Publications

Rising costs for exploration and development and the commitment to boost profitable reserves in current market trends have put operators’ margins under increasing pressure. It calls for efficiency and diligence to be the main drivers for formation evaluation planning and execution. The subsurface geology and formation properties of bypassed targets and re-entry oilfields are often complex and structurally heterogeneous. The lack of historical data and details of formation setting complicates the field management and production forecasts, and hence there is a need for comprehensive logging assessments and evaluation workflows. Even when the specific calculation of hydrocarbon volumes and producibility at the time of drilling is available, variable depletion rates and changes in wellbore dynamics and well integrity after years of production or standby affect the current reservoir value. It is necessary to validate and monitor a well’s remaining capacity while looking for potential bypassed zones. In this context, cased-hole pulsed neutron logging (PNL) is currently routinely utilized to estimate hydrocarbon volumes and saturation. However conventional technologies have difficulties in providing a reliable evaluation in presence of complex completions and borehole settings, multiple fluid phases and distributions, variable mineralogy, or need to be assisted by external information. A holistic log data acquisition and interpretation program based on advanced pulsed neutron and elemental spectroscopy logging technology can cover all aspects, from the characterization of rock and fluid volumes to the detection of bypassed pay and remaining potential, in challenging wellbore environments with or without a prior knowledge of downhole parameters. By employing a state-of-art neutron generator and high-resolution gamma ray detectors, the multifunction spectroscopy technology obtains highly accurate elemental concentrations for robust description of mineralogy in addition to traditional sigma, porosity, and carbon/oxygen ratios. The fast neutron cross section measurement differentiates gas-filled porosity from liquid-filled zones and provides an independent formation property for a comprehensive volumetric standalone analysis of rock and fluids. Moreover, the study of the oxygen activation curves and other borehole indicators, simultaneously recorded, helps investigating well integrity issues and potential crossflow for water management, continuously while logging. More than traditional saturation monitoring, the technology proved to be a viable and effective alternative for formation evaluation in slim holes or complex wells where openhole logging is risky. It also plays a critical role in mature fields and as part of production enhancement strategies to design completion of new zones and intervention programs, derisk water shutoff opportunities, and find the additional hydrocarbon required to extend the life of existing assets, up until plugging and abandonment operations or repurposing of depleted fields for potential carbon and capture storage. Relevant log examples are presented to show the value of the technology application for improved characterization and wellbore diagnostics for production enhancement, and its ability to deliver critical rock and fluids parameters in new wells in place of traditional openhole logging, safely and efficiently. The information is key to defining future field development management strategy. It clarifies the role that cased-hole logging can play information evaluation processes and remediation programs for production enhancement.