The study of the thin bed responses and correction methods in cased hole density logging can provide a theoretical basis for research to improve data processing methods. By using the Monte Carlo program MCNP, the chan...The study of the thin bed responses and correction methods in cased hole density logging can provide a theoretical basis for research to improve data processing methods. By using the Monte Carlo program MCNP, the change of detector count from thin beds with the vertical depth was calculated at different casing thicknesses. The calculation showed that with the low density thin bed moving upward, detector count first increased to a maximum then decreased. The responses of a thin bed with a high density were opposite to those of a thin bed with a low density. The change curve was symmetrical, and the maximums or minimums appeared at the midpoint between the detector and source. Besides, detector count increased with increasing thin bed thickness. At a specific thin bed thickness, further increase of thin bed thickness resulted in a slow increase of detector count then the count rate leveled off. In actual logging, the influence of adjacent formations on density log measurements can be ignored. Finally, based on numerical simulation correction methods for the dual influence of casing and thin beds are discussed.展开更多
The reflection of elastic wave from thin bed in porous media is important for oil and gas reservoir seismic exploration.The equations for calculating frequency-dependent reflection amplitude versus incident angle(FDAV...The reflection of elastic wave from thin bed in porous media is important for oil and gas reservoir seismic exploration.The equations for calculating frequency-dependent reflection amplitude versus incident angle(FDAVA)from thin bed in porous media are obtained based on porous media theory.Some conclusions are obtained from numerical analysis,specifically,slow compression wave may be ignored when considering boundary conditions in most situations;the dispersion of reflection from thin bed is much higher than that from thick layer and is periodic in frequency domain,which is affected by the thickness of thin bed,velocity,and incident angle;the reflection amplitude envelope in frequency domain decays exponentially,which is affected by the thickness of thin bed,attenuation,and incident angle;the reflection amplitude increases with thickness of thin bed increasing,and then it decreases when the thickness reaches to a quarter of wavelength.展开更多
The location of singularities may be detected by local maxima of the wavelet transform modulus. The digital modeling and focusing process to wavelet transform of the reflecting seismic signals have been done. It has b...The location of singularities may be detected by local maxima of the wavelet transform modulus. The digital modeling and focusing process to wavelet transform of the reflecting seismic signals have been done. It has been found that the locations of singularities after wavelet transform are only affected by two factors, their original locations and the seismic wavelet length, which says it does not matter with what shape the wavelet will be. The wavelet length can be determined according to the wavelet transform results and be eliminated thereafter so that we are able to detect thin bed seismic signal with resolution of l/32 wavelength. The singularities have been recovered with improved resolution of the seismic section by real data processing.展开更多
This paper provides a detailed description of the cepstrum and its application to computing the thickness of thin beds.By building several models,including models with a single reflection pair,a single layer,wedge mod...This paper provides a detailed description of the cepstrum and its application to computing the thickness of thin beds.By building several models,including models with a single reflection pair,a single layer,wedge model and multi-layered models,and comparing the cepstrum computed for all of them to the actual spacing values we conclude that the results of cepstral analysis are more accurate in predicting the thickness of the thin bed structures.展开更多
Seismic processing characterizing thickness and borders of thin inter-beds has gradually evolved fi＇om post-stack migration to pre-stack migration, and the latter considers both vertical and lateral resolutions. As t...Seismic processing characterizing thickness and borders of thin inter-beds has gradually evolved fi＇om post-stack migration to pre-stack migration, and the latter considers both vertical and lateral resolutions. As the key processing methods for improving vertical and lateral resolution, conventional deconvolution and pre-stack time migration （PSTM） are not simply dominated by the estimation and compression of the wavelet because of its instability. Therefbre, considering the variations of wavelet frequency belbre, during and alter PSTM can obtain good common reflection point （CRP） gathers and imaging profiles of thin inter-beds. Based on the frequency characteristics of the wavelet before, during and after PSTM, a joint high-resolution processing method for thin inter-beds is proposed in this paper, including inverse Q filtering for high-frequency compensation before PSTM, optimum weighting Kirchhoff PSTM for preserving high-frequencies during PSTM, and wavelet harmonizer deconvolution tier consistent processing and frequency-band broadening after PSTM. An application to real data characterized by mudstone beds in the Oriente Basin proved that the joint high-resolution processing method is effective for determining the thickness and borders of thin inter-beds and is favorable for subsequent reservoir prediction and seismic inversions.展开更多
