Magnetic and gravity signatures of the Kifl oil field in Iraq

Abstract

Potential field methods are capable to provide satisfactory results on the tectonics and geology, especially when dealing with the hydrocarbon reservoirs and ore-bearing mineralization. In this study, magnetic and gravity survey were conducted at the west of Kifl area in central Iraq to image the subsurface geological structure and consequently the characteristics of the oil and gas reservoirs. Ground measurements were conducted on an area of 16 by 24 km with a regular grid spacing of 250 m. The results clarified the tectonic setting of the study area, where the fault system in the Kifl oil field was recognized by resembling both magnetic and gravity anomalies with distinct trends along NS and NW. A 3D inversion algorithm based on a weighted minimum length solution was used for reconstruction of the subsurface physical properties of magnetic susceptibility and density contrast. Weighting matrix is composed of multiplication of compactness and depth weighting functions, and truncated singular value decomposition (TSVD) was used for regularization. 3D inversion was first applied to a synthetic model to simulate the geological reality of the study area, while satisfactory results were obtained. Implementing the algorithm on the real potential field data, the physical properties of the hydrocarbon reservoir were determined. Four cross sections have been extracted from the inversion result to show geometric characteristics (depth and shape) of the main reservoir in the Kefl oil field. The results indicated the presence of a fault system in the middle area within a column of sedimentary sequences represented as a graben-horst structure. This phenomenon in the area could be attributed to the tectonic deformation and tension over the area and the Eurasian and Arabian plates collided back to the Permian - Paleocene periods.