Soft Sensor Fusion Model for Multi-Annuli Temperature and Pressure Monitoring in Oil and Gas Wells

Summary Subsea wellhead design has always rendered the B annulus on subsea wells inaccessible for monitoring. One of the leading causes of sustained casing pressure especially inside the B-annulus during production is annular pressure buildup as a result of thermal expansion of the annulus fluid. Without the ability to bleed this pressure off, casing failure ensues in the form of collapsed production casing or burst intermediate casing. Such failures lead to catastrophic well integrity loss consequences documented in several literature. In this work we introduce a model for monitoring the temperature in the A and B annulus without installing sensors in either annulus. This monitoring consequently gives an indication of the pressure change due to thermal expansion in the annuli and allows safer production and increased life of the well. Real-time temperature measurements are taken from a sensor installed in the production tubing, a soft sensor model that uses heat transfer thermodynamics and sensor fusion data analytics then uses this tubing temperature measurement to reconstruct the temperature and pressure in the A and B annulus. The results show that the model correctly predicts the temperature and pressure in both the A-annulus and the B-annulus. For subsea wells, this dismisses the need for a physical sensor in the B-annulus as suggested in some literature. Improved well integrity, reduced sensor installation and intervention costs and longer well life are the benefits of the system.