Implementation of High Resolution Diagenetic Features into the Static and Dynamic Reservoir Models of a Giant Offshore Oil Field, Abu Dhabi

Abstract

Lower Cretaceous-aged carbonate sediments in a supergiant Middle Eastern oil field are characterized by extensive diagenetic overprints (e.g., dolomitized burrows, dissolution fabrics and fractures) which occur over areas of several kilometers. Due to the permeability contrast with respect to surrounding fine-grained matrix, the diagenetic features are believed to play an important role in reservoir fluid-flow, particularly as a major contributor to early water breakthrough observed in the field. Uncertainties associated with three-dimensional subsurface reservoir models can be mitigated by incorporating the results of detailed reservoir characterization studies. How these study findings are successfully and meaningfully implemented into the reservoir model can be a challenge and requires an integrated effort by reservoir geologists, modelers, and engineers. This paper discusses a comprehensive reservoir characterization and modeling study conducted to capture the impact of diagenetic features on reservoir flow properties. A novel method was developed to map the spatial and stratigraphic distribution of these features from cores. Dolomitized burrows generally appear in core as randomly oriented features on a scale of cm to 10's of cm. They are characterized by grainier fill (packstone or grainstone), often dolomitized, within a background of muddier sediment (wackestone to packstone). Dissolution vugs are associated with algal rock type and can vary from few cms to 10's of cm. Fractures are generally layer specific and occur at the reservoir-dense boundaries. The origin of diagenetic processes and prediction of their occurrence is very difficult. However, the difference in texture and associated pore characteristics lead to heterogeneous porosity and permeability regimes that can have significant impact on sweep efficiency and recovery in oil fields that are subjected to waterflood. A simplified, fit-for-purpose, rapidly updateable static model has been developed to ensure accurate stratigraphic and lateral distribution of diagenetic features based on cores, logs and dynamic data. Whole core data revealed potential guidance for assigning permeability in diagenetic features. A consistent SCAL framework has been developed to capture the relative effects of these diagenetic features on flow. After incorporation in the model, simulation results clearly shows water movement through these features and rapid water cut. This is in agreement to the field observation that has experienced earlier than expected water breakthrough and steady increases in water cut over time.

Reservoir Characterization and an Integrated Approach of Reservoir Modeling for Miano Gas Field, Middle Indus Basin

“…Post-modeling operations aim at to test the model accuracy, to refine the model, and to summarize the model [2]. The post-modeling operation for the static models includes model accuracy testing using producer performance in dynamic simulation [42][43][44] and reservoir property uncertainty analysis based on the static reservoir model. The reservoir properties (porosity and permeability) were imported into a commercial numerical simulator of Eclipse and a numerical simulation was conducted to calculate gas production rates of the two producers.…”

Compressional and shear wave attenuations from walkway VSP and sonic data in an offshore Abu Dhabi oilfield

“…Fractures have been reported in TH1 and TH3 [Edwards et al, 2006, Skeith et al, 2015. These fractures generally occur at the boundaries of dense zones and reservoir units [Shekhar et al, 2017].…”