On methods of seals identification in terrigenous formations

UDK: 551.31

DOI: 10.24887/0028-2448-2025-12-30-35

Key words: seal, reservoir, permeable non-reservoirs, hydrocarbon saturation, natural reservoir, well logs

Authors: А.М. Khitrov (Oil and Gas Research Institute of the RAS, RF, Moscow); Е.M. Danilova (Oil and Gas Research Institute of the RAS, RF, Moscow); I.N. Konovalova (Oil and Gas Research Institute of the RAS, RF, Moscow); M.N. Popova (Oil and Gas Research Institute of the RAS, RF, Moscow)

Methods of seals identification above the prospective reservoir horizons are considered for the purpose of researching and predicting the petroleum potential of natural reservoirs in terrigenous formations, including those in the West Siberia. It is shown that cyclically structured terrigenous formations contain not only high-capacity, high-production reservoirs and seals, but also layers, packs and stratums of interbedded clays, mudstones, siltstones, clay sandstones, dense carbonate interlayers and coals that are neither reservoirs nor seals. These layers are composed parts of natural reservoirs in which hydrocarbons migrate under the seals. Seals in non-reservoir stratums are identified by signs of a lack of hydrocarbon saturation based on the interpretation of well logging data. Hydrocarbon-permeable non-reservoir rocks, deposited between reservoirs and seals, are determined by the presence of hydrocarbon saturation which is considered as evidence of the permeability of layers, packs and stratums non-reservoir rocks. The process of identifying a seal in an Upper Jurassic-Lower Cretaceous sequence of interbedded non-reservoir rocks is described using well logging data and author's methodology - NEGAEL. Main part of the methodology is the determination of non-reservoir-seal boundary values using a special parameter F. This parameter is represented by neutron-gamma (or neutron logging) readings reflecting hydrogen content, divided by gamma ray readings reflecting clay content. A method is proposed for comparing the F parameter and electrometry (lateral logging) in two well sections: inner and outer. This enables to identify and correlate seals between wells and also to construct fundamentally new reservoir models by mapping seal bottoms above reservoir horizons.

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