The Method Of Thermal Gas Mass Flowmeter Used In Measuring The Production Profile Of Coalbed Methane Well

CH4 is the main component of the coalbed methane,it is a clean energy as perfect as natural gas.This resource is very rich in our country,and it has lots of advantanges,for example,centralized distribution,a large of proportion suit to develop.In these years,with the development of coalbed methane,coalbed methane is taking an industrial development road.Because dynamic monitoring technology for the production of coalbed methane wells starts late in our country,the evalution method of coalbed methane wells production and performace are quite short.For these reasons,this phenomenon makes the capacity of wells production decay.So we need a feasible dynamic monitoring method for the coalbed methane wells.The measurement method that thermal mass flowmeter for gas production profile of coalbed methane above the liquid surface was first proposed in this article.The thermal gas mass flowmeter has some advantages,such as no moving parts,no radiation,no pollution and high reliability on one hand,and the measuring time is unrestricted on the other hand.This article first introduces the measurement principles and basic structure of the thermal mass flowmeter and analyzyed two ways of working of thermal flowmeter.Finally,constant-current source circuit has been set up with constant current.Aimed at the subsurface environment of the coalbed methane and the characteristics of thermal flowmeter,Pt20 was chosen as velocity sensor and Pt1000 as temperature sensor.Signal processing circuit has been set up about the up two sensors.And according to the experimental analysis on the velocity sensor as well as the temperature sensor,the response rules of the sensors in different environment temperatures were obtained.For underground environment of coalbed methane,first combining with the characteristics of thermal flowmeter,we selected a temperature sensor and velocity sensor,and analyzed the performance of the temperature sensor and velocity sensor by testing,and then focused to identifing the relationship between the velocity sensor and the ambient temperature,at last finded a new method of temperature compensation of thermal mass flowmeter.In this article,the simulation software----FLUENT is used to simulate the temperature field and velocity field of flow road in order to find the reasonable positions of temperature sensor and velocity sensor.After that we finished the dynamic experimental study of the different angles of the sensors and wind speed in the simulated wellbore and we found that with the reduction of the angle between speed sensor and the velocity sensor,the response value of speed sensor also gradually reduced.Through the pre-indoor research and theoretical simulation analysis.Based on the preliminary work we have designed a prototype and a acheived the dynamic experiments of simulated wells,we carried out the dynamic experimental studies of wind velocity sensors in Daqing Oilfield multiphase flow experimental apparatus.The results show that the instrument response and reproduce well,and the measurement accuracy is so perfect that it can meet the requirements of the design.Flow rate with the standard flow shows a good linear relationship by measuring.These show that the thermal of mass flowmeter can be applied to the test of coalbed methane wells above the liquid surface gas production profile.