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Which Fault Matters: Evaluation Of Reservoir Compartmentalisation By Integration Of Borehole Image And Real-Time Isotope Data δ13C1

Abstract

Shell Malaysia has drilled 11 development wells targeting two reservoirs (R1 and R2) in a Deepwater Field offshore Northwest Borneo, between November 2016 and February 2018. M field is a complex and highly faulted 4-way dip closure. The shallower R1 reservoir comprises unconfined distributary channels consisting of high-permeability sandstones. The deeper R2 reservoir is dominated by a channel levee system consisting of fine laminated sand-shale sequences. Pressure data acquired during appraisal evaluation indicate that prior to production, each reservoir is comprised of a single tank. Faults are major structural features that critically impact the field’s reservoir behaviour in terms of hydrocarbon flow and could create compartmentalisation of the field during production and injection. Thus, understanding the presence and behaviour of seismic and sub-seismic scale faults allow for optimisation of recovery and economic value of the field throughout its production life. To achieve this, high resolution borehole images (BHI) were acquired for 1) fault and fracture interpretation, 2) formation tops identification and 3) lithofacies analysis. Secondly, real-time isotope (δ13C1) data was acquired in each well during drilling to aid identification of potential barriers to flow by observing the isotope variation. Through the integration of seismic, BHI, real-time isotope and pressure data, the presence of fault and other barriers are bolstered and help to unravel compartmentalization. As an example, Well A was drilled after the first production well of R2 reservoir started up. Pressure data gathered in this section shows differential depletion suggesting compartmentalisation during production. We employed an integrated method to identify and validate presence of faults and their barrier behaviours during drilling. Six clear sub-seismic scale faults were identified. The real-time isotope log highlights 2 significant isotope shifts within the section. This suggests the likely presence of 3 reservoir compartments by the inference of sealing faults within R2 reservoir in the production realm. The interpreted BHI faults were overlain with seismic, of which some correlated well with discontinuities identified seismically. At the field scale, the extent of integration allows us to improve our understanding of differential compartmentalization within the field, thus improve the reservoir evaluation, in term of sweep efficiency and optimization of field development.