3D resistivity imaging survey to delineate Um El-Githoaa cavity in Hit area, Western Iraq

Abstract

The 3D resistivity imaging survey was carried out over Um El-Githoaa cavity in Hit area, western Iraq. Resistivity data were collected along four parallel traverses using Dipole-dipole array with electrode spacing of (2m) and (n) factor equal to 6. Inversion 3D models of standard least-squares method and robust constrain method for Um El-Githoaa cavity showed horizontal slices of the 3D resistivity distribution with depth. The first three slices, which represented the resistivity changes from ground surface to depth approximately equal to (3m), showed relatively higher resistivity reflecting the dry sediments of gypsum rocks, and some of these rocks visible on ground surface .The slices after (3m) depth showed the effect of the subsurface cavity by noticeable increasing in resistivity contrast (more than 800 ohm.m)with surround sediment, and the dimensions of the cavity equal approximately to the actual dimensions of this cavity. The comparison between the two methods of inversion appeared that the invers model produced by the robust constrain method has sharper and straighter boundaries, and the dimensions of the Um El-Githoaa cavity appeared closer to the actual dimension of this cavity (maximum diameter equal approximately to 19.3m, while the minimum equal to 15.8m and perpendicular to the first diameter). Therefore, the 3D resistivity imaging survey was delineated Um El-Githoaa cavity at depths ranges from (3 to 6 m). It is concluded that, the dense measurements along 2D lines in small area can be increasing the 3D imaging resolution.