Mechanic Analyse And Calculate Of Casing Failure In Jilin Oilfield

Failure process of casing well is complicate. Technique and practice used in drilling, production and development program all affect casing failure, which involves some subjects, such as rock mechanics, percolation flow mechanics, pipe string mechanics. All these decide the factors that affect casing failure are variety and complexity. In recent years, many scholars have studied the causes and mechanism of casing failure. Some mechanisms of casing failure are recognized, but there are not effective measures to prevent or retard casing failure, and methods to calculate stress acted on casing by formation in view of specific situations. Jilin Oilfield is a typical low permeability and fracture oil reservoir, its geologic characters including oil-bearing formation discontinuity, large permeability resistance force and so on. When it began to achieve waterflood development in 1973, casing failure phenomena were very serious because of special complicated geological setting and long time waterflood development. In this paper, information of 613 wells with casing failure about Xinli Tract and Fuyu Tract in Jilin Oilfield and the factors affecting the well failure are analyzed statistically. The main characters of casing failure are preliminary grasped, and some conclusions are gotten: most locations of casing failure is in mud shale rock; and water encroachment in mud shale is a precondition of casing failure; water injection pressure is direct dynamic force to drive formation moving that casing failure results from, and formation dip speeds up casing failure. In order to complete the study of the casing failing's mechanical calculation, the paper set up an in-situ stress model. In the part of parameters calculation, inverse algorithm is used to derivation the relationship between the fracture pressure and the in-situ stress. On the basis of the field's fracture data, the tectonic stress parameter is defined. mechanics parameters of the whole hole in every formation can be calculated with rock static data of experiment in laboratory and long wave log. Combining four dimensions with three fields inseparably, the casing failure's formation calculative model of finite element fluid-solid coupling is developed. Reservoir numerical simulation about complicated geological configuration can be solved by using combined grid method; applying FEPG software to simulative calculate with the model in Xinli Tract, calculated result prove the main characters and the trends of casing failure in Jinli Oilfield.