One of the most important research task in reservoir engineering now is to resolve the fine thin layer. What are the characteristics of the fine thin layer? This paper gives the answer in frequency domain. The frequen...One of the most important research task in reservoir engineering now is to resolve the fine thin layer. What are the characteristics of the fine thin layer? This paper gives the answer in frequency domain. The frequency feature of fine thin layer set obtained is grating. The frequence effects of rhythmic thin layer, on the other hand, is different from those of graded thin layer; the grating effect of fine layer is affected by several factors, but the thickness and its inner layer number are the most predominant factors over others affecting grating effect.展开更多
AIM： To investigate the long term（≥5 y） efficacy, predictability, and safety of laser in situ keratomileusis（LASIK） in eyes with thin corneas [central corneal thickness（CCT） 〈500 μm]. METHODS： A total of 33...AIM： To investigate the long term（≥5 y） efficacy, predictability, and safety of laser in situ keratomileusis（LASIK） in eyes with thin corneas [central corneal thickness（CCT） 〈500 μm]. METHODS： A total of 339 patients met the criteria of this study. Finally, 175 eyes of 89 patients who had thin corneas and underwent LASIK≥5 y ago returned to our clinic and included in this study. Preoperative parameters recorded included uncorrected visual acuity（UCVA）, corrected distance visual acuity（CDVA）, manifest refraction, CCT and corneal topography. At returning visits, in addition to visual acuity and manifest refraction, ultrasound CCT and corneal topography were performed. Optical coherence tomography was used to measure the CCT, LASIK flap thickness, and residual stromal bed thickness（RSBT）. Safety index, efficacy index, percentage of eyes within ±0.5 D and ±1.0 D of refraction, percent tissue altered（PTA）, and percentage stromal bed thickness（PSBT） were calculated. RESULTS： The safety index was 1.09 and efficacy index was 0.99. The percentages of eyes within ±0.5 D and ±1.0 D were 71.2% and 87.7%, respectively. The mean PTA was 40%±6%（range 20% to 55%）; 76 eyes（43.4%） had PTA 〈40% and 99 eyes（56.6%） had PTA≥40%. The mean RSBT was 303±27 μm（range 240 to 390 μm）, and 2 eyes had RSBT〈250 μm. The mean PSBT was 61%±9%（range 51% to 85%）. No eyes developed ectasia. CONCLUSION： In this cohort with the PSBT of 50% or more, LASIK is safe with follow-up for at least 5 y.展开更多
Steel mesh is used as a passive skin confinement medium to supplement the active support provided by rock bolts for roof and rib control in underground coal mines. Thin spray-on liners(TSL) are believed to have the po...Steel mesh is used as a passive skin confinement medium to supplement the active support provided by rock bolts for roof and rib control in underground coal mines. Thin spray-on liners(TSL) are believed to have the potential to take the place of steel mesh as the skin confinement medium in underground mines.To confirm this belief, large scale laboratory experiments were conducted to compare the behaviour of welded steel mesh and a TSL, when used in conjunction with rock bolts, in reinforcing strata with weak bedding planes and strata prone to guttering, two common rock conditions which exist in coal mines. It was found that while the peak load taken by the simulated rock mass with weak bedding planes acting as the control sample(no skin confinement) was 2494 kN, the corresponding value of the sample with 5 mm thick TSL reinforcement reached 2856 kN. The peak load of the steel mesh reinforced sample was only2321 kN, but this was attributed to the fact that one of the rock bolts broke during the test. The TSL reinforced sample had a similar post-yield behaviour as the steel mesh reinforced one. The results of the large scale guttering test indicated that a TSL is better than steel mesh in restricting rock movement and thus inhibiting the formation of gutters in the roof.展开更多
文摘The study of the thin bed responses and correction methods in cased hole density logging can provide a theoretical basis for research to improve data processing methods. By using the Monte Carlo program MCNP, the change of detector count from thin beds with the vertical depth was calculated at different casing thicknesses. The calculation showed that with the low density thin bed moving upward, detector count first increased to a maximum then decreased. The responses of a thin bed with a high density were opposite to those of a thin bed with a low density. The change curve was symmetrical, and the maximums or minimums appeared at the midpoint between the detector and source. Besides, detector count increased with increasing thin bed thickness. At a specific thin bed thickness, further increase of thin bed thickness resulted in a slow increase of detector count then the count rate leveled off. In actual logging, the influence of adjacent formations on density log measurements can be ignored. Finally, based on numerical simulation correction methods for the dual influence of casing and thin beds are discussed.
