«OIL AND GAS GEOLOGY» № 1/2016
OIL AND GAS POTENTIAL PROSPECTS AND EXPLORATION RESULTS
The article presents the result of the research on the Russian West-Arctic Shelf structure, its formation characteristics and regularities which allowed to develop a new structural-tectonic map and to conduct oil-geological zonation of the region based on the map. Proved stratigraphic volume of the western and central Laptevskii Shelf cover (from the Upper Riphean to Cenozoic) significantly increases oil component in hydrocarbon phase content and therefore this area can be considered as aquatorial extension of the Lena-Tungusskaia potential oil and gas province within the limits of the Siberian platform. Potential oil and gas provinces (Lena-Tungusskaia, Novosibirsk-Chukotskaia, Vostochno-Arkticheskaia) and regions were defined. Zonation of territories within their limits is shown on the map according to their potential degree. The characteristics for potential oil and gas complexes of sedimentary cover are given by the sea shelves. Suggestions for prospecting and parametric wells location are proposed.
Correlation between the Paleozoic-Cenozoic sections of Russian Western Arctic regions and American Arctic regions allows to predict the sedimentary cover age and structure, stratigraphic confinedness and quality of oil source roks, the degree of katagenetic maturity of organic matter and hydrocarbon systems preservation within the limits of the North-Chukchi and South-Chukchi basins. At the present stage generative and accumulative properties are typical mostly for the Upper Cretaceous and Cenozoic systems. The Paleozoic-Mesozoic systems used to have high potential in the geological past, but deep submersion and numerous tectonic movements resulted in the fact that the systems almost lost their potential. Both basins of the Russian Chukchi Shelf potentially oil and gas-bearing. Hydrocarbon resources of the North-Chukchi basin are supposed to be 30 times larger than the South-Chukchi basin resources.
METODS OF OIL AND GAS DEPOSITS PROSPECTING
The paper presents an update structural-tectonic zonation of the central and eastern regions of the Timano-Pechora oil and gas province conducted along the main reference horizon – domanik deposits bottom. Space-time model for the formation of oil and gas accumulation areas was constructed based on the complex geological criteria. As the result new directions of hydrocarbon deposits exploration were proposed for the lower horizons of sedimentary cover of the Chernyshov Ridge in the Pre-Ural foredeep. The benchmark assessment for the initial total resources of promising oil and gas accumulation zones and predicted located oil resources D1l of the defined structures was substantiated. Stage-by-stage plan was proposed for the development of hydrocarbon potential of the Middle Ordovian-Lower Devonian carbonaceous oil and gas complex located in the southern part of the Chernyshov Ridge. The plan includes areal and regional seismic profile shooting, prospecting and parametric well drilling.
The paper describes the results of hydrodynamic research and reserves production on exploited oil deposits in terms of their correspondence with standard geological models. Presented data shows the presence of high-permeable filtration channels developed in jointing zones of productive strata. The impact of the channels during the early stages of deposit exploration provokes uneven reserves production and due to this fact 10-20 % of wells contain 80 % of oil. During the advanced exploration stages when flooding starts the channels provoke the formation of anticipated flooding zones and decrease the efficiency of reserves production in general. The obtained data shows that enhancing deposit geological models with the information about filtration channels structure could improve the efficiency of the models and deposit exploration control.
HYDROCARBON RESOURCES AND RESERVES
In the paper the present state and trends for oil reserves and production are analyzed for the deposits of different size categories marked for current reserves of A+B+C1+C2 categories. The proportion of exploited and unexploited reserves is considered including the proportion for oil and gas complexes. Exploited reserves development is shown and general trends for raw materials base and oil production are estimated.
Unsolved issues concerning Kazansko-Kazhimskii aulacogen structure were defined after the analysis of present concept of its structure and factual data. The major problems are lack of understanding of the following aspects, they are the structure of the most promising lower horizons of the sedimentary cover, basement surface and abyssal crustal horizons; the borders and structure of the northern and southern (south-western) aulacogen closings; features of joint between aulacogen and adjacent large tectonic elements. At the same time commercial oil inflow from the Devonian sediments of the Provorovskoe deposit in the Syrianskii swell and oil show in other areas give evidence for the Kazansko-Kazhimskii aulacogen prospects.
Paragenetic relations between uranium content and oil and gas content in the Volga-Ural province were defined and used for petroleum prospects estimation in the northern Kazansko-Kazhimskii aulacogen. Uranium-hydrocarbon paragenesis which is brought about in oxidation-reduction conditions of epigenesis in activated oil and gas basin, should be taken into account for assessment zonation and exploration.
In the article conditions for traps and deposits formation in the southern part of the Pechora-Kozhvinskii megaswell are considered. Two centres of oil and gas generation were defined which are characterized by different types of the initial organic matter and different regularities in liquid and gas hydrocarbon fluids generation. Models of deposits submersion and heating were cons-tructed, hydrocarbon generation and migration periods and the time of potential formation and filling of traps were substantiated. In accordance with the multistage migration principle it was assumed that oil accumulations in the West-Pechorogorodskii and West-Pechookozhvinskii deposits could have formed due to oil redistribution from the surrounding oil and gas condensate deposits. Separate prediction provided basis for the development of oil and gas prospects map of the region.
In the article lack of correspondence between accepted oil and gas reserves and resources classification and major principles which were supposed to be taken as a basement for the classification is considered. In the new classification economic factor is not taken into account for extracted reserves estimation. Also the new classification does not inherit principles from the previous ones. This fact provokes difficulties for retrospective analysis and resource base development forecast for national planning and control of subsoil resources use. These remarks are suggested to be considered for final version of classification.