The five detector pulsed neutron (FDPN) tool is one of the most advanced tools in cased-hole reservoir evaluation. The evolution of multi-detector pulsed neutron tools (MDPN) created a turning point in the methodology to properly handle the different challenges within petrophysical cased-hole evaluation either in conventional or unconventional formations. This study demonstrates the applications of the FDPN tool and the methodology to handle the challenges in the multi-barrier well bore systems. The FDPN tool was used in two double-barrier well bore field cases in addition to one case with a triple casing system. Each case was unique in terms of objectives and challenges: Case 1 (13.375 inch, 9.625 inch and 7 inch casings) aimed to estimate the presence of gas in the annulus between the two casings and the formation gas behind the double-barrier wellbore system, while Case 2 (7 inch liner and 4.5 inch ICD) required to perform a three-phase calculation. In Case 3 (13.5 inch, 10.75 inch and 7.625 inch casings) diffusion-corrected sigma was recorded to be able to determine the water saturation in a triple casing system. In all these case studies, Monte Carlo simulations (MCNP) were performed to characterize tool response and to determine if the data to be recorded will achieve the objectives of these jobs. In Case 1, the FDPN tool helped to establish the presence of gas in the annulus between casings and determined the gas saturation profile in the formation using the difference between the normalized capture and inelastic ratios. This case was unique since other MDPN tools were not able to quantify the volume of gas in the formation due to their lower gas sensitivity. In Case 2, the objectives were successfully achieved. Also, it was possible to differentiate between the formation gas and the gas pockets between the 7 inch liner and the 4.5 inch ICDs using the comparison between inelastic and capture measurements. In Case 3, a diffusion-corrected sigma was measured and identified formation water movement in the zone of interest which helped to make a decision about drilling of the offset well. The FDPN tool provides a higher spacing between the detectors and neutron generator which gives a better quantification of hydrocarbons especially for large casing and borehole sizes. Furthermore, the spacing between the long and proxy detectors is increasing the gas measurement sensitivity compared to other MDPN tools. Also, the 1.69 inch pulsed neutron logging tool was successfully run for first time in Kuwait to record diffusion corrected Sigma over a triple casing interval.
In 2009 a new Inflow Performance Relationship (IPR) model "SPE- 124041"was built using simulation and field data sets. Reservoir simulation was used firstly to accurately select the best fit between the oil mobility function and the average reservoir pressure. The new IPR was developed based on the resulted oil mobility-pressure profile. Then, many field cases were used to develop an oil mobility-pressure relationship. Accordingly in this work, an attempt to apply the new IPR was proposed. To check the applicability and accuracy of the new IPR model, multi-rate test with bottom hole pressure is required to plot the actual IPR curve. Many Portable Gas Oil Ratio (PGOR) tests integrated with ESP bottom hole pressure data and Flowing Bottom Hole Pressure (FBHP) surveys were used to create actual IPR curve for each well. Also, bottom hole pressure and flow profile obtained by Production Logging Tool (PLT) data for each entire producing interval in a layered reservoir system is used to plot each actual IPR curve. Then, the new IPR model was tested and compared to the most common IPR models to get the IPR curve for each well as well. The applicability for different fields (KOC fields) of the new IPR model was tested and compared to the most common single point IPR models known in the industry (Vogel, Wiggins, and Sukarno). Many PGOR field cases were used for comparison. The best method for PGOR and PLT cases was the new method and that with average error of around 3.6 %, while the errors from the other models are higher than 4 % ranging from 4.5 to 5.3 %. For PLT cases. To combine layered reservoir production testing, which could be conducted under pressure transient conditions with the inflow performance; it will help accurately to determine the optimum production rate for each well of interest. The results showed this method is accurate, reliable and simple. Is general for oil reservoirs, requires only one test point and has a wide range of application.
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.
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