Because flow regimes in highly deviated and horizontal wells are quite different from those of vertical wells, velocity and hold up distribution are required for accurate flow rate and fluid entry determinations in multiphase flow. Production logging in horizontal wells can be challenging due to undulations and completions such as sand screen. In this paper, we present a field example that utilized advance production logging tool with distributed velocity and hold up distribution using tractor conveyance in sand screen completion. In this job, advanced production logging tool was further integrated with an additional spinner and pulse neutron tool to detect fluids in possible annulus space between screen and open hole. Results were exceptionally good measuring hold up and velocities. All the measurements showed that annulus space was filled with sand and fluid entries were determined confidently. In addition, it was shown that the single spinner in multiphase horizontal flow could not determine velocities of each phase unless totally immersed in one phase. The observations and recommendations were further discussed in this challenging production logging environment. Introduction Horizontal production logging operation has a main objective of obtaining flow profile of oil, gas and water contributions. The integration of flow profile with petrohysical and geological data will help to characterize the reservoir. Flow profile in vertical and horizontal wells is required for the proper evaluation of well performance. The determination of water entry intervals is very essential in the well performance evaluation. Increasing water production will influence well performance and considerably reduce oil production. As stated by many studies1,2, measuring or calculating the productivity of horizontal wells has been difficult because of their long length in the formation compared to vertical wells. The conventional production logging tools developed for vertical wells do not perform well in horizontal wells due to highly segregated flow in the horizontal section. For instance, gradiomanometer totally loses its accuracy, and spinners and capacitance holdup measurements are significantly affected by the stratified flow regimes that are common in horizontal wells if the deviation is more 70 degrees. Small changes in well deviation can cause large changes in fluid velocity and holdup, particularly at lower flow rates. In this paper, a field example of oil and water flow in horizontal well is presented. The presented horizontal well has a very complicated completion in the openhole section. The horizontal well produces relatively heavy oil and water from this complicated completion, which was designed to prevent the sanding in the wellbore. Flow Regimes in Horizontal Wells In vertical wells or near verticals wells that have deviations less than 20° mixed flow of water and oil flows with smooth velocity profile as shown from Fig.1. For the wells with deviations between 20° and 85°, flow regimes are generally quite complex.3 Heaviest phase segregates to the bottom of the pipe due to gravity and mixing layer is located on the upper side of the hole with dispersed bubbles of oil. This flow structure has large gradients in the velocity and holdup profiles. For wells with deviation between 85° and 95°, the flow becomes stratified. Water flows at the bottom with oil on the top and the flow has a strong dependence on the well deviation for low flow rates. At high flow rates the dependence on borehole deviation is smaller because the increasing shear frictional forces against the wall and interface dominate.
Assessing heavy oil composition of a green field, with an accepted level of uncertainty so it can be used for refinery capacity planning is a critical challenge. Knowledge of heavy crude oil properties is vital to understand potential adverse impact on process performance and total costs of the whole value chain, downstream (corrosion, catalyst deactivation, fouling and pumping) and upstream (corrosion, fouling, obstruction, producibility, lifting, pumping and transportation). The usefulness of heavy oil properties is highly dependent upon how samples are representing the bulk of hydrocarbon resources that will be developed and the reliability of the sampling procedure which becomes even more challenging when performed in a geologically complex, multilayered, supergiant green field with wide variations of fluid properties vertically and aerially. In this paper we present a field case with the methodology used to design, plan and execute a heavy oil sampling and essay for refinery capacity planning and the lessons learned, in an area of the field representing the first phase of development, in a supergiant heavy oil green field located in north of Kuwait. This heavy oil sampling and essay was planned and executed under high levels of uncertainty, using previous crude assays, PVT data from appraisal and thermal pilot wells and reservoir static and dynamic model. Extensive statistical analysis was applied to understand and map uncertainties related to sampling, completeness and representativeness of laboratory tests vs. accepted international standards. The methodology was applied by a multidisciplinary project team involving specialists from upstream and downstream who performed the work using project management tools to design and implement the execution of sampling in the field. The project took near one year to complete and results are now used for refinery capacity planning at short and midterm. Lessons learned were documented so the future sampling and assays can be improved as data from more wells is going to be available during execution of development phase.
