珠江口盆地惠州地区珠江组砂体上倾尖灭的地质-地球物理“逐级预测”方法

砂体上倾尖灭油气藏是岩性油气藏中重要类型之一,砂体上倾尖灭的刻画与描述是上倾尖灭圈闭有效性评价的关键。在以三角洲前缘沉积为主构成的三级层序内,三角洲沉积相关砂体上倾尖灭的地质-地球物理“逐级预测”描述方法对于认识上倾尖灭油气藏分布规律及其油气勘探具有重要意义。该方法由5个部分组成:在三级层序识别的基础上,运用高精度层序地层划分技术建立了四级层序构成的高频层序地层格架;在高频层序约束下,利用地震沉积学技术描述沉积相的平面分布;在地质模型指导下,利用频谱成像技术定性确定尖灭带的分布;利用相控储层反演半定量、定量预测砂体尖灭线;根据不同成因砂体的沉积特点,利用正演模拟技术开展尖灭线的外推预测。     

重庆南川三泉奥陶系宝塔组碳同位素特征及地层对比

对重庆市南川区三泉镇宝塔组进行连续而高密度的碳、氧同位素和牙形刺采样与分析。分析结果显示,碳同位素值及曲线形态与晚奥陶世凯迪期碳同位素正漂移事件Gutternberg Inorganic Carbon Excursion (GICE)一致,并显示出的三个次级峰值。宝塔组自下而上发育牙形刺:Protopangerodus insculptus带和Hamarodus brevirameus带。通过与四川盆地及周缘地区其他剖面宝塔组碳同位素曲线的对比,发现GICE事件在不同剖面发育程度不完全一致,南部发育较北部更全,宝塔组起始沉积时间有差异。通过与湖北、安徽、塔里木盆地、北美和瑞典地区的对比,认为中扬子地区宝塔组可能发育不完全;塔里木盆地其浪组与四川盆地宝塔组可对比;再次证实GICE事件具有全球性属性,其多次波动的特征可能与地球古海洋环境变化和奥陶纪生物大辐射有密切关系。     

Stratigraphic evolution of the nearshore to fluvial plain of the Upper Cuyo Group,Neuquén,Argentina

The upper portion of the Cuyo Group in the Zapala region, south‐eastern Neuquén Basin (Western Argentina), encompasses marine and transitional deposits (Lajas Formation) overlain by alluvial rocks (Challacó Formation). The Challacó Formation is covered by the Mendoza Group above a second‐order sequence boundary. The present study presents the stratigraphic framework and palaeophysiographic evolution of this Bajocian to Eo‐Calovian interval. The studied succession comprises the following genetic facies associations: (i) offshore and lower shoreface–offshore transition; (ii) lower shoreface; (iii) upper shoreface; iv) intertidal–subtidal; (v) supratidal–intertidal; (vi) braided fluvial to delta plain; (vii) meandering river; and (viii) braided river. The stratigraphic framework embraces four third‐order depositional sequences (C1 to C4) whose boundaries are characterized by the abrupt superposition of proximal over distal facies associations. Sequences C1 to C3 comprise mostly littoral deposits and display well‐defined, small‐scale transgressive–regressive cycles associated with fourth‐order depositional sequences. Such high‐frequency cycles are usually bounded by ravinement surfaces associated with transgressive lags. At last, the depositional sequence C4 delineates an important tectonic reorganization probably associated with an uplift of the Huincul Ridge. This is suggested by an inversion of the transport trend, north‐westward during the deposition of C1 to C3 depositional sequences (Lajas Formation) to a south‐west trend during the deposition of the braided fluvial strata related to the C4 depositional sequence (Challacó Formation).     

渤海海域黄河口南斜坡火山岩地层划分及意义

渤海海域黄河口南斜坡新生代火山岩规模大,喷发期次多,非均质性强,地震反射杂乱,地层划分对比难度大。为了厘定渤海海域黄河口南斜坡火山岩系地层层位,对研究区火山岩的岩石学特征及火山岩系夹层中的化石展开系统研究。薄片分析结果表明,渤海海域黄河口南斜坡火山岩主要分为火山熔岩和火山碎屑岩两大类,其中火山熔岩主要有杏仁状玄武岩、气孔玄武岩、致密玄武岩、辉绿岩以及角砾熔岩四种,火山碎屑岩以凝灰岩为主。结合渤海海域黄河口南斜坡火山岩中常见铁方解石、沸石、绿泥石等热水沉积矿物、部分玄武岩保存有淬碎结构、氧化系数(Fe2O3/FeO)低以及火山岩与黑色泥岩互层等四方面,证据证实研究区部分火山岩具有水下喷发特征。渤海海域黄河口南斜坡火山岩系夹层中发现了丰富的介形虫、藻类和孢粉化石,指示火山岩系上段为东营组二段沉积,火山岩系下段主体为东营组三段。根据化石的层位指示意义,明确黄河口南斜坡东营组三段沉积时期物源主要来自莱北低凸起的中生界和沙河街组一段地层。通过化石的古环境指示意义,对这套地层的形成过程进行恢复。这套地层层位的落实对明确黄河口南斜坡新生代油气成藏规律具有重要意义。     

