oa Reservoir characterisation of a heterogeneous hydrocarbon field, Khuff (Kangan-Dalan) Formation, Middle East

Analysis of previously unpublished data from a major Middle East gas field has resulted in an integrated study of the Khuff Formation. Conceptual geological models for the field will be presented, providing an opportunity for comparison with other published data in the region. Detailed sedimentological work of three extensively cored wells has enabled the identification of a suite of lithofacies, which are grouped into seven facies associations. Depositional settings range from marine grainshoals, through to restricted tidal flat settings with common evidence of exposure. Shallowing-upwards cycles form the basic building blocks in the sequence stratigraphic framework. Cycles are organised into packages, termed high-frequency sequences (HFS), which possibly reflect<br>fourth-order relative sea-level variation. At a larger scale, HFS’s are grouped to form four major depositional sequences (K4 – K1). These are comparable to the thirdorder sequence described by Sharland et al. (2001). Cycles show distinct trends in thickness variation, which can be traced in all cored wells. Thicker cycles typically occur within marine ooid-grainstone facies of the transgressive systems tract (TST) of large scale sequences, whilst thinner cycles are more typical of restricted facies of the highstand systems tract (HST). Diagenesis has significantly modified the primary depositional facies. The key diagenetic processes include: (1) cementation: primarily calcite and anhydrite; (2) dissolution: dissolution of grains, in particular ooids; (3) dolomitisation: both early evaporitive (in late HST) and hydrothermal processes associated with faults. Reservoir potential is related to the interplay of primary depositional facies and subsequent diagenesis. The best reservoir quality is associated with dolostones, although overdolomitisation and anhydrite cementation are commonly detrimental. TST grainstone facies are prone to calcite cementation; however, dissolution of grains significantly improves porosity. Conceptual geological models have been built based on the HFS stratigraphic framework, and these models are the input for the flow-unit and geo-modelling.