| In recent years,the domestic focus of oil and gas development is turning to difficult-to-produce resources such as high water cut reservoirs,heavy oil reservoirs,tight reservoirs and shales.Directional well technology plays a significant role in the exploration and development of these reservoirs.Measurement-while-drilling technology can transmit the engineering parameters measured at the downhole to the ground in real time,which is one of the key factors to ensure the completion of a high-quality directional well.In comparison with mud pulse measurement-whiledrilling,electromagnetic measurement-while-drilling(EM-MWD)can work effectively in gas drilling and leakage formation drilling,and has a good application prospect in the directional drilling.In present,domestic research on EM-MWD technology has made great progress,but the EM-MWD developed are all unidirectional systems that transmit data from the downhole to ground.In comparison with unidirectional system,the bidirectional EM-MWD can adjust the working state of downhole instruments while drilling through signal downward communication technology,which solves the problems of poor adaptation of unidirectional EM-MWD to complex formations and short downhole continuous working time.It can also form rotary steering drilling system based on electromagnetic signal bidirectional communication,and can assist the rotary steering drilling system to be used in gas drilling and leaky drilling.Therefore,the bidirectional EM-MWD is desirable from the point of engineering applications.Given the gap of the current research of signal uploading and actual drilling,the numerical model and transmission characteristics of the downward signal are rarely reported.The domestic bidirectional EM-MWD technology is still in the preliminary stage.Thus,the dissertation studied the mechanism of bidirectional EM-MWD signal transmission,proposed a bidirectional signal assisted transmission method of interwell receiving-transmitting,realized the bidirectional signal communication,and carried out the bidirectional signal transmission and communication experiments on the ground shallow well and in well.The following are the main research results and innovations of the dissertation:1.Considering the obstacles of the current bidirectional signal transmission mechanism research,the electric field radiated by the current on drill pipe,electrode,and cable in homogeneous formation was calculated using homogeneous space Green's function.The electric field in layered formation was calculated based on C-type spectral domain Green's function and the two-level discrete complex image method.On this basis,based on the line antenna theory,volume equivalence principle,and moment method,using piecewise triangular basis function,SWG basis function,and Galerkin test function,the numerical model of signal download considering layered formation,well type,drilling fluid,flushing zone,cable,and electrode was developed.Compared with the existing upload model,the numerical model of signal upload considering flushing zone was developed.The accuracy and efficiency of the numerical model were verified by finite element software,ground shallow well and well experiments.The results indicate that the model has good accuracy and high calculation efficiency.The calculation time is 1 ? 2 orders of magnitude less than that of the finite element model.2.Based on the numerical model of bidirectional signal transmission,the effects of well type,electrode position,drill pipe size and conductivity,formation conductivity and layer position,drilling fluid and flushing zone conductivity and thickness on the bidirectional signal transmission were discussed.And the effects of cable type and size,source location,electrode length and diameter on downward signal were discussed.The results demonstrate that the effect of flushing zone on signal intensity exceeds 30%.The bidirectional signal intensity increases with the increase of high invasion zone thickness and decreases with the increase of low invasion zone thickness.In comparison with the insulated cable,applying the bare cable with larger diameter and setting the source near the wellhead can effectively increase the intensity of downward signal.In well test,applying the bare cable can increase the intensity of downward signal by 4.7 times.By using electrodes with large length and diameter and setting large pole distance,the intensity of downward signal can be increased by nearly 9 times.3.An assisted transmission method of bidirectional signal using interwell receiving-transmitting was proposed.Considering the dual horizontal wells and cluster wells,the numerical model was employed to compare and analyze the interwell receiving-transmitting and traditional schemes.The dual-well signal transmission experiments on the ground were carried out.The results indicate that the interwell receiving-transmitting scheme can effectively enhance the signal intensity by 1 ? 4 orders of magnitude when the signal of traditional scheme attenuates severely.In addition,the interwell receiving-transmitting scheme is applicable to a larger signal frequency,that is,the scheme can obtain a larger data transmission rate.4.A interaction scheme of bidirectional signal is proposed,and then the bidirectional signal communication is designed and realized.The interaction scheme of intermittent bidirectional signal is designed to control the underground transmitter and receiver to stop or start working through the surface system.The frequency shift keying modulation and demodulation scheme is applied to realize the conversion of digital signal and analog signal.Digital filtering of the wavelet is used to further filter the noise in the received signal.The hardware circuits of underground and surface transceiver are designed and realized.On this basis,a set of underground receiver transmitter instrument,external insulated gap,ground receivers and transmitters are designed and processed.5.The bidirectional communication system is applied to carry out the bidirectional communication and transmission experiments in shallow well and mine well.The experimental results show that the bidirectional signal interaction method is reasonable.The interwell receiving-transmitting method can effectively increase the signal strength.Under the experimental conditions,the maximum increase proportion of upward and downward signal intensity of interwell receiving-transmitting method is 171.7% and 145.5% respectively.In the downhole environment,the bidirectional signal modulation,demodulation and filtering performance are reliable,and the bidirectional communication system works stably.The error range between the calculated value of the numerical model and the experimental measured value is 7.82%? 29.21%.The numerical model has good accuracy in analyzing the bidirectional signal transmission in the well,and can be used for prediction and feasibility evaluation of bidirectional signal intensity.Based on the above work,the established bidirectional signal transmission numerical model can be used to predict the signal intensity and evaluate the feasibility of bidirectional EM-MWD.The research on the characteristics of bidirectional signal transmission is helpful to guide the system design and application of bidirectional EM-MWD.The proposed interwell receiving-transmitting scheme can significantly enhance the signal intensity and expand the application depth.The design,implementation and in well test of bidirectional communication system can accumulate experience and provide reference for the research and development of domestic bidirectional EM-MWD.In a word,the dissertation provides a theoretical and engineering perspective for the development of bidirectional EM-MWD technology and directional drilling(especially directional drilling in gas circulating medium and leakage formation). |
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