Development and Testing of a Compact Liquid-Gas Auger Partial Separator for Downhole or Surface Applications

Abstract

Summary In some applications, complete separation of liquid and gas is not required and removing only a portion of the gas is sufficient. One application that was developed fully is separation of gas from one well for raw gas lift of other wells. This can be done either on the surface or downhole. The auger separator is a new, patented device that was initially developed to fit inside production tubing and, thus, is an ultra-compact separator design. It differs from other separators in that it requires no complex controls or power to operate and, for most applications, has a diameter of only a few inches. The multiphase fluid enters an auger section where the pitch of the stationary auger blade causes the flow to rotate. Centrifugal forces created by this rotation cause the liquid to flow along the outer wall with the gas flowing in the center. A portion of the gas is ported through a crossover to the annulus in downhole applications or to a gas line in surface applications. The downhole separator can be placed by wireline in the tubing. The surface version is placed as a spool piece in the production line. Equations were developed to predict performance and were incorporated into a spreadsheet for ease of design. Laboratory tests were performed to validate the predictions and to explore various design details. Following successful lab testing, the prototype separator, which was 3½ in. in diameter, was placed downhole inside 4½-in. tubing. The separated gas was ported to the annulus through a gas-lift mandrel. This test showed that the equipment could be placed in the well with wireline, that downhole separation was feasible, and that the theoretical pressure-drop calculations were accurate. Following this test, an 8-in.-diameter auger separator was designed for separation of gas on the surface as a full-scale pilot test. This was placed in the production line from a well, and the separated gas was used to provide raw lift gas for other wells on the drillsite. These two field tests showed that partial separation was feasible with this device, and that the equations used for design were reasonable. The surface auger separator was left in place after the test and continues to provide lift gas. This paper presents the concept, design equations, laboratory test results, and field-test results of both a downhole and a surface application. Although raw gas lift is an application that has been fully developed, other potential uses also are discussed.