Title : Application of seismic cube for facies trend in reservoir characterization: Glacial sandstone formation, Southwest Libya.
Abstract:
Seismic attributes can be applied in the modeling process as probability trends to improve the facies model and guide the distribution property within the reservoir. This seismic volume has the potential to establish relationships between the original sedimentological facies and the subsequent diagenetic overprint in heterogeneous reservoirs. It is widely recognized that diagenetic processes can strongly impact the infill well planning and production performance of a field. In this research, Seismic-derived properties were used as secondary data to account for the diagenetic direction within reservoir facies to obtain a reliable predictive facies model.
The Mamuniyat Formation, a glacial sandstone, suffered intense diagenesis in compaction and pervasive quartz cementation. This created permeability variations of at least two orders of magnitude. A detailed modeling strategy was implemented by a multidisciplinary team, including sedimentological information, seismic interpretation, and petrophysical analysis, to honor the geological concept and the dynamic response in the field model. Initially, six facies’ associations were identified in the reservoir, dominated mainly by the sandy outwash fan. Subsequently, these facies were rearranged later to represent the diagenetic overprint in the main reservoir zone. The reservoir quality variation was represented using a total of five rock types, defined by ranges of critical pore-throat radius, using a modified Pittman equation. Acoustic Impedance (AI) was then introduced in the facies model as a 2D trend to manipulate the distribution lithology and direction of continuity in the target zones. Variogram analysis was performed to describe the spatial relationship between all reservoir layers. Gaussian algorithms were used for porosity and permeability modeling, and both were constrained to rock types. Finally, water saturation was modeled based on individual height functions for each rock type, based on capillary pressure data. Our study revealed that, despite the extremely clean nature of the reservoir along all the wells and its identical sedimentological origin, both porosity and permeability are notably poor in the northern area. The distribution of the diagenetic processes that caused this reservoir degradation could be modeled thanks to the seismic response and well-defined relationship between seismic attributes and petrophysical properties. This real field case enabled the integration of multi-source and multi-scale data from various disciplines, including geophysics, sedimentology, petrophysics, and reservoir engineering. This integration facilitated the assessment of multi-realization numerical simulations to optimize the current development plan.