This paper presents a field application of an advanced slim Pulsed Neutron Logging tool (PNL) for improved determination of hydrocarbon saturation as a key basis to evaluate the reliability of an ongoing enhanced oil recovery (EOR) cyclic steam stimulation (CSS) process in an unconsolidated heavy oil sand in Kuwait. The new PNL tool was used to evaluate changes in oil saturation and to track steam movement as part of the ongoing EOR CSS project in the field. This improved determination of hydrocarbon saturation is performed as a baseline prior to CSS and then used for future time-lapse evaluation of effectiveness of recovery during and after CSS using both PNL sigma and inelastic/capture or carbon/oxygen measurements. Its features enhanced capture and inelastic spectroscopy performance, particularly at high temperatures in places where CSS is ongoing due to its 175°C rating compared to 150°C from legacy tools. Gas, Sigma and Hydrogen Index (GSH), Thermal Decay Porosity (TPHI), lithology, Inelastic Capture (IC) mode was ran at 200 feet per hour (fph); twice the speed legacy PNL tool. Its 3 passes provided better performance than the 5 passes of legacy tool deployed under the same conditions, illustrating its better measurement accuracy. Inelastic spectroscopy logs from near, far detectors provided data for fluid analysis, which demonstrated the benefits from its elevated specifications. Its spectral yields’ results showed better accuracy and improved repeatability between different passes under the same well conditions in spite of logging at twice the speed. Compared to legacy tool, the new PNL technology provided enhanced detectors, new pulsed neutron generator (PNG) and pulsing scheme designed to optimize the gas/steam, sigma and neutron porosity measurements in terms of accuracy. Its faster logging and less exposure time makes it a better fit. Its PNG source and detectors minimize the spectrum degradation caused by high temperatures, hence better signals. The hydrocarbon saturation from its Carbon/Oxygen ratio and Total Organic Carbon (TOC) derived methods demonstrated consistency and cross validation over the logged interval. The advanced PNL tool fits better compared to the legacy PNL with improved repeatability and excellent precision. It now provides the basis for a reliable determination of hydrocarbon saturation, which will improve the evaluation of EOR CSS ongoing project.
A steam flood pilot in unconsolidated sandstone reservoir is being performed for the first time in Kuwait with inverted 5 spot configuration and pattern areas of 5 and 10 acres and a total of 26 wells. Prior to the steam flood, two cyclic steam stimulation (CSS) cycles were applied in all wells. This paper provides a detailed description of the well completions and challenges during CSS and the ongoing steam flood operations. Different designs of well completions were evaluated for injection and production wells. Injection well completion designs were evaluated by comparing actual vs. expected injection rates and review of operational issues. Production well completion designs were evaluated by comparing peak production rates, decline rates and sand issues. Two different injection well completion designs were evaluated. In the 5 acre, the steam injectors target two sand sub layers and hence initially completion were designed with downhole steam splitters but later removed due to injectivity issues. In the 10 acre, steam injectors target a single sand layer using packer less completions. Production wells were completed with 7" case hole perforated with 3.5" completion tubulars and insert sucker rod pump (ISRP). Sand screens were installed in some producers, but 50% of them were removed later due to very sharp production declines. When the screens were pulled out, screens were found completely plugged with debris. The responses from the 2 CSS cycles were very good with average peak well production rates of higher than 100 BOPD. The steam flood pilots have been running for around 6 months and the preliminary results are very encouraging. There is a clear initial response to steam flood, characterized by an overall increase in gross and oil production. The experience and the lessons learned from the CSS and evaluation of initial response of steam flood pilots are very useful in risk identification and mitigation applicable to the commercial phase.
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