Study On The Factors Affecting The Cementing Properties Of Casing Cement Ring Interface

In the process of oil&gas well drilling operation, cementing is one of the crucial stages in which the cementation quality at the interface between casing and cement sheath will directly affect the life of the oil&gas well and the subsequent production efficiency after the cementing operation is finished. The cementation between casing and cement sheath is not only the important part of interface integrity, but also the groundwork for improving the quality of cementing operation fundamentally. In the following operation of stimulation, good cementation performance at the interface between casing and cement sheath is better for extending the life of well production by diversified measures. If the cementation performance at the interface between casing and cement sheath is not ideal and the cementing system fails, it may result in serious problems such as annulus crossflow, etc. For instance, the root cause for Incident12.23is that the cement sheath eroded by the sour gas after cementing operation resulted in bad cementation quality and then crossflow happened.At present, pay zone and interlayer are very thin due to detailed series of strata divided. In order to improve oil recovery and yield, a series of stimulation treatment are taken, such as perforation, acidizing and fracturing, high-pressure water injection and steam injection, etc. These measures as well as formation load may exert additional load to casing-cement sheath and easily cause casing damage such as casing fault and deformation, which may change the cementation performance at the interface between casing and cement sheath, and result in cracks and debonding at the interface between casing and cement sheath under the condition of excessive load. Therefore, more requirements for cementation performance at the interface between casing and cement sheath and for cementation quality at cementing interface are put forward.Based on the thorough investigation and survey on the factors affecting the performance at interface between casing and cement sheath, this paper analyzes those factors at four aspects which are casing geometrical parameters and mechanical properties, cement slurry design, engineering factors, and geological factors. On the basis of the analysis on casing damage and the mechanism of casing micro-annulus development in steam injection well, under the theory of elastic mechanics, this paper focuses on building mathematical model of casing thermal stress, mechanical model of casing-cement sheath contact interface and thermal stress model of cement sheath-formation. And through the superposition of thermal stress and compressive stress, the stress conditions on casing and cement sheath under steam injection are achieved. And then, with ANSYS simulation on practical conditions, the temperature is used as load in structural analysis, therefore, stress distribution of casing, cement sheath and formation during steam injection in practical conditions is obtained. Thus it is possible to see whether casing and cement sheath fails, and whether the cementation fails at the interface between casing and cement sheath fails due to the material is damaged. This paper also presents the calculation formulae for casing-cement sheath micro-annulus and the effective way to improve the cementation performance at the interface between casing and cement sheath, which is guidable and applicable for analyzing and solving present quality problems on cementation at the interface between casing and cement sheath.