Blockfall – Monitoring and Block-Fall Detection System

Example of tubings damaged by salt-block falls (Courtesy Geosel)

Salt falls are relatively frequent in salt caverns and may sometime damage inner strings. A broken string can usually be detected if the depth of the break is located above the product-brine interface; in this cased the brine string is rapidly filled with product, increasing the pressure on the brine string. However, in many cases, these block falls remain unobserved until they are revealed by a sonar survey or a gamma ray, performed several months or years after the incident, that detect a cavern-shape change or a bottom heave.

Blockfall system principal scheme
Blockfall system principal scheme

Non-intrusive automated solution

Blockfall system manifold installed on the wellhead
Blockfall manifold installed on the wellhead (Courtesy Geosel)

Brouard Consulting developed a monitoring and data-acquisition system named Blockfall to automatically detect block-fall events in underground storage. The proposed solution is not intrusive and based on the measurement of wellhead-pressure oscillation. Sensors of the blockfall unit are located at the wellhead in hazardous area, and connected to the data-acquisition assembly (DAQ) including intrinsically safe (IC) barriers, electronic board with integrated circuit and memory and 3G/4G router. ATEX certifiable version of the detection system is available.

The system manifold includes two pressure sensors installed at the wellhead on tubing and dedicated to measure low and high frequency brine-pressure oscillations. The system may also include also additional manifold with a low frequency-pressure sensor to be setup on the annulus. This pressure sensor is recommended in order to measure product pressure variations which are taken into account in analysis of recorded data and further processing, and allows a better understanding of the actual nature of brine pressure variations improving the quality of block-fall event detection.

Blockfall DAQ installed in safe area
Blockfall DAQ installed in the non-hazardous area (Courtesy Geosel)

Electronic acquisition assembly (DAQ) is intended to be installed in the non-hazardous area, several dozen of meters away from the wellhead (limited by sensors cable lengths and can be extended with additional cabling). In order to conform to ATEX requirements, it includes corresponding IC barriers between signal amplifiers and output connectors for pressure sensors, interconnecting board, electronic board with configurable logic integrated circuit and memory storage, mobile network router for recorded data real-time transfer to remote server for real-time data treatment and numerical analysis.

Electronic acquisition assembly includes 3G/4G mobile network router which allows to establish and to keep secured and encrypted channel with remote server in order to transfer the data acquired by the system. Event data is transferred immediately after detection of the event and finishing data recording; static data is transferred on a regular base (once per hour for instance). The Blockfall system can be considered as a connected object in the sense that it can be monitored remotely and data acquisition parameters can be easily adjusted.