Study On Leakage Mechanism Of Terrestrial Stratum In Northeast

The continental stratum in northeastern Sichuan Basin has a very complex geological structure with stratum breaking and fracture development, so that different levels of leaks occur in almost every exploratory wells during the drilling process, which severely restricts the drilling efficiency. Well leakage problems, therefore, must be promptly solved in order to realize safe and speedy drilling, and thereinto, understanding the mechanism of drilling fluid leakage is the key to preventing and plugging.Well logging data is the response of rock physics information, which can be utilized to calculate the formation of rock mechanics parameters, establish a formation pressure profile, and to calculate the formation’s safe weigh window of drilling fluids and verify its rationality according to the dynamic, static rock mechanical parameters of transformation model. Also, the well logging response characteristics of leakage layer can help partition leakage zone, describe the property of leak channel, and clear the regularity of leakage. This paper identified the continental strata fracture leakage formation, established the safety window of drilling fluid density in the work area, and found that some leakage formation density window were narrower or negative. What’s more, the occurrence of fractures was assessed to calculate parameters such as the crack width, porosity, permeability and radial stretch degree, and to define the regularity of leakage loss, which provides the basis for optimization of plugging construction measures and of the plugging materials.Then, the leakage pressure of the fractured leakage layer was divided into nature leakage pressure, fracturing leakage pressure and fracture expansion leakage pressure, and the corresponding model was given according to the characteristics of the work area of geological structure and the leakage law of work area. In view of the leakage channel nature, type of leakage pressure and drilling fluid properties, this paper established the natural leakage and cracks extensibility leakage mathematical model based on non-newtonian fluid mechanics and crack deformation law, and compared the simulation results with fractured natural loss evaluation experiment as well as the actual leakage. It turned out that the basic error range was less than25%, which verified the leakage model, to a certain extent.In conclusion, this paper formed a set of methods and techniques in the leakage layer division and interpretation of channel properties on the basis of logging data, and established a leakage mathematical model, which provided the basis for guiding leakage and plugging material selection according to the leak of the law.