This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 160282, ’Artificial-Lift Optimization With Foamer Technology in the Alliance Shale-Gas Field’ by Lisa Farina, Claudio Passucci, Alberto Di Lullo, and Emanuele Negri, Eni; Osvaldo Pascolini, Eni US Operating; and Shawn Anderson and Stan Page, Quicksilver, prepared for the 2012 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, 8-10 October. The paper has not been peer reviewed.
Recently, Quicksilver Resources and Eni E&P, through its subsidiary Eni US Operating, began a common effort to optimize production and lift costs in the Alliance shale-gas field in the prolific Barnett shale play in Texas. Such efforts included a deeper analysis of artificial-lift performance and exploitation of other deliquefication technologies. Previously, foaming agents had been seldom deployed, but now a comprehensive assessment of their technical and economic performance has been conducted.
Introduction
Hydraulic fracturing is the key technology in unlocking production of shale-gas wells. The production of huge amounts of pumped water affects the life of a shale-gas well; the first phase and dewatering methods have to be considered as crucial aspects of a shale-gas development. In fact, as a consequence of reservoir depletion, the gas rate decreases to a point at which the water cannot be transported out of the wellbore and starts to accumulate.
Methods such as gas lift and plunger lift and the use of smaller tubing diameters, pumps, and foaming agents are commonly adopted to control this situation. Foaming agents do not need downhole modification, can be tested easily on existing wells and facilities, and are chemically compatible with corrosion inhibitors, so the same injection points and devices can be used.
Shale-Gas Production Wells and Liquid Loading: Alliance Field. As of March 2012, gas production for Alliance is approximately 176 MMcfD. The field counts more than 200 wells spread over an area larger than 65 km and clustered in more than 60 well pads, each enclosing a variable number of wellheads. Most wells are horizontal and packerless, with a vertical depth of approximately 7,400 ft, and are stimulated by hydraulic fracturing.
To stimulate the entire lateral length, hydraulic-fracturing treatments are performed by isolating smaller portions of the lateral, called stages. The number of stages depends on the length of the horizontal drain and the spacing of each treatment. In the Alliance field, a spacing of approximately 400 ft is usually considered, with up to 20 stages. For each stage, approximately 10,000 bbl of water is injected, so a typical well of 6,000 ft of horizontal length with 15 stages implies a water volume close to 150,000 bbl. Almost all the wells have gas lift valves (typically 9 to 12), with the last one set at the deepest injection point in the tubing.
During the first development phase of the field, lift gas was fed by a multistage gas compressor installed at the well pad. At the beginning, the well produces through the annulus [outer diameter (OD) of 5.5 in.], with a gas-production peak of 4 MMcfD and a water production between 1,000 and 2,000 B/D. As the reservoir pressure decreases and gas production drops to approximately 2 MMcfD, production is switched to the tubing to increase flow velocity.
