The Evolution Law And Experiment Of Downhole Casing Valve Pressure In The Whole Process Of Underbalanced Drilling

We will encounter a variety of problems and many risks in underbalanced drilling process,Especially the formation undervoltage value changes,likely to cause an accident occur underground,such as blowout,kick.Sleeve valve allows UBD more simple,secure,reduce conventional underbalanced drilling process risks,and can be shortened from the time of drilling and drill,from which UBD has great benefits.This technology is slowly used for many companies oilfield in underbalanced drilling process.However,in the practical application of the sleeve valve,which faced with a series of questions,such as the downhole pressure unpredictable dynamic rule after the sleeve valve is closed,after the valve is closed the valve sleeve gas pressure increases too fast,which cause the sleeve valve can not open properly,after the sleeve valve closes downhole pressure increased dramatically,prone to leakage.After passing through the work process of the casing valve,Found that the most critical factor in controlling these problems is the study of pressure evolution after sleeve valve closes.In this paper,research results are as follows:(1)Gas reservoirs established under less equilibrium conditions of dynamic mathematical model to predict the flow law,through the establishment of the model,forming strata flow law Prediction wellbore pressure levels under different wellbore pressure levels conditions.This model is used to calculate the final pressure under sleeve valve.(2)Complete mathematical model of drilling fluid leakage amount of positive pressure conditions through the establishment of the physical characteristics of the reservoir under different densities combined Darcy,to determine the effects of various factors on the loss.(3)Through the establishment of a gas stick cut in a non-Newtonian fluid,the inner pressure,the coupling relationship between form and theoretical study of the expansion and formation porosity medium primary dynamic motion media bubble rises law,forming an open tube hydrodynamic theory unidirectional flow of zero-flow theory,eventually forming a one-way model of a closed pipe flow,used to calculate the valve casing under pressure variation.(4)To simulate the pressure change at the valve casing through the design of experiments.