EFFECT OF STRATAL WATER, OIL, AND OIL PRODUCTS WITH HYDROGEN-SULFIDE IMPURITIES ON THE CRACK RESISTANCE OF STEELS

Abstract

In the course of the production of natural gas and oil from wells, one usually obtains, in addition to hydrocarbons, stratal waters differing in chemical composition, mineralization, pH, etc. at different deposits. To evaluate the actual corrosiveness of technological media in the oil-gas extracting industry, it is necessary to study the effect of H2 S impurities in the water and hydrocarbon phases. Most investigations of corrosion and the corrosion-mechanical properties of steels and alloys were carried out in a 5% NaCl + 0.5% CH 3 COOH aqueous solution saturated with H 2 S [1 ‐ 3] according to the requirements of the standard NACE TM0177-90 [4]. In what follows, we describe our studies of the influence of the chemical composition of an aqueous hydrogen-sulfide medium, crude oil, and oil products saturated with hydrogen sulfide on the crack resistance of steels under cyclic loading. We extracted stratal oil at well No. 12 of the Borovs’k oil field and filled glass thick-walled vessels with this oil, where it was degassed during ~ 0.5 h and, further after their sealing, was divided into crude oil and stratal water. To prevent the depressurization due to a possible excessive increase in the pressure of the oil and other gases, we filled the vessels only 1 / 3 full. Stratal oil from this field had the following parameters. The content of gases was 0.013 m 3 / kg, the density was 914 kg / m 3 , and the content of fractions was as follows (in vol. %): H 2 S — 0.04, CO2 — 0.11, N2 + inert gases — 0.34, CH4 — 0.17, C2 H6 — 0.39, C3 H8 — 0.96, C4 H10 — 1.02, C5 H12 — 0.98, C 6 H 14 — 1.44, C 7 H 16 — 1.38, and hydrocarbons C 8 and higher ones — 93.17. After degassing, the content of light hydrocarbons CH 4 ‐ C 4 H 10 in crude oil decreased by 3 ‐ 17 times, N 2 and inert gases were absent, and the content of H 2 S was ~ 0.02 vol. % and that of CO 2 was up to 0.02 vol. %. Stratal water contained the following components (in mg-eq./liter): Cl ‐ — 145.35, SO 4 2 − — 1.07, HCO 3 − — 0.22, Ca 2 + — 9.73, Mg 2 + — 2.86, Na + + K + — 78.27; its density was 1159 kg / m 3 and pH ~ 5.8 ‐ 6.3. We loaded plane specimens (100 × 10 × 2 mm) with a V-shaped cut 1.5 mm in depth (the angle of opening was 60°) by sign-preserving pure bending with a frequency of 4 Hz at 20°C. The stress intensity factor is given as