Qualification of Downhole Valves Used in Continuous Injection Systems

Abstract

Downhole Continuous Chemical Injection (DCI) systems, including both Downhole Continuous Injection systems (DHCI) and Gas Lift Chemical injection (GLI) are increasingly being installed in new wells for the application of a range of chemicals. These systems have one or more check valves at the point of injection to control the chemical flow into the wellbore and prevent wellbore fluids from entering the injection lines. In-line filters are included to remove particulates that may prevent the check valves from sealing. The performance of the injection valves is key to the success of continual injection systems. Valve failure would lead to uncontrolled injection into the wellbore, forming low pressure gas pockets within the injection lines which can lead to changes in the physical properties of the chemical causing issues such as corrosion or gunking. In addition, if the hydrostatic pressure within the injection line drops below wellbore pressure, then wellbore fluids can start to enter the capillary tubing. Currently, the qualification of valves is conducted using either fresh water or nitrogen. In conjunction with considerable developments made in qualification of chemicals for DHCI and GLI which were introduced in previous papers1, 2, work has been undertaken to improve the qualification of the injection system itself. This means that in addition to showing compatibility and good performance, the chemical must be suitable for the application system, and the equipment suitable for the chemical selected. Results demonstrate how different valve/chemical combinations can perform well during fluid injection but fail to hold pressure within the injection line when the flow is stopped. The paper will present results from an extensive series of valve tests conducted in a newly designed and commissioned rig capable of operating at full reservoir temperatures (up to 200 °C) and elevated line pressures (up to 5,000 psi). The results from this work are expected to form the basis of a new range of system qualification protocols to be proposed for Statoil DHCI systems.