基金National Natural Science Foundation of China(Grant Nos.41764006,41364004,and 41504095)the Chinese Study Abroad Fund(Grant No.201508360117)+1 种基金the National Key Research and Development Program of China(Grant No.2018YFC0309901)the COMRA Major Project,China(Grant No.DY135-S1-01-01).
文摘The reflection of elastic wave from thin bed in porous media is important for oil and gas reservoir seismic exploration.The equations for calculating frequency-dependent reflection amplitude versus incident angle(FDAVA)from thin bed in porous media are obtained based on porous media theory.Some conclusions are obtained from numerical analysis,specifically,slow compression wave may be ignored when considering boundary conditions in most situations;the dispersion of reflection from thin bed is much higher than that from thick layer and is periodic in frequency domain,which is affected by the thickness of thin bed,velocity,and incident angle;the reflection amplitude envelope in frequency domain decays exponentially,which is affected by the thickness of thin bed,attenuation,and incident angle;the reflection amplitude increases with thickness of thin bed increasing,and then it decreases when the thickness reaches to a quarter of wavelength.
文摘The location of singularities may be detected by local maxima of the wavelet transform modulus. The digital modeling and focusing process to wavelet transform of the reflecting seismic signals have been done. It has been found that the locations of singularities after wavelet transform are only affected by two factors, their original locations and the seismic wavelet length, which says it does not matter with what shape the wavelet will be. The wavelet length can be determined according to the wavelet transform results and be eliminated thereafter so that we are able to detect thin bed seismic signal with resolution of l/32 wavelength. The singularities have been recovered with improved resolution of the seismic section by real data processing.
基金The research was supported by the Notion's Fifteenth Scientific and Technological Breakthrough Project: Research of Vector and Mountain Seismic Exploration (No.2001BA605A-12).
基金Project 2005CB422104 supported by the National Basic Research Program of China
文摘This paper provides a detailed description of the cepstrum and its application to computing the thickness of thin beds.By building several models,including models with a single reflection pair,a single layer,wedge model and multi-layered models,and comparing the cepstrum computed for all of them to the actual spacing values we conclude that the results of cepstral analysis are more accurate in predicting the thickness of the thin bed structures.
文摘Seismic processing characterizing thickness and borders of thin inter-beds has gradually evolved fi＇om post-stack migration to pre-stack migration, and the latter considers both vertical and lateral resolutions. As the key processing methods for improving vertical and lateral resolution, conventional deconvolution and pre-stack time migration （PSTM） are not simply dominated by the estimation and compression of the wavelet because of its instability. Therefbre, considering the variations of wavelet frequency belbre, during and alter PSTM can obtain good common reflection point （CRP） gathers and imaging profiles of thin inter-beds. Based on the frequency characteristics of the wavelet before, during and after PSTM, a joint high-resolution processing method for thin inter-beds is proposed in this paper, including inverse Q filtering for high-frequency compensation before PSTM, optimum weighting Kirchhoff PSTM for preserving high-frequencies during PSTM, and wavelet harmonizer deconvolution tier consistent processing and frequency-band broadening after PSTM. An application to real data characterized by mudstone beds in the Oriente Basin proved that the joint high-resolution processing method is effective for determining the thickness and borders of thin inter-beds and is favorable for subsequent reservoir prediction and seismic inversions.
