Jet Pump Deployment Lifts Well To New Operating Heights

Operators tapping into the sizeable oil and gas resources in the U.S. Arctic—up to 23 Bbbl of recoverable oil and 3 Tcm (108 Tcf) of natural gas by some estimates—have to navigate a complex set of challenges. These include intrinsically high E&P costs related to the remoteness of the region, extremely low-temperature operating conditions, and stringent well containment and emergency response requirements mandated by government regulatory bodies.    This was the environment an operator faced in 2010 when attempting to complete an offshore Alaska well with an artificial lift option that would boost declining production rates and also restore production to some wells that were closed due to completion problems. The operator considered a number of artificial lift solutions but had to carefully weigh their suitability against factors such as the production potential of the well and anticipated installation and operating costs.    Exploring alternatives  Sucker-rod pumping, the most widely used artificial lift method in onshore operations, offers low upfront installation costs and a wealth of well-established operational knowledge. In this offshore Alaskan well, however, rod pumping would have been difficult to execute given the small deck space available on the platform. The risks of frequent and costly workovers to replace worn-out rods also proved too great.    The operator considered gas lift, but the lack of adequate and long-term volumes of gas supplied from the well would have made this a relatively short-lived solution. Gas lift also requires large and cost-intensive gas compressors at the surface that take up considerable space on the platform and add to maintenance costs.     Electric submersible pumps (ESPs) represented another option. While ESPs have been successfully deployed in offshore wells throughout the world, their low tolerance for sand and need for workovers to make repairs made them a prohibitively expensive option in this particular application.    The optimal lift solution for this well, and one that the operator had successfully used in the past, came in the form of hydraulic jet pumping.    Jet pumping basics  In a jet pump lifting system, a power fluid—typically oil or water produced from the reservoir—is pressurized and pumped down the well via a surface pump. The power fluid travels through the downhole jet pump, which is equipped with a nozzle, throat and diffuser. Power fluid flows through this nozzle to create a low-pressure jet core at the end of the nozzle. The low pressure draws reservoir fluid into the pump intake, and the jet core drags reservoir fluids into the throat or “mixing tube,” where the two streams of fluid combine and momentum transfer takes place. The mixed homogenous flow then transfers to the pump diffuser, where static pressure is increased to raise the combined fluids to the surface.    With no moving parts and a compact, durable design, jet pumps have a reputation for reliability and long runlives. Pumps are deployed without a rig simply by using pressurized fluid to set the pump downhole. Redirecting the flow of the power fluid brings the jet pump back up the wellbore for easy retrieval. Recovery of a gas-lift system or ESP typically requires a workover rig.    A common drawback cited with jet pumps is their relative energy inefficiency. It is true that jet pumps commonly run at 20% to 30% efficiency—which means that only 20% to 30% of the total power supplied goes to lifting fluids out of the well—vs. other forms of lift that operate at 30% to 50% energy efficiency. But its other operational benefits, like low installation costs, ease of retrieval and repair, high reliability, low downtime, and tolerance to sand and gas production, combine to make jet pumps a dependable and economical solution for offshore wells. These benefits also enable hydraulic jet pumps to work where other artificial lift systems cannot.