THE JINADRIYAH ANTICLINE IN EASTERN SAUDI ARABIA OIL FIELDS; STRUCTURAL MODEL DEDUCED FROM GRAVITY AND MAGNETIC MAPPING

The Jinadriyah Anticline (JA) is located 15 km northeast of Riyadh city where it is developed on the Platform deposits of Saudi Arabia. It actually consists of two anticlinal segments, called South and North JA: (a) The 3.5 km long South JA is an open doubly-plunging asymmetric anticline; its western flank is dissected by 13 minor reverse faults oriented north-south, (b) The North JA is 5.5 km long and is dissected by as many as 18 minor faults. Further, two perpendicular fracture sets are recorded in both anticlines. Available seismic section crossing the North JA reveals folded reflectors in the same location of the anticline, thus providing evidence for downward continuation of the folding. Cross-section proposed by some authors for the South JA suggests the intimate relationship between the anticlinal limb and an intricate fault system. However, such schematic geologic sections needed to be quantified by geophysical modeling, in particular, by gravity-magnetic data. Accordingly, several east-west gravity-magnetic traverses are taken across the JA to determine the potential field anomalies associated with the anticline and also to demarcate their smaller amplitude variations associated with the respective parts of the anticline. It is observed that while the former anomaly variation is due primarily to anticlinal structures developed over the basement, the second-order variation in gravity-magnetic anomalies are developed due to later deformations consequent to the Late Tertiary Alpine Orogeny on the Arabian plate. Gravity-magnetic mapping for the Ghawar Anticline located further east provide clear evidences for its associated positive Bouguer anomalies and magnetic signatures for basement folding and related block faulting. Most of the oil-gas fields in this part of the Arabian Platform are known for salt diapirism and their distinctive gravity signatures. This is also corroborated by our recent gravity study for the Riyadh Salt Basin where the Jurassic salt layer could be mapped in deeper part of the basin using forward modeling. Present gravity-magnetic mapping for JA provides structural details on deeper part of the anticline, its subsurface continuation, sediment deformation pattern as well as the relationship of faulting to basement tectonics.