Determining Infracambrian Hormuz Salt and Basement Structures Offshore Abu Dhabi by Joint Analysis of Gravity and Magnetic Anomalies

Abstract

Summary Hydrocarbon fields that are located offshore Abu Dhabi, United Arab Emirates (UAE), are known to be associated with undulating thick sedimentary sequences. These undulations are mostly influenced by variations in the depth of Infracambrian Hormuz salts that generate negative gravity anomalies. Nonetheless, a few known oil fields are uncorrelated with the airborne gravity observations. This is attributed to the interference from large positive gravity anomalies from basement highs. To filter out the effect of basement, we calculate the pseudogravity effect of the airborne magnetic anomalies and subtract it from the gravity anomalies. The resultant gravity anomalies mainly represent the effect of the salt domes. The results uncover deep salt structures and introduce potential traps for hydrocarbons that have proved difficult to map accurately with current seismic techniques. A nonlinear 3D inversion modeling of corrected magnetic and decreased gravity data is also used to determine the depth to basement and the Infracambrian Hormuz salts over two regions. Our findings demonstrate that the depth to basement in these regions changes from 7100 to 9700 m, and the depth to Infracambrian Hormuz salt changes from 5800 to 9400 m, with a variable thickness with a maximum of 2700 m.

Microgravity effect of inter-seismic crustal dilatation

“…We developed a more accurate model by considering the crust as a finite slab and modeled the gravity effect of volumetric dilatation within a rectangular prism with equal upper face sides (Sc). Plouff's relationship 65 is used to calculate the gravity effect at the center of the upper face of the prism [66][67][68][69] :…”

Joint gravity and magnetic inversion with trans-dimensional alpha shapes and autoregressive noise models

“…The density of the sediment is assumed to be the reference value of 2.6 g cm −3 and the density contrast is assumed to be zero. We compute susceptibility for the basement based on its density contrast by assuming a constant ratio of Δρ χ = 50 [39,40]. The prior for the number of nodes is uniform between 6 and 50.…”