Cement Placement With Tubing Left in Hole During Plug-and-Abandonment Operations

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper IADC/SPE 178840, “Cement Placement With Tubing Left in Hole During Plug-and-Abandonment Operations,” by Bjarne Aas, Jostein Sørbø, and Sigmund Stokka, SPE, IRIS/DrillWell; Arild Saasen, SPE, Det Norske Oljeselskap; Rune Godøy, SPE, Statoil; øyvind Lunde, ConocoPhillips; and Torbjørn Vrålstad, SPE, SINTEF Petroleum Research/DrillWell, prepared for the 2016 IADC/SPE Drilling Conference and Exhibition, Fort Worth, Texas, USA, 1–3 March. The paper has not been peer reviewed. One way to reduce costs during plugging and abandonment is to leave most of the production tubing in the well. A major concern with such an approach, however, is whether the cement will displace the original fluid improperly because of lack of tubing centralization and possible unfavorable flow dynamics in the annulus. This paper presents full-scale tests that show it is possible to obtain good cement placement when the tubing is left in the hole. Introduction The fundamental goal of plugging and abandonment is to restore caprock functionality to maintain well integrity permanently. Normally, these operations are conducted by removing completion equipment and placing a series of cement plugs. One way to reduce costs is to leave most of the production tubing in the well, which would save significant rig time. A major concern with such an approach, however, is whether the cement has displaced the original fluid properly in the annulus outside the tubing where the plug is planned. Poor cement quality there may result from designing the original cement job with insufficient cement slurry, from a lack of tubing centralization, or from unfavorable flow dynamics in the annulus. Regardless of the equipment used for the operation, the most economical way is to leave as much of the tubing as possible in the well. If tubing can be left in hole in a way that satisfies long-term abandonment criteria, a significant restriction to cost-efficient plugging and abandonment is overcome. This paper presents full-scale tests that confirm the possibility of obtaining good cement placement when the tubing is left in the hole. This is the case both with and without control lines attached to the tubing. Experimental Equipment and Methods Full-scale tests, with several assemblies of 7-in. tubing cemented in 9 5/8-in. casing, were performed to determine the sealing ability of annulus cement when tubing is left in hole. Tests were performed with both conventional cement and expandable cement, and with and without control lines present. The quality of the cement placement was determined 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.