文摘One of the most important research task in reservoir engineering now is to resolve the fine thin layer. What are the characteristics of the fine thin layer? This paper gives the answer in frequency domain. The frequency feature of fine thin layer set obtained is grating. The frequence effects of rhythmic thin layer, on the other hand, is different from those of graded thin layer; the grating effect of fine layer is affected by several factors, but the thickness and its inner layer number are the most predominant factors over others affecting grating effect.
基金Supported in part by the National Natural Science Foundation of China(No.11402161)the Programs for Science and Technique Development of Shanxi Province,China(No.20120313025-3)+1 种基金the Science and Technology Research Projects of the Shanxi Provincial Health Department,China(No.201201018)an unrestricted grant from Research to Prevent Blindness,New York,NY,USA
文摘AIM： To investigate the long term（≥5 y） efficacy, predictability, and safety of laser in situ keratomileusis（LASIK） in eyes with thin corneas [central corneal thickness（CCT） 〈500 μm]. METHODS： A total of 339 patients met the criteria of this study. Finally, 175 eyes of 89 patients who had thin corneas and underwent LASIK≥5 y ago returned to our clinic and included in this study. Preoperative parameters recorded included uncorrected visual acuity（UCVA）, corrected distance visual acuity（CDVA）, manifest refraction, CCT and corneal topography. At returning visits, in addition to visual acuity and manifest refraction, ultrasound CCT and corneal topography were performed. Optical coherence tomography was used to measure the CCT, LASIK flap thickness, and residual stromal bed thickness（RSBT）. Safety index, efficacy index, percentage of eyes within ±0.5 D and ±1.0 D of refraction, percent tissue altered（PTA）, and percentage stromal bed thickness（PSBT） were calculated. RESULTS： The safety index was 1.09 and efficacy index was 0.99. The percentages of eyes within ±0.5 D and ±1.0 D were 71.2% and 87.7%, respectively. The mean PTA was 40%±6%（range 20% to 55%）; 76 eyes（43.4%） had PTA 〈40% and 99 eyes（56.6%） had PTA≥40%. The mean RSBT was 303±27 μm（range 240 to 390 μm）, and 2 eyes had RSBT〈250 μm. The mean PSBT was 61%±9%（range 51% to 85%）. No eyes developed ectasia. CONCLUSION： In this cohort with the PSBT of 50% or more, LASIK is safe with follow-up for at least 5 y.
文摘Steel mesh is used as a passive skin confinement medium to supplement the active support provided by rock bolts for roof and rib control in underground coal mines. Thin spray-on liners(TSL) are believed to have the potential to take the place of steel mesh as the skin confinement medium in underground mines.To confirm this belief, large scale laboratory experiments were conducted to compare the behaviour of welded steel mesh and a TSL, when used in conjunction with rock bolts, in reinforcing strata with weak bedding planes and strata prone to guttering, two common rock conditions which exist in coal mines. It was found that while the peak load taken by the simulated rock mass with weak bedding planes acting as the control sample(no skin confinement) was 2494 kN, the corresponding value of the sample with 5 mm thick TSL reinforcement reached 2856 kN. The peak load of the steel mesh reinforced sample was only2321 kN, but this was attributed to the fact that one of the rock bolts broke during the test. The TSL reinforced sample had a similar post-yield behaviour as the steel mesh reinforced one. The results of the large scale guttering test indicated that a TSL is better than steel mesh in restricting rock movement and thus inhibiting the formation of gutters in the roof.
