Abstract
Abstract. In this work, we have investigated the wettability of Bazhenov Formation rock samples using a nuclear magnetic resonance (NMR), the methods of vapor adsorption, and wetting contact angle. We have conducted the petrographic description of rocks using ultra-thin sections and scanning electron microscopy (SEM). In addition, we used data on the organic content (TOC) obtained by the Rock-Eval method and the results of lithological typing on thin sections for detailed analysis of NMR and contact angle methods results. Thus, for target rock, the groups with a similar rock wettability were highlighted by the lithological description of thin sections. The calculation of the wetting angle provided an initial assessment of the surface wettability of the rock and made it possible to establish the relationship between the wetting angle and the TOC, which is relevant for rocks of the Abalak-Bazhenov group. The NMR method described the core plug wettability proved to be less sensitive to the rock lithotype and organic matter (OM) texture in the rock and, therefore, used for the integral characterization of core plugs. Correlations of calculated wetting angle and adsorption wettability index vs. TOC and OM texture illustrated the dependence of rock wettability behavior on both the lithological specifics and the OM properties.
Highlights
In recent years, the share of unconventional reserves in global oil production has grown significantly (Ahmed and Meehan, 2016; Prishchepa et al, 2014)
Petrographical characterization of thin sections and XRD showed that according to the classification proposed by Lazar et al (2015), the target collection of Abalak-Bazhenov group (ABG) rock samples are composed of different types of siliceous mudstones, which are enriched with organic matter (OM)
Samples are mostly homogenous in mineral composition; lithotyping was performed on the basis of specific peculiarities such as the organic content (TOC), texture, pyrite fraction, bioturbation, and presence of carbonates
Summary
The share of unconventional reserves in global oil production has grown significantly (Ahmed and Meehan, 2016; Prishchepa et al, 2014). Exploration and development of unconventional resources require novel effective laboratory methods for characterizing the reservoir properties. The wettability of reservoir rock is one of the most critical factors affecting the residual saturation and flow properties in the formation. Wettability is an ability of a rock surface to interact with a reservoir fluid molecularly, and it is one of the essential characteristics associated with the development of oil and gas fields and reserves estimation (Morrow, 1990; Ogunberu and Ayub, 2005). The nature of the rock surface wettability in the reservoir significantly affects the residual saturation, total recovery factor, etc. The preliminary recovery of fully or partially hydrophobic reservoirs leads to an artificial overestimation of the residual water saturation when estimated by indirect methods
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