AAPG Middle East Region Geoscience Technology Workshop:
3rd Edition Carbonate Reservoirs of the Middle East

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Cenomanian Shilaif Unconventional Shale Oil Potential in Onshore Abu Dhabi, UAE


The Cenomanian Shilaif formation of Abu Dhabi (UAE) is currently explored and appraised for its shale oil and shale gas potential. The objective is to assess the hydrocarbons resources, the spatial variability of rock and fluid properties as well as highlighting sweet-spots. The exploration efforts started in 2014, conducting some regional depositional and petroleum system studies complemented with exploration wells and the acquisition of comprehensive suites of logs, cores and pressured (sidewall) cores. Multidisciplinary interpretation is ongoing and accompanied by the acquisition of new data and the drilling of appraisal wells. More recently, seismic attribute extraction is used to map potential fairways. The Shilaif formation was deposited in a deeper water intrashelf basin and is time equivalent to the adjacent shallow water higher energy Mishrif formation. Non-eroded Shilaif thicknesses vary from 500 to 900 ft from deep basin to slope respectively. The formation can be subdivided into 3-4 composite sequences each with separate source rocks and clean tight carbonates. • The carbonate calcisphere-foraminifera source rocks with 10% TOCo vary from Type I/II to II/III with some vertical and lateral variability due to depositional environments. Porosity (up to 15 %) dominated by nanopores, low water saturation and nano- to first microDarcies permeability range. • Clean tight limestone (less than 10 % porosity) are calcisphere packstones with inter- and intracristalline porosity, filled by locally or lateral migrated oils and permeability range from tens to hundreds microDarcies. The present day structural configuration is inherited from two related regional compressional events, a) a NW-SE compression responsible for the anticline/syncline, lasting from Late. Cenomanian to Early Eocene was created by India's continental drift, b) the late Cretaceous (starting in Turonian) emplacement of the Semail ophiolite from NE direction responsible for loading the continental plate and resulting in the creation of a large scale foreland basin. Reactivation of this NE compression occurred during Late Tertiary. The resulting structuration created two synclines in the south of Abu Dhabi with maximum maturity of 1.1 Vr (TR 0.65). The foreland basin towards the North East has maturity values reaching the dry gas window. The continuous present day stress from a NE direction combined with high overpressures has a strong geomechanical impact with Hmin close to overburden in synclinal areas. The collected geologic data allowed to propose appraisal wells in this unconventional play. First results in the south of Abu Dhabi do deliver oils within the range of 38-40 API and GOR in the range of 350-1050 scf/bbl Following the encouraging early results, ADNOC as an NOC is presently in the process to develop strategic partnerships.