Sensitivity analysis on tailpipe design for mitigating terrain slug in horizontal wells

Abstract

Terrain slugs are a common challenge faced in horizontal well completions, leading to significant operational difficulties and reduced well performance. The lateral wellbore can cause hydrodynamic slug problems, even severe terrain slug issues. With undulations along the lateral, gas pockets can build up within the peaks and valleys of the wellbore. These gas pockets can restrict liquid flow until bottom hole pressure builds up enough energy to push the liquid slug to the surface. The terrain slug flow not only frequently results in foaming or emulsions at the surface but also causes downhole equipment failures, especially for Electrical Submersible Pumps (ESPs). Even with the downhole separator and gas handling pump stages, the ESP system is challenged by the elongated gas pocket that results in gas locks and electrical failures. To mitigate these issues, the use of Tailpipes (TP) in combination with ESP has become a popular solution. This study aims to explore the impact of tailpipe design on the performance of ESP systems in horizontal wells. With the help of oilfield operating companies, 5 representative wells are selected from 24 horizontal ESP wells that are facing or will potentially face the slugging issue.A total of 284 simulations are conducted using the transient simulator (OLGA, 2019) to comprehensively investigate the tailpipe design methodology for well conditions that are comparable to this study, i.e., flow rate from 500 to 2000 bpd, GLR from 500 to 2000 scf/bbl, 5 ½” and 7” casing, 9000–12000 ft well depth. Different TP diameters and lengths are simulated to evaluate the TP effectiveness at different flow rates, Gas-Liquid Ratios (GLRs), and well conditions. The results of this study can provide valuable insights and recommendations to the ESP tailpipe design for a wide range of horizontal wells applications, and help to improve their overall performance and reliability.