Laboratory Testing of Downhole Gas Separators in Inclined Wellbore Configurations

Abstract

Abstract This paper attempts to establish the effects, if any, of wellbore inclination on the performance of downhole gas separators. Different downhole gas separator designs have been extensively studied in the laboratory and far reaching conclusions have been drawn from observations made in the laboratory for vertical wellbores. However, it is pertinent to note that most wellbores are not truly vertical and a survey which shows the deviation of the wellbore from a vertical reference point is often present in most wellbore configurations. Hence, this paper compares the performance of different downhole gas separator designs in a vertical wellbore set up with that of the same downhole gas separators operating under similar conditions but installed in an inclined wellbore set up. Technology has made it possible to drill horizontal wells which are fast becoming ubiquitous in most oilfields. With gravity forces dominating separation in static downhole gas separators; it is certainly logical to study the effect of wellbore inclination on the separation efficiency of downhole gas separators as transport properties of multi-phase fluids are affected by gravity. With the above mentioned arguments, it becomes imperative to study downhole gas separators under conditions which best simulate oilfield operations. The approach utilizes an instrumented full scale model of an inclined well-bore and separator constructed with clear acrylic pipe. The base case consists of the entire wellbore and separator set up installed vertically and subsequent experiments were performed with the wellbore inclination angle at 45o. An air and water mixture is injected through the well's perforations. The air and water flow rate measurements define a performance plot of each separator design with respect to wellbore inclination. Continuous flow conditions were applied in all tests Results obtained from laboratory annular bubble rise experiments show that in an inclined set up, the bubbles tend to move along the walls of tubing where the effect of drag is maximum. Results from the annular bubble rise experiments in an inclined wellbore equally show that the upwards motion of the smaller bubbles tend to be considerably reduced and sometimes halted by drag while on the contrary, the larger bubble (Taylor type bubbles) have higher mobility along the walls of the tubing. Also, results from the downhole gas separator performance tests conducted in a wellbore inclined at 45o indicate that at similar operating conditions, a gravity driven downhole gas separator installed in a wellbore inclined at 45o would perform better than the same gravity driven downhole gas separator in a vertical wellbore. While at similar operating conditions, a centrifugal force driven downhole gas separator installed in a vertical wellbore would perform better than the same centrifugal force driven downhole gas separator in a wellbore inclined at 45o. Introduction Laboratory testing of downhole Gas Separators (also known as gas anchors) have been ongoing at the University of Texas at Austin Petroleum Production Engineering Facility (UTAPPEF) since January, 2005. Numerous tests have been conducted on a full scale laboratory vertical well equipped with different downhole gas separator designs with a view of understanding the various parameters that influence the separation performance of downhole gas separators. Bohorquez R, Ananaba V, Alabi O et al (2009) have presented far reaching conclusions regarding factors that influence downhole gas separator performance. However, it is instructive to note that results presented by Bohorquez R, Ananaba V, Alabi O et al (2009) were conducted only on a truly vertical laboratory well. Furthermore, since it is common knowledge that no wellbore is truly vertical; the best laboratory simulation of actual field operations utilizing downhole gas separators is that laboratory experimental model that introduces a deviated wellbore setup.