Cement Placement with Tubing Left in Hole during Plug and Abandonment Operations

Abstract

Well abandonment operations can be very time-consuming and costly, and thousands of wells need to be permanently plugged and abandoned offshore Norway during the upcoming years. One possible way to reduce costs during P&A operations is to leave most of the production tubing in the well, as this would save significant rig time. A major concern with such an approach is, however, whether the cement will properly displace the original fluid, due to lack of tubing centralization and possible unfavorable flow dynamics in the annulus. In this paper, we demonstrate by full-scale experimental tests that it is possible to obtain good cement placement when the tubing is left in the hole, with and without control lines. Full-scale tests have been performed with both conventional and expandable cement to determine the sealing ability of annulus cement when tubing is left in hole. The quality of the cement placement was evaluated by pressure tests with water; where leakage rates and pressure drops over the test sections were recorded, and by visual inspection after cutting the test assemblies at different places. It is seen from the experiments that cement is well placed in the annulus when tubing is left in hole, but some microannuli are detected.

General Principles of Well Barriers

“…Water was pumped at 725 psi to the A-annulus and 1450 psi to inside of the tubing. Aas et al [32] observed no leakage through the established barrier.…”

“…Figure 2.29 shows . 2.30 Full-scale test set-up used for investigating the sealing ability of cement plug when tubing and control lines are left in hole [32] two different types of control lines; a control line equipped with four small-diameter hydraulic lines, and a control line equipped with two small-diameter hydraulic lines and one conductor line (electric line to the right). Two major concerns exist regarding control lines that persuade engineers to plan for control line retrieval; flow potential of hydraulic line(s) and quality of the bonding between plugging material and surface of the control line.…”

“…There are different opinions regarding the risk of leakage or well integrity issues concerning control lines as part of the well barrier envelope. Aas et al [32] performed a full-scale test on the sealability of annulus cement when tubing is left in hole with control lines. In this study, a 7-in.…”

“…If the production tubing is in a good condition, it can be used as work string for cementing. However, mechanical strength of a tubing for being used as work string should be analyzed [32].…”

Analytical and Experimental Investigation of the Critical Length in Casing–Liner Overlap

“…Matching the field data with the model resulted in a cement permeability value that was close to the one obtained from the numerical model. Aas et al [39] conducted a series of full-scale experiments to examine the cement sealability using conventional and expandable cements. The authors evaluated the sealability of the cement by pressurizing the set cement with water.…”