滇黔北威信凹陷晚二叠世沉积环境与层序地层格架下的聚煤规律浅析

针对滇黔北威信凹陷晚二叠世含煤岩系的“海相-海陆过渡相-陆相”三相变化地带,利用地层剖面上的沉积构造、岩石组合、古生物特征等沉积相判别标志分析研究区的沉积环境及其空间演化,并总结煤质变化规律。在此基础上,通过识别层序与体系域关键界面,建立研究区晚二叠世含煤岩系的层序地层格架,充分讨论研究区厚煤层在层序地层格架下的聚煤规律。研究区自西向东依次为河流冲积平原体系、三角洲-潮坪体系及碳酸盐岩台地体系,成煤环境主要为河流冲积平原中的泛滥盆地河漫沼泽和三角洲-潮坪沉积体系中的上三角洲平原;厚煤层在层序地层中的位置与古地理背景有关,研究区C15,C19煤层形成于最大海泛面附近,C25煤层形成于初始海泛面附近;根据煤质变化规律和煤厚变化特征,在研究区西部的彝良-盐津一带有寻找优质煤炭资源的潜力。     

冀中饶阳凹陷西柳10断块古近系沙三段-沙二段层序地层及沉积演化

为了探讨饶阳凹陷蠡县斜坡北东缘西柳10断块古近系沙河街组沙三段-沙二段(Es~3-Es~2)层序地层特征及其沉积特征,依据高分辨率层序地层学理论,结合岩心、测井等资料,对研究区沙三段-沙二段层序地层进行划分,对其沉积特征、相带展布及其演化规律进行研究。研究结果表明,沙河街组沙三段-沙二段可划分为4个III级旋回,11个IV级旋回,32个V级旋回。沉积物岩性以细砂岩、粉砂岩及泥岩为主,沉积环境主要为辫状河三角洲平原和三角洲前缘,划分出7种沉积微相。结合研究区区域构造演化及沉积背景,认为沙三段-沙二段沉积时期,主要经历湖退到湖进的演变过程。     

四川盆地元坝地区长兴组—飞仙关组高精度层序地层格架的建立及礁滩储集层预测

为进一步落实四川盆地元坝地区上二叠统长兴组—下三叠统飞仙关组超深层海相礁滩大气田沉积相带及储集层发育特征,通过井震互馈建立了高精度等时层序地层格架,并揭示沉积相带展布和储集层发育明显与层序地层格架密切相关。在此基础上,开展了针对台缘礁滩带的沉积相敏感性属性提取、反演及沉积相对应性分析,系统刻画了礁滩体的生长特征。钻井验证分析揭示,依据高精度层序地层格架预测的礁滩储集层发育特征与钻井揭示的情况吻合度高,有效地解释了多口井在礁滩发育相带试获超百万方高产工业气流的原因。刻画了元坝气田陆棚相、台缘斜坡相、台缘相、开阔台地相、局限台地相,及次级相包括生屑滩、台缘礁滩、台缘生物礁、鲕粒滩和滩间海的平面展布特征,为元坝地区勘探开发一体化建设奠定了良好的基础。     

Large‐scale connectivity of fluvio‐deltaic stratigraphy: Inferences from simulated accommodation‐to‐supply cycles and automated extraction of chronosomes

Multiscale simulation of fluvio‐deltaic stratigraphy was used to quantify the elements of the geometry and architectural arrangement of sub‐seismic‐scale fluvial‐to‐shelf sedimentary segments. We conducted numerical experiments of fluvio‐deltaic system evolution by simulating the accommodation‐to‐sediment‐supply (A/S) cycles of varying wavelength and amplitude with the objective to produce synthetic 3‐D stratigraphic records. Post‐processing routines were developed in order to investigate delta lobe architecture in relation to channel‐network evolution throughout A/S cycles, estimate net sediment accumulation rates in 3‐D space, and extract chronostratigraphically constrained lithosomes (or chronosomes) to quantify large‐scale connectivity, that is, the spatial distribution of high net‐to‐gross lithologies. Chronosomes formed under the conditions of channel‐belt aggradation are separated by laterally continuous abandonment surfaces associated with major avulsions and delta‐lobe switches. Chronosomes corresponding to periods in which sea level drops below the inherited shelf break, that is, the youngest portions of the late falling stage systems tract (FSST), form in the virtual absence of major avulsions, owing to the incision in their upstream parts, and thus display purely degradational architecture. Detailed investigation of chronosomes within the late FSST showed that their spatial continuity may be disrupted by higher‐frequency A/S cycles to produce “stranded” sand‐rich bodies encased in shales. Chronosomes formed during early and late falling stage (FSST) demonstrate the highest large‐scale connectