Advancing Geostopping and Formation Evaluation Efficiency During PMCD in Challenging Losses Condition Through Ultra-Deep Reservoir Mapping

Abstract

This paper describes the utilization of ultra-deep azimuthal reservoir mapping (UDAR) LWD technology in a complex carbonate reservoir for two distinct applications: geostopping and profiling qualitative resistivity during Pressurized Mud Cap Drilling (PMCD) operations in two development wells off the coast of Sarawak, Malaysia. The deployment of this technology represents a significant advancement over conventional at-bit resistivity for geostopping application and overcome the standard logging-while-drilling (LWD) resistivity limitation during PMCD operation in complex carbonate pinnacle reservoir. The ultra-deep reservoir mapping technology provides the automated resistivity inversion which inverts the formation boundaries with horizontal and vertical resistivity (Rh, Rv) properties. During planning stage, the transmitter and receiver sub spacing is optimized in the bottom hole assembly (BHA) to ensure proper depth of detection is achieved for geostopping requirement. Then, the tool sensitivity analysis was conducted using multiple geological scenarios of carbonate top structure, then aligned with geostopping operational strategy. While in reservoir section, the resistivity inversion with capability of 100ft range is used as qualitative resistivity indicator for hydrocarbon confirmation while conventional LWD resistivity is not favorable during PMCD operation. During the geostopping operation, the ultra-deep reservoir mapping tool enabled early detection of top of carbonate approximately 70 ft TVD below the tool, corresponding to about 100 ft MD prior to intersecting the reservoir. The resistivity inversion provided a high-resolution image of the top carbonate, revealing that the actual reservoir top was approximately ±100 ft deeper than the geological prognosis. Upon initial detection, the rate of penetration (ROP) was proactively reduced from 250 ft/hr to 100 ft/hr, allowing sufficient time for confident interpretation and timely decision-making. This approach successfully facilitated timely cessation of drilling for the intermediate hole section Total Depth (TD) to prevent excessive penetration into the reservoir, mitigating the risk of potential fluid losses. In the reservoir section drilled under PMCD conditions—where conventional formation evaluation was limited due to absence of returns— resistivity inversion data proved critical. The ultra deep bulk resistivity measurements from the inversion served as reliable indicator of hydrocarbon presence, overcoming suppressed conventional LWD resistivity caused by seawater invasion. The resistivity inversion confirmed no water contact within several tens of feet from the borehole, validating a hydrocarbon-bearing zone. This information effectively bridged the resistivity data gap, eliminating the need for complex trajectory adjustments or potential sidetracking. The reservoir mapping technology has been a matured technology in the industry for more than a decade. In this new application, for the first time, by integrating ultra deep bulk resistivity measurements at multiple depth of investigation with limited geological and petrophysical information, the technology significantly enhanced real-time decision-making for well placement and providing reliable information for the reservoir fluids characterization in a challenging carbonate pinnacle environment.