The objective of this case study is to show the value of the NMR real-time log data, acquired while drilling, for reservoir characterization as a lithology independent porosity logging solution and most important for permeability computation. The applied methods are being discussed with much focus on the added value of the transverse relaxation time T2 spectrum analysis in a highly heterogeneous, upper Jurassic carbonate reservoir, to characterize the pore size distribution while geosteering the wellbore to track the better quality pore systems and generate a real-time permeability profile, supporting the later advanced completion run for the first time, in this offshore field. The current field development plans are based on drilling multi-lateral horizontal and highly deviated wellbores along the layers of Reservoir-D to enhance the injection and production efficiency. Running radioactive-based porosity logging tools with such complicated well trajectories poses a high operational risks and collide with environmental regulations, this paper presents a case where nuclear magnetic resonance (NMR) as a source-less porosity logging device, run with the conventional resistivity-gamma ray logging while drilling combination achieved effective real-time formation evaluation and supported efficient well placement to maximize the reservoir contact. The NMR formation evaluation supported the design of the following Inflow Control Device (ICD) well completion operation for water injection, in a timely effective process, later validated with production logging data. The application is focused on maximizing the value of the real-time LWD (NMR) data for the time-critical (ICD) design and deployment in the highly deviated/ horizontal drains drilled, offshore Abu Dhabi.

Well control situation in high angle wells put challenging environment for the acquisition and interpretation of formation evaluation data on wireline. This case study puts a highlight on a new technology, which allows mitigating the well deviation and trajectory-related complications in addition to wellbore stability to acquire accurate wireline quality data, resulting in an improved completion design and an increase in production. The discussed well was drilled and completed as a horizontal open hole producer in 1994. It showed unstable production and was put on schedule for re-completion to increase production. The planned fishbone well completion design implied high-resolution caliper data acquisition to ascertain the borehole geometry in detail. Moreover, a time-lapse water saturation analysis was mandatory. On the other hand, a considerable operational risk was associated with conventional wireline tools deployment, pushing the toolstring downhole. However, this risk was minimized using the new compact well shuttle system (CWS) which has all the logging sensors housed inside the drill pipe before they can exit it to the open hole at the start of the operations. This conveyance method gave the drillers full well control, having the ability to rotate the pipe and even circulate mud in this 95-degree inclined, unstable well. Using open-end bit allowed reaming during RIH and POOH. Also, memory data acquisition allowed getting the required well log data in one run. Consequently, the well objectives were achieved, and operational risks were minimized. Also, the total well cost was optimized without sacrificing data quality, which supported formation evaluation of Mauddud reservoir drain. Finally, this led to an efficient completion and production decision-making. The advanced conveyance method discussed in this case study has been deployed in a Horizontal well within Mauddud reservoir (onshore Kuwait) for the first time, reduces the risk and cost of accessing high angle wells and wells with well control situation.

No abstract

No abstract

Pulsed-neutron capture (PNC) logs are commonly used to determine formation water saturation in cased-hole environments, often for time-lapse monitoring purposes. This paper describes a new diffusion-corrected sigma algorithm developed for a pulse neutron logging tool. In southeast Kuwait, diffusion-corrected sigma log data was recorded in three wells using an array of four optimally spaced gamma ray detectors above a neutron generator. To calculate a diffusion-corrected sigma, an algorithm based on a dual exponential fit was applied to the time-decay spectrum of the near and far detectors. This calculation separates the formation and borehole decays. This approach provides an apparent formation sigma for the near and far detectors. The algorithm uses the near detector for final sigma, and a diffusion correction to the near sigma is determined by a function of a near-far sigma difference. The diffusion-corrected sigma matched the expected results and provided a good statistical quality—even at high sigma values—because it is based on the near detector with its higher count rate, as demonstrated in the examples presented. Also, the formation sigma was independent of different borehole conditions in which the data was recorded. The final formation sigma results were compared to volumetric results from open-hole data (volume of shale, effective porosity and water saturation) and sigma calculated from open-hole volumetric using material balance. The PNC data recorded in the three wells allowed determination of the most recent oil-water contact (OWC) and update of water encroachment maps from the time-lapse monitoring. Comparing with previous sigma data recorded in these wells, it was concluded a normalization transform is not needed because R2 value of the linear regression is close to 1. The diffusion-corrected sigma algorithm using dual exponential fit showed that this technique was able to extract independent values for borehole sigma and formation sigma for each detector and to perform an accurate diffusion correction. This algorithm will provide reliable sigma values regardless of the borehole conditions in which the data was recorded.