Experimental, analytical, and numerical investigations of gas leakage through annular cement

Abstract

Cementing operations present many difficulties worldwide attributable to shallow flows. Cement sheath integrity and durability play key roles in the oil and gas industry, particularly during the drilling and completion stages. Failure of cement to seal the annulus can lead to serious dilemmas that may result in loss of well integrity. The use of liners instead of full casings is one of the most common practices for drilling offshore wells. In field applications, the length of a casing–liner overlap is selected randomly. In this research, cement sealability is investigated experimentally. A novel wellbore model was designed and fabricated to serve the objective of this study. The results from this experimental study revealed that cement without anti-gas migration additives doesn’t have the ability to seal the annular space nor to prevent gas migration. This research also investigated the critical length of the casing–liner overlap and the current casing pressure test duration by modeling gas leakage through the cement placed within the overlap using experimental, analytical, and numerical approaches. Leakage scenarios were developed to mimic gas migration within the cement in the casing–liner overlap. The results showed that the current casing pressure test duration of 30 minutes may not be adequate to verify the integrity of the cement within the overlap. In addition, the results suggest that the length of the casing–liner overlap should not be less than 300 ft to maintain the integrity of the well in the case of gas influx.