning, design and subsequent implementation of UBD in the first well in ADCO, which involved a truly integrated and multi-disciplined team effort. An initial assessment of the business benefits obtained from the trial compared to the results of the initial screening studies is also provided.

The field under study is structurally and stratigraphically complex, which increases the uncertainties associated with field development. To optimize reservoir characterization using seismic data, seismic inversion (Deterministic, Stochastic and Simultaneous) was planned to be performed using the 3D seismic data covering the field. Given that well log data provide constraints and calibration in the inversion workflow, their quality has a direct impact on the robustness of inversion results. This paper focuses on corrections made to sonic and density log data to make them suitable for seismic inversion.Sonic and density logs have shallow depths of investigation and are affected by borehole irregularity and filtrate invasion. Errors due to borehole irregularity in the section overlying the reservoir impact two key stages of the inversion process: wavelet extraction using well-seismic ties, and construction of the low frequency or a priori model. Invasion within the reservoir impacts the accuracy of porosities obtained from seismic impedance data. Typically porosity estimation is done using a regression relationship between porosity and acoustic impedance derived from well log measurements. The log impedance data (both velocity and density) are affected by saturation changes related to filtrate invasion which must be corrected for, to obtain a reliable porosity-impedance relationship.A robust and practical workflow to address log quality issues begins with log data quality QC: identifying zones with missing logs or borehole affected log readings. Shear sonic logs are unavailable for many wells, which limits their use for Simultaneous inversion, and for invasion correction using a rock physics model. We constructed shear sonic logs from compressional sonic logs using a rigorous, iterative process. Gassmann's equation was then used to correct for filtrate invasion effects. Invasion effects were found to change impedance values within reservoir intervals by as much as12 %, which has implications for 4-D seismic monitoring of the reservoir.

The field under study is an elongated NE-SW faulted anticline which has a main axis length of around 25 km and a width of approximately 6km located onshore UAE. The main hydrocarbon accumulations occur in the Lower Cretaceous-Thamama Group. This group is comprised of a series of carbonate reservoirs with well-developed porosity, but low to moderate permeability. This paper discusses the implementation of acquiring Formation Pressure While-Drilling (FPWD) applied for better understanding and mitigating the geological structure uncertainties. The results were used to obtain accurate reservoir pressure measurements while drilling horizontal wells that intersected multiple fault blocks. Formation pressure measurements acquired while drilling (FPWD) have numerous applications including mud weight optimization to reduce drilling risk, control well placement in pay zones to maximize reservoir contact (MRC), and for better reservoir management by evaluating the connectivity between different fault blocks. This paper will discuss the theory and the operational sequences of the FPWD tool as well as the results of some case studies in the implementation of the FPWD runs in an onshore Abu Dhabi carbonate field.