Unraveling Geological Complexity and Implementing Risk Mitigation Strategies in EOR Pilots Within Carbonate Reservoirs
Authors: Eadulapally Satish Kumar , Taha Al-Murayri Mohammed , Khan Mohammed Yunus , Ali Al-Mayyan Haya Ebrahim , Fahad Al-Mutairi , Deema Alrukaibi 
Published: November 2024

EOR pilot initiatives, integral to the company's strategy, are conducted within limited areas, typically less than ∼5 acres, to assess the commercial feasibility of selected EOR methodologies for specific reservoirs. This study examines subsurface challenges encountered throughout the execution of EOR projects, focusing on geological uncertainties. It proposes pragmatic remedies by addressing constraints in geological data and devising risk mitigation strategies during the pilot implementation phase.

Drawing upon insights gleaned from EOR pilot initiatives, various strategies are employed to mitigate geological uncertainties within and surrounding the pilot zone. These encompass the acquisition of directional surveys in pilot and adjacent monitoring wells, as well as the collection of core samples, RFT data, fluid specimens, CBL logs, FMI, and VIT data in a minimum of two pilot wells to facilitate correlation. Additionally, comprehensive analyses such as complete core CT scans, sedimentological assessments, XRD analyses, and petrographic studies are conducted. Surveillance during the pilot phase involves obtaining baseline and time-lapse data through methods like HPT-SNL, PLT, induction resistivity, and pulse neutron logging. Furthermore, interwell tracer data is acquired at least twice and integrated with geological correlations.

In the first case study, a three-well pilot comprising two injectors and one producer, alongside an existing central producer, was initially designed. The first injector well was drilled based on the predetermined plan. Subsequent analysis of the most recent deviation surveys revealed alterations in the target subsurface distances between the injector and central producer wells, prompting adjustments to the design to align with the updated surveys.

In the second case study, the acquisition of cores from multiple wells within a conventional five-spot chemical EOR pilot proved instrumental in accurately determining the depths and widths of highly permeable zones in each well. This core data was then correlated with HPT-SNL logs to delineate the extension of permeable layers within the pilot area. Furthermore, insights derived from formation mineralogy aided in understanding issues related to siderite precipitation resulting from chemical injection, particularly in zones with large perforation intervals.

The third case study involved a miscible gas EOR pilot, cores from pilot wells aided in avoiding weathered zones for perforation. VIT, guided by FMI and openhole logs, identified six lithological barriers; unexpectedly, only two were leak-free. These findings shed light on gas breakthroughs and guided perforation strategies.

The study focus lies on tackling geological uncertainties and suggesting solutions like thorough data acquisition. Adaptation of pilot designs using deviation surveys, accurate zone identification through core data, and employing Vertical Interference Testing (VIT) for lithological barrier assessment in miscible gas EOR projects are highlighted as essential insights.