Abstract
The experimental and numerical modeling of thermal enhanced oil recovery (EOR) requires a detailed laboratory analysis of core properties influenced by thermal exposure. To acquire the robust knowledge on the change in rock saturation and reservoir properties, the fastest way is to examine the rock samples before and after combustion. In the current paper, we studied the shale rock properties, such as core saturation, porosity, and permeability, organic matter content of the rock caused by the combustion front propagation within the experimental modeling of the high-pressure air injection. The study was conducted on Bazhenov shale formation rock samples. We reported the results on porosity and permeability evolution, which was obtained by the gas pressure-decay technique. The measurements revealed a significant increase of porosity (on average, for 9 abs. % of porosity) and permeability (on average, for 1 mD) of core samples after the combustion tube experiment. The scanning electron microscopy showed the changes induced by thermal exposure: the transformation of organic matter with and the formation of new voids and micro and nanofractures in the mineral matrix. Low-field Nuclear Magnetic Resonance (NMR) was chosen as a primary non-disruptive tool for measuring the saturation of core samples in ambient conditions. NMR T1–T2 maps were interpreted to determine the rock fluid categories (bitumen and adsorbed oil, structural and adsorbed water, and mobile oil) before and after the combustion experiment. Changes in the distribution of organic matter within the core sample were examined using 2D Rock-Eval pyrolysis technique. Results demonstrated the relatively uniform distribution of OM inside the core plugs after the combustion.
Highlights
Unconventional reserves are of strategic importance to replenish the resource base in Russia and worldwide, and their successful development can play a crucial role in increasing oil production and repeatedly compensate for the decline in production from depleted traditional reservoirs [1,2,3].Recently, thermal enhanced oil recovery methods have attracted a high level of interest because of their possible application to shale reservoirs [4,5]
Before 1and after the combustion tube test, the entire set of core samples underwent testing on a Scanning included using secondary electrons (SE) and backscattered electrons (BSE), magnification range standard gas permeameter used for 10–15 determining reservoir such 5–6 as nm porosity and
Rock samples from the Bazhenov Formation were subject to the combustion tube experiment and analyzed by the suite of both conventional laboratory and novel non-destructive techniques such as Nuclear Magnetic Resonance (NMR) relaxometry
Summary
Unconventional reserves are of strategic importance to replenish the resource base in Russia and worldwide, and their successful development can play a crucial role in increasing oil production and repeatedly compensate for the decline in production from depleted traditional reservoirs [1,2,3].Recently, thermal enhanced oil recovery methods have attracted a high level of interest because of their possible application to shale reservoirs [4,5]. One of the effective techniques is high-pressure air injection (HPAI), which involves the initiation of an oxidation front in the formation which does displace the oil by combustion gases, heated fluids, and steam and causes an increase in the reservoir pressure and temperature [6,7]. The most critical experiment for evaluating the effect and obtaining technological parameters is a combustion tube test [7,8]. The combustion tube (CT) test is the physical modeling of thermal exposure on porous media in formation conditions. It is conducted to assess the HPAI potential for a particular reservoir type as well as to obtain parameters for further upscaling of the technology in the field
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