The Fundamental Research Of Azimuthal Density Imaging Logging While Drilling

The complex drilling conditions of high-angle and horizontal (HA/HZ) wells call fornew demands in well logging instruments. Since LWD azimuthal density tool plays importantroles in geosteering, formation interface identification and reservoir characterization, whichdraws great attentions in well logging and petroleum engineering industry. Based on the basicprinciple of density logging and the traditional structure of density tool, this paper studies thekey technology and basic parameters of LWD with Monte Carlo simulations, combined withimaging techniques to explore the fundamental research of azimuthal density logging whiledrilling in complex drilling conditions.The paper optimizes the density tool structure model using Monte Carlo simulationmethod, studies and discusses basic parameters of the instrument on the basis of research ondensity tool and its application development both at home and abroad. The results show thatthe range of the detector energy window is affected by the mud type. The range of thelithology window and the density window can be reduced if barite is added to the mud, whichleads to considerable errors. Also it is found that the depth of investigation is different fromdeviation angle. The horizontal wells have the lowest radial investigation and highest verticalresolution, while the vertical wells have opposite case. These above basic researches lay thefoundation for spectral processing, analysis of influencing factors and the application ofazimuthal density image.By comparison with four smoothing methods and four peak researching methods basedon the spectral data obtained by density tool, results show that the variable parameterexponent smoothing method is the best choice to the original data and the background data,which achieves the purpose of removing noise effectively and smoothing. Multiple Gaussianfunctions joint weighted—fitting peak searching method is proposed by improving thetraditional peak searching method—Gaussian function fitting by least squares, and the generalreduced gradient method is adpoted to solve the problem of the optimal solution in theGaussian function fitting peak searching, which gets higher precision than that of the otherfour methods and improves the accuracy of the spectral data processing. Spectral dataprocessing software is designed after the completion of the spectral data processing such as the smoothness, peak searching, energy calibration, background subtraction and dead-timecorrection and so on. The validity and accuracy of the software is verified throughexperimental scale data.Tool azimuth sensitivity is further explored in this paper. It is pointed out that azimuthsensitivity is different across an interface in a horizontal well, but the instrument orientationsensitivity region is essentially the same (about45°), which is a characteristic of theinstrument. Factors which affect LWD azimuth density response such as borehole conditionsand formation properties are analyzed. The results show that well diameter has little effects onazimuth density, while gap and filler have important effects, which can be corrected using theridge-rib graph. Logging response to thin layer and thin interbed was influenced by shoulderbeds in different deviation angles, which is solved by establishing correction chart of the ratioof apparent density and shoulder beds density and the ratio of the corrected density andapparent density to improve the credibility of test data.Finally azimuthal density imaging methods are studied further. An improved imageenhancement algorithm—Fast Gray-Level Grouping based on Histogram Equalization, whichremove the image noise effectively and improve image quality. Due to the combination of theadvantages of traditional image enhancement algorithms, the clarity of processed images bothin high-contrast regions and in low-contrast areas is improved, and it has uniform colorreflecting more stratigraphic characteristics, which will ensure the next geological application.On the basis of analysis of density image, the optimal segmentation firstly applys to formationinterface identification is proposed. The results show that this method can improve theaccuracy of the identification, overcoming the shortcomings of traditional interfaceidentification such as the low precision, large errors and high demands on basic data. Basedon the method, the height H of the density image is obtained, which offer accurate parametersin the calculation of the relative dip angle. Combined with the effective depth of investigation,the calculated parameters of the relative dip angle are optimized, overcoming large errors andlow precision in the traditional calculation. The validity and accuracy of the method isverified by simulation data, and the calculation accuracy of formation relative dip is improved,which lays the foundation for geosteering, formation heterogeneity and geological structuralinterpretation in high-angle and horizontal wells.