3‑D inversion and accuracy assessment of gravitational data to determine the depth of sedimentary layers; An Application in the Burg El‑Arab Area, Northwestern Desert of Egypt

Abstract

The study aims to determine the depth of subsurface sedimentary layers using a Fourier‑based 3‑D stripping inversion method and assess its accuracy. The seismic‑based depth maps of the top
Dabaa, Kharita, and El Alamein Formations in the Burg El‑Arab Area were utilized to evaluate the inversion process’s accuracy. The calculated gravity effects of the top Dabaa, Kharita, and El Alamein Formations range were analytically estimated from thickness and density contrast and assigned to the surface observation level (Bouguer stations) before sequential stripping. The apparent density was calculated in addition to the upper and lower depth bounds of each sedimentary layer, which were used as constraints during 3‑D Fourier‑domain inversion procedure. The inversion results showed satisfactory fit statistics compared to seismic‑based depth data. The analysis of the inversion’s performance for the three inverted sedimentary layers showed that the percentage error between the inverted‑based depth and the seismic‑based depth was ranging from ±0.004 to 21.67%. The seismic and inverted‑based depths of the top Dabaa, Kharita, and El Alamein Formations were found to have correlation coefficient values of 0.88, 0.82, and 0.75, respectively. A 2‑D model was created for four horizons, including the basement layer. The 2‑D modeling indicated that the study area is affected by a number of normal faults that cross most of the layers and dip into the NE and SW directions, with dipping angles ranging from 70° to 80° and 75° to 85°, respectively. The 3‑D inversion results demonstrated that gravity measurements can accurately determine the depth of the sedimentary layer when stripping is performed at the Bouguer‑station level and the inversion is constrained by density and seismic information, with a tolerance of up to 21.67% and decrease until it matches the true depth in some locations.