This paper describes the development and results obtained from an encapsulated surfactant pilot designed to deal with liquid loading in gas wells located in Centenario field in Neuquén province of Argentina, which is a mature field in an urban area. Due to the field location, subsurface valves were installed into tubing during 2010-2017 to prevent possible blowouts, hence capillary string, which was a proven technology to deal with liquid loading, was discarded. To deal with liquid loading and production losses, Pluspetrol and SUEZ (the chemicals & services provider company) developed field application of a new technology of encapsulated surfactant that consists of an inert carrier soaked with liquid active chemical. This product allows constant dosage for a long period of time eliminating the need of installing a capillary string inside the well. Due to the architecture of the wells and commingled production, liquid loading problems and unstability started at rates of 30 Mm3/d, leaving 30% of the well remaining recoverable resources unproduced. These issues were dealt with successfully using capillary strings until 2010, when urbanization of the productive area made it necessary to install subsurface valves. From then on, production stability was affected, losing up to 70% of it in several zones. The pilot consisted of five wells. Candidates were selected using dynamic gradients and telemetry systems to evaluate liquid loading, confirmed by unstable production and favorable response to shut-ins. The project is currently in test phase. It was carried out initially in one well with a 100% increase in daily production, as well as high stability of gas and liquid production. The liquid level in wells, solid surfactant concentration and liquid rates were considered to estimate the treatment duration. Wellhead telemetry and physical measurements such as dynamic gradients, allowed an accurate analysis of results. Measurements during the treatment showed a pressure reduction of 7 kg/cm2 in front of the perforations, compared to the best production conditions of the well before liquid loading. In addition, four more wells were treated similarly, and by the time this work is presented only have preliminary results are obtained. In order to evaluate this project continuous flow meters are being used. In case these positive results remain, it is expected that this application will be expanded to more than 40 wells. Using encapsulated surfactant implies several advantages. One of them is the possibility to run physical measurements during treatment in order to continuously evaluate its performance and pressure change. In addition, the absence of a capillary string allows the treatment to be held on wells with complicated production systems, such as velocity strings, diameter reductions, or subsurface valves diminishing operative risks. Another positive feature is to avoid installing pumps and chemical recipients at the location, making this suitable for urban fields. Last but not least, the technology price is lower than others, resulting in an attractive solution.

Since 2015, scale problems have appeared when gas production decreased below 30 Mm3/day and wells could not evacuate liquid and solids to the surface due to liquid loading. Scale depositions were found in casing and tubing at different depths close to Quintuco Formation perforations. During 2019, more than 30 wells were mechanically cleaned using slick line to remove scale every 30 days approximately. This paper describes the study of the origin of scale in gas wells producing from multiple formations and the chemical technology applied to solve this problem in the mature urban field Centenario (Neuquén - Argentina). Core and water analysis were performed to study the scale phenomenon at the productive formations and to determine the compatibility between fracturing and formation waters. In addition, it established the scale origin and served to detect further wells susceptible to suffer scaling problems. Scale is produced in the casing, not in the formation, due to changes of pressure and temperature related to the expansion of gas and changes in water mix compatibility at Quintuco perforations depth. Due to the field location, subsurface safety valves were installed in the tubing to prevent possible blowouts. Thus, capillary string for product injection was discarded. A proven chemical technology for oil wells-encapsulated scale inhibitors-was adapted to treat gas wells aiming for a treatment duration of three months. The method consisted of a mechanical clean-up followed by a batch treatment of encapsulated product with water and, finally, a slick line run to ensure it reached the bottom-hole. The chemical treatment pilot was carried out in 6 wells. Candidates were selected based on abnormal production decline, scales showed after slickline intervention, favorable response after mechanical clean-up, and high intervention frequency. The pilot held in 2019 showed an increase in gas rate production of 12 Mm3/day on average representing 40% of well production, high stability in gas production and a reduction of slickline intervention frequency. The duration of the treatment was initially estimated according to the liquid rate of the well and the product concentration used. During 2020 the pilot will be expanded to 32 wells in the field. Solid scale inhibitor for gas wells is relatively new in the industry and there is not much bibliography about application and results in this type of wells. This paper describes the methods used for scale characterization, the prediction of its formation in gas wells, the selection method for scale inhibitors, the product application technique to the wells and the results obtained in the pilot, demonstrating its technical and economic feasibility for field use.