Plug and Abandonment of a Deep High-Pressure and High-Temperature Gulf of Mexico Well Using Coiled Tubing: A Case History

Abstract

As a result of production having drained once-prolific reservoirs, Gulf of Mexico (GOM) operators are dealing with an increase in well abandonment activity spurred by environmental concerns and government regulatory agencies. Many well plugging and abandonment (P&A) activities are performed using coiled tubing (CT), which eliminates the need for a rig. Cement placement is an essential part of every P&A operation. Deep wells (exceeding 20,000-ft measured depth) with high bottomhole static temperature (BHST) (greater than 400°F) and an aggressive H2S/CO2 environment add additional challenges to the cement slurry design. Furthermore, operations need to be executed safely and within the limits of CT equipment. An operator needed to P&A a well in the Mobile Bay block of the GOM. No previous high-pressure, high-temperature cementing operations through CT at BHSTs greater than 400 °F in the Gulf had been performed. One of the key challenges for this CT intervention was designing a cement system for 425 °F BHST to be pumped through a 23,620-ft, 1-1/2-in. OD CT string. Concentrations of 75 ppm H2S and 4% CO2 increased the complexity of the operation even further. After several unsuccessful attempts with wireline to dump-bail cement, the operator successfully used CT to plug the bottom zone of this deep, high-pressure well with cement.