Performance Evaluation of Wireline-Retrievable Downhole Chemical Injection System Used in HPHT Wells

Abstract

Downhole chemical injection (DHCI) systems provide precise wellbore production chemical management by pumping down chemicals via dedicated injection lines. Worldwide installation of DHCI systems has steadily increased as a large proportion of high-pressure, high-temperature (HPHT) wells are continuously drilled and completed in deepwater and ultra-deepwater fields. Ultra-low variable rate application in HPHT wells can help to control deposition of scales and enhance injection efficiency, which can lead to improved environmental protection, lower operating costs, high equipment reliability, and improved topside space usage. One of the most common failures in DHCI systems is the breakdown of check valves. This issue is significant. Stringent requirements exist for a continuous injection rate above a certain cracking pressure, preventing flow from the injection line to the wellbore at shut-in conditions and creating a zero-leak seal that prevents reverse flow from the wellbore to the injection line. To meet these requirements, a so-called "check valve" design is generally used, in which a pressure differential valve is put in series with a check valve. The pressure differential valve sets the cracking pressure and shut-in pressure of the system while the check valve prevents reverse flow from the wellbore. This paper is part of a series effort for developing chemical injection solutions for HPHT wells. Previous work summarizes development and qualification of a pressure differential valve at higher flow rates, while this paper presents qualification tests conducted to assess the performance of the pressure differential valve and check valve as a system for HPHT applications under extreme low flow rates. The qualification tests include initial material selection based on a sophisticated gas test, a liquid flow endurance test and a post inspection, followed by a second-round test. Test results indicate that a bubble-tight check valve can be qualified to 0.0016 gpm to 0.047gpm with a pressure rating greater than 10,000 psi and 350° F. The pressure differential valve and check valve can be used in different applications other than DHCI systems.