The deterministic analysis of cement sheath behavior under varying wellbore loads aids design and deployment of cement. Assurance of the ability of cement to achieve and retain zonal isolation is safety critical requirement for the successful drilling of a well and subsequent production operation. Exploitation of hydrocarbon resources in more challenging environments such as high pressure and high temperature (HPHT) intervals continues to push the frontier of cement design for zonal isolation purpose.
Severe temperature in HPHT environments has been known to result in degradation of cement over time. In addition to this risk of thermal degradation, the cement sheath is also subjected to varying pressure loads during well construction and production operations. The implication of the pressure load cycles is that mechanical properties of conventional cement recipe may not able to guarantee long term zonal isolation especially in HPHT wells with the high magnitude of pressure load variations. Proper understanding of the scale of the varying pressure loads in the wellbore and the corresponding stresses generated in the three components of the wellbore system (i.e. casing, cement and formation) is pivotal to designing a suit for purpose cement recipe that will eliminate loss of zonal isolation during the entire life span of a well.
Finite element analyses tools have been successfully used to gain knowledge of material behavior when subjected to varying stresses. In this project, investigation of the cement sheath behavior using finite element analysis was carried out to determine the mechanical properties of cement required to ensure retention of zonal isolation under continuously changing wellbore pressure loads during drilling and production phases of typical HPHT well in deltaic depositional environment. The analysis also aided drilling operation optimization in the ongoing HPHT campaign by Shell Petroleum Development Company in the Niger Delta.