This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 94293, "Downhole Capillary Surfactant-Injection System Pilot on Low-Pressure Gas Wells in the San Juan Basin," by J.P. McWilliams, SPE, and D. Gonzales, SPE, Burlington Resources, prepared for the 2005 SPE Production and Operations Symposium, Oklahoma City, OK, 17–19 April. Depletion of San Juan basin reservoirs is causing production rates to drop below the rate required for the minimum critical velocity (MCV) in a large number of wells. Traditional methods used to remedy this situation include plunger lift, pumping units, foam lift, and recirculation. With declining reservoir pressures, plunger lift and recirculation become less effective, and often the expense of purchasing and operating a pumping unit cannot be justified. In some cases, surfactant injection may offer the most cost-effective fluid-removal method. Introduction As gas reservoir pressures are depleted and production rates decline, liquid loading becomes a problem. When flow rates fall below the MCV, liquid accumulates in the wellbore, causing additional backpressure on the formation that reduces production rates. A downhole capillary surfactant-injection system (DCSIS) has been shown to aid in removing these fluids. The DCSIS delivers surfactant directly to the bottom of the wellbore where it is needed to be effective. A stainless-steel capillary-tubing string is run in the wellbore and is attached to a fluid pump and a chemical-storage tank. Once installed, a metered amount of surfactant is injected downhole to help unload the well. Promising results were seen from installation of a DCSIS on a slimhole well in the San Juan basin. A 10-well pilot was proposed to test the system. Initial criteria for the pilot required that a well be experiencing liquid loading and that all other artificial-lift methods had been ineffective or were uneconomic. The primary objective of the pilot was to determine the best applications for the system in the San Juan basin. Foam Flow Surfactant injection reduces density, gas slippage, and surface tension of the liquid/surfactant mixture. Most attempts to model the MCV required to lift foam to the surface are based on the Turner model, which is based on drop-entrainment mechanics. The Turner model calculates the velocity required to lift the largest liquid droplet to the surface. This velocity is a function of the liquid-drop density and diameter, gas-phase density, drag coefficient, and acceleration resulting from gravity. Typical values for surface tension and liquid density are 60 dynes/cm and 67 lbm/ft3, respectively. However, proper surfactant treatment can lower the surface tension to less than 40 dynes/cm and also reduce the density significantly. Because the Turner model is based on the physical properties of a water droplet, some assumptions made by Turner probably are not valid for foam flow.