ASSESSMENT OF THE APPLICABILITY OF GEOCHEMICAL GEOTHERMOMETERS FOR FORMATION WATERS OF THE TOMSK REGION

Abstract

The relevance. When constructing various hydrogeochemical models of basins, accurate data on the temperature of formation waters are required. In the case of thermal waters, where it is difficult to measure temperatures at depth, calculated or empirical expressions – geothermometers – have long been used. For formation waters of sedimentary basins, they are rarely used, since temperatures are lower here, water salinity and pressure are higher. However, even here it is necessary to check the data of deep-seated thermometers, the accuracy of which varies greatly, and, in the absence of data on temperature or the impossibility of measuring it, to reliably calculate them. To do this, it is necessary to select the most suitable geothermometers in these conditions. The main aim: get acquainted with a wide range of geothermometers used, calculate several varieties from the available database of the chemical composition of formation waters in the Tomsk region, compare these calculations with each other and between actually measured data from deep thermometers, identify and justify the most suitable for specific conditions. Objects: formation waters taken during the development of oil fields, mainly waters of Cretaceous and Jurassic deposits, with a depth from near surface conditions to 4,5 km. Methods. When processing the database on the chemical composition of formation waters, basic statistical methods were used; as a result, samples with abnormally high and abnormally low concentrations of components were rejected, as well as those that did not comply with the law of electrical neutrality. The formulas for calculating geothermometers are taken from numerous literary sources. The calculation results were compared with the available data on actually measured temperatures, among themselves, with the depths of water circulation and the geothermal gradient of the region. Results. The types of geothermometers and the conditions for their use were studied in detail according to numerous literary sources. The most suitable in these conditions were selected. As a result, nine different chemical geothermometers were calculated for the first time using the available database of the chemical composition of formation waters in the Tomsk region. It is shown that classical geothermometers (Si, Na-K, Na-K-Ca, K-Mg) do not work in these waters, they do not correlate well with the actually measured data of deep thermometers. Mg-Li and Na-Li geothermometers are recommended, as well as Na-K-Ca geothermometer with Mg correction. These geothermometers filled in the gaps in the database of 650 missing temperatures. It is concluded that it is necessary to further develop geothermometers for formation waters of oil fields, taking into account more modern and accurate data. As a practical result of this work, the possibility of using the obtained temperatures in calculating equilibria in the water-rock system and other calculations is indicated.

Keywords

• chemical geothermometers
• formation water temperature
• oil waters
• tomsk region
• «water–rock» system