Decentralized Continuous-flow Gas Anchor

Abstract

Abstract A new gas separator has been developed and successfully field-tested in more than 40 beam pumped wells which were subject to severe gas interference. The new design is based on several innovations:Decentralization of the gas separator in the casing ensures that a maximum amount of liquid enters the separator.The presence of two or more ports on the gas separator near where it touches the casing wall.Construction of the gas separator so that the outer tube of the gas separator is pressed against the casing wall to prevent cross-flow of liquid and gas.The addition of a diverter at the bottom of the separator to direct most of the gas flow, towards the wide side of the annulus. These innovations have resulted in a gas separator efficiency much greater than that of conventional designs. Introduction Numerous studies have been performed in recent years in an attempt to improve the performance and efficiency of a beam pumped system [see References (1) through (8)]. The studies include the motor or power unit, the surface pumping system, the rod string and the downhole pump. In wells which produce gas, the inefficient separation of gas from liquid at the pump inlet often results in very poor pump performance and low overall efficiency of the entire pumping system. This can be verified by obtaining a dynamometer pump card which indicates considerable free gas in the pump even though liquid is present in the casing annulus in the form of a high gaseous liquid column. Terminology When discussing downhole gas separators in pumped wells, there appear to be various terms which are used indiscriminately: gas anchor, mud anchor, dip tube, perforated sub, etc. In order to avoid confusion, the terminology adopted in this paper is as follows:Gas Separator: The complete assembly of elements installed below the seating nipple and the pump intake with the purpose of maximizing the amount of liquid entering the pump.Outer Barrel: The outermost element of the gas separator which is connected to the tubing (often called mud anchor).Dip Tube: The innermost element of the gas separator which is attached to the pump intake (often called gas anchor). Natural Gas Separator The preferred technique for separating gas from the pump is to place the tubing fluid entrance ports (or gas separator ports) below the bottom of the formation's perforated interval as shown in Figure 1. The natural separation of gas and liquid by gravity will result in relatively gas-free liquid entering the pump intake if the downward liquid velocity in the casing/tubing annulus is less than approximately 6 in./sec. The gas separator inlet should be placed at least l0ft. below the formation gas entry zone to allow free gas separation from liquid between the tubing outer diameter and the casing inner diameter See Table 1 for natural gas separator capacities. For greater capacity, it is necessary to use a modified gas separator with an outer diameter smaller than the tubing (see Figure 2).