Improved Carbonate Reservoir Characterization: A Case Study from a Supergiant Field in Southern of Iraq

Al-Ali, Ali (Heriot Watt University) | Stephen, Karl (Basra Oil Company) | Shams, Asghar (Heriot Watt University)

OnePetro 

Abstract

The objective of this work is to characterize the porosity distribution and the types of carbonate facies in the Mishrif Formation in the West Qurna/1 Oil Field using seismic inversion results, well log data and rock physics modeling. Identification of the pore system and the spatial distribution of lithofacies are keys for constructing Mishrif reservoir model, which have a great impact on the development of the most prolific reservoir in the field (Mishrif zone).

Seismic inversion involves the interpretation of elastic properties for facies based on the seismic response. It enables the modelling of lithology and porosity distribution in 3D space away from well control. In order to achieve the aim of the work, a step wise approach will be taken. First of all, deterministic seismic inversion was applied across the high resolution of 3D-seismic survey data over the West Qurna/1 Field. Then, the vertical distribution of porosity and facies recognition based on well log data and its relationship with elastic properties, integrated with seismic inversion results for validating at Mishrif intervals.

Deterministic seismic inversion was undertaken on the post-stack seismic dataset. The interpretation of seismically derived characterization in Mishrif reservoir indicated a different lateral distribution of acoustic impedance and three regions of channel (north, southwest and east). It can be seen a high acoustic impedance anomaly outside the channel in the western field sector which is heavily mud supported by peritidal carbonates (low quality facies of the reservoir). Whereas, carbonate tidal channel displayed a low acoustic impedance which reflect high porosity and good reservoir quality (grainstone channel or sholas). Furthermore, the interpretation of the well log and rock physic model was correlated with seismic inversion volume in terms of the lithology and porosity. Consequently, some zones which included carbonate tidal channel, displays a wide range of porosity and lithology fluctuations due to the impact of depositional environment (subaerial exposure).

The workflow provided insight into the distribution of petro-physical properties and quantification of their influence on dynamic reservoir behavior. The results also indicated the areas of high permeability and its component that may include fractures or connected vug systems. Water flood design and completion strategies (well trajectories) will be developed and succeeded according to the heterogeneous geological regions. Overall, this will ultimately lead to improve the development plan of wells in terms of production performance, recoverable reserves and economic value.