Research On A New Prediction Model Of Surge Pressure Appropriated To Horizontal Well

Surge pressure is a critical parameter in the bottom-hole pressure control. In the process of oil field drilling especially the horizontal well drilling, down hole complex problems like wellbore unstability and other accidents often take place as a result of inaccurate prediction of bottom-hole surge pressure or the absence of surge pressure predicting methods which can not give an available guidance to the drilling parameters adjusting and optimizing. In response to the problem, this paper developed a new prediction model of surge pressure appropriated to horizontal well. First studied the traditional analysis methods of surge pressure theory and established a new research way of combining the steady-state analysis and the transient analysis dialectically. Given the features of horizontal well that differ from conventional well of which an exact matched drilling fluid rheology model is nessesary, so this paper proposed an integrated method of using linear regression method, least square method and golden section method together to optimize the rheology model,in the meanwhile, a corresponding computer program is generated. Then fully took most of the influence factors into account including drilling fluid properties, the velocity of drilling string, string working condition, mud pump displacement, string and annulus ratio, what's more, divided the annulus into different sections according to the borehole size and type. On that basis, described the flowing physical model of surge pressure predicting appropriated to horizontal well and established the final new prediction model of surge pressure in four kinds of rheology models separately under three drilling string working conditions and developed its programming. By contrasting the traditional model and new model through field example computation it shows that the new model is more precise and convenient for the field engineers to use. Last through the influence factors analysis on the basis of field example, it illustrates how to use the developed surge pressure predicting software for the new model to adjust the relative drilling parameters and drilling fluid properties in field work, such as maximum rate of tripping out and tripping in, maximum displacement of the mud pump, the drilling fluid rheology properties and its safe density window, which provides a reliable basis for the safety control in field drilling work.