Summary The paper considers results of laboratory experiments on the effect of an acid composition consisting of hydrochloric and hydrofluoric acids on core samples taken from clastic reservoirs in Perm Region. The research included determination of porosity and permeability properties of the samples before and after treatment with the composition, taking anisotropy of rock properties into account. The paper presents the research program and the experimental results obtained that showed a significant change in permeability after filtration of the acid composition and the influence of anisotropy on this parameter. The specific feature of the research carried out is the study of the combined effect of the acid reagent and varying effective stresses on permeability of core samples.

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The complex interbedded heterogeneous reservoirs of the Severo-Komsomolskoye field are developed by horizontal wells in which, as part of the pilot project's scope, autonomous inflow control devices (AICD) are installed to prevent early coning and gas breakthroughs in long horizontal sections and reduce sand production, which is a problem aggravated by an extremely low mechanical strength of the terrigenous deposits occurring in the Pokur formation of the Cenomanian stage in this area. The zones produced through AICDs are separated by swell packers. The issue of AICD effectiveness is discussed in the publications by Solovyev (2019), Shestov (2015), Byakov (2019) and some others. One of the methods used for monitoring horizontal sections with AICDs is production logging (PLT). However, due to the complexity of logging objectives, the use of conventional logging techniques makes the PLT unfeasible, considering the costs of preparing and carrying out the downhole operations. This paper provides some case studies of the Through-Barrier Diagnostics application, including passive spectral acoustics (spectral acoustic logging) and thermohydrodynamic modelling for the purpose of effective estimation of reservoir flows behind the liner with AICDs installed and well integrity diagnostics. As a result of the performed diagnostics, the well completion strategy was updated and optimised according to the log interpretation results, and one well intervention involving a cement squeeze with a straddle-packer assembly was carried out.

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