In this paper, we derive an approximation of the SS-wave reflection coefficient and the expression of S-wave ray elastic impedance （SREI） in terms of the ray parameter. The SREI can be expressed by the S-wave incide...In this paper, we derive an approximation of the SS-wave reflection coefficient and the expression of S-wave ray elastic impedance （SREI） in terms of the ray parameter. The SREI can be expressed by the S-wave incidence angle or P-wave reflection angle, referred to as SREIS and SREIP, respectively. Our study using elastic models derived from real log measurements shows that SREIP has better capability for lithology and fluid discrimination than SREIS and conventional S-wave elastic impedance （SEI）. We evaluate the SREIP feasibility using 25 groups of samples from Castagna and Smith （1994）. Each sample group is constructed by using shale, brine-sand, and gas-sand. Theoretical evaluation also indicates that SRE1P at large incident angles is more sensitive to fluid than conventional fluid indicators. Real seismic data application also shows that SRE1P at large angles calculated using P-wave and S-wave impedance can efficiently characterize tight gas-sand.展开更多
This paper aims to study the influence of the number and distribution of drill samples on the simulation accuracy of the lithology field. This research mainly applies the variation function method in geo-statistics, a...This paper aims to study the influence of the number and distribution of drill samples on the simulation accuracy of the lithology field. This research mainly applies the variation function method in geo-statistics, and determines important indicators such as the variation, and then the lithology field is simulated by sequence index simulation. It is shown that(1) simulation error decreases with the increase of sampling density;(2) at the scale and complexity of this study, when the sampling density reaches 40/km^2, the average error of the lithology field simulation can be less than 2.0%;(3) in the study mode of examples, the simulation results of random sampling in the whole region are the most ideal, with an average error of 5.4%. The average error of the simulation results of the centralized sampling is about 10 times that of the random sampling method;(4) known from the influence analysis of the degree of study sample unevenness influence on the imitation results, under the same sample size, the simulation error decreases with the increase of the most adjacent index. When the nearest index reaches 1, the simulation error will be less than 6%, and the error variable range is within 3%.展开更多
The Douala-Buea Region(DBR;4°-5°N,9°-10°30’E),a portion of the southern Cameroon passive margin,developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcanosedimenta...The Douala-Buea Region(DBR;4°-5°N,9°-10°30’E),a portion of the southern Cameroon passive margin,developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcanosedimentary cover,was explored in order to evaluate the lithology and tectonics controls on its landscape usingthequalitativeandquantitative geomorphological analyses based on 30 m resolution Digital Elevation Models(DEM)and field evidences.This area displays an uneven and complex landscape differentiated into four morphological units:Douala,Nkondjock,Kumba and Buea Units.The Douala Unit corresponds to the Coastal Plain and is extended on the Douala-Kribi/Camposedimentarybasin.The Nkondjock Unit represents a middle plateau developed on a Proterozoic granito-gneissic basement.The Kumba Unit matches with the southernmost volcanic Western Cameroon High Plateau.The Buea Unit corresponds to the Mount Cameroon stratovolcano.The relief analysis through mountain-front sinuosity(Smf,1.19–1.43)and relative relief ratio(Rr,0.10–2.31)vary from one unit to another.The drainage network analysis including drainage patterns,stepped longitudinalriverprofiles,theassociated morphometric indexes,notably the concavity index(IC,0.56–0.88),deviation(D,267–2912 m),basin asymmetry factor(A_(F),6.37–42.12),hypsometric integral(HI,0.10–0.29),valley floor width to valley height ratio(V_(f),0.36–2.75),elongation ratio(R_(e),0.30–0.50),watershed slope(S,6.88–88.88)and stream length gradient index(SL,0–3332)vary from one basin to another too.These results also show the heterogeneous and uneven DBR landscape controlled by its lithology and active tectonics.The drainage system reveals concave to concavo-convex longitudinal river profile shapes with knick points,asymmetric basins,and fault reactivations,and highlights the tectonics activity that used to occur through the time and their control on the morphology.Together,they document the lithostructural controls on the DBR landscape evolution,extendable in the whole SW Cameroon margin.展开更多
