Reservoir Characterisation in Upper Khuff Reservoirs and Its Importance in Field Optimisation
Authors: Insalaco E. , Cassou E. , Derbez E. , Hansen O.-P. , Legorjus C. , Fraisse C.J. , Javaux C. 
Published: February 2016

This reference is for an abstract only. A full paper was not submitted for this conference.

The Khuff Formation is a major reservoir in Qatar and the rest of the Middle East Gulf region, and contains some of the world's biggest gas reserves. Geologically the carbonate platform system is complex with fine-scaleheterogeneities which impact the static and dynamic reservoir characteristics. These heterogeneities are depositional, stratigraphic and diagenetic in nature and therefore reservoir characterization needs to be an integrated multidisciplinary and multiscale approach. In order to address these issues a large multidisciplinary and multiscale subsurface study has been launched on a large database including fields from across the region. The aim is to better understand the facies distributions, sequence stratigraphic architecture and the regional reservoir development, in order to better characterize dynamically reservoir behavior.

Geologically-based fine-scale reservoir characterization is needed in all field optimization projects' and this starts at the appraisal phase of field evaluations, and not just in mature field scenarios. This necessitates an "anticipation" of the kind of field optimization issues that will be eventually needed. It is also important to think of geological reservoir characterization in dynamic terms at the earliest stage possible, but this must always be underpinned by a strong geological framework. This is achieved by calibration of various dynamic data (well tests, production profiles and well interference tests) with the geological understanding, particularly the sedimentological and diagenetic reservoir characterization.

The static reservoir model in Khuff reservoirs is highly dependent on the precise type of sedimentary facies, the stratigraphic context and the type of diagenetic overprint, since these control the fine-scale heterogeneity. However, the dynamic reservoir heterogeneity (characterized by the dynamic data available) is particularly sensitive to the diagenetic overprint (i.e. the development of dolomite in grain-supported facies), and it is seen that the fine-scale permeability modeling and 3D permeability architecture is highly diagenetically influenced and fundamental to understanding the dynamic behavior of the field. Moreover the understanding of the 3D permeability architecture(particularly the high permeability zones around the dolomite-limestone transitions) is important for the application of stimulation techniques, such as acidification.

The integration of the fine-scale reservoir characterization into the reservoir model is a key step, but governed by the precise objectives of the reservoir model. In particular the resolution of model must be appropriate to the reservoir model objectives (large scale pore volume calculations vs. fine-scale dynamic sensitivity to geological heterogeneity, and adapted if necessary). In-house reservoir-scale modeling tools have been used to model the fine-scale reservoir heterogeneity, and create multiple realizations of the static reservoir properties. Finally these are modeled dynamically to assess the impact of the geological parameters on the production profiles.