Display of Gas Deposits by Ob-Tazovskoe Shoal in Anomalies of Potential Fields

Abstract

Abstract The gravitational field of Obsko-Tazovsky shoal and the adjacent areas is presented by large areas of positive and negative anomalies (fig. 1). In an average part of territory the positive gravitational field by places of mosaic character with display in it of large anomalies intensity to 30 mgl is observed. Anomalies have various trend – mainly latitudinal strike, sometimes indistinctly expressed. To the majority of large positive anomalies of a gravitational field there correspond the same positive anomalies of a geomagnetic field. Their density, in the assumption of the basic structure, can reach 2.78–2.8г/cm3. For example, large isotropic maxima gravitational and geomagnetic fields, located to West-Geophysical structure, and also maxima of fields of northwest trend to the north from Geophysical structure. These monogenetic maxima, most likely, are caused by influence of blocks of the base rocks combined by more dense and magnetoactive rocks. Their density, in the assumption of the basic structure, can reach 2.78–2.8g/cm3. In whole, in the field of a positive gravitational field in an average part of investigated region presence of large negative anomalies to which there correspond the similar magnetic on a sign is marked. Judging by intensity (to -5mgl) adjacent gravitational minima and settlement density of rocks of the base (an order 2.58–2.65 g/cm3) the last are combined by sour rocks. Gravitational field basic elements well mirror a region structure. So, the configuration isoanomalies specifies in separateness of Hambatejsky and North Kamennomyssky deposits, and at the same time, on communication of it with Chugorjahinsky. In the field of Kamennomyssky and Nulmujahinsky deposits sharp lifting of the base with 6km to 4.5km and to the West to 3.3km precisely corresponds further to accurately expressed abnormal zone in which limits character of a gravitational field essentially differs from the adjacent sites. This gradients zone of type of a gravitational step in which limits of value of a field decrease with +7 to-25mGal from the east for the West, i.e., base uplift is accompanied by gravity reduction. And, within a zone of the raised base its surface remains concerning quiet. It gradually raises in east direction. At the same time the gravity field goes down in the same direction with very big gradient. In the east of investigated region the strip of the localised minima of gravity of northeast trend is traced. To the south this strip of anomalies is divided on two strips with the advent of two extensive minima of gravity over major fields of hydrocarbons: Jamburgsky and Nahodkinsky. To these deposits in a magnetic field correspond monogenetic minima.