Production allocation is required in hydrocarbon accounting to determine the hydrocarbon volume at the point of sale and for back allocation to the field, platform, well, and down to the individual reservoir levels. Production allocation is not only important for the purpose of reporting to the host government but also to understand the remaining hydrocarbon reserves which are crucial for reservoir management and input to the full field review studies. For wells producing from commingle zones, the individual zonal contribution determination is important. The Production Logging Tool (PLT) is commonly used to measure each reservoir's contribution downhole. Latest technology advancement in directional drilling over time has allowed for more deviated and horizontal wells. Well deviation is one of the factors affecting fluid flow pattern in a borehole apart from the phase holdups and fluid properties (PVT). As production fluid flows upwards in a deviated well, the movement of the lighter phase to the high side of the well displaces the dominant heavier phase liquid, causing it to flow downwards. This borehole phenomenon is commonly known as Apparent Down Flow (ADF). A standard PLT has a centralized spinner configuration and when run in wells experiencing ADF will likely cause the spinner to measure an incorrect fluid velocity. Depending on the degree of the holdup of the heavier phase, the spinner may show a reduced or even negative rotation if it is immersed in the heavier phase fluid. Conversely, the spinner may show faster rotation if it is located in the lighter phase fluid. The advanced PLT, with its array of mini spinners and holdup sensors, was developed in part, to measure the effects of ADF and was designed to cover the well's cross section area, giving a more accurate description of the flow behavior; thus better measurement and understanding of ADF phenomena. It has been observed from many production logging surveys that were conducted using a standard PLT, where the spinner shows negative readings during the flowing condition, indicating fluid re-circulation (or fluid fallback). However, information from other sensors such as fluid density identifier and temperature tool does not support these findings (of fluid re-circulation), which results in inaccurate rate calculation to determine zonal contribution. To overcome this challenge, the advanced PLT can be used to measure the contribution for each zone more accurately as the effects of ADF can be further understood. The calculated production rates from the advanced PLT were found to be more representative despite the presence of ADF in the wells. This paper discusses some case studies on the application of the advanced PLT in overcoming the challenges of quantifying zonal contribution in wells experiencing ADF.
High concentration of CO2 in various fields of Malay basin, offshore Peninsular Malaysia pose major challenges in monetizing the resources in a sustainable way. Focused study to understand the source, origin and distribution of CO2 is essential to make informed decisions on developing the fields. This paper is part of the basin scale study to address the distribution of CO2 and its risk assessment. Modelling of the petroleum system including CO2 contaminant was adopted to validate the fluid accumulations in the basin with observed results from fields. An Earth Model was built using maps generated from an integrated study of seismic and 65 key wells. The depth to basement and depth to Moho were incorporated from previous gravity modelling study. The CO2 content and isotope data compiled from reports facilitated in building the knowledge on the source, origin, and distribution over the study area. Play segments identified based on tectonic features were used to divide the basin into subset areas for analysis.
The Alpha field is located offshore of East Malaysia and operated by PETRONAS. Alpha-C development wells were often completed with the wire-wrap screens (WWS) for sand control over multiple zones separated by packers. This completion design was deployed in more than 20 wells which include the oil or gas producers and water injectors. Some producers were converted to injectors for reservoir pressure maintenance with several attempts to convert producers to injectors hampered by poor or no injectivity. Remedial efforts to restore injectivity, including stimulation, proved unsuccessful. This prompted the Alpha production team to look for a way to investigate the possible causes of inadequate injectivity, without the expense of retrieving the completion string. PETRONAS suspected that fines migration was either plugging the outer WWS or filling the annulus between the screen and the tubing, thus reducing the injectivity. A series of pulsed-neutron logs were recorded in five (5) problematic wells. The objective was to determine if fines migration was the cause of the blockage, using silicon activation and neutron-gamma ray spectroscopy. Silicon activation, also known as Gravel Pack (GP) logging is a technique traditionally used to evaluate the quality of the gravel distribution in a gravel pack. The measurement is sensitive to silicon around the borehole, hence a technique was adapted to detect sand blockage in the wellbore by logging the pulsed neutron tool inside the tubing. The technique is sensitive to silicon both outside the screen and inside the annulus between the screen and tubing. The inelastic and capture spectra measured by the near and far detectors of the tool were used to derive further details on the sand distribution in the wellbore. The difference in depth of individual measurements, with GP logging "seeing" deeper than the inelastic and capture spectra, has allowed for varying degree of sand buildup outside and inside the screen. The proposed method has helped to detect sand blockage around the wellbore, computing the height of the sand fill and inferring the depth of any damage to the screen. This paper discusses the innovative application of pulsed-neutron inelastic and capture spectra for detecting sand fill. The results successfully identified the location of the sand blockage in all five (5) wells. This has helped PETRONAS to decide on the ideal way to remove the sand blockage in the borehole before performing the next injectivity test. The remedial plans are to focus on removing the sand fill, rather than trying to treat plugged screens. This will include attempting to perform sand clean out operations (via coiled tubing), selectively performing tubing punches or opening sliding sleeves as appropriate and circulating out as much of the sand as possible. Obviously, the restoration of the injectivity rates will be highly dependent on the success of these attempts.
This paper introduces and evaluates a next-generation acoustic conformance-monitoring system that helps identify the depth and accurate radial location of undesirable leaks in a well. Determining the leak's flow pattern in and around the wellbore is also used to understand activity within the surrounding wellbore region. The acoustic conformance tool was run employing a memory slickline operation in a well located offshore Sarawak, Malaysia. The tool successfully acquired both low- and high-fidelity data, which were subsequently used for leak characterization analysis. Using an array of acoustic sensors, the tool is capable of detecting undesirable flow throughout the well structure. The vertical accuracy is within inches and estimates the radial location around the wellbore. Before the operation, careful and thorough prejob design is necessary for data acquisition to help reduce uncertainty in post-interpretation. These include detailed operational sequences in terms of leak stimulation of various annuli in the well to obtain optimum results. Subsequently, the signals are analyzed using a beam-forming method to identify leak distances and a flow map to further understand flow characteristics. The study well is a gas producer completed with a 7-in. single string. Post-data processing and interpretation revealed a continuous high-frequency noise spectrum from the bottom of the logging interval to the surface, indicating gas movement, which was further confirmed by two-dimensional (2D) flow map analysis. Results indicated gas movement in Annuli C and B. Based on results, production logging sensors, and well completion statuses, inferences were made regarding this gas movement and its possible sources—a cement window in Annulus C and cement channel in Annulus B. This technology accurately identifies and pinpoints leak sources, assisting the asset owner with planning and designing remedial work to help reduce undesirable fluid, which benefits total production.
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