| Deep water oil and gas exploration and development has become an important new field for increasing oil and gas storage and production and strategic replacement of oil and gas resources in the world.It is also the development trend and new bright spot of oil and gas exploration and development.China's South China Sea is a vast deep water area,with an estimated oil and gas equivalent of about 30 billion tons,known as the second "Persian Gulf".It has become an inevitable trend for the development of domestic oil and gas industry to march into deep water and develop deep water oil and gas resources in China.However,the offshore deep-water drilling operation is faced with various difficulties and challenges.Deep-water long-distance drilling results in both high-temperature operation difficulties and deep-water operation difficulties.The superposition of the upper ultra-low temperature and the lower high temperature caused by the coupling of the two makes the performance of drilling fluid and formation rock extremely unstable,which further narrows the safe density window of drilling fluid and makes it easy to build The borehole wall is unstable,which leads to complex drilling accidents such as sticking,mud bag,drilling tool damage,and even oil well abandonment.Therefore,it is of great significance to accurately predict the safe density window of deep well drilling fluid for accident prevention of deep-water drilling operation.According to the characteristics of deep-water drilling,this paper takes block L25 in Qiongdongnan Basin of South China Sea as the background of the project,and mainly carries out the following research:(1)According to the conservation principle of heat convection and heat conduction energy in heat transfer,the temperature field control equation of the whole well is established,and the temperature field of the whole well is solved by the finite difference solution method.On this basis,the temperature field distribution characteristics of the whole well under the drilling and circulation conditions are analyzed,and the temperature distribution characteristics with and without casing are compared to determine the subsequent thermal stress analysis ideas.(see Chapter II)(2)According to the hole stress concentration analysis method in elastic mechanics,taking the temperature analysis result as the boundary condition,the stress distribution law around the well under the influence of temperature change is analyzed by two methods of theory and numerical simulation,and a set of dynamic change sequence of stress around the well is formed by combining the programming result.(see Chapter 3)(3)According to the existing fracture pressure analysis methods,this paper summarizes and puts forward a reasonable prediction model of formation fracture pressure,introduces the stress distribution around the well under the influence of temperature into the prediction model of formation fracture pressure,establishes a dynamic chart of deep-water formation fracture pressure,and uses the chart to analyze the dynamic change of deep-water formation fracture pressure.(see Chapter IV)Applying the research results of this paper,a case study of deep water well L in South China Sea is carried out.The results show that the dynamic fracture pressure chart method proposed in this paper can improve the prediction accuracy of the fracture pressure of the deep-water formation.The prediction chart of the dynamic fracture pressure of the deepwater formation established on the premise of considering the temperature provides certain theoretical support for the stability analysis of the well wall and the subsequent fracturing construction of the deep-water drilling,which is of great significance for the safety and efficiency of the deep-water drilling and the subsequent fracturing construction. |
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