The paper covers the distinctive features of thermogas stimulation for Bazhenov formation, gives data resulted from the experimental work performed at Sredne-Nazym field of OJSC "RITEK" At present structural deterioration of reserves is in progress due to the increased share of heavy-to-recover and unconventional hydrocarbons in the total structure of the Russian raw-material base. Most of unconventional hydrocarbon resources of Russia are found in Bazhenov oil source rocks (further on referred to as BS). The urgency of BS effective development is necessitated by the fact that now the land of Russia stores nonessential quantity of actual reserves. While, nonconventional reserves are estimated at over 1 trillion tons, and a potential increase of recoverable reserves greatly exceeds local current recoverable reserves. Virtually, all non-conventional reserves are spread through the regions with developed infrastructure making it possible to cut the period for field tests and commercial application of new engineering decisions to involve into effective development the BS deposits being a form of the giant world shale hydrocarbon resources. According to foreign and local experts the potential of BS recoverable oil reserves amounts to minimum 30-40 bln. tons, and that is multiply higher than a possible increase of oil reserves owing to exploration of new Eastern Siberia and Arctic fields. To develop BS deposits the technical and technological complex to increase oil recovery based on integration of thermal and gas methods is under designing.

Heavy oil and bitumen are found in many places worldwide, with the largest deposits in the world being in Canada (Alberta), Venezuela and the former Soviet Union. Among huge conventional and unconventional oil resources so-called Bazhenov series represent one of the highest hydrocarbons potential in Russia. Its resources of light oil considerably exceed conventional oil resources, and extra heavy oil resources are estimated to be hundreds of billion tons (some estimates go beyond 2 trillion tons). Despite huge geological HC resources allocated in BS technology for their effective development is still a challenge. Thermogas is one of the promising EOR technologies that are under development in Russia. First theoretical as well as experimental and pilot results indicate that this technology could be successfully deployed for the development of hydrocarbons located in Bazhenov series. It is anticipated that the use of Thermogas technology for extraction of hydrocarbons from BS, based on successful application of similar technology for enhanced recovery of light oils from fractured dolomite formations in USA, can result in recovery of at least 35–40% of their resources. This could open up huge yet poorly estimated world unconventional oil resources that enable sustainable production of hydrocarbons at a global scale for many decades. Technology of "cold" mechanical oil processing is another "attraction point" of intensive research in Russia. This new approach is based on extremely localized "injection" of required amount of energy in order to break intermolecular and intramolecular chemical bonds in hydrocarbon compounds and molecular conglomerates. Technological effect is gained by means of initiation of the cavitation processes in the treated medium. Heavy organic molecules (asphaltenes, long paraffin and other complexes) and their conglomerates present in crude oil and subjected to this technology undergo breakdown of chemical bonds and, as a result, drastic changes in crude oil properties like viscosity and, to a lesser extent, density. Although technology is at its initial, i.e. "nucleus" development phase, its applications are perceptible in many potential areas of application, from up- to mid- and to downstream petroleum sectors. Recent developments in Thermogas EOR as well as in cold mechanical oil processing are described in this paper.

At present time; there is change in the structure of Russian oil raw materials production by increasing the share of hard and unconventional hydrocarbons. The main reserves of unconventional hydrocarbon deposits in Russia are concentrated in Bazhenov Formation (BF). BF deposits occur at depths 2500–3000 m, the thickness is from 10 to 44 meters. Reservoir temperature varies from 80 º C to 134 º C. BF deposits are similar to the oil shale, but their distinguishing feature is that the process of converting organic matter into oil is not complete yet. So alongside with light oil, collector contains hydrocarbons directly in the form of the rock-forming constituent parts, called kerogen. Thus, the organic part of the BF is presented in two forms: liquid hydrocarbons – light oil with an average grade of 7.2% of the volume of rock and kerogen with an average grade of 23.3% of the rock volume. Kerogen is the main part of the organic material in the sediments of the Bazhenov Formation and is considered as a substance that generates on stage katagenesis major amount of oil and gas. BF Hydrocarbon resources are estimated in 50 to 150 billion tonnes according to many experts. At the present time BF hydrocarbon resources is used inefficiently. Experience shows that the use of traditional methods of development has led to the recovery of only 3–5% of oil contained in the pore space. OJSC "RITEK" is developing thermogas technology, taking into account the huge potential of the production of hydrocarbons from the BF. The most important condition for applying thermogas impact on the rocks of the BF is based on the field and laboratory results that the filtration and capacitive characteristics of rocks of the BF is largely determined by the level of temperature (Fig.1). For all types of kerogenic rocks noted an increase in porosity and permeability, the initial flow rate, cumulative production, hence the drainage area with the increase in temperature. Numerous experimental studies have shown that increasing the micropore (matrix) temperature to 250–350 not only allow to produce 70–80% of the initially contained therein light oil but to convert part of kerogen in hydrocarbons (Fig.2).

