Safe distance between debrining tubing inlet and sediment in a gas storage salt cavern

Abstract

The proper determination of the distance between the debrining inner tubing (DIT) inlet and sediment during the debrining of an underground gas storage (UGS) salt cavern both can increase the expelled brine volume and decrease the risk of blocking the DIT caused either by brine crystallization or by sucking in of large chunks of insoluble solids. Based on the fluid distribution and the force applied to the insoluble particles around the DIT inlet, a mathematical model is built to describe the movement of insoluble particles in a cavern. The equations are deduced for the forces applied to the particles, the critical fluid rate of the brine, and the critical diameter of particles being sucked in. An equation is given to determine the critical distance between DIT inlet and sediment. Based on the diameter distribution of the insoluble particles, the critical distance is proposed between DIT inlet and sediment under different DIT sizes and debrining rates. Results show that increasing the DIT size can decrease the distance between DIT inlet and sediment greatly, as well as the risk of sucking in insoluble particles. Increasing the diameter of the particles permitted to be sucked in has a slight effect on increasing the debrining volume but notably increases the risk of blocking the DIT. Not permitting insoluble particles being sucked in is proposed as the criterion to determine the distance between the DIT inlet and sediment for an actual debrining. Numerical simulation and field testing results show that the proposed mathematical model has a high accuracy and can effectively guide the field debrining operation.