Screening for EOR and Estimating Potential Incremental Oil Recovery on the Norwegian Continental Shelf

摘要

This paper presents an improved approach for rapid screening of candidate fields for EOR and estimation of the associated incremental oil recovery, and the results of applying it systematically to oil fields on the Norwegian Continental Shelf (NCS), an area that already has a high average recovery factor (47%). Identifying, piloting and implementing new improved recovery methods within a reasonable time is important if substantial remaining oil volumes on the NCS are not to be left behind. The approach uses up-to-date screening criteria, and has more sophisticated routines for calculating screening scores and incremental oil recovery compared to previous published methods. The EOR processes screened for are: hydrocarbon miscible and immiscible WAG, CO2 miscible and immiscible WAG, alkaline, polymer, surfactant, surfactant/polymer, low salinity, low salinity/polymer, thermally activated polymers and conventional near well gel treatments. Overall screening scores are derived from sliding-scale scores for individual screening criteria, weighted for importance, and with the ability to define non-zero scores when non-critical criteria are outside their desired range, so avoiding the problem of processes being ruled out completely even though rock or fluid properties are only marginally outside the threshold of applicability. Incremental recoveries are estimated taking into account the existing recovery processes in the field and are capped by theoretical maximum recovery factors derived from theoretical/laboratory values for displacement and sweep. The methodology calculates the expected increment (and uncertainty range) for each EOR process and the increments for the top three compatible process combinations. The methodology was implemented in a spreadsheet-based tool that allowed multiple fields to be screened and the results compared and evaluated. The new tool was used to estimate the potential EOR opportunity for 53 reservoirs from 27 oil fields on the NCS. The results indicate a mid case EOR technical potential of 592 million standard cubic metres (MSm3) with a low- to high case range of 320-860 MSm3. The most promising processes are low salinity with polymer, surfactant with polymer, and miscible hydrocarbon and CO2 gas injection. Some field clusters were identified that could provide economies of scale for such processes. The EOR screening study has enabled the Norwegian Petroleum Directorate to advocate EOR-technology studies, including pilots, in specific regions or fields. Such pilots will play an important role in verifying process feasibility and narrowing the uncertainty range for incremental recovery potential.