Casing Strength Theoretical And Experimental Study Of Thermal Recovery Steam Injection Wells

Thermal recovery method, which can be subdivided into steam flooding, steam stimulation, in-situ combustion and so on, is commonly adopted for heavy oil production. When adopting steam flooding or steam stimulation method, the issue of oil well casing damage has been a serious impact on many enterprises' heavy oil production and economic efficiency. Based on actual conditions of heavy oil thermal recovery wells, it is researched in this paper how to reduce well casing's stress to prevent or lighten its damage. Main research work is summarized as follows:(1)The calculation methods of well casing fluid parameters are researched to obtain fluid parameters and their variation laws, and further well casing temperature, well casing pressure and cement hoop temperature are obtained to study well casing's strength. Fluid thermo-physical properties in engineering thermal physics and the theory of wet steam two-phase flow are effectively integrated to creatively solve the problem of continuous calculation of fluid parameters. The accuracy and speed of calculation are both increased.(2)According to working conditions of the thermal recovery wells, the mechanical model of heavy oil thermal recovery well casing is established. Calculation methods of various internal forces and external forces are researched, especially thermal stress and external squeeze pressure. The interaction between the casing and formation is taken full account of in the mechanical model. External squeezing forces of the casing were separately calculated under the conditions of creep formation, ideal rigid formation and flexibility formation. The information of various influence factors resulting in the dangerous well casing sections' damage are obtained by contrast. The research of interaction between the casing and formation are perfected by this study. It is concluded that thermal stress is the most important reason causing thermal recovery well casing's damage, and so how to reduce the thermal stress should be the emphasis of thermal recovery well casing damage's research. The creep of formation should be the most important reason resulting in well casing's damage for ordinary oil wells. The creep properties of the formation can not be changed. Therefore, the production process, the casing material and the quality of the casing should be researched to prevent ordinary oil well casing's damage. In addition, the improvement of thermal recovery well casing's stress condition resulting from pre-stress is proved by the research on well casing's axial stress. But the magnitude and direction of pre-stress should be distinguished because of different oil wells.(3)A steam flooding experiment is carried out in a test well casing in Liaohe oil field to verify calculation methods and conclusions proposed in this paper. Calculation methods and conclusions proposed this paper are proved to be correct.(4)The vacuum-insulated casing with excellent insulation properties can simplify the steam stimulation process, so as long as the appropriate increase in the intensity of vacuum insulated casing technology will have broad prospects for development. Based on calculation methods proposed in this paper, the insulation performance and strength of the testing vacuum insulated casing in Liaohe oil field are evaluated. The insulation performance of vacuum insulated casing is better than the current well casing. The strength residue of the internal tube of vacuum insulated casing is small, especially when high-pressure steam is injected, but the strength residue of the external tube is relatively great. The vacuum-insulated casing with excellent insulation properties can simplify the steam stimulation process. So as long as the internal tube's strength is improved, vacuum insulated casing will have broad prospects for development. The evaluation of insulation casing is firstly carried out in the world.It should be pointed out that the research conclusion proposed in this paper is based on the study of a thermal recovery well with a depth of 1000 meters and has its applicability. The magnitude of various forces acting on well casing should vary with the increase of well's depth.