Integrated Multidisciplinary Approach to Complex Reservoirs: Insights from the Balingian Oil Field

Abstract

In the complex clastic reservoirs of the Balingian area, Malaysia, stacked reservoir systems are characterized by intricate fault networks and significant compartmentalization. These conditions challenge the definition of reservoir compartments and connectivity, both laterally between fault blocks and vertically across stratigraphic sublayers. Resolving these uncertainties is essential for accurate reservoir characterization and prediction of dynamic behaviour. An integrated, multidisciplinary workflow combined with rigorous concept testing using all available dynamic data was implemented to develop an effective reservoir modelling strategy. The approach includes detailed well stratigraphic correlation, depositional environment interpretation, and seismic analysis within a robust geological framework. Structural mapping of fault geometries, throw distribution, sealing potential, and sand-to-sand juxtaposition supports evaluation of compartmentalization and connectivity. Seismic attributes such as coherence and curvature aid identification of subtle faults and fracture networks, while amplitude-based attributes highlight lithological variability and potential fluid-related anomalies. Interpretations are calibrated with well data, core measurements, pressure information, and established stratigraphic frameworks, while acknowledging seismic resolution limitations in thin-bedded intervals. Establishing reliable fluid contacts in this compartmentalized and dynamically evolving system remains a key challenge. Limited initial pressure data, insufficient optical fluid analyzer measurements, and depletion effects in recently drilled wells complicate conventional gradient-based contact interpretation and fluid typing validation. Gas expansion within originally oil-bearing intervals further obscures differentiation between primary gas-cap presence and secondary gas liberation. To reduce these uncertainties, a novel compositional data analysis approach was introduced through implementation of Isometric Log-Ratio (ILR) transformation on mud gas chromatograph data. Transforming hydrocarbon components into orthonormal log-ratio space mitigates closure effects inherent in conventional wetness and heaviness ratios and enables statistically robust fluid discrimination. The ILR framework improves separation between gas, oil, and depletion-influenced signatures, enhancing identification of subtle vertical fluid transitions and compartment boundaries. Special attention is given to interpreting different pressure data sources—such as MDT, SGS, and PDG—and understanding how each links to reservoir dynamics. Integrated fluid typing results derived from petrophysical logs and mud logs are coupled with sand-specific pressure data from wireline testing (or while-drilling counterparts) in a time-lapse framework for systematic evaluation of reservoir connectivity. This integrated view is crucial for distinguishing observed fluid contacts as initial or production-induced. Systematic assimilation of pressure–production data reduces key uncertainties while maintaining focus on development-critical risks. The integrated methodology improves understanding of well performance, fluid contact movement, and residual oil distribution, establishing the most plausible connectivity and characterization scenario for base-case modelling in this structurally complex field.