Laboratory Study of Down-Hole Gas Separators in Inclined Wellbore Configurations
Creators: name: Alabi, Oluwagbenga Ajagbe
Publisher: name: The University of Texas at Austin
Year: 2009
Subjects: Gas separator
Wellbore

description: This report attempts to establish the effects, if any, of wellbore inclination on the performance of down hole gas separators. Different down hole 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 thesis compares at similar operating conditions, the performance of different down hole gas separator designs installed in both a vertical and inclined wellbore configuration. Technology has made it possible to drill horizontal wells which are fast becoming ubiquitous in most oilfields. With gravity forces dominating separation in static down hole gas separators; it is certainly logical to study the effect of wellbore inclination on the separation efficiency of down hole gas separators as transport properties of multi-phase fluids are affected by gravity. With the above mentioned arguments, it becomes imperative to study down hole 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 annulus (the upper part of the annulus wall) 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 (bubble size diameters less than 0.25 in.) tend to be considerably reduced by drag while on the contrary, the larger bubble (Taylor type bubbles) have higher velocities along the upper walls of the annulus. Also, results from the down hole gas separator performance tests conducted indicate that at similar operating conditions of 800BPD/105MSCFD, a gravity driven downhole gas separator installed in a wellbore inclined at 45o would perform better (by 46%) than the same gravity driven downhole gas separator in a vertical wellbore. While at similar operating conditions of 650BPD/105MSCFD, a centrifugal force driven down hole gas separator installed in a vertical wellbore would perform comparatively with the same centrifugal force driven down hole gas separator installed in a wellbore inclined at 45o (less than 2% difference in separation efficiency).