Vol 53, No 3 (2019)

Global experience in oil exploration and the discovery of the Tupi field in Brazil and the Tiber field in the Gulf of Mexico in the last decade have confirmed the existence of giant oil fields with abnormally high formation pressures at depths of 10 km or greater. Until recently, the discovery of large oil accumulations in deeply buried reservoirs was considered as theoretically impossible. This work suggests that giant oil accumulations at great depths (6–10 km) should be considered important hydrocarbon exploration targets in the Russian Federation and the Eurasian Union. The first-priority oil and gas exploration targets at great depths are deeply buried horizons of the sedimentary cover of the Precaspian basin, whose subsalt hydraulic system is characterized by ubiquitous abnormally high formation pressures. The deeply buried reservoirs in the Astrakhan oil and gas accumulation zone are considered the most promising for the discovery of giant oil accumulations. Data discussed below demonstrate that hydrocarbon exploration and the discovery of giant oil accumulations at great depths require specific exploration procedures and techniques.

The article discusses the ratio of the size and spatial position of ancient and modern areas of geodynamic processes (tectonic-sedimentary systems) and the resulting geological bodies. It has been established that regardless of the rank and geodynamic affiliation of tectonic-sedimentary systems at all levels, from local to supra-regional, the implementation of geological processes proceeds along the path of least energy expenditure. In the modern structure of the Atlantic-Arctic Rift System, this trend is expressed in the development of strike-slips on the principle of maximum straightening of transfer zones between its segments. In the future, it will also determine progradation of the rift system through Eurasian platform region.

In our paper we produce new evidence of the tectonosphere and hydrosphere structure of oil and gas sedimentary basins and confirm significant influence of geofluid-dynamic processes on formation of hydrocarbon accumulations in the crust at the great depths. In our opinion the theory based on obsolete views on the tectonosphere structure lessen the importance the sedimentary migration theory of hydrocarbon generation. We prognosticate a particular stagnant type of post-elysionic water-drive systems in the crust at the great depths in conditions of increased hydrodynamic isolation. Absence of regionally sustained vertical and lateral drainage layers characterizes geological environment where stagnant type developed, and, corollary, fluids outflow into external environment is practically unfeasible. The subsalt filling complexes of the epicontinental deepwater basins are included into the post-elysionic water-drive systems. These complexes occur at the great depths and possibility of striking unique and large oil and gas fields there is inherent. We propose a system of fluid-dynamic conditions for preserving hydrocarbon accumulations in the lower crust as a result of developing sedimentary-migration theory for oil and gas formation. We consider the refinement of methods for prospecting and exploration large deposits at the great depths will pave the way for expanded reproduction of hydrocarbon reserves in the “old” oil and gas producing regions in our country.

Diagenesis is a necessary process for the development and formation of clastic reservoirs and ultimately determines the reservoir physical property. The evolution of pores is the comprehensive outcome of compaction, cementation, and dissolution in the process of burial history, and diagenetic material and diagenetic field control the type of diagenesis and its intensity. This systematic procedure and the coupling relationship among them are discussed using geology prediction technique to simulate the evolution of the diagenetic stages, diagenetic facies, and porosity of clastic reservoirs and ultimately for favorable reservoir prediction, particularly a reservoir of low porosity and low permeability. The essence of this method is illustrated using Ed₁ clastic sandstones in the Bozhong depression. Core data shows that the diagenetic stages of Ed₁ lake sandstones is classified into early diagenetic stage B, middle diagenetic stage A1.The major diagenetic processes that influence the porosity of the sandstones in study area are mechanical compaction (Com), carbonate cementation (C-Car), quartz cementation (C-Qua), clay cementation (C-Clay), feldspar dissolution (D-Fel), and carbonate dissolution (D-Car). Quantitative analysis of porosity evolution show that pore change rates in per million years caused by Com, C-Car, C-Qua, C-Clay, D-Fel, D-Car are 1~3, 0~2, 0~3, 1, 0~4, and 0~1%, respectively, in different diagenetic stages. C-Car is mainly in early diagenetic stage A and early diagenetic stage B, while D-Car is in middle diagenetic stage A1. D-Fel is mainly in early diagenetic stage B and middle diagenetic stage A1. Diagenesis including Com, C-Clay, and C-Qua is all well developed in these stages. Finally, based on single well simulation, diagenesis model and diagenesis strength model are summarized to simulate the porosity of the study area.

We present a new technique for shear wave splitting analysis in anisotropic mantle by combining the splitting analysis of Ps phases in receiver functions and SKS splitting analysis. Ps converted phases reveal evident variations in the effective arrival time as a function of back-azimuth in the anisotropic layer. This variation can be used to stacking to obtain the fast polarization direction and split time for an anisotropic layer. Our method was applied to data collected from the Iranian broadband permanent stations. Using teleseismic data, from 2004 to 2008, with magnitudes greater than 5.5 recorded at 14 permanent stations, we attempted to study crustal anisotropy beneath the stations. Then, we combined our results of the crustal anisotropy obtained from the receiver function analysis with the results of the SKS analysis to discrimination of crust and mantle deformation. The fast directions were parallel to the suture zone in the mantle beneath lower boundary of Central Iran micro-plate. The fast direction was almost parallel to the Alborz Mountain zone and perpendicular to the Zagros orogenic belt. Assuming that the fast polarization direction in the mantle is parallel to mantle flow, our investigation reveals the occurrence of horizontal melt flow which causes movement of the Arabic plate towards the Central Iran micro-plate.