Turbidite Petroleum Geology Updates in the Deepwater and Subsalt Gulf of Mexico

The past six years （2008-2014） was a prosperous time for exploration and production in the dGOM （deepwater Gulf of Mexico）. Recent exploration and production activities can be divided into three major categories： drilling new wildcat wells, appraising and developing newly discovered fields and enhanced oil recovery of mature fields. Seismic imaging, complex geology, high pressure drilling, greater depth, and higher temperature are key challenges for the exploration and production of dGOM reservoirs. Complex geology includes salt-related structures and traps, reservoir compartmentalization, and the sequence stratigraphy of turbidite reservoirs. Turbidite sequence stratigraphy helps the asset team to fred the best target intervals. Sheet and channelized sandstones with good downdip aquifer support are preferred reservoir conditions. All the drilling, development and production challenges are related to high pressure, greater depth, higher temperature and lack of existing field analogs. Various IOR （improved oil recovery） methods are studied and applied in the development stage of the Wilcox fields, which have an average primary recovery factor of 10%-15%. With ideal tabular reservoir geometry and IOR methods, recovery factor of the Wilcox reservoirs can reach up to 42% of OOIP （origional oil in place） through the field life cycle.

Geochemical characterization of aromatic hydrocarbons in crude oils from the Tarim,Qaidam and Turpan Basins,NW China

Based on the systematic study of aromatic hydrocarbons in over 100 crude oil samples collected from the Tabei and Tazhong uplifts in the Tarim Basin,the western depression area in the Qaidam Basin and the Tabei depression in the Turpan Basin,the geochemical characteristics of the marine（Tarim Basin）,saline lacustrine（Qaidam Basin）,and swamp（Turpan Basin） oils were investigated.The marine oils from the Tarim basin are characterized by relatively low abundance of diaromatic hydrocarbons such as biphenyl and naphthalene,and relatively high abundance of triaromatic hydrocarbons including phenanthrene,dibenzothiophene and fluorene.In contrast,the swamp oils from the Turpan Basin are dominated by the highest relative abundance of diaromatic hydrocarbons and the lowest relative abundance of triaromatic hydrocarbons in all the oil samples in this study.The relative abundance of diaromatic and triaromatic hydrocarbons in the saline lacustrine oils from Qaidam Basin is between that in Tarim oils and Turpan oils.Aromatic parameters based on the isomer distributions of dimethylnaphthalenes（DMN）,trimethylnaphthalenes（TMN）,tetramethylnaphthalenes（TeMN） and methylphenanthrenes（MP）,i.e.,1,2,5-trimethylnaphthalene（TMN）/1,3,6-TMN ratio,1,2,7-TMN/1,3,7TMN ratio,（2,6-＋2,7-）-dimethylnaphthalenes（DMN）/1,6-DMN ratio,1,3,7-TMN/（1,2,5-＋1,3,7-）TMN,1,3,6,7-TeMN/（1,3,6,7-＋1,2,5,6-＋1,2,3,5-）-TeMN ratio and MP index,may reflect the diversity of organic source input,thermal maturity and depositional environments.In addition,the dibenzothiophenes（DBTs）/fluorenes（Fs） and dibenzofurans（DBFs）/Fs ratios were found to the very useful and effective in determining genetic types of crude oils for the marine,saline lacustrine,and swamp depositional environments,and for oil-oil correlations.

Unusual N-Alkane Distributions in Extracts from Marine Carbonate Rocks at High Levels of Maturity and Overmaturity

N\|alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field of the Sichuan Basin, are characterized by bimodal distributions with the dominant carbon numbers in the range C\- 17 \|C\- 21 and C\- 25 \|C\- 29 . In most samples, the lower carbon number components are present in greater abundance than the higher carbon number ones. Most samples contain significant concentrations of waxy hydrocarbons(C\- 22+ ) with C\- 21- /C\- 22+ ratios between 0.50 to 3.16, and an average value of 1.34. The n\|alkanes in extracts of outcrops and shallow core samples of Upper Proterozoic and Lower Palaeozoic carbonate rocks in the western and southern parts of the North China Basin are of unimodal distributions dominated by n\|alkanes maximizing in the C\- 25 \|C\- 29 range. These extracts have very high concentrations of waxy hydrocarbons with C\- 21- /C\- 22+ ratios all <1.0, ranging from 0 14 to 0 90 and averaging 0.36. All of the extracts have a marked odd/even predominance in the high molecular weight n\|alkane range regardless of whether they are from shallow or deep cores or outcrop samples. Simulation experiments were performed using typical sapropelic\|type kerogens from the immature Sinian Lower Xiamalin Formation carbonate\|rich shales collected at Jixian, Hebei Province, North China Basin, and the contemporary microplanktonic blue\|green algae Spirulina subsala. Results indicate that the unusual distribution of n\|alkanes in the extracts of Upper Proterozoic and Lower Palaeozoic carbonate rocks possibly originated from algae in the source rocks at high levels of maturity and overmaturity.

