This paper presents the development and installation of a modified stimulation system, based on an existing system, field-proven for more competent formations. The system simultaneously deploys 0.8 cm diameter, 12 m long needles from the main bore by jetting into the formation. Modifications have been made to facilitate production from a soft chalk formation, which is prone to plastic deformation and liquefaction under the stresses of production. The original design of single titanium needles has been changed to a combination of an aluminum outer needle for the deployment phase, and a titanium slotted inner needle for the production phase. The aluminum needle is dissolved by pumping hydrochloric acid, enabling production through the inner needle.
The objective of the system is to reduce cost by simplifying the stimulation to a single pumping job, while achieving production enhancement for wells drilled in pay zones of less than 25-meter thickness. The objective of the field trial was to confirm the system could be deployed offshore, and to evaluate its production performance.
A series of functional tests to ensure pressure integrity of the modified design were performed in the lab. Promising lab test results were extended to functional yard trials, to verify the chance of success at downhole-like conditions. The running procedure was modified to honor well control requirements, while optimizing the likelihood of successful deployment of the system.
The paper presents the results of the qualification testing. The experiences from the installation and jetting are discussed in detail. Interpreted pumping pressure charts are presented for discussion. The productivity results are presented and compared to conventionally stimulated Valhall producer wells.
The installation of the jetted needles system with solids-control slotted laterals is the first of its kind in the world. The results of lab and yard testing presents a solution for achieving solids control in laterals jetted out from the main bore. Analysis of the deployment data provides grounds for future optimization of the system. The productivity results are used to evaluate whether the system is ready for full scale deployment across an entire horizontal well.