Magnetometric Identification of Sub-basins for Hydrocarbon Potentialities in Qattara Ridge, North Western Desert, Egypt

Abstract

The present work aims to detect the Phanerozoic sedimentary sub-basins and their hydrocarbon potentialities within the Qattara Ridge in the northern Western Desert, Egypt, through the interpretation of high-resolution land magnetic data. The in-depth relations between observed magnetic anomalies and the magnetic mineralogy of the underlying rocks and the associated chemical reactions are essential to understanding the hydrocarbon potentialities. A high-resolution land magnetic survey has been conducted covering an area of 3600 km2, and several filters have been applied to the measured total field including reduction to pole, normalized source strength, tilt-depth and 3D Euler deconvolution with un-prescribed structural index, to accomplish the goals. Regularized focused inversion was applied to six selected profiles on the total magnetic intensity field to model variations in subsurface magnetic susceptibilities and to study the relation with hydrocarbon reservoirs in the area. Results show perfect structurally controlled sub-basins, with variable thickness of the sedimentary cover ranges for the Paleozoic to Miocene units. The depth of the top basement rocks ranges from 1500 to 7000 m. The calculated depths to the edges from magnetic analysis ranges from 292 to 3322 m. Some faults can be detected at 3900 m, and five possible sedimentary basins (depocenters) can be detected within the Qattara Ridge, trending NW–SE and N–S. Magnetic results also show that the central part of Qattara Ridge is affected by low magnetic anomaly, and many magnetization sources can be detected in the northern directions. The common trend in these sources is NW–SE. Most shallow depth to magnetic sources is concentrated at the northern part of the area, while the deeper sources are distributed in the west and south of the study area. The maximum depth recorded is about 3988 m. Inversion shows remarkable relations between the inverted magnetic susceptibilities and the different hydrocarbon productive and sealing zones in and close to the study area. The localized variations in the inverted anomalous magnetic susceptibilities in the Qattara Ridge were possibly produced by different intrasedimentary mineral magnetic phases developed near the surface due to hydrocarbon occurrences. Reducing gases, coming from the possible underlying hydrocarbon reservoir, play a critical role in the formation of these secondary magnetic minerals. The reservoir in the Qattara Ridge, based on the present study, is characterized by low magnetic susceptibility and low surface magnetic anomaly in the studied locations of productive wells. The interpretations show matching between the sedimentary thickness and position of the faults deduced from both the available drilled wells and seismic data with our magnetic results.