Reservoir Characterization and Strati-structural Play of Minagish Formation, SE Kuwait

Abstract

Abstract: The Middle Minagish (Minagish Oolite) of Berriasian-Valanginian age is oil bearing carbonate reservoir in the Minagish, Umm-Gudair and Burgan fields in Kuwait. This Formation was deposited in an overall eastward-prograding carbonate ramp setting. Spatial variation of lithofacies and reservoir quality such as porosity, permeability and saturation are mainly due to changes in the interplay of deposition, sedimentation and diagenesis within them. The challenge here is to establish a new play concept to ascertain the geometry & nature of reservoir properties in relation to depositional lithofacies in South-East Kuwait. In this study, a systematic approach has been adopted to integrate sedimentology, petrography, petrophysics, sequence stratigaphy and seismic amplitude & attributes to understand reservoir quality and distribution vis-a-vis depositional environment. Ten lithofacies were envisaged from core and petrophysical analysis, out of which peloidal, bioclastic and oolitic grainstone and packstone have good reservoir quality with intraparticle and moldic pores as well as good permeability. A 3rd order Sequence stratigraphic framework was constructed incorporating well and seismic data to identify genetically related reservoir facies and its distribution. A package of forced regression shoal facies is recognized where inner ramp coarse grainstone overlies outer ramp bioturbated pack/wackestone. Seismic amplitude anomaly and waveform facies classification was used to identify lateral facies distribution constrained with conceptual depositional model. 2D seismic inversion was judiciously used to visualize the geometry and spatial distribution of reservoir facies and a new play concept towards north beyond the area of field development. Locally developed shoal in inner ramp and patch reef & reworked carbonate were found to be good locales for porosity development and preservation. The sequence stratigraphic framework shows lateral continuity and cycle of vertical heterogeneity of reservoir architectures. These led to a new play concept of strati-structural play of Minagish Formation towards deep basinal part to the north of SE Kuwait. Introduction: The Minagish Oolite is the primary reservoir in the Minagish Field and significant contributor in Umm Gudair and Burgan Fields. The Minagish Oolite, which is Berriasian-Valanginian in age, is the Middle member of the Minagish Formation (Figure-1). The Minagish Oolite/ Middle Minagish are equivalent to the Ratawi Oolite of the nearby Wafra Field and the Yamama Formation of Southern Iraq. Ten lithofacies were envisaged from core and petrophysical analysis, out of which peloidal, bioclastic and oolitic grainstone and packstone have good reservoir quality with intraparticle and moldic pores as well as good permeability. The most important lithofacies are peloidal wackestones-grainstones, Oolitic grainstones and bioclastic wackestones which together form = 85% of the reservoir. Middle Minagish was deposited on a broad, prograding carbonate ramp. It was deposited within a single third order, sea level cycle, composed of stacked, broadly coarsening upward fourth or fifth order cycles. Lithofacies and Depostional environment: The Minagish Formation is devided into upper and lower dense members characterized by relatively tight lime mudstones and wackestones separated by middle bioclastic Oolitic grainstone member. A detail core study of Minagish Formation was carried out in Minagish, Umm Gudair, Burgan and khasman fields. Ten lithofacies were identified based on core studies which are given below with corresponding sedimentary structure and depositional environment.