The Identification Of Leakage Zone And Research Of Leakage Mechanism Based On Comprehensive Data

Lost circulation is the phenomenon that a large amount of drilling fluid leaks into the formation and it is one of the most troublesome drilling problems.The damage is due to the cost of drilling time and due to the loss of drilling fluid,If untreated,losses may lead to well control issues,borehole collapse,well blowout and stuck pipe,and even lead to the poor hole cleaning,resulting in significant economic losses.In the process of drilling in the south area of Dagang Oilfield,the problem of lost circulation is becoming more and more serious,which leads to many problems such as well control issues,long drilling cycle and high drilling cost,It is necessary to accurately identify the lost circulation horizon,research the lost circulation mechanism,and provide technical parameters and theoretical support for lost circulation prevention and control technology.The paper surveyed the study of lost circulation in recent years at home and abroad research,analyzed the three essential conditions and influence factors of lost circulation,and summarized the types and the reasons of lost circulation.Based on the analysis of drilling fluid leakage mechanism,combined with the situation of the south area of Dagang Oilfield,the paper established log interpretation models of the lithology identification and physical property parameters with geological logging and well logging data.In consideration of the limitations of the current methods of diagnosing lost circulation zone,the paper puts forward with analysis by synthesis method of lost circulation and establishes two assessment criterions of critical lost conditions.Based on the data of well logging,drilling and geology,the paper analyze and predicate the formation pressure,formation fracture pressure and bottom hole pressure.Based on the results of lithology and physical property interpretation,and the profiles of pore pressure,fracture pressure and bottom hole pressure,taking into account the necessary conditions for the lost circulation: positive differential pressure is the driving force,leakage channel and space is the basic condition,the paper establishes PLC,which is the indication parameters of the lost circulation,and two formulas for calculating PLC of lost circulation are given.The paper uses PLC and the three essential conditions of lost circulation to identify the lost circulation horizon and analyze the lost circulation mechanism The paper utilize the method to deal with the well logging data in the south area of Dagang Oilfield,it is proved that the method can be used to identify the lost circulation horizon,which is consistent with the actual situation.The paper also puts forward the Countermeasures of drilling fluid leakage prevention and control in the study area.