PRACTICAL APPLICABILITY OF TECHNICAL REQUIREMENTS FOR CASING PIPES USED IN THE PRESENCE OF HYDROGEN SULFIDE IN THE FORMATION FLUID

Abstract

The optimal ratio of the level of manufacturability of the applied solutions and their cost is one of the key tasks in planning and designing well construction. According to [1] as well as the Casing Design Instructions, in the presence of hydrogen sulfide in the formation fluid, depending on the amount of its content and partial pressure, the well design must provide for casing pipes in a hydrogen sulfide-resistant design. However, the construction of wells in the Volga-Ural region, where most of the fields with H2S content are carried out for about 100 years, and at the same time there were no serious incidents or accidents associated with the destruction of casing pipes from the impact of the mechanism of sulfide-corrosion cracking under stress. In addition, based on the results of analysis of the results of well logging to determine the technical condition of the production strings, it was established that there is no relationship between the cases of revealed casing leaks in the wells and the level of hydrogen sulfide content. In this regard, it became necessary to update the requirements for calculating the design of wells in the presence of a small amount of hydrogen sulfide in the formation fluid. In this case, when calculating casing strings, the level of stress in casing strings arising from tensile loads and overpressures is limited due to the introduction of a factor for reducing the bearing capacity. In other words, this factor corresponds to the ratio of threshold (test) stresses during tests of samples for sulfide-corrosion cracking under stress to the value of the standard minimum yield strength of steel of the corresponding strength group. Based on this, an analysis of the production loads on the casing strings in the wells of the Volga-Ural region was carried out, and the potential for reducing the threshold stress was identified during laboratory tests of samples from casing strings for sulfide-corrosion cracking under stress. Based on the results of analysis of the results of laboratory tests of samples for sulfide cracking under stress in a model medium, it was determined by operating conditions that for seamless casing pipes of strength groups N80Q and R95, the threshold stress can be set to 60% of the minimum yield strength. This article is a follow-up to the publication of the casing specification.