Sedimentology, sequence stratigraphy and their control on reservoirs quality in mid-Cretaceous Mishrif formation in East Rub al Khali Basin, Western UAE

The Cretaceous Mishrif Formation in the west UAE, East Rub al Khali Basin has got new discoveries; however, there is a lack of systematic and detailed research on the sedimentology, sequence stratigraphy and reservoir distribution of Mishrif Fm. Based on large amount of core and thin section observations, well logging and seismic interpretation, the sedimentary facie association, sequence stratigraphy, and sedimentary evolution of the Mishrif Formation are studied. Moreover, the distribution law and quality of the reservoir are characterized and evaluated. A set of platform carbonate rocks deposited as the Mishrif Formation in the research area, and five typical facie associations are recognized, including rudist-bearing reef, grain shoal, inter-shoal channel/hollow and fore-shoal slope. On this basis, a comprehensive sedimentary evolution model is established. The Mishrif Formation is interpreted as three third-order sequences and six forth-order sequences. In SQ1 and SQ2 sequences, a set of rimmed platform deposited, and ramp deposited in SQ3. Multi-stage platform margins and rudist-bearing reefs develop in HST (highstand systems tract cycles), and successively progradation to the Shilaif sub-basin in the east. The Mishrif reservoir is mostly composed of rudstone, grainstone, and packstone, with well-developed intergranular and dissolved pores. The total porosity reaches above 20%, and the permeability is 1–100 md. The reservoir quality is strongly controlled by facies’ associations and dissolution near sequence boundaries. Reef-shoal reservoirs near sequence boundaries in top of HST have higher porosity and permeability than those in other facies belts and position of sequence.