Robust Saturation Computation for Three-Phase Fluid Reservoir Determination: A Service Company's First Successful Disposition of 3D Reservoir Monitoring Memory Logging on Slickline Deployment, Peninsular Malaysia
Authors: Srikampha Bancha , Hazwan Zainal Abidin Mohd , Himawan Glen Ricky , Parashar Sarvagya , Iyer M. S. , Najmi Farhan Zulkipli Siti 
Published: November 2020

Often, casedhole petrophysics provide essential information for reservoir surveillance and monitoring in mature field reservoirs for recovery optimization. One of the vital casedhole data acquisitions involves a pulsed-neutron tool for formation evaluation. The service company's recently developed multidetector pulsed-neutron tool (MDPNT) with a long-spacing detector provides a unique measurement [sigma, carbon-oxygen, and saturation gate (SATG)], which significantly helps improve sensitivity for formation gas saturation.

The multidetector pulsed-neutron tool (MDPNT) is the only casedhole formation evaluation tool within the industry to be used with a memory system simultaneously acquiring the inelastic carbon/oxygen (C/O) ratio and capture (sigma) logging modes. The high-power battery pack provides up to 11 hr of continuous logging with superior data quality. A memory-based logging system provides advantages in terms of a smaller footprint, improved operational safety, and easier logistics handling, which results in significant operation cost reductions.

A successful application of the first MDPNT memory logging on slickline deployment in Field A of Peninsular Malaysia is discussed. Pulsed-neutron data were acquired in the well with the objectives of validating hydrocarbon fluid types for additional perforation operations and determining current hydrocarbon saturation to derisk openhole log interpretation uncertainties and fluid contact delineations. The targeted sand is located above the top packer section, and based on openhole logs alone, there is a high uncertainty of distinguishing between the presence of oil and water. The well consists of a complex completion string with 3.5-in. tubing inside a 7-in. casing along with a packer and sliding side door (SSD). Gas trapped under the packer is a common scenario and poses another challenge in saturation computation.

Post-data acquisition results exhibited a positive indication of oil presence within the targeted reservoir. Gas-oil contact (GOC) was successfully determined within one of the reservoirs despite the thin oil rim presence, which could be easily overlooked. The discovery has led to the assessment of a nearby well to be the potential add-perf candidate within the same reservoir for quick gain monetization. The add-perf operation was conducted in two reservoirs and flowed successfully at 500 B/D instantaneous production. The effort was well paid in reactivating an almost four-year idle well status with sustained production and a 0.2 MMSTB reserves addition.

In other words, the three-phase pulsed-neutron analysis consisting of the C/O, sigma, and SATG combination has convincingly generated a robust saturation computation covering all the zones of interest. The case study described in this paper emphasizes the benefits of the MDPNT memory logging, particularly within a challenging offshore environment with a limited footprint profile and logistics arrangement, and yet successfully unlocked the low-hanging fruits for production enhancement.