Development of a novel Silicone Rubber/Cement Plugging Agent for Cost Effective Thru' Tubing Well Abandonment

Abstract

Abstract Large scale well abandonment campaigns will soon become a major cost issue for most Operators. Traditional well abandonment comprises the removal of the production tubing followed by well plugging by mechanical plugs (as primary seal), backed up by (potentially non sealing) cement plugs. The classical abandonment operation is very costly, especially in an offshore environment, since it requires the utilization of a workover or drilling rig. Significant savings could be achieved if wells could be abandoned by a Coiled Tubing operation, during which the production tubing could be left in- situ. After long negotiations, a major Dutch Oil and Gas Operator (NAM, Nederlandse Aardolie Maatschappij), convinced the legislative body of the Dutch Mining Department (SodM) that non workover rig assisted abandonment operations could be equally reliable as conventional abandonment methods provided certain operational precautions were taken. This entailed the rigorous cleaning of the production tubing and production liner by solvents and hot surfactant flushes and the utilization of (rotating) jet nozzles on CTU prior to setting of the sealing plugs. Furthermore, in critical (gas prone) wells special attention had to be devoted to the plugging material itself, since it now had to fulfill the duty of the mechanical seal, as well. Inherently, it had to display much-improved sealing characteristics (gas tightness, resilience, bonding) compared to conventional cement formulations. Novel Silicone Rubber/Portland Cement plugging materials have been developed for this application at Shell International Exploration and Production, Research and Technical Services (SIEP-RTS). This paper describes the laboratory development and screening (Sealing Ability, Mechanical Characteristics, Setting Kinetics, and Adhesion) of various candidate sealants and the optimization of these characteristics for a large scale well abandonment campaign. Trial well abandonment's using the new sealing agent(s) in NAM's Schoonebeek and Ijsselmonde/Ridderkerk Fields are discussed. P. 483