Research Of Enhancement And Restoration Method For Ultrasonic Logging Images

Due to the advantages of covering the entire borehole wall with intuitive image and large detection range,ultrasonic well logging has been widely used in the field of exploration and development of oil and gas resources.ultrasonic imaging logging can not only reflects the borehole geometry in a borehole,identify formation heterogeneity that includes fractures,holes and texture,but also determines the quality of perforation,analyzes the casing damage and evaluate cementing quality in cased hole well.However,during the process of ultrasonic imaging logging,impacted by the complex logging operating environment and the non-ideal sound spot of the ultrasonic transducer,ultrasonic logging images often suffer from low contrast and indistinct local details,which makes it difficult to analyze and interpret geologic features of small target in the images.Under this background,according to the engineering requirements of ultrasonic imaging logging,based on the principles of ultrasonic imaging logging and information processing,from the perspective of signal generation and processing,this dissertation uses a combination of physical simulation and numerical simulation to do some research on the method of image enhancement and restoration of ultrasonic logging.The main work of this dissertation is as follows:1.Research on the method of enhancement method for ultrasonic logging image based on contrast limited adaptive histogram equalizationFor the problem of ultrasonic logging image enhancement,based on the drawback of low contrast for ultrasonic image,according to the requirements of real-time in engineering,many histogram equalization methods including HE,BBHE,RMSHE,POSHE,BOHE,MLBOHE,CLAHE were researched and implemented.Based on the algorithm performance analysis,the power-law transformation method is introduced to perform non-linearly transformation on the gray level through parameter adjustment.The relationship between the enhancement effects and selection of parameters such as the number of sub-blocks,cut-off threshold,power is analyzed.Combined with the CLAHE method and power-law transformation,the CLAHE-PL image enhancement method is proposed.Comparison and verification tests were conducted on the ultrasonic images of laboratory equipment,model well and field logging to test the performance of the proposed method.Experimental results based on visual perceptual evaluation and quantitative measures(MG,PSNR,AMBE,IE,and LC)showed that the proposed method CLAHE-PL is effective in enhancing the ultrasonic logging image.2.Research on the method of enhancement method for ultrasonic logging image based on partially overlapped sub-block histogram-equalizationFor the problem of excessive enhancement in the partially overlapped sub-block histogram-equalization,the idea of contrast-limited enhancement is introduced to modify the cumulative distribution functions of the POSHE.Taking the night vehicle surveillance image with low-contrast as an example,the effect of different cut threshold on the enhancement performance is analyzed,and the POSHEOC image enhancement method is proposed.This method build a new quality evaluation index considering the effects of the mean gradient and mean structural similarity.The new index is designed to obtain the optimal clip-limit value for histogram equalization of the sub-block.It makes the choice of the optimal clip-limit automatically according to the different input image.taking model well and two ultrasonic logging images measured in the field as an example,combined with five objective evaluation indicators such as PMGSIM,PSNR,IE,AMBE and LC,the performance of the POSHEOC and CLAHE-PL proposed in this dissertation are compared with other six methods including HE,BBHE,RMSHE,POSHE,BOHE and MLBOHE.Experimental results based on visual perceptual evaluation and quantitative measures demonstrate that the proposed method is effective in processing ultrasonic logging images and yields better quality in enhancing the contrast,emphasizing the local details while preserving the brightness and restricting the excessive enhancement compared with the other histogram equalization based techniques from the literatures.3.Research on the best K-value wiener filter restoration method based on APEX point spread function estimationAiming at the problem of ultrasonic logging image restoration,the factors of image degradation are analyzed,and it is clarified that the sound spot formed by the sound beam diffusion on the wall is the main reason for the degradation of ultrasonic logging images.Under the fact that the degradation model of the ultrasonic logging imaging system is unknown,the transmission characteristics of the acoustic wave transducer are studied,and the feature points are selected as reference objects in the degraded image by the test estimation method,and the point spread function model is derived as class G function.Using the APEX algorithm,the model parameters are estimated,the APEX parameters fitting are extended to the horizontal and vertical directions,the curve fitting of log-amplitude spectrum cross-section is performed,and the point spread function is estimated.Based on the estimated point spread function,the Wiener filtering method is used for image restoration.For the problem of the unknown value of the noise signal ratio K in the Wiener filter restoration method,an automatic search for the optimal noise signal ratio K based on guided filtering and minimum mean square error is proposed.Based on the known clear image,computer is used to simulate the degraded image with the class G function and Gaussian noise of different powers are added to carry out the restoration performance test.Combining five objective evaluation indicators including MG,PSNR,IE,AMBE and LC,the quality of the restored image was analyzed to verify the correctness of the proposed restoration algorithm.On the basis of restoration test for simulated degraded images,a large number of simulation experiments were carried out on the ultrasonic images of laboratory equipment,model well and field logging to test the performance of the proposed method.Experimental results based on visual perceptual evaluation and quantitative measures demonstrate that the proposed optimal K-value Wiener filter restoration method based on the APEX point spread function estimation is effective for the restoration of ultrasonic logging images,and it shows good performance in restoring image details,enhancing clarity,and suppressing noise.The main achievementof this dissertation:1.A series of image enhancement methods based on histograms are studied,and two effective methods CLAHE-PL and POSHEOC for ultrasonic logging image enhancement are proposed.The proposed methods can be embedded in the field logging data processing and interpretation software to serve for oil and gas exploration and development,it can also be applied for the enhancement of underwater acoustic images.2.The blind image restoration method based on experimental estimation is studied,and the degradation model of the ultrasonic image is estimated.The APEX algorithm is introduced into the parameter estimation of the point spread function of the ultrasonic logging image.An automatic search method for the optimal noise signal ratio K based on guided filtering and minimum mean square error is proposed.An ultrasonic logging image degradation model estimation method and logging image restoration algorithm are explored.The research results have good application prospects in oilfield exploration and development.