The efficient method of water content determination in low-permeable rocks of Bazhenov formation (Western Siberia)

UDK: 553.98.556.3
DOI: 10.24887/0028-2448-2019-7-73-78
Key words: Bazhenov formation, shale reservoirs, Dean-Stark method, evaporation method, water content, pore water
Authors: E.S. Kazak (Lomonosov Moscow State University, RF, Moscow; Skolkovo Institute of Science and Technology, RF, Moscow), A.V. Kazak (Skolkovo Institute of Science and Technology, RF, Moscow), Ya.V. Sorokoumova (Lomonosov Moscow State University, RF, Moscow), A.D. Alekseev (Gazprom Neft NTC LLC, RF, Saint-Petersburg)

Hydrocarbon resource assessment and estimation oil and gas reserves source-rock reservoirs within the Bazhenov formation of Western Siberia require a comprehensive study of their water content. So far, the petroleum industry has been using known laboratory methods for direct determination of water content for low-permeable shale Bazhenov formation rocks. However, the question of data validity and quality remains open since the legacy methods have been developed for conventional reservoirs. The article presents a new laboratory method for measuring the water content, explicitly designed for shale rocks with initially low water content (less than 5% wt.). The proposed evaporation method allows determining the amount of free and physically bound water in rock samples with a mass of 25-70 g within 1-3 h. The error in determining the mass water content for in evaporation method depends on the initial water content and is 0.2-6.8% wt.

Testing of the evaporation method included a target collection of whole core samples with the maximum preserved natural water content, taken from five wells of various fields within the Bazhenov formation interval. The study reveals the temperature ranges for extracting free (121°C) and physically bound water (250°C). The measured water content of the Bazhenov formation rocks samples is 0.28-4.27 wt.% with the free water content from 0.04 to 2.53% wt. Water content decreases in carbonate interlayers and increases in the clay-rich units. We experimentally studied the effect of storage conditions and sample size on the results of water content determination. We also established that reliable water content data requires fragmenting a core sample into pieces with specific dimensions of at least 5-7 cm immediately after opening the protective shell. Comparison of water content data obtained using the Dean – Stark method and the evaporation method showed that the latter delivers much more accurate results for the oil and gas source Bazhenov formation.


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