A Comprehensive Study of Unconventional Reservoirs: The Case of Rechitskoe Field Sediments of Rock Units I-III

Abstract

Due to the deterioration of petroleum resources in the Republic of Belarus, unconventional reservoirs, which contain hydrocarbons in "shale-like" low-permeable rocks, which include Domanic deposits, become increasingly important. These rocks containing hydrocarbons are both producing oil and at the same time they are not reservoirs in the traditional sense (Varlamov A. I. et al., 2017). The most common technology for developing unconventional reservoirs is drilling horizontal wells with multi-stage hydraulic fracturing. The technological efficiency of drilling such wells will primarily depend on getting into the so - called "sweet spots" - places characterized by the best petrophysical, pyrolytic and geomechanical properties. This ultimately determines the need for a comprehensive study of hydrocarbon deposits in unconventional reservoirs. This article describes the workflow for studying unconventional reservoirs of one of the fields of the Pripyat trough of the Republic of Belarus. Studying these reservoirs was a challenge because due to geological and surface conditions no seismic data was available. The first well logging results showed the absence of significant rock anisotropy detected by standard methods of acoustic logging. This caused difficulties in determining the direction of drilling horizontal wells. There were also insufficient results of core studies of wells, including fully geochemical and geomechanical studies. Carrying out a comprehensive study of promising formations and confirming their oil bearing capacity required making a comprehensive program presented below, which outlined the types of studies that would provide necessary information about lithological, petrophysical, pyrolytic, and geomechanical characteristics of unconventional reservoirs of the field under study. Core studies performed within the integrated study confirmed that the studied sediments are source rocks. At the same time, according to the results of pyrolytic research, it was found that the rocks contain both in-situ hydrocarbons, and the ones which migrated from the underlying formations. The set of geophysical studies carried out on the legacy wells, including logging, hydraulic fracturing and surface seismic monitoring, allowed determining the direction of maximum stress, which eventually allowed determining the direction of drilling horizontal wells. The set of studies described in this article can be used in the study of other unconventional deposits of the Pripyat trough, belonging to the Domanic type.