Gas-lift is one of the artificial methods in which gas is injected down the production casing–tubing annulus and enters the production tubing through a number of gas-lift valves. During the production of a gas-lift well, the injected compressed gas might cause changes in pressure, temperature as well as fluid composition. When the temperature of the oil falls below the wax appearance temperature, it leads to the formation of organic wax deposits. Wax precipitation in well tubing and processing equipment might lead to dramatic reduction in production, equipment failures, loss of storage and transport capacity, and loss of efficiency. This paper presents a detailed study of wax formation in a gas-lift well. Taking into account changes in the oil component composition during gas injection, the depth of wax formation has been determined by applying a highly accurate developed algorithm. The optimal operating regime of the gas-lift well has been determined using a compositional multiphase model.

Severe problems accompany the production of abnormal oils with high pour point (with a paraffin content of over 30% by weight) in Kraynego Severa, Russia, due to the intensive formation of asphalt-resin-paraffin deposits (ARPD) in the bottom hole zone of the productive formation and downhole equipment. Possessing many advantages, the existing methods and technologies for coping with ARPD cannot fully solve this problem. As a result, complications arising from the production of high-wax oils lead to a significant decrease in oil production, a reduction in the production wells' maintenance and intertreatment periods, and an increase in dewaxing unit operating costs. The obtained results of theoretical and laboratory studies show that one of the promising approaches to improve the efficiency of wells equipped with electric submersible pumps when exploitation of abnormal oils with high pour point from multilayer deposits of the Timan-Pechora oil and gas province is the use of the new integrated technology based on the joint production of abnormal oil with high pour point with the oil, characterized by a lower wax content and the manifestation of structural and mechanical properties, in conjunction with regulating the parameters of the electric submersible pump. In this paper, the authors also describe a promising scheme of downhole equipment for the simultaneous-separate production of high-wax oil from multilayer deposits. The proposed downhole equipment allows us to separate the perforation zones of two productive formations using a packer-anchor system during simultaneous-separate exploitation of the formations by a double electric submersible pump installation.

Within the past few decades, the production of high-wax oils at offshore fields in Vietnam has been fraught with severe problems due to the intense formation of asphalt-resin-paraffin deposits (ARPD) in the downhole oil and gas equipment. The formation of organic wax deposits in the tubing string led to a significant decrease in gas-lift wells production, efficiency of compressor units, transport capacity of the piping systems, along with an increase in equipment failure. Subsequently, the efficiency of gas-lift wells dramatically decreased to less than 40% as a whole. The existing methods and technologies for combating organic wax deposit formation in downhole equipment have many advantages. However, their use in producing high-wax anomalous oil does not entirely prevent the wax formation in the tubing string and leads to a significant reduction in oil production, transport capacity, and treatment intervals. The results of theoretical and experimental studies presented in this article demonstrate that a promising approach to improve the efficiency of gas-lift wells during the production of high-wax oil is to use the technology of periodic injection of hot associated petroleum gas (APG) into the annulus of an oil-producing well. The effectiveness of the proposed method of combating wax formation in gas-lift wells highly depends on the combination of a few factors: the determination of wax deposit formation intensity in the well and the implementation of a set of preparatory measures to determine the optimal injection mode of hot APG (flow rate and injection depth) into the annulus between tubing strings and technological pipes. The injection depth of the hot APG should not be less than the depth of wax formation in the tubing string. The optimal injection rate of hot APG is determined by analyzing and mathematically modeling the APG injection system based on well-known thermodynamic laws.

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