Geochemical characteristics of saturate hydrocar-bons in crude oils and source rocks of the Qaidam,Tarim,Tupran basins,NW China

Based on the systematic analyses of fifteen typical crude oils and ten typical potential source rocks col-lected from the Qaidam,Tarim and Turpan basins,Northwest China,the geochemical characteristics of the oils and source rocks were investigated and oil-source rock correlations undertaken.The oils and source rocks deposited in saline lacustrine environment from the western Qaidam Basin were characterized by n-alkanes with even car-bon-number preference in the C20-C28 range,low pristane/phytane(Pr/Ph) ratios(less than 0.5),and high abundances of C27 steranes,gammacerane and C35 hopanes.The oils and source rocks deposited in marine environment from the Tarim Basin were characterized by n-alkanes with even carbon-number preference in the C14-C18 range,relatively low Pr/Ph ratios(near to 1),high abundance of C28 steranes,and relatively high gammacerane.In contrast,the oils and source rocks deposited in terrigenous bog environment from the Turpan Basin were characterized by relatively high Pr/Ph ratios(oil samples greater than 6) high abundance of C29 steranes,and relatively low gammacerane and C31-35 hopanes.The higher amounts of C37 and C38 n-alkanes of source rocks from the western Qaidam Basin and the Tarim Basin suggest an origin of these alkanes from functionalized C37 and C38 n-alkadienes and alkenones in prymnesiophytes living in lacustrine and marine environments.Oil-source rock correlations suggest oils in the west-ern Qaidam Basin were derived from the Oligocene Lower Ganchaigou Formation(E3),oils in the Tabei and Tazhong uplifts from the Tarim Basin have a genetic relationship with the Middle-Upper Ordovician source beds.Oils in the Turpan Basin generally fall into two genetic types.Most oils in the Taibei depression from the Turpan Basin were derived from the Lower-Middle Jurassic coal measures,but the fewer oils in this region are a mixed source derived from the Lower-Middle Jurassic coal measure and the Upper Permian source rocks.

Light hydrocarbon geochemistry:insight into oils/condensates families and inferred source rocks of the Woodford–Mississippian tight oil play in North-Central Oklahoma,USA

The Woodford–Mississippian"Commingled Production"is a prolific unconventional hydrocarbon play in Oklahoma,USA.The tight reservoirs feature variations in produced fluid chemistry usually explained by different possible source rocks.Such chemical variations are regularly obtained from bulk,molecular,and isotopic characteristics.In this study,we present a new geochemical investigation of gasoline range hydrocarbons,biomarkers,and diamondoids in oils from Mississippian carbonate and Woodford Shale.A set of oil/condensate samples were examined using high-performance gas chromatography and mass spectrometry.The result of the condensates from the Anadarko Basin shows a distinct geochemical fingerprint reflected in light hydrocarbon characterized by heptane star diagrams,convinced by biomarker characteristics and diamantane isomeric distributions.Two possible source rocks were identified,the Woodford Shale and Mississippian mudrocks,with a variable degree of mixing.Thermal maturity based on light hydrocarbon parameters indicates that condensates from the Anadarko Basin are of the highest maturity,followed by"Old"Woodford-sourced oils and central Oklahoma tight oils.These geochemical parameters shed light on petroleum migration within Devonian–Mississippian petroleum systems and mitigate geological risk in exploring and developing petroleum reservoirs.

Retraction Note to:Light hydrocarbon geochemistry:insight into oils/condensates families and inferred source rocks of the Woodford-Mississippian tight oil play in North-Central Oklahoma,USA

Retraction Note to:Petroleum Science(2020)17:582-597https://doi.org/10.1007/s12182-020-00441-1The authors have retracted their article(Wang et al.2020)because of significant textual overlap with previously published works(Atwah et al.2019;Wang and Paul Philp 2019).All authors agree with this retraction.

