Challenges, Opportunities Abound for Artificial Lift

Abstract

Artificial Lift Artificial lift systems are among the most widely used production technologies in global oil and gas operations. Wells that cannot produce liquids to surface under their own pressure require lift technologies to enable production. Some liquid wells need lift assistance from the beginning, and almost all require it sooner or later. Rod pump, electric submersible pump (ESP), and gas lift technologies are the most common methods of providing artificial lift to these wells. Gas wells also require artificial lift methods in most cases to pump liquids to the surface, chiefly water but also oil, so that free gas can flow through the wellbore without impediment. There is no global repository of artificial lift statistics; however, industry observers estimate that 90% to 95% of the world’s producing wells currently use artificial lift, said Bill Lane, vice president of artificial lift systems emerging technologies at Weatherford. “It is trending more toward 95% than 90%, and probably 100% of producing wells would use artificial lift at some point in their lives, except for wells shut in prematurely because of economic factors.” With the ubiquity of artificial lift, “there are so many engineering opportunities in this field,” said Shauna Noonan, wells technology supervisor at ConocoPhillips and SPE technical director for production and operations. Those who embrace those opportunities will face abundant challenges, many of them related to the integration of artificial lift into unconventional horizontal wellbore designs and frontier subsea projects in deep water. Horizontal Well Challenges “Today, our technologies to sweep liquids through the lateral sections of horizontal wells are very limited,” Lane said. “To understand the challenge, note that a 5,000-ft lateral with a cased 4-in. inside diameter has the same slenderness ratio as a ¼-in. drinking straw as long as a football field. Along that straw are numerous undulations, each of which results in a sump in which liquids collect. Wherever this phenomenon occurs, the pressure beyond each sump must increase until the collected liquids are blown further toward the heel of the producing zone. This phenomenon is particularly evident in gassy liquid wells, less so in primary liquid producers.” In a perfect world for artificial lift, “the obvious solution would be toe-up straight lateral sections free from undulations,” Lane said. “But that is easier said than done.” Making wellbores straighter would help from a pumping standpoint. However, other factors usually take precedence. Bores must target the reservoir’s “sweet spots” with the most total organic content. Petrology and geophysics determine where stimulation can be most effective. Well pad designs and lease boundaries can also constrain well placement and design. Mechanical pumps have been deployed into lateral wellbore sections with limited success, experiencing higher than normal failure rates when operating on their sides and encountering problems in keeping gas separate from liquids—a necessity for efficient pump operation. Pumps with single intakes can only pull liquids from one low spot. Thus, locating a pump along a lateral bore with multiple sumps becomes a matter of compromise. For the most part, mechanical pumps are landed in the vertical or near vertical sections of horizontal wells, and are typically not landed beyond 60° deviation.