Seismic prediction workflow based on architecture analysis for carbonate ramp shoal reservoirs: a casestudy for the Upper Cretaceous Hartha Formation of the M Oilfield, Mesopotamia Basin

Due to the effects of sedimentation and diagenesis, the complexity and heterogeneity of carbonate ramp deposits pose significant challenges to seismic prediction of high-quality reservoirs. Conventional seismic prediction workflows for carbonate reservoirs typically rely on horizon flattening, seismic coherent bodies, and seismic attributes to delineate geological boundaries, complemented by seismic inversion to convert seismic data into petrophysical properties. However, the low vertical resolution of seismic data has hindered studies on the stacking patterns of shoal bodies and corresponding variations in reservoir quality. In this study, an architecture analysis-based seismic prediction workflow was proposed for carbonate ramp shoal reservoirs in the Upper Cretaceous Hartha Formation of the M Oilfield (Mesopotamia Basin). It integrates reservoir architecture analysis with seismic waveform characteristics, aiming to overcome the limitations of low-resolution seismic data under geological constraints. Specifically, we adapted the architecture analysis method originally developed for fluvial sedimentary systems to carbonate ramp shoal reservoir prediction and identified three ramp shoal facies associations at the fifth-level architecture. Their corresponding seismic waveform features were determined by integrating seismic forward modelling. Subsequently, a favorable reservoir distribution map revealing different stacking patterns of shoal bodies was generated. High-quality reservoir prediction was further achieved through the intersection of acoustic impedance (P-impedance) and gamma ray (GR) volumes derived from seismic waveform indicator inversion, which revealed the internal reservoir heterogeneity. 90.2% of log-interpreted high-quality reservoirs with thicknesses below the seismic resolution limit were successfully predicted. The research results have been verified by the production performance of development wells, demonstrating their effectiveness in reducing uncertainties associated with reservoir heterogeneity. This study provides a replicable geology-seismic integration workflow for the efficient development of similar carbonate ramp shoal reservoirs.