Inverse spectral decomposition using an I_p-norm constraint for the detection of close geological anomalies

An important application of spectral decomposition(SD)is to identify subsurface geological anomalies such as channels and karst caves,which may be buried in full-band seismic data.However,the classical SD methods including the wavelet transform(WT)are often limited by relatively low time-frequency resolution,which is responsible for false high horizonassociated space resolution probably indicating more geological structures,especially when close geological anomalies exist.To address this issue,we impose a constraint of minimizing an lp(0<p<1)norm of time-frequency spectral coefficients on the misfit derived by using the inverse WT and apply the generalized iterated shrinkage algorithm to invert for the optimal coefficients.Compared with the WT and inverse SD(ISD)using a typical l1-norm constraint,the modified ISD(MISD)using an lp-norm constraint can yield a more compact spectrum contributing to detect the distributions of close geological features.We design a 3 D synthetic dataset involving frequency-close thin geological anomalies and the other3 D non-stationary dataset involving time-close anomalies to demonstrate the effectiveness of MISD.The application of 4 D spectrum on a 3 D real dataset with an area of approximately 230 km2 illustrates its potential for detecting deep channels and the karst slope fracture zone.

龙门山断裂带隆起造山独特性探讨

龙门山断裂带位于四川盆地西缘,青藏高原东部,为四川盆地与松潘—甘孜地块的接触构造边界。龙门山地区海拔从东侧100 km外四川盆地的500 m突升至3 000 m高度,明显地标注了青藏高原的东部边界,其隆升机制也引起了国内外地质工作者的广泛兴趣,并且提出了多种隆升机制模型。在本次研究中,我们利用SinoProbe-02深反射地震剖面数据对龙门山地区的隆升机制进行研究,从而进一步探讨龙门山地区隆起造山的独特性,并讨论其与传统意义中的造山带的区别,认为龙门山断裂造山带为板块内部构造活动引起岩石圈隆起所形成的。本文的研究结果将使我们更深刻地了解龙门山地区的构造活动特点,并且有助于了解青藏高原东缘对印度-欧亚板块碰撞的构造响应。

宽角反射、折射地震数据与重力数据综合解释龙门山及邻近地区地壳结构

青藏高原东部的隆升机制一直都是地学界的研究热点，研究学者们提出和发展了多种岩石圈变形模型，而存在多种模型的主要原因之一是对青藏高原东部地壳及岩石圈结构认识不足。本文主要针对SinoProbe-02项目横跨龙门山断裂带、全长400多公里的宽角、折射地震数据及重力数据进行联合反演和综合解释。研究结果表明，龙门山及邻近地区地壳结构可明确划分为上地壳、中地壳和下地壳。上地壳上层为沉积层，龙门山断裂带以西大部分区域被三叠纪复理岩覆盖，而在龙日坝断裂与岷江断裂之间出现了密度为2．7g／cm^3的高速异常体；向东靠近龙门山地区，沉积层厚度逐渐减薄。中地壳速度变化不均一，而且变形强烈；若尔盖盆地和龙门山断裂带下方出现明显低速带；中地壳在龙门山西侧厚度加厚，在岷江断裂下方和四川盆地靠近龙门山断裂带地区附近厚度达到最大。莫霍面整体深度从东往西增厚，最厚可达56km。本次研究得到的地壳结构和密度分布分析结果表明现有的地壳厚度和物质组成不足以支撑龙门山及邻近地区目前所达到的隆升高度，因此四川盆地刚性基底西缘因挤压作用产生的弯曲应力也是该地区抬升的重要条件之一。

江汉和泌阳盆地中卟啉化合物的分布

卟啉化合物在江汉、泌阳两盆地中的分布,受沉积环境及热成熟作用的控制。五元侧环上具有甲基的C_(32),C_(33)DPEP卟啉异构体在石油中的高丰度指示了一种出现在较高盐度环境中特殊生源前体以及低成熟度。在热成熟作用下,卟啉化合物的主要变化为DPEP的逐渐消失及ETIO中脱烷基及烷基化作用。DPEP/ETIO或DPEP/(DPEP+ETIO),C_(31)ETIO-A/C_(28)ETIO-B及ETIO-AC_(31)/C_(30)等比值可用作热成熟度指标。

基于ALOS—PALSAR卫星数据对青藏高原东缘龙日坝断裂带地表构造伸展的研究及其大地构造指示意义

龙日坝断裂带位于青藏高原最东缘，呈北东—南西向延伸，平行于其东侧的龙门山断裂带，二者大约相距150km。与龙门山断裂带不同的是，龙日坝断裂带在青藏高原东缘相关GPS测量中表现为一明显的速度梯度带，说明龙日坝断裂带可能具有很重要的构造属性。然而有关龙日坝断裂带的地表结构构造延伸问题一直悬而未决，目前还存在许多的争议，这在一定程度上也阻碍了我们对青藏高原东缘相对于印度—欧亚板块碰撞地球动力学响应的了解。在本次研究中，我们将首次采用ALOS—PALSAR卫星数据，并结合地表地质和前人的地球物理学研究成果，来监测与龙日坝断裂带的构造活动相关的细微地表形变，并由此控制龙日坝断裂带的延伸范围。研究结果表明，龙日坝断裂带与其西南侧的抚边河断裂带相交且近乎垂直，而非前人研究所认为的龙日坝断裂带延伸至其西缘的鲜水河断裂带。综合研究结果也为了解龙日坝断裂带的大地构造属性提供了数据支持。

