Mishrif Diagenetic Trapping Potential in Western Onshore Abu Dhabi

Abstract A diagenetic trapping style is proposed for an oil accumulation found in the Mishrif Formation in the southwestern part of onshore Abu Dhabi. A diagenetic trapping scenario, which assumes updip sealing by cementation is much riskier than a structural trapping scenario, but has large up-side potential. Oil accumulations in diagenetic traps represent an equilibrium state between buoyancy forces trying to move oil through rocks and capillary pressures in the low permeable layer that resists this movement. The only requirement for a diagenetic trap to exist is that the capillary pressure in the sealing formation is greater than the migration (buoyancy) force in the reservoir rock. In addition to that, smaller pore throat sizes in the sealing formation and larger oil molecules, for instance the product of an early oil migration stage, in the reservoir, can enhance the sealing capacity of the stratigraphic trap and result in bigger oil columns. The potential of this particular Mishrif prospect was assessed on the basis of regional analogs and a geological model was developed. The prospect was matured by the acquisition of a 3D seismic survey in 2004 (Fig. 1), with the aim to delineate the limits of the stratigraphic trap. A detailed seismic reservoir characterization study was carried out and porosity maps were prepared on the basis of a calibrated acoustic impedance cube. Seismic attributes were generated with the aim to detect the fault/fracture patterns in the area. The Mishrif stratigraphic trap in southwestern onshore Abu Dhabi is highly prospective since it is located adjacent to the mature Shilaif kitchen in the Ghurab Syncline (Rub’ al Khali Basin). The Shilaif source rock, which is time equivalent to the Mishrif shelf facies (Fig. 2), was deposited under restricted water circulation and anoxic conditions. Basin modeling suggested that the timing of hydrocarbon charge from this kitchen into the Mishrif reservoir started as early as Late Miocene. The Mishrif play prospectivity evaluation, including the detailed and integrated geological model and 3D seismic interpretation will guide future appraisal drilling. In addition, the knowledge gained from this study can serve as a basis for further exploration activities related to unconventional trapping styles in the Mishrif Formation.