Paleo-structural conditions of formation and conservation of hydrocarbon deposits as a rational method of their extraction
The cyclic filling of the trap is fixed in hydrocarbon deposits in the form of preserved ancient water-oil contacts (WOC). Due to the substantial dissolution of the minerals of cement and the skeletal part of the rocks under the influence of products of oils biogenic and abiogenic oxidation (carbon dioxide, hydrogen sulphide, organic acids, etc.), a zone of rocks dissolution (decompaction) in ancient WOCs is formed. Below it is the region of diffusion current of soluble components in plantar waters (gypsum, anhydrite, calcite, dolomite, quartz and clay minerals dissolve). The dissolution zones of modern and ancient WOC are not always preserved. With the rapid withdrawal of hydrocarbons from the traps along the faults, there occurs a violation of salt balance in the plantar water and the loss of minerals. The reservoir rocks of the destroyed parts of the deposit are either compacted by cementation of minerals (calcite, dolomite, anhydrite, halite), or they do not undergo significant changes. Two gas-oil fields are considered in the article: the Irelyakhskoye and the Machchobin of the Mirninsky arch of the Nepsko-Botuobinskoe anteclise (NBA), in which the paleo conditions of deposits formation and destruction in the process of double filling of the trap were studied in detail. This approach contributes to the understanding of the complex structure of two modernly disconnected gas and oil fields, which were originally a single Irelyakh-Machchobin deposit. Instead of a single deposit, two deposits were formed during the tectonic reorganization, which are also divided into blocks.