EAGE Workshop on Detective Stories Behind Prospect Generation - Challenges and the Way Forward

This study investigates the impact of growth timing on the presence of hydrocarbons. It is believed that the use of this analysis substantially increases the confidence in assessing prospect risk ahead of drilling.

The basin modeling study concluded presence of active charge up to present day in the northern part of Offshore Abu Dhabi. Some onshore leads could have received secondary migration as a result of spill from paleo-structures especially in the northeastern onshore during Tertiary tilting.

A gas accumulation in a field in North Oman has been quoted as an extreme example of high residual gas saturation underlying well-saturated pay, on the basis of the discovery well in the late 1990’s. The residual gas and the free gas zones were tested separately: the residual gas zone produced dry gas at a low rate, with water, whereas the free gas zone tested dry gas at a high rate without water. A free-water level was established, with limited uncertainty, on the basis of pressure data collected.

The diagenetic trapping scenario, which assumes up-dip sealing by cementation is much riskier than the 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 to develop a diagenetic trap is that the displacement (capillary) pressure is greater than the migration (buoyancy) force. Smaller pore throat sizes will greatly enhance the seal capacity, especially for the larger oil molecules expulsed during early oil migration, resulting in longer oil columns. The Mishrif stratigraphic trap in the southwest onshore Abu Dhabi is highly prospective since it is located adjacent to the mature Shilaif kitchen located in the Ghurab Syncline (Rub’ al Khali Basin). 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.

The paper adresses the stratigraphic and structural evoulution of offshore SW Oman. The Cirle Oil operated Block 52 comprises 91,000 sq km of the region ranging in water depth from the shoreline to greater than 3000m. Aspects of the petroleum system and petroleum prospectivity are presented.

The Jeza-Qamar Basin is a Mesozoic sedimentary basin across the Oman-Yemen border. The basin was formed as a rifting depositional site linked to the Mesozoic breakup of Gondwanaland. The basin is geographically and geologically akin to hydrocarbon-producing basins in the region. This study provides initial results of a multiennial research project to decipher the stratigraphic framework, sedimentologic attributes and hydrocarbon potential of the basin, in general, and of the Oman sector, in particular. Data collected so far show encauraging signs of excellent reservoir and source intervals within the Mesozoic strata of the basin along with appreciable trapping mechanisms.

The Unayzah formation is a nonmarine siliciclastic unit. It consists of massive quartzose sand to argillaceous sandstone, silty sandstone, siltstone, mudstone, and minor carbonaceous shale. The Unayzah is typically 300-350 ft thick at Awali. The Unayzah consists primarily of braided stream and related floodplain deposits. The depositional model includes flood plain deposits, meandering channels, point bars and alluvial fans. Six Lithostratigraphic units were identified based on the log character in the Unayzah sequence. These units are named as U1, U2, U3, U4, U5 and U6 from top to bottom. Impedance contrasts at the top Unayzah gas reservoir are strong enough to generate a negative reflection at the interface and the resultant amplitude can be directly related to reservoir porosity. This was confirmed by evaluating 1-D forward modeling (synthetic seismogram) results from several wells in the study area. The reflection response was validated in 3-D seismic data by a sharp negative reflection at the top of Unayzah reservoir with good correspondence between reflection intensity and reservoir quality as observed at well penetrations. This study is to test the above mentioned method in the flanks of Awali structure outside the known production area.

In the recent years North Kuwait area has gained further importance with the establishment of commercial quantities of oil and gas in the Jurassic Reservoirs. These Jurassic Carbonate reservoirs present many challenges for field development due to the inherent heterogeneity coupled with a dual porosity system viz.., porosity development due to primary porosity / dolomitisation and natural fractures. Till date 29 wells have been drilled in the six fields of North Kuwait, for Jurassic reservoirs. In particular, in the structurally more complex Sabriyah area the oil & gas production is mostly from the naturally fractured tight carbonate reservoirs in the depth range of 13500’ to 16000’. Seismic attributes play a key role in identifying fracture corridors and help in locating ‘sweet spots’ for placing appraisal / development wells. In this study a suite of seismic attributes were used in the identification of such ‘sweet spots’ in the Middle Marrat and Najmah-Sargelu fracture play of North Kuwait. The surface derived attributes like Dip, Azimuth, DipAzimuth and Edge; the surface associated attribute Coherency augmented with the 3D Volume Curvature attribute were utilized in high grading areas of potential fracture corridors and contributed to the selection process of development locations for this play.

The Lower Cretaceous Zubair Formation in Kuwait ranges in thickness from around 1150ft in to 1450 ft . It consists of sandstone and shale alternation. Thin sands were encountered at the base of the formation in many wells in a northern field of Kuwait. The sands are isolated and discontinuous. Later a thick reservoir fluvial sand (of about 54 ft) was encountered in a single deep exploratory well in the field. This sand could not be mapped on conventional way on amplitude seismic data volume due it's complex geometry, low signal to noise ratio and complex fault system at reservoir level. However this sand was delineated by use of state of art interpretation tools like spectral decomposition and RGB image blending. Subsequent drilling of the play confirmed the channel geometry of the reservoir. The study, for the first time, upgraded the prospectivity of the Zubair Formation in the field and highlighted potential sweet spots for further exploration and development.

As conventional hydrocarbon plays have become highly mature after more than 50 years of exploration, Petroleum Development Oman (PDO) is increasingly focusing towards un-conventional plays. The Ghudun stratigraphic play is one example where Ordovician Ghudun sandstone reservoirs are sealed by shales of the Safiq Group. The Safiq Group consists of three member formations named Saih Nihayda, Hasirah & Sahmah listed from late to young. The later is not dominantly present over most of North Oman but forms some reservoirs in West and Central Oman. The Ghudun reservoirs sit between shallower oil dominated Mesozoic to Permian producing formations and deeper Cambrian to pre-Cambrian oil and gas producing formations.