Evidences for New Attractive Gas Exploration Targets in Abu Dhabi Upper Permian Section

摘要

The great Paleozoic system of the Arabian Gulf forms one of the most prolific hydrocarbon producing systems in the world. The Primary elements of this system like source, reservoir, seal and traps are extended throughout the eastern Arabian Peninsula and have exceptional scale and quality. Modeling of the structural growth history, in conjunction with the hydrocarbon generation and migration in the area, has shown that early growth and charge were essential conditions for the formation of economic hydrocarbon accumulations. The recent basin modeling of the Silurian Hot Shale source rock showed that the gas generation deadline was during the Late Tertiary (20 Ma), while the onshore fields main phase of structural growth was during the Late Cretaceous Semail Ophiolite Obduction. Also, the potentiality of gas accumulations was further enhanced by the Late Tertiary tilting. The tilting resulted in spilling and migration of gas from the palaeo-structures in the east towards the giant structures in central Abu Dhabi. The Upper Permian Fluid Inclusion Volatile (FIV) analysis proved the presence of strong gas migration through much of the Abu Dhabi area and based on that, no source risk is present as previously suggested for the Upper Permian and Lower Permian reservoirs. The fluid inclusion analysis generally observed more mature source that resulted in drier gas in the onshore area and wetter gas to the northwest in the offshore fields. The drilling results evaluation indicated the presence of significant hydrocarbon shows while drilling the Upper Permian porous carbonate intervals. Also, the log data indicated the presence of high hydrocarbon saturation that ranges between 50 and 90% in most of the onshore Upper Permian drilled structures. However, the longer diagenesis process and the deeper depth of the burial of onshore structures have greatly affected the reservoir properties and possibly resulted in high non- hydrocarbon content. The causes of failure of some Upper Permian reservoirs in Abu Dhabi are most probably related to the limited data and experience at that time; which resulted in drilling and testing difficulties that possibly caused formation damage of the Upper Permian reservoirs. Also, the seal preaching and the limited charge could not be ruled out as negative factors for lack of gas accumulations in the Upper Permian section. However, the current technology improvement in basin modeling, deep drilling and tight reservoirs testing may turn the Upper Permian negatively tested reservoirs in Abu Dhabi fields to an attractive exploration targets.