Using Near Wellbore Upscaling to Improve Reservoir Characterization and Simulation in Highly Heterogeneous Carbonate Reservoirs

Abstract

Carbonate reservoirs host a major portion of the world's remaining conventional and unconventional hydrocarbon reserves, typically containing multi-scale geological heterogeneities varying over many orders of magnitude in size. Characterizing and representing them robustly in reservoir models is a prime challenge in carbonate reservoir simulation. One of the key aims of this paper is, hence, to present a novel near wellbore upscaling (NWU) workflow that addresses the challenges associated with conventional carbonate modelling workflows. The NWU workflow provides a systematic geostatistical approach to obtain more realistic representation of multi-scale geological-petrophysical heterogeneities in complex carbonate reservoir simulation models. Using well log and core data, near wellbore regions were recreated to represent the core scale heterogeneities via high resolution geostatistical models. These core/centimeter scale permeability models were then upscaled into wireline/decametre scale using flow-based upscaling. The results, coupled with wireline data were used to generate global porosity-permeability and vertical-horizontal permeability relationships for reservoir simulation. Importantly, the workflow mitigates sample bias, which is frequently observed in the core data for carbonate reservoirs. We have applied our approach to a mature carbonate field, to model and upscale crucial multi-scale heterogeneities ubiquitous in the reservoir. These heterogeneities, such as mechanically weak zones of enhanced micro- and macro-porosity, leached stylolites and associated tension gashes, were caused by diagenetic corrosion. Core plugs representivity is always an issue in carbonates and these highly corroded features were very difficult, if not impossible, to sample due to their fragility. As a result, the field suffers from inherent sample biasing and insufficiency of Routine Core Analysis (RCA) data, consequently underestimating the permeability in the simulation model. The workflow presented here has enabled the authors to re-evaluate the reservoir permeability model by accounting for as yet under-sampled geological heterogeneities. The paper represents a focused individual study addressing this specific issue and doesn't necessarily reflect the operator's full understanding of this multifaceted field. Our new permeability model has addressed the need for artificial permeability multipliers and provided insight on the potential causes of the original mismatch. As a result, a new alternative model scenario has been built to help guide the on-going development plans and forecasting incremental oil recovery.

Analysis of Vertical Permeability and Its Influence on CO2 Enhanced Oil Recovery and Storage in a Carbonate Reservoir

“…The k z /k x ratio is typically assumed to be 0.1. However, several studies on sandstones (Jones et al 1987;Hanks et al 2011;Baker et al, 2005) and carbonates (Chandra et al 2013;Sun et al 2017;Dernaika et al 2018), including the work presented here, showed the occurrences where k z > k x . The underlying geological causes should be well understood for reliable geomodels and multiphase flow simulations.…”

“…Unlike clastics, carbonates appear to show weaker k z /k x trends with scale, perhaps decreasing by 1 or 2 orders of magnitude from the core-to large-scale (e.g., Wang et al 1994;Chandra et al 2013;Pamungkas et al 2020). This smaller change than sandstones may be partly resulting from better core-scale sampling because carbonates tend to be well consolidated, have good core recoveries, and are exhaustively measured (in the vertical direction) when using whole-core samples.…”

“…For example, in sandstone reservoirs with burrowing or dewatering horizons, k z /k x > 1 (Jones et al 1987;Hanks et al 2011). Carbonates also may show k z /k x > 1 in dissolution enhanced or stylolite-bearing samples (e.g., Chandra et al 2013;Sun et al 2017;Dernaika et al 2018).…”

Gravity Drainage Mechanism in Naturally Fractured Carbonate Reservoirs; Review and Application

“…Carbonate reservoirs host about 70% of the conventional oil reserves in the Middle East, and most of them are naturally fractured [4]. The Naturally Fractured Carbonate Reservoirs (NFCR) are well known for their low recoveries [5,6] compared to the clastic reservoirs due to the multiscale of geological heterogeneities, [5,7,8]. Therefore, accurate modelling of reservoir heterogeneities is a critical and an essential stage for further improvements in the modelling and simulation process, which enhance historical matching or future prediction.…”

A new method for determining the equivalent permeability of a cleat dominated coal sample

“…Moreover, the measurement scales of core analysis, wireline logs, and pressure transient analysis vary from a few microns to several metres (Barnett et al, 2013). However, most of these measurement scales are different from the scale that is used in reservoir simulation and analysis, which is of the order of metres 55 vertically and tens to hundreds of metres laterally.…”