Modelling of the Upper Jurassic Petroleum System, Abu Dhabi: Implications for Play and Prospect

Abstract

Abstract As part of a reassessment of the Upper Jurassic Hanifa and Tuwaiq Mountain (TWQM) formations, regional basin modelling was undertaken on the Jurassic (‘Diyab’) petroleum system of Abu Dhabi to investigate hydrocarbon generation, migration pathways and to confirm the play fairway concept. Specific objectives were: To investigate the source rock kerogen transformation, maturity and generation potential,Assess the expected kitchen area in relation to charge and expulsion timing,Calibrate the model thermally and establish an event chart. The model was built from surface to the Permian Khuff Formation to provide stratigraphic granularities to better understand the Upper Jurassic petroleum system. Sediment decompaction was modelled to illuminate structural evolution and associated properties through time. A total of 16 and 31 wells were used for temperature/pressure and porosity calibration respectively, to reduce uncertainties in the 3D model.Geochemical data filtering of outliers was performed on over 35 wells with Total Organic Carbon (TOC) data in the Hanifa-TWQM formation. The present-day map was refined with updated GDE maps used to estimate the original TOC maps following Peters et al. (2006) principles. The model of the Upper Jurassic petroleum system is consistent with measured data including, well calibrated pressure, source rock maturity and temperature data. The original TOC map shows organic richness in the Western part of Abu Dhabi decreasing towards the east. The maturity output shows that from the Late Albian (100Ma) to present-day, the source rock is mainly within the late oil to gas window, showing almost complete conversion of kerogen to hydrocarbon with a transformation ratio of over 95%. Generation of hydrocarbon started as early as 150 Ma (Kimmeridgian), shortly after Hith formation deposition, however, it became significant during the Cenomanian (90 Ma). Simulation results indicate that the kitchen area is located in Western and South-Western Abu Dhabi where the original TOC, deposited in an intra-shelf basin, is highest compared to the upper slope and shelf andlean organic contents towards the east. The main reservoir zone (NNW-SSE shoal belt) is charged from the west with up-dip migration into Hanifa reservoirs both onshore and offshore, with some potential long-distance migration from the North-East Neo-Tethys shelf slope. The constructed petroleum systems event chart confirms the establishment of a working relationship between different petroleum systems elements and processes. Refined TOC maps honoring environment of deposition as an input helped to improve the confidence in the modelling output that led to the validation of a working play with multiple leads identified. The results helped to subsequently update the play maps. In addition, the parameters generated assisted in de-risking identified leads. This provides a framework for detailed and informed prospect maturation studies.