Novel approaches to core analysis

UDK: 550.8.023
DOI: 10.24887/0028-2448-2020-8-34-37
Key words: сore, soft rocks, carbonate rocks, classification, extraction, aging
Authors: I.V. Yazynina (Gubkin University, RF, Moscow), E.V. Shelyago (Gubkin University, RF, Moscow)
Standardization and methodological support of rock sample studies is an urgent task. Great part of industrial laboratory research standards was written in the last century. Current paper examines a number of methodological aspects of core studies starting with sample preparation. We should consider that the reliability of determining the reservoir properties of fractured, cavernous, unconsolidated and soft rocks is significantly lower than that of sandstone rocks due to great heterogeneity. Measurement of the porosity (static property) can be solved by increasing the accuracy of the experimental equipment, but the permeability measurement (dynamic property) requires taking into account a set of additional factors. Nowadays, laboratory specialists use a modern X-ray tomography method to assess reservoir rock properties, which allows not only to obtain initial information for heterogeneous reservoirs, but also to establish various lithological types in the petrophysical plots. It is proposed to calculate characteristics of rock heterogeneity at the scale of a single core sample. The new technique was tested for core samples from eight Russian oil fields. It is possible to classify formations with different types of pore space using only the heterogeneity characteristics, which opens up new possibilities in predicting of the oil field development.
The basic task of core studies is the picking of a representative sample collection. Statistical analysis of the X-ray tomography data performed for a number of oil deposits shows it makes no sense to standardize a collection with the same number of samples. Another issue of the core preparation process is the extraction stage. Some proposals for soft extraction in order to preserve the original wettability do not take into account the processes taking place in oil-saturated rock during well drilling and coring. The most correct way to simulate the initial natural state of the reservoir rock is the saturation of the extracted core sample with reservoir water and oil in the laboratory. However, this brings additional question about the sufficient “aging” time of the oil-saturated sample before flooding tests. Here we propose to determine aging time experimentally by measuring the electrical resistance dynamics of the core at reservoir conditions.
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