Abstract
Wellbore stability issues associated with mechanical failure of the formations frequently present a challenging environment for running openhole logs. Alternatively, casedhole logs can be used to provide multiple physical properties of the formation to help in reservoir characterization. Generally, conventional casedhole measurements have limitations due to the effect of borehole fluids as well as cement integrity. Therefore, it can be challenging to complete an accurate full reservoir evaluation using conventional casedhole measurements. In a field example from the Western Desert, Egypt, a state-of-the-art advanced slim pulsed neutron technology was deployed for the first time to provide a comprehensive standalone formation evaluation without openhole data.
When hydrocarbon exploration and development move into more challenging environments, deployment of fit-for-purpose technologies is required. The advanced slim pulsed neutron processing algorithms were used for recording capture and inelastic elemental spectroscopy for rock elemental concentrations, including total organic carbon, detailed mineralogy, and matrix properties, simultaneously with sigma and other neutron-based outputs. By integrating the independent pulsed neutron measurements that are borehole self-compensated, casedhole reservoir characterization is now feasible with high accuracy and precision where the conveyance of openhole logging is of high risk due to borehole conditions and wellbore stability issues.
This case demonstrates the applicability of advanced slim pulsed neutron logging for comprehensive reservoir characterization in casedhole environments without any openhole data. It presents this innovative approach for the first time in the Egyptian Western Desert in a field with complex geological background, mixed lithology, and reservoir fluids types. The characterization paved the way to a new gas discovery in a complex clastic environment with a total net pay of 36m of gas condensate. Detailed mineralogy, reservoir porosity, fluid types identification, and hydrocarbon saturation were obtained with high accuracy behind the cased borehole independent of cement integrity and borehole fluid invasion. Leveraging this novel approach, the same methodology can be applied to old reservoirs with limited openhole data available to provide a robust formation evaluation that would aid in re-assessing brownfields.
The advanced slim pulsed neutron spectroscopy establishes a paradigm shift in reservoir characterization for casedhole environments to provide a comprehensive formation evaluation and fluid saturation without any openhole input. The workflow can be implemented in various scenarios as a cost-effective solution for reservoir evaluation or reservoir management applications.