Study On EM-MWD Signal Transmission Mechanism In Foam And Application

Since 2003, China has become as the second largest oil consuming countries after UnitedStates. In 2005, China has become as the third largest oil importing countries subsequent to UnitedStates and Japan. Large oil consumption and import seriously impacted the economic growth rateof China and threatened our national security. Therefore, China must take positive and effectivemeasures for the development of new oil drilling and production technology to increase oilproduction.Underbalanced drilling have many advantages such as reduce pay formation harmed, timelyidentify and evaluate low pressure and low permeability reservoirs, significantly enhance thepenetration rate, effective control leakage and reduce differential pipe sticking, so it has been trendas the current domestic development of low pressure, low permeability and low reservoir.Underbalanced drilling technology associated with directional well, horizontal well, and extendedreach well technique can greatly improve economic efficiency. One of the key problems in thiscombinative technology is the measured signal transmission downhole in drilling. One of the fluidtechniques usually used in underbalanced drilling is the low-pressure gas-based drilling fluidmedium Series (air, mist, foam, aeration). However, mud-pulse MWD commonly used in China isdifficult to transmit measured signal to surface to achieve real-time monitoring well trajectory andidentifying formation because of disturbance from multiphase fluid in signal channel. InEM-MWD, the downhole instrument sends electromagnetic signals to the surface antenna andreceives data, the requirement of fluid is much lower than mud-pulse MWD, and thereforeEM-MWD has board prospects in underblanlanced drilling. Compared with Europe and UnitedStates, Russian EM-MWD is paid lower. China University of Geosciences(Wuhan) firstlyimported the Russian EM-MWD(ZTS) in China, which has production tested in Shengli oilfield,CCSD, Liaohe oilfield and have achieved some results.EM-MWD top and bottom ends are insulated by electrical divider, electromagnetic signalsbuildup loop through drillstring and formation, the surface equipment receive and decode signals.The signals transmission by formation must firstly penetrate annular medium, then spreadformation. In china, there is no EM-MWD used in underblanced drilling, it is widely used foam drilling fluid in underbalanced drilling and the electromagnetic signals of EM-MWD whether canpenetrate annular foam to formation has not been researched.This paper seeks to analyze the operating principles of EM-MWD, the structure of foam,make up foam used in oilfield and test its electric conductivity. Meanwhile, study on themechanism of impact EM-MWD signal transmission to formation when using foam in annularmedium in underbalanced drilling by ultra low frequency electromagnetic wave near field electriccircuit characteristic, the attenuation and reflection theories of electromagnetic wave. It introducesthe United States EM-MWD application in the underbalanced drilling, detailed describes theRussian EM-MWD (ZTS type) application in China, analyzes how to solve problems whenRussian EM-MWD applied in underbalanced drilling.The paper has seven chapters, and the main contents of each chapter are as follows:The first chapter introduces the topic origin, research goal, significance, domestic and foreignresearch present situation, the research difficulties, the main research contents and technical route.The second chapter introduces the mud-pulse MWD limitation in underbalanced drilling. Itcontains the underbalanced drilling types, advantages, the principle of mud-pulse and its limitationused in underbalanced drilling.The third chapter discusses the EM-MWD related theories. First introduce the operationalprinciples of EM-MWD, and then introduce the effective transmission line method. Finally,analyzes the affecting factors of EM-MWD signal transmission, including the lead role of drillpipe, excitation frequency, formation resistivity, the relationship between special drillpipe antennaparameters and excitation current, surface metal casing and annular medium.The forth chapter introduces foam and its conductivity research. First, analyzes the foamdrilling fluid structure on the basis of introduction in the composition of foam. Then it introducesthe foam conductivity test in the laboratory in detail and analyzes the obtained data combined withthe present situation of the domestic and foreign scholars' research on foam conductivity.The fifth chapter discusses the electromagnetic wave transmission model in foam. Makingmodel by ultra low frequency electromagnetic wave near field electric circuit characteristic, theattenuation and reflection theory of electromagnetic wave, and analyzes the influences ofEM-MWD signal transmission from annular to formation. It includes three factors. The first iselectromagnetic wave partial current because of foam resistivity, the second is electromagneticwave absorbed by foam and the third is electromagnetic wave being reflected seriously because ofthe heterogeneous structure of foam.The sixth chapter introduces EM-MWD application. First it introduces application in theUnited States several companies' EM-MWD system in underbalanced drilling. Then detailedanalyze structural characteristic of the Russian EM-MWD (ZTS type) and the production tests inShengli Oilfield and Liaohe oilfield. Finally analyzes how to solve problems when using RussianEM-MWD in underbalanced drilling.The seventh chapter is conclusions and recommendations. To sum up the whole paper and givesome suggestions for further study.