Downhole Continuous Injection (DHCI) Systems are increasingly being installed in wells for the delivery of a range of chemicals, including application-specific formulations and multi-component chemicals. Although costly, these systems offer the advantage of controlling chemical doses, preventing interruptions to production by providing constant delivery of chemicals and can be used in place of squeeze treatments that can be costly or inappropriate if formation damage is a risk.
However, such systems are not without challenges for engineering design, operation and the effective qualification required for the chemicals before use. DHCI involves chemical injection through multi-kilometre capillary tubing, as well as injection through inline filters and one or more injection valves. Failures of continuous injection systems have been linked to a variety of causes such as corrosion, particulate formation or chemical gunking, resulting in line plugging or blockage of injection valves and filters. The work described in this paper was initiated to investigate known DHCI issues within Statoil fields and to develop laboratory tests to identify characteristics of chemical formulations that result in similar behaviour, and thus allow such formulations to be de-selected prior to use.
The paper describes a range of chemical qualification methods for DHCI systems, focusing on qualifying the chemical for use in a DHCI. Test methods have been developed which demonstrate the ways in which changes in physical properties can readily occur under downhole injection which can have a considerable detrimental impact on the integrity and effectiveness of the DHCI system. These methods have now been finalised into a set of chemical qualification protocols for Statoil.
This paper will present the basis of these test protocols and thereby intends to present best practice for chemical/system qualification for DHCI. Results from both extensive laboratory method development studies and field case histories will be included throughout the paper to illustrate the challenges faced and the qualification solutions developed.