An Engineering Approach to Gas Anchor Design

Abstract

Abstract Free gas is the most common cause for low pump efficiency in sucker rod pumping pump efficiency in sucker rod pumping wells. The installation of a gas anchor on the bottom of the downhole pump is a method used to help combat this problem. This paper describes improved gas anchor design for sucker rod pumping wells with gas problems. A computer program is described which will aid in the design of a gas anchor system and which evaluates pressure drops to determine the pressure drops to determine the efficiency of the gas anchor. The major parameters in gas anchor design are gas bubble velocity, diameter of the mud anchor, length of the dip tube, and the pressure drops associated with the gas anchor system. Validation of rules of thumb used in the past for gas anchor design is made. Gas bubble velocity of 0.5 ft/sec is a valid assumption if the API gravity of the liquid is greater than 300, the flow is turbulent and the temperature is greater than 100 degrees F. The principles behind the operation of an efficient gas anchor are presented with suggestions on how more efficient gas anchors may be designed by production engineers. Introduction Pump Efficiency Pump Efficiency Gas interference continues to be one of the major contributors to low pump efficiency in sucker rod pumping wells. Free gas entering the space between the travelling valve and standing valve reduces the volumetric efficiency of the pump and large volumes of free gas passing through the pump will interfere passing through the pump will interfere with normal valve action and reduce the volumetric efficiency of the pump. Therefore, downhole separation of gas and oil become desirable to improve volumetric efficiency whenever the well must be pumped. To separate the gas from the oil, it is necessary to cause the oil to flow downward at a rate less than the rate of rise of the gas bubbles. If an ideal separation of gas and liquid is to be accomplished, all of the gas would flow up the annulus between the casing and tubing and would enter the gas gathering system at the casing head. The degassed liquid would enter the suction of the pump and be produced up the tubing. The actual separation of the gas from oil is accomplished by gravity. Bubbles will rise through oil at a rate dependent principally on the viscosity of the oil relative to the viscosity of the gas. The installation of a properly designed gas anchor system on the bottom of the downhole pump will allow this separation process to occur. process to occur. P. 71