Safe and Economic Gas Wells through Cement Design for Life of the Well

Abstract

Abstract Natural gas is one of the cleaner sources of energy, and our challenge is to produce it safely and economically. The extreme operating conditions that occur in gas-storage and gas-producing wells could cause the cement sheath to fail, resulting in fluid migration through the annulus. Designing cement sheaths that can withstand the stresses induced by the various operations and maintain integrity during the life of the well will help minimize the risk of cement failure. A design procedure has been developed to estimate the risk of cement failure as a function of cement sheath and formation properties and well-stress loading. A few examples of the loading are cement hydration, pressure testing, gas injection, and gas production. The design procedure simulates the sequence of events from drilling to cement hydration, hydraulic fracturing, injection, production, etc. Cement failure modes simulated are de-bonding, cracking, and plastic deformation. An appropriate nonlinear material model, including cracking and plasticity, is used in the analysis. The sustained casing pressure observed on a number of wells after they have been put on production emphasizes the need to design a cement sheath that will maintain integrity during the life of the well. Field cases and applications are discussed. From the process discussed in this paper, one can estimate the risk of failure of different cement systems and select the system that can help minimize the overall cost. The process should improve the economics of constructing and producing gas and oil wells and also improve the safety due to the reduced risk of zonal isolation failure.