The Bafoussam-Mamfe Region(BMR)belongs to the Western Cameroon Highland margin,an amalgam of transient landscape that evolved from the interactions between tectonics,lithology and climate forcings.This area is tectoni...The Bafoussam-Mamfe Region(BMR)belongs to the Western Cameroon Highland margin,an amalgam of transient landscape that evolved from the interactions between tectonics,lithology and climate forcings.This area is tectonically active and shows differential tectonic uplift,contrasting relief,variations in erosion rates,in river incision,and in channel gradient.In order to appraise the BMR tectono-geomorphic evolution,it is essential to understand relationships between internal and external processes and their geomorphic expression at a river basin scale.For this purpose,we use drainage texture(Dt),stream frequency(Fs),drainage density(Dd),asymmetry factor(AF),the transverse topographic symmetry factor(TTSF),the mean of mountain front sinuosity per unit(Smf),concavity factor(Cf),hypsometry integral(HI)and streamlength gradient index(SL-index)based on 30 m Digital Elevation Models(DEM)and field survey.The results reveal considerable variations in geology,relief,topography and geomorphic indices values differentiated into three geomorphic units;the Mamfe unit developed on the Mamfe Cretaceous basin,the Nguti and Bafoussam high plateau units build up on the Precambrian granito-gneissic basement overlaid by a volcanic cover.The stepped(longitudinal and normalized)river profiles and complex hypsometric curves show the lithostructural control of the hydrographic network.Dt(from~1.21 to~4.59),Fs(from~0.26 to~1.91),Dd(from~0.66 to~1.71)geomorphic indice values indicate a part of lithologic control on this morphology while the AF(from~1.16to~24.91),TTSF(from~0.20 to~0.71),Smf(U2=1.11 and U3=1.19),Cf(from~-20.91 to~78.93),HI(from~0.12 to~0.52)and SL-index designate the active tectonics as the main factor that had controlled the morphology of this same area.Above results pinpoint the combined post-Pan-African to Recent tectonic features,lithologic heterogeneities and the differential erosion processes as main factors that have controlled the BMR landscape.These results highlight how the Central African surface and the West African passive margin evolved since Proterozoic time.展开更多
基金sponsored by National Natural Science Fund Projects (No.41204072 and No.U1262208)Research Funds Provided to New Recruitments of China University of Petroleum-Beijing (YJRC-2011-03)Science Foundation of China University of Petroleum-Beijing (YJRC-2013-36)
文摘In this paper, we derive an approximation of the SS-wave reflection coefficient and the expression of S-wave ray elastic impedance （SREI） in terms of the ray parameter. The SREI can be expressed by the S-wave incidence angle or P-wave reflection angle, referred to as SREIS and SREIP, respectively. Our study using elastic models derived from real log measurements shows that SREIP has better capability for lithology and fluid discrimination than SREIS and conventional S-wave elastic impedance （SEI）. We evaluate the SREIP feasibility using 25 groups of samples from Castagna and Smith （1994）. Each sample group is constructed by using shale, brine-sand, and gas-sand. Theoretical evaluation also indicates that SRE1P at large incident angles is more sensitive to fluid than conventional fluid indicators. Real seismic data application also shows that SRE1P at large angles calculated using P-wave and S-wave impedance can efficiently characterize tight gas-sand.
文摘This paper aims to study the influence of the number and distribution of drill samples on the simulation accuracy of the lithology field. This research mainly applies the variation function method in geo-statistics, and determines important indicators such as the variation, and then the lithology field is simulated by sequence index simulation. It is shown that(1) simulation error decreases with the increase of sampling density;(2) at the scale and complexity of this study, when the sampling density reaches 40/km^2, the average error of the lithology field simulation can be less than 2.0%;(3) in the study mode of examples, the simulation results of random sampling in the whole region are the most ideal, with an average error of 5.4%. The average error of the simulation results of the centralized sampling is about 10 times that of the random sampling method;(4) known from the influence analysis of the degree of study sample unevenness influence on the imitation results, under the same sample size, the simulation error decreases with the increase of the most adjacent index. When the nearest index reaches 1, the simulation error will be less than 6%, and the error variable range is within 3%.