No abstract

Today, there is a clear tendency towards structure and quality deterioration of reserves. One of the reasons lies in low initial oil saturation (about 0.45–0.55 for the regions of Western Siberia). Average residual oil saturation is equal to some 0.3 (in this case displacement efficiency - 0.4). With displacement efficiency being that low, final oil recovery factor will be just over 25% even if the reservoir sweep factor can be increased to about 70%. In the mid-XX century the method of oil field development using gas injection which theoretically allows 100% displacement was developed. The paper discusses two technologies for implementation of gas methods used in oil field development. - alternating gas water injection (AGWI) and water-gas stimulation (WGS) in which combined injection of displacement agents (gas and water) is used. It describes the principle of operation and features of special equipment developed on the basis of a multi-purpose booster compressor unit operating under the principle of a single-stage "compressor with hydraulic seal". The paper presents procedures for realization of AGWI & WGS, as well as practical developments allowing to prevent typical problems which occur in the process of field equipment operation when pumping high pressure gas. Actual results of WGS introduction in one of the JSC "RITEK" fields are presented and technological benefits of the process are assessed using 3D geologic-hydrodynamical simulation data. Introduction Today, there is a clear tendency towards structure and quality deterioration of reserves both in Russia and worldwide. With the recovery of reserves in the fields discovered and started to be developed last century, the share of reserves classified as hard-to-recover is increasing. Deterioration of reserves can be partially explained by the decrease in initial oil saturation of formations. A great amount of Western Siberia oil reserves is concentrated in reservoirs with 0.45–0.55 saturation. Average residual oil saturation in these reservoirs according to numerous core analyses equals to 0.3. In this case displacement efficiency is 0.33- 0.45. But most of geological reserves still remain in reservoirs due to the only fact that oil and replacing water are mutually unsoluble and in the porous media at oil-water contact there occur capillary forces and significant capillary gradient which in the conditions of micro heterogeneity bury (close from any sides) remaining oil. With this low displacement efficiency, even if the reservoir sweep factor reaches about 70%, the final oil recovery factor will be just a little higher than 25%. It is natural that the situation when only a quarter of all geological reserves can be recovered is unacceptable, nevertheless it is absolutely objective in the conditions of normal flooding for these reservoirs. The situation can be practically improved if the production technology of these fields can be fundamentally changed. Among these absolutely new approaches is gas flooding of oil bearing formations (RF Patent # 2142045) based on alternating gas-water injection. Gas flooding differs in concept from water-gas stimulation, i.e. injection of water-gas mixture into oil-bearing formations. In gas flooding oil is replaced by frontal gas fringe being as broad as possible followed by water flood. The technology is based on the concept that gas flood ensures high displacement efficiency, while water flood ensures high sweep factor. After gas breakthrough into producing wells every injection well is transfered from gas injection to water injection. The pumped water buries gas but not oil, the gas fringe which separates oil and water becoming gradually short. Under favourable conditions when strata heterogeneity by permeability is relatively low the gas fringe will be available to the final production stage. Under less favourable conditions after broad water fringe the second broad gas fringe is required followed by another water flood. Thus, provided displacement efficiency is doubled and sweep factor remains the same, final oil recovery will be twice increased.