Study On Channnel Simulation Of Drill String Under Drilling Condition And Acoustic Telemetry Test System

The acoustic telemetry can transmit the data of the formation parameter and the down tool condition and solve the speed and applicability problems,which have been the bottleneck of Measuring While Drilling in the intelligent drilling technology.Acoustic telemetry can provide technical support for air drilling,underbalanced drilling,foam drilling,and supercritical carbon dioxide drilling and so on.The drill string is the transmission channel,so the sizes of drill string is the main factor affecting the channel characteristics.The channel model of related research at home and abroad is mainly based on drill string with periodic cross section abrupt structures,which can not analyze influence of channel characteristic with the inconsistency of drill string size and the small scale structure of drill string structure,and can also not be used for quantitative analysis of channel characteristics.To solve these problems,a models have been established for analyzing the characteristics of aperiodic drill string;the small scale transfer model has been constructed to study the transmission characteristics of the acoustic insulator with a single drill string structure;a test system of acoustic telemetry while drilling has been built,in which the design method of the transducer while drilling has been studied;the field test of drill string channel has been carried out.The main innovations and contributions of this paper are outlined as follows:1.Considering the condition of using non periodic drilling string while drilling,a drill string model with equivalent transflective film is constructed,which has be verified by a comparison.The influence of the structural parameters of drill string is analyzed,which shows that the depth of drilling does not affect the frequency and bandwidth of the pass band,the length of the joint has a fixed inverse proportion to the cycle period of the channel,the more band pass and the narrower the bandwidth in the cycle period with the increase of the length of the drill rod pipe,and the attenuation amplitude of the channel is affected by the cross section area of the drill string.The superposition effects significantly affect the frequency characteristics of drill string until the passbands disappear,which are caused by the inconsistent variation in the size of each drill string and the use of aperiodic structural stabilizers in the channel.Therefore,it is necessary to ensure the consistency of drill string sizes while acoustic telemetry,while the inconsistency of drill string length is within 5%,and the less number of structures such as stabilizers can be used in the channel the better.2.Aiming at the structures similar to the stress transition zone in the drill string,a small scale vibration transfer model of drill string is constructed,which is verified by the finite element simulation.The research results show that the stress transition zone decreases the frequency cycle period and reduces the signal attenuation.Then the method of effectively improving pass band is studied by taking advantage of the wider passband at the periodic frequency,when the short drill collars can be connected between each drill string to reduce the cycle of channel frequency.The acoustic isolator while drilling has been designed.3.Based on the requirement for the laboratory test of acoustic data transmission,an acoustic transmission test system is constructed,of which the control software can generate the linear sweep,2FSK and BPSK wave under controlling the signal generator.The acoustic data simulation software has designed to cover the shortage of hardware platform,which can generate the data files of the OFDM modulation.The files can be output by the generator after the format conversion.The simulation software also can decode the encoded data above;the design method of tubular piezoelectric transducer with half circle composite structure is studied,which must meet the installation requirements of downhole equipment while drilling.Based on the theoretical design of acoustic telemetry transducer and the finite element simulation,the prototype of transducer is completed,and the parameters of the test data are consistent with the design.4.The acoustic telemetry transceiver test prototype for wellsite has been designed,while the design and installation of the mechanical and electrical system have been completed.The passband characteristics of the actual drill string are obtained based on the test data analysis,which is quite different from the simulation,therefore,it is necessary to take into account the small scale structures of drill string for the channel characteristics.A wider bandwidth passband has been tested below 3kHz of the drill string channel,which is close to the channel frequency periodic point of simulation.Considering the simplification in the model,it can verify the feasibility of decreasing frequency period and expanding bandwidth with series of drill collars.