AP Sensing Monitors Underground Gas Storage in China
In order to provide efficient and safe gas storage operations, continuous, real-time well monitoring systems are needed during both the injection and withdrawl phases. As a part of it's gas storage monitoring infrastructure, the China National Petroleum Corporation (CNPC) required continuous downhole temperature and pressure sensing for its underground gas storage (UGS) project in Daqing Oil in order to ensure well integrity and evaluation.
In addition to monitoring downhole parameters, the customer also faced the challenge of selecting a technology that functions in the harsh conditions of the installation site. The systems installed onsite had to be compliant with the ATEX Zone 1 requirements (meaning normal duties are accompanied by the occasional presence of explosive gases or combustible dust), and also withstand cold winter temperatures down to -30 °C.
Conventionally, a well integrity assessment is carried out by special tools and equipment, these tools typically do not allow continuous and simultaneous measurements of the entire well length. One of the possible alternatives to continuously monitor downhole parameters during injection and withdrawal is fiber optic sensing (FOS) technology.
Within the current UGS project, CNPC decided to deploy Distributed Temperature Sensing (DTS) technology in combination with Fiber Bragg Grating (FBG) pressure sensors along three horizontal wells at two of the oilfield’s well sites in order to record downhole conditions, assess casing integrity and identify crossflow behind the casing.
AP Sensing, alongside local partner Anton Oilfield Services Ltd., provided CNPC with FOS technology that allows continuous temperature sensing during the well operations at Daqing Oilfield. Two AP Sensing interrogator units (DTS N4386B) with ATEX housing were permanently installed at two well sites and connected to fiber optic cable running on the production tubing. The FOS cable was permanently installed down to the position of the production packer. Additionally, AP Sensing’s SmartVision software was utilized for real-time data aquisition and analysis, with the pressure gauge connected to SmartVision via Modbus TCP.