Oil And Gas Well Cementing Ring Mechanics Study

The primary cementing is in order to islate the annulus between the casing and wellbore and prevent the fluid migration during drilling and oil producing. It also can form the cement sheath to sustain and protect casing. During the process of drilling and oil producing, many kinds of loads are applied to the cement sheath, such as internal burst pressure, confine pressure of rock and temperature stress. These loads usually do harm to the isolation of cement sheath. Based on the preceding investigation and aimed at the microannulu problem and integrity of cement sheath, a series of mechanic model of the cement sheath were designed to research the bond interface and integrity of cement sheath.Firstly the statics mechanic model of the casing-cement-formation is designed for the uniform cement sheath in this paper. The analysis and computation of the bond interface stress of cement sheath dued to the change of internal burst pressure have been done. The critical condition of microannulu in the bond interface is described based on the test of the radial bond strength between the cement and steel. The influence of many factors such as wellbore enlargement, the elastic parameters, wall thickness of the casing are analysed. The critical condition of cement sheath breakage is discussed.Subsequently, the mechanics model of the cement sheath for the uncentering casing is analysed in this paper. At this foundation, the mechanics coupling model of the casing-cement-formation system is designed. The analysis and computation of the mechanics problem of cement sheath dued to the change of internal burst pressure is done by using the FEM software. The object is to research whether the microannulu can be formed and the critical conditions of microannulu. The cement sheath breakage are also discussed in this paper.Next, the mechanics model of the cement sheath for the ellipse wellbore is also designed and its mechanics problem is analysed in this paper. The influence is analysed of ellipticity on the distribution of cement sheath stress. The influence of the elastical parameters on the cement stress in the ellipse wellbore is also researched. The critical conditions of microannulu and cement sheath breakage are also discussed for the cement sheath in the ellipse wellbore.