How to detect the surface casing cement level with exisiting technology

Abstract

The increased awareness regarding wellhead fatigue has led to an ongoing joint industry project led by Det Norske Veritas (DNV). There is lack of a standardized procedure of performing a wellhead fatigue analysis. The joint industry project aims to develop a new recommended practice in how to perform a thorough wellhead fatigue analysis. A PhD written by Lorents Reinås studies the surface casing cement boundary condition and its effects on the fatigue analytical models. It proves that the cement level between the conductor and the surface casing is a sensitive input parameter in terms of fatigue calculations. This thesis will investigate how to detect this particular cement level in large sized casings, i.e. 20”, by utilizing existing technology. Common practice is to cement the surface casing all the way up to the mudline. However, the actual cement level is never measured. Pressure testing, displacement calculations and cement returns is the common documentation of a successful cement job, however none of this can provide sufficient information to document the cement height. By locating this cement level, one could provide a more accurate fatigue calculation. The conservative assumptions used in fatigue calculation today provides conservative fatigue estimates. By not knowing, one have to perform preventive measures. The reason for wanting to detect this cement level is to enable a better utilization of the wellhead. The industry provides several methods of locating top of cement, but not many are compatible with logging in large sized casings. After investigating the most common cement evaluation methods available, some of the existing methods proves to support logging in 20” surface casings.