Study Investigates Highly Deviated Shroud-Type Downhole Separators
Authors: Carpenter Chris 
Published: January 2022

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201127, “An Experimental Investigation of Highly Deviated Shroud-Type Downhole Separators,” by Jorge Lopez, Eduardo Pereyra, SPE, and Cem Sarica, SPE, The University of Tulsa, prepared for the 2020 SPE Virtual Artificial Lift Conference and Exhibition—Americas, 10–12 November. The paper has not been peer reviewed.
An experimental study of a shroud-type downhole separator for a pumped horizontal or deviated well is presented in this study. The separator is located at high deviation angles (i.e., 45° to 80° from vertical). The effects of the upstream gas and liquid flow rates are evaluated in the performance of the downhole separator. The findings complement previous studies on shroud-type downhole separators and demonstrate the operational capability of downhole separators under a range of conditions.

Introduction
Even though free gas and gas interference at the pump intake is a well-known problem, a limited understanding exists of the mechanisms that result in free gas in the pump. The lack of knowledge may lead to installation of ineffective downhole separator pump assemblies that, in some cases, may be detrimental to pumping-system performance.
Among downhole-separator types, gravity-driven separators take advantage of the density difference between the gas and liquid to achieve separation. The shroud-type separator is an uncomplicated yet robust design and the most well-known and applied in the field.
Current horizontal wells present challenging operational problems to down-hole separators and artificial-lift systems. The correct design of the downhole separator must consider proper handling of new challenges. A limited number of studies exist on the current challenges of downhole separators. A few of these studies considered the flow upstream of the separator as a variable, a limited amount studied deviated cases, and none focused on high deviation angles.

Experimental Setup
The complete paper details the experimental facility and instrumentation. The Tulsa University Horizontal Wells Artificial Lift Projects’ low-pressure outdoor downhole separator facility was used in this study.
Four gas and eight liquid flow rates were used in the experimental matrix. The deviations tested were from 45° to 80°. Some of the tests at higher liquid flow rates were not completed because, as the deviation increases, the higher liquid flow rate causes the casing to overflow, making completion of these experiments impossible. The considered gas and liquid flow rates allow the analysis of gas/liquid ratios varying from 5 to 1,800 scf/bbl.

Experimental Results
The authors found that separation efficiency depends strongly on the liquid flow rate and deviation angle. At 45° and 60°, the separator seemed to perform efficiently for all tested conditions. At higher liquid flow rates, the separation efficiency showed a slight decrease, but, because of facility limitations, not enough evidence existed to confirm the tendency. Therefore, an additional two tests at 45° were performed to validate this trend. The tested conditions were 1,360 B/D with 7 Mscf/D and 11.28 Mscf/D. The two additional tests at 45° confirmed that efficiency decreases as liquid production increases. The authors observed two regions of operations of the separator for vertical cases and different deviation angles (the highest deviation tested was 45°). For their conditions, the separator performed in a high-efficiency region (efficiency between 80 and 100%) for low liquid flow rates. As the liquid production increased, the separator efficiency decreased. The authors denote this area of operation as a disrupted-efficiency region. The authors did not observe the separator to fail at 45° despite testing the separator at higher liquid flow rates.