Field Test Results for a Subsea Wireless Annulus Monitoring System

Abstract

The objective of this paper is to present the field test results of a subsea casing annulus monitoring system utilizing wireless through-wall communication technology which recorded and transmitted pressure and temperature data from a casing annulus in real-time during the drilling, logging, and capping phases of a subsea well. The annulus monitoring system used off-the-shelf sensors to acquire pressure and temperature data in the casing annulus. The data was communicated from inside the casing annulus to the outside of the subsea wellhead system using a novel wireless telemetry technique through solid casing layers instead of traditional bulkhead connected equipment to avoid penetrations to the high pressure housing. The sensor module was attached to a 13-3/8" casing joint below the casing hanger and was configured to fit into the annular space between the 13-3/8" casing string and a 20" casing string. Additional telemetry equipment was adapted to the outside of the low pressure wellhead housing and a 30" conductor casing string which received and processed the transmitted data. Once installed, the monitoring system continuously transmitted temperature and pressure data throughout the rest of the drilling program until the well was plugged and abandoned. The annulus data revealed how high the annulus pressure increased due to thermal effects while drilling and circulating fluids in the wellbore bottoms-up. Upon completion, the system confirmed that the trapped annulus pressure below the 13-3/8" casing hanger annulus seal assembly was low enough that the wellhead and casing could be safely cut and retrieved. The field test confirmed that the monitoring system is suitable to survive drilling operations and communicate data from the wellhead casing annulus to the end user in real-time. This marks a first for a drilling-centric wirelessly transmitted annulus monitoring product that takes the guesswork out of annulus pressure well-control or remediation concerns. It allowed the drilling group to see live data on the fluid pressure and temperature in the annulus of a wellhead system without any type of penetration while drilling the remaining critical sections of the well and did not require any modification to existing subsea wellhead components or operating procedures.