Implications on oil trapping in the Kifl field of Iraq through geophysical investigations

Potential field geophysical measurements were conducted in the west of Kifl region in central Iraq to image a plausible oil-trapping reservoir. Ground-based magnetometry and gravimetry surveys were conducted to investigate this region by covering an area of 16  24 km by designing a regular grid spacing of 250 m. After preprocessing potential field data, different filters were utilized to separate the residuals from the regional anomalies. The complicated tectonic setting of the studied area was imaged by recognition of the fault system through simulation of the magnetic and gravity anomalies, which facilitates the configuration display of the oil-trapping mechanism. The geometry of a fault system was derived from parametric inversion of gravity data. The magnetic anomalies were extended with the trends of NS, NW, and NE and reached a maximum value of 55 nT. However, the gravity anomalies appeared with the same extensions and values ranging from -3.3 to 1.5 mGal. The intense magnetic susceptibility amount of the reservoir rocks is arising from chemical processes and iron-oxide ion replacements, accompanied by the migration and accumulation of hydrocarbon. Incorporating the results from the Euler’s depth estimation, parametric data modeling along with logging data assisted simultaneous modeling of the magnetic and gravity data. The 2D geological model of the subsurface layers at the Kifl area presents a graben-horst fault system within a thick sequence of sediment. Geological characteristics extracted from geophysical data modeling provided insightful information on the nature and essence of the hydrocarbon reservoirs in the Kifl area. It has formed through tectonic deformation and tension over the Arabian plate during the Permian – Paleocene cycle. Hence, it can be concluded that the aforementioned fault system has divided the hydrocarbon reservoirs

New improved formulas for calculating gravity and magnetic anomalies based on a cylinder model

RÉSUMÉ Nous avons développé deux nouvelles formules pour calculer les anomalies de gravité et de magnétisme basées sur un modèle de cylindre librement orienté dans l'espace. Comparé à la méthode conventionnelle, notre nouveau développement considère des facteurs multiples qui ont un impact sur les observations géophysiques - certains ont été ignorés dans les études précédentes - comme l'angle d'inclinaison, l'orientation par rapport au nord, la grandeur, la profondeur et les propriétés physiques d'un cylin re. Nous pouvons utiliser ces nouvelles formules pour calculer l'anomalie des trois composantes du champ magnétique aussi bien que l'anomalie gravitationnelle. En outre, basé sur une série de modélisations directes en utilisant ces nouvelles formules, deux systèmes de régression linéaire multiples (un pour la gravité et un autre pour le magnétisme) ont été développés pour estimer les paramètres du cylindre à partir de la gravité observée et des données de magnétisme. Mots clés: Calcul direct, calcul inverse, régression linéaire multiple, interprétation conjointe, gravité et magnétisme.----------ABSTRACT We have developed two new formulas for the calculation of gravity and magnetic anomalies over a cylinder model freely oriented in space. Compared with the conventional method, our new development considers multiple factors that have impact on geophysical observations (some neglected in previous studies) such as the dip angle, the strike direction, the size, top depth and the physical properties of a cylinder. We can use these new formulas to calculate the anomaly of the three components of magnetic field as well as its gravitational anomaly. Furthermore, based on a series of forward modeling by using these new formulas, two multiple linear regression systems (one for gravity and another for magnetism) have been developed in order to estimate the cylinder’s parameters from observed gravity and magnetic data. Keywords: Forward problem, Inverse problem, Multiple Linear Regression, Joint interpretations,gravity and magnetism