RITEK Thermal Gas Treatment at the Bazhenov

Although the development of unconventional resources is a challenging task, the need to focus on this area is becoming ever more important. As a result, new and improved technologies are being implemented to produce more hydrocarbons from unconventional fields. At RITEK, we are working hard on innovative methods that will allow cost effective production for the challenging reserves found at the Bazhenov formation

The Bazhenov formation is found in Western Siberia, and is spread over an area in excess of 1 mln km2. Hydrocarbon deposits are found at an average depth of between 2500–3000 m, and their thickness varies between 10 and 44 meters although the abnormally thick zones of Bazhenov formation can reach 100 m. The reservoir temperature varies between 80 °С and 134 °С. Bazhenov formation deposits are analogous to shale oils, however the formation’s distinctive feature is that the process of transformation from organic matter to oil has not yet been completed. This is why, apart from light oil, the reservoirs also contain kerogen.

Because the reservoir properties are generally determined by the temperature levels, we decided to use thermal gas treatment. According to the results of experimental trials that were done on core samples taken from the Bazhenov formation, microfractured rock yielded light oil in volumes comparable to, or exceeding the volume of of light oil contained in macrofractured rock when heated to 250-350 °C. (Figure 1).

The percentage of the fractures in the drainage rock at the Bazhenov formation are roughly 3 to 6%, and the oil yield from the matrix, when heated to above mentioned levels, may reach 3 to 9% of the rock volume. An important premise for heat treatment of Bazhenov rock is the significant kerogen content in all of its lithology types (from 12-30% in kerogen-clayish and up to 35-40% in clayish-silicious-kerogen type rock). Based on the results of field and laboratory tests, we went ahead with heat, gas and hydrodynamic treatment for these challenging reserves.

The thermal gas treatment was developed domestically, and involves an injection of a mixture of air and water into the reservoir. Combined with the in situ conditions of the formation, this triggers a spontaneous oxidation processes between the oxygen in the air and the formation’s hydrocarbons. The reaction produces a highly efficiency gas type displacement agent.

In order to fine tune the process, we started a pilot project at its Sredne-Nazymskoye field. The project includes five wells (one injection well and four producing wells) (Fig.2) and the relevant ground equipment (air compressor unit, pumping unit, diesel genset, control room, separate wellhead measuring units for each of the producing wells, as well as other necessary equipment).

Firstly, fresh air is fed into a compressing unit and is pressurized to the required level. It is then fed into the well together with water pumped from an artesian well using a pumping unit (Fig. 3).

Before the wells were treated with this technology, they were in severe decline. From 2007-2009 production drastically fell from approximately 45 tonnes per day, to just to 5 tonnes per day. During this period, the formation pressure decreased from 300 to 160 atm, on average. Since the launch of the pilot project, a total of about 6 mln nm3 of air has been injected into injection well #219 and the formation pressure on all treated wells has increased by by 20-100 atm.
The data from the field trials confirms the potential effects of thermal gas treatment, namely:
»    active intraformational oxidation processes (produced gas features a significant increase of nitrogen content to 45%, carbon dioxide to 16% with no oxygen);
»    kerogen is used as the main fuel for intraformational oxidation processes: up to a double volume increase of produced hydrocarbon gas and increased carbon dioxide content which are observed are possible results of pyrolysis and kerogen cracking;
»    the fractional composition of oil shifted to higher contents of light fractions (Fig. 4)
»    oil density and viscosity decreased significantly;

Currently, air is being injected in to the wells in cycles in order to further research the process. At the same time, the construction of the second thermal gas treatment area near well #210 of the Sredne-Nazymskoye field is underway (fig. 5). We plan to launch the project in the near future.

Following the successful pilot project at the Sredne-Nazymskoye field, as well as the development of new technologies that can enhance production in reservoirs with varying properties at the Bazhenov formations, we can be confidant of a significant increase in oil yield for Bazhenov type reservoirs. Having said that, these experiments are time consuming and expensive to implement and require comprehensive technical and technological studies.

In July 2013 a new law on graduated mineral tax for unconventional oil was put into effect. In particular, zero coefficient will be applied to the mineral tax for mining of oil from formations related to Abalak, Bazhenov, Khadum and Domanic productive formations during 180 taxation periods. Starting when hydrocarbon deposit depletion exceeded 1%.

The new taxation benefit should make oil mining from Bazhenov formation commercially profitable.

With the aim of fostering technology and innovation, and to attract more investment for the development of unconventional resources at the Bazhenov formation, we are working closely with the Skolkovo foundation, Zarubezhneft OJSC, the Russian Ministry of Education and Science and others.