Evaluating the impact of a late-burial corrosion model on reservoir permeability and performance in a mature carbonate field using near-wellbore upscaling

Abstract

Field X comprises a giant Palaeogene limestone reservoir with a long production history. An original geomodel used for history matching employed a permeability transform derived directly from core data. However, the resulting permeability model required major modifications, such as horizontal and vertical permeability multipliers, in order to match the historic data. The rationale behind these multipliers is not well understood and not based on geological constraints. Our study employs an integrated near-wellbore upscaling workflow to identify and evaluate the geological heterogeneities that enhanced reservoir permeability. Key among these heterogeneities are mechanically weak zones of solution-enhanced porosity, leached stylolites and associated tension-gashes, which were developed during late-stage diagenetic corrosion. The results of this investigation confirmed the key role of diagenetic corrosion in enhancing the permeability of the reservoir. Insights gained from the available production history, in conjunction with petrophysical data analysis, substantiated the characterization of this solution-enhanced permeability. This study provided valuable insights into the means by which a satisfactory field-level history match for a giant carbonate reservoir can be achieved. Instead of applying artificial permeability multipliers that do not necessarily capture the impacts of geological heterogeneities, our method incorporates representations of fine-scale heterogeneities. Improving the characterization of permeability distribution in the field provided an updated and geologically consistent permeability model that could contribute to the ongoing development plans to maximize incremental oil recovery. Field X is a giant offshore oil and gas field with a long production history from a limestone reservoir. Permeability has been identified as one of the biggest uncertainties associated with the reservoir simulation model during field optimization studies that have been carried out by the operator previously. A reduction in the uncertainties for the permeability distribution is needed to evaluate the feasibility of the next development phase.In this study we attempt to resolve these issues through a systematic re-evaluation of the reservoir simulation model, considering, in particular, the field's diagenetic history. Our aim is to understand the fundamental controls on fluid flow that need to be adequately captured in the reservoir model. Geological studies carried out by the operator suggest that the key permeability pathways are strongly related to the mechanism of reservoir porosity -permeability evolution during late-burial corrosion (Wright & Barnett 2011). Late-burial corrosion in Field X is referred to as deep burial/ mesogenetic corrosion associated with the corrosion of limestone by burial-derived (hypogene) fluids. However, it is unclear how a diagenetic model that accounts for late-burial corrosion should be included in the reservoir simulation model and how such an updated reservoir simulation model could i...

Solid bitumen in calcite veins from the Natih Formation in the Oman Mountains: Multiple phases of petroleum migration in a changing stress field

“…A high porosity zone, which occurs along tectonic stylolites in SBV infers post-stylolitization marginal dissolution where stylolites served as conduits for corrosive, calcium undersaturated fluids. These stylolites can have opened by tectonic uplift and decompression (Chandra et al, 2015), especially as the stress field changed after tectonic stylolitisation during doming and unroofing to E-W perpendicular to the stylolite strike facilitating opening of the stylolites. This stress change is indicated by the strike of open joints and the youngest, untwinned microveins in the study area (Gomez-Rivas et al, 2014, Holland et al, 2009a, Virgo, 2015.…”

Fundamental controls on fluid flow in carbonates: current workflows to emerging technologies

“…A wide range of rock-typing methods has been proposed for carbonate reservoirs (e.g. Lucia 1999;Gomes et al 2008;Hollis et al 2010;Xu et al 2012;Kazemi et al 2012;van der Land et al 2013;Chandra et al 2014;Skalinski & Kenter 2014). However, these methods are commonly more oriented towards practical industry workflows, such as defining empirical porositypermeability transforms that translate porosities measured at the wireline scale to permeability values in reservoir models.…”

“…Such simulations enable us to explore the nature and controls of spatial heterogeneities typically observed in carbonate stratigraphy over a variety of scales (e.g. Paterson et al 2006Paterson et al , 2008Hantschel & Kauerauf 2009;Hill et al 2009) and the impact of these heterogeneities on production behaviour (Chandra et al 2014;Whitaker et al 2014). An area for future development is the design of efficient methods to couple process-based models more closely to subsurface data (e.g.…”

“…Chandra et al (2014) show how sampling bias for petrophysical properties can lead to the generation of inadequate carbonate reservoir rock types and the subsequent construction of a static model that is very difficult to calibrate using production data. For example, the undersampling of core plugs from a poorly recovered and mechanically weak reservoir zone comprising numerous dissolution seams, tension gashes and stylolites in a giant carbonate reservoir has led to the construction of a reservoir model that was biased towards the low-permeability rocks.…”

“…Instead, they employ empirical relationships that may work well for a given reservoir but are not necessarily widely applicable. Work such as that of Chandra et al (2014) can underpin the traditional carbonate reservoir rock-typing workflows because it incorporates efficient, yet robust, porositypermeability transforms of small-scale geological structures, which can impact reservoir quality. At even smaller scales, pore-scale studies such as those of Mousavi et al (2013) or Van der Land et al (2013) can be used to quantify how individual diagenetic events impact reservoir quality and change reservoir rock types.…”