文摘The Douala-Buea Region(DBR;4°-5°N,9°-10°30’E),a portion of the southern Cameroon passive margin,developed on the Proterozoic granito-gneissic basement and the Cretaceous to Recent volcanosedimentary cover,was explored in order to evaluate the lithology and tectonics controls on its landscape usingthequalitativeandquantitative geomorphological analyses based on 30 m resolution Digital Elevation Models(DEM)and field evidences.This area displays an uneven and complex landscape differentiated into four morphological units:Douala,Nkondjock,Kumba and Buea Units.The Douala Unit corresponds to the Coastal Plain and is extended on the Douala-Kribi/Camposedimentarybasin.The Nkondjock Unit represents a middle plateau developed on a Proterozoic granito-gneissic basement.The Kumba Unit matches with the southernmost volcanic Western Cameroon High Plateau.The Buea Unit corresponds to the Mount Cameroon stratovolcano.The relief analysis through mountain-front sinuosity(Smf,1.19–1.43)and relative relief ratio(Rr,0.10–2.31)vary from one unit to another.The drainage network analysis including drainage patterns,stepped longitudinalriverprofiles,theassociated morphometric indexes,notably the concavity index(IC,0.56–0.88),deviation(D,267–2912 m),basin asymmetry factor(A_(F),6.37–42.12),hypsometric integral(HI,0.10–0.29),valley floor width to valley height ratio(V_(f),0.36–2.75),elongation ratio(R_(e),0.30–0.50),watershed slope(S,6.88–88.88)and stream length gradient index(SL,0–3332)vary from one basin to another too.These results also show the heterogeneous and uneven DBR landscape controlled by its lithology and active tectonics.The drainage system reveals concave to concavo-convex longitudinal river profile shapes with knick points,asymmetric basins,and fault reactivations,and highlights the tectonics activity that used to occur through the time and their control on the morphology.Together,they document the lithostructural controls on the DBR landscape evolution,extendable in the whole SW Cameroon margin.
文摘The Bafoussam-Mamfe Region(BMR)belongs to the Western Cameroon Highland margin,an amalgam of transient landscape that evolved from the interactions between tectonics,lithology and climate forcings.This area is tectonically active and shows differential tectonic uplift,contrasting relief,variations in erosion rates,in river incision,and in channel gradient.In order to appraise the BMR tectono-geomorphic evolution,it is essential to understand relationships between internal and external processes and their geomorphic expression at a river basin scale.For this purpose,we use drainage texture(Dt),stream frequency(Fs),drainage density(Dd),asymmetry factor(AF),the transverse topographic symmetry factor(TTSF),the mean of mountain front sinuosity per unit(Smf),concavity factor(Cf),hypsometry integral(HI)and streamlength gradient index(SL-index)based on 30 m Digital Elevation Models(DEM)and field survey.The results reveal considerable variations in geology,relief,topography and geomorphic indices values differentiated into three geomorphic units;the Mamfe unit developed on the Mamfe Cretaceous basin,the Nguti and Bafoussam high plateau units build up on the Precambrian granito-gneissic basement overlaid by a volcanic cover.The stepped(longitudinal and normalized)river profiles and complex hypsometric curves show the lithostructural control of the hydrographic network.Dt(from~1.21 to~4.59),Fs(from~0.26 to~1.91),Dd(from~0.66 to~1.71)geomorphic indice values indicate a part of lithologic control on this morphology while the AF(from~1.16to~24.91),TTSF(from~0.20 to~0.71),Smf(U2=1.11 and U3=1.19),Cf(from~-20.91 to~78.93),HI(from~0.12 to~0.52)and SL-index designate the active tectonics as the main factor that had controlled the morphology of this same area.Above results pinpoint the combined post-Pan-African to Recent tectonic features,lithologic heterogeneities and the differential erosion processes as main factors that have controlled the BMR landscape.These results highlight how the Central African surface and the West African passive margin evolved since Proterozoic time.