SegNet-based first-break picking via seismic waveform classification directly from shot gathers with sparsely distributed traces

Manually picking regularly and densely distributed first breaks(FBs)are critical for shallow velocitymodel building in seismic data processing.However,it is time consuming.We employ the fullyconvolutional Seg Net to address this issue and present a fast automatic seismic waveform classification method to pick densely-sampled FBs directly from common-shot gathers with sparsely distributed traces.Through feeding a large number of representative shot gathers with missing traces and the corresponding binary labels segmented by manually interpreted fully-sampled FBs,we can obtain a welltrained Seg Net model.When any unseen gather including the one with irregular trace spacing is inputted,the Seg Net can output the probability distribution of different categories for waveform classification.Then FBs can be picked by locating the boundaries between one class on post-FBs data and the other on pre-FBs background.Two land datasets with each over 2000 shots are adopted to illustrate that one well-trained 25-layer Seg Net can favorably classify waveform and further pick fully-sampled FBs verified by the manually-derived ones,even when the proportion of randomly missing traces reaches50%,21 traces are missing consecutively,or traces are missing regularly.

Deep resistivity "turnover" effect at oil generation "peak" in the Woodford Shale,Anadarko Basin,USA

The Devonian Woodford Shale in the Anadarko Basin is a highly organic,hydrocarbon source rock.Accurate values of vitrinite reflectance(R_o)present in the Woodford Shale penetrated by 52 control wells were measured directly.These vitrinite reflectance values,when plotted against borehole resistivity for the middle member of the Woodford Shale in the wells,display a rarely reported finding that deep resistivity readings decrease as R_o increases when R_o is greater than 0.90%.This phenomenon may be attributed to that aromatic and resin compounds containing conjugated pi bonds generated within source rocks are more electrically conductive than aliphatic compounds.And aromatic and resin fractions were generated more than aliphatic fraction when source rock maturity further increases beyond oil peak.The finding of the relationship between deep resistivity and R_o may re-investigate the previously found linear relationship between source rock formation and aid to unconventional play exploration.

C_(30)-C_(32) LANOSTANES——A NOVEL SERIES OF TETRACYCLIC TRITERPENOID HYDROCARBONS IDENTIFIED IN CHINESE TERTIARY LACUSTRINE SEDIMENTS

A series of novel tetracyclic triterpanes based on the lanostane skeleton, ranging in cars-bon number from C_(30) to C_(32), were identified for the first time in Eocene lacustrine depo-its of Biyang Depression, China. These compounds have been identified by GC, GC- MS, andcoinjection with authentic standard, as 8β(H), 9α(H)- lanostane (C_(30)), 24-methyl- lanostane(C_(31)) and 24- ethyl- lanostane (C_(32)). Mechanisms are proposed for the origin and geologicalfate of these compounds. To the best of our knowledge, this is the first confirmed occur-rence of lanostanes in the sedimentary record.

综合地球物理资料揭示青藏高原东缘龙日坝断裂带构造属性和大地构造意义

龙日坝断裂带位于松潘-甘孜地块的东北部,距离其东侧龙门山断裂带大约200km.龙日坝断裂带具有右旋逆冲活动特征,呈北东向展布,与龙门山断裂带基本平行.这条新发现的陆内走滑断裂带由于其特殊的地理位置,目前已引起了广泛的关注.本文利用重力数据的处理和解释,并结合SinoProbe-02深反射地震剖面数据进行由段到面的综合研究,揭示了扬子板块西部边界的伸展和龙日坝断裂带的构造属性.结果显示扬子板块西边界呈不规则分布,而龙日坝断裂带的形成与扬子板块的不规则分布有关.扬子西边界的北段已越过龙门山断裂带延伸至龙日坝断裂带附近,南段则逐渐沿龙门山断裂带分布.龙日坝断裂带代表了扬子板块结晶基底延伸的最西端.印度-欧亚板块碰撞造成了青藏高原物质北东-东向运移.至松潘地块东缘,由于受扬子板块结晶基底的阻挡,在龙日坝断裂带附近产生了应力差而形成了龙日坝断裂带.本文的研究结果将有助于我们更好的了解青藏高原东缘对印度板块与欧亚板块陆陆碰撞所产生的构造响应,以及揭示青藏高原东缘地震灾害发生机制.