HTR refers to reserves trapped between layers of rock which cannot be accessed using conventional, vertical drilling. It requires techniques including drilling horizontal wells and fracking, similar to methods used to extract shale gas and shale oil.
Currently, there is no precise definition for hard-to-recover hydrocarbon reserves in the Russian legislation. In accordance with the order of Ministry of Natural Resources and Environment of Russian Federation from 1st November, 2013, to the recoverable reserves refer “the part of geological reserves, which could be extracted from the formation (reservoir) during the whole period of developing within optimal project decision with the appliance of available technology, considering environmental and subsurface using requirements”.
Taking into account this definition, the reserves of the developing formations could be referred to the recoverable reserves, and the reserves from the exploration deposits – to the hard-to-recover reserves (ranging of deposits according to the degree of commercial development
For petroleum industry the basic criteria is the quality of oil, consequently, considering abnormal physical and chemical properties, the following types of oil could be defined: hard, viscous, sulfurous, paraffin oil, tarry oil, with high (more than 500 m3 /t ) or low (less than 200 m3/t ) gas saturation, with the presence of more than 5% of aggressive components (hydrogen sulfide, carbon dioxide) in non-associated and (or) associated gas.
Hard-to-recover reserves start playing a bigger role in the operations of oil and gas companies. In general, these include economically marginal reserves in conventional reservoirs in case of traditional development by the existing level of technology, utilization of reserves and accessibility of territories under development.
The share of hard-to-recover oil reserves, principally from unconventional hydrocarbon sources, has significantly increased in the world petroleum market. The strategic task of Russian oil and gas sector is to intensify the development of such fields with governmental support in the form of tax incentives.
Russian Ministry of Natural Resources has highlighted that hard to recover oil is becoming ever more prevalent in Russia, with two thirds of proven reserves (73 billion barrels out of a total of 110 billion) now being defined in this way.
As of today, the most relevant direction in improving of development hardto- recover reserves is horizontal wells drilling with multistage hydraulic fracturing.