Comprehensive Approach Tackles Systemic Failures in Gas-Lift Valves in Presalt Wells

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30943, “Comprehensive Approach To Tackle Systemic Failure in Gas-Lift Valves in Presalt Wells,” by Elaine Daniele M.P.C. Real, Thiago Geraldo Silva, and Otavio Borges Ciribelli, Petrobras, et al., prepared for the 2021 Offshore Technology Conference, Houston, 16–19 August. The paper has not been peer reviewed. Copyright 2021 Offshore Technology Conference. Reproduced by permission. This work describes a comprehensive approach to tackle systemic failure in gas-lift valves (GLVs) in presalt wells. Failure analyses in GLVs were performed after unexpected early failures leading to tubing/annulus communication. Understanding the root causes of this problem generates value for assets by increasing equipment life, preventing unnecessary workover, and reducing costs. Equipment and Processes Historically, the operator used conventional orifice GLVs. The complete paper provides a history of the development of the first GLVs, with a flat seat, into a model having a seat in the venturi shape. While GLV designs have evolved since the adoption of the venturi-shaped valves, a cause of failure was identified as blocking of the injection orifices as a result of the displacement of the venturi caused by the rupture of the elastic ring lock. Failure analyses also brought to light important information on the flow of liquid through the valve that is common in workover operations and ramp up of production in oil wells. For high liquid flow rates, the erosion of the internal parts of the valve causes failure. Thus, it was necessary to develop a new GLV that supported higher liquid flow rates. As a result, high-reliability GLV designs emerged. The maximum liquid flow rate through these valves was increased to 2 bbl/min because of improvements in metallurgy and a new geometric design inverting the position of the check valve (CV) and the venturi. An example of this high-reliability GLV, called the “alpha model” by the authors, is presented in Fig. 1. The CV of this model, considered to be of high reliability, has five parts, two more than the CV of the conventional venturi GLV. These two new parts are the ring (elastomer) and the nozzle retainer (metal). This design change eliminated the elastic ring lock that was thinner and made of a more-fragile material than the metal ring. Additionally, this new design uses a double-sealing system of elastomer/metal and metal/metal. The operating mechanism of the high-reliability valve is characterized by the fact that only the dart and the CV’s compression spring are mobile. A second type of high-reliability GLV is called the “beta model” by the authors. The CV of this GLV is comprised only of the spring and dart. When the tubing pressure is greater than that of the annulus pressure, the spring is relaxed and the valve is in the closed position. When the annulus pressure is greater than the tubing pressure, however, the spring is compressed and the CV seat is pushed in the direction of the nose of the valve. At that point, the dart holes line up with the nose holes and the valve is in an open position. The beta model GLV features only metal/metal sealing, which causes small leaks caused by poorly executed polishing or dirt deposition between the seal area and the dart.