Development and First Field Pilot of Gas-Assisted Liquid Lift Oscillating Pressure (GALLOP): A Novel Artificial Lift Method for Unloading Mature Horizontal Wells from the Lateral

Abstract

Late-life production problems in horizontal wells pose an inevitable challenge for the industry, and will intensify over the coming years. Liquid loading in vertical wells was a much lower priority prior to the 1990s, when circumstances and technology aligned to make it worthwhile to understand the difference between a loaded well and a plugging candidate. Over the next decade, thousands of horizontal wells will need to be plugged or produced, with limited production options. Currently, very few viable options exist for producing the volumes accumulated beyond the heel after reservoir pressure declines to the point where it can no longer lift liquids to typical conventional artificial lift (AL) set depths. Gas Assisted Liquid Lift using Oscillating Pressure (GALLOP) was specifically designed to tackle this impending problem. As previously profitable wells accumulate liquids in and beyond their build sections that would otherwise choke off and restrict flow, excess liquids can, instead, be lifted. Using two flow strings, a single check valve, and intermittent lift gas injection, GALLOP can produce moderate liquid volumes from anywhere along the horizontal section, from reservoir pressures that have fallen almost as low as surface facility backpressures. Once installed, the system is similar in complexity to intermittent single-point gas lift. The overall development of GALLOP took advantage of many technologies. Starting from a simple idea, valve mandrel prototypes were made of wood and plexiglass. A garden hose and air compressor served as an inexpensive flow loop for proof of concept and formed the basis of patent filings. Building on that foundation, large-scale instrumented laboratory testing further refined the design criteria. Transient and time-slice mathematical modeling were used to calibrate additional design parameters. The most important unknowns were then field tested in isolation and models were refined to match these observations. In June 2022, the first installation of this new artificial lift method was installed with a high-resolution control system and prototype downhole equipment that had been designed through rigorous engineering and testing workflows. The pilot well had been experiencing severe loading below the production tubing for the preceding two years, so GALLOP was its last resort. Since installation, nearly four years and counting, the well has produced consistently at the capacity of the reservoir, even weathering and recovering from offset frac communication. In addition to results and reliability far exceeding expectations, this first installation provides many lessons. With almost four years of field performance demonstrating the method's suitability and reliability on a difficult, low-rate well, future GALLOP installations will target higher production rates and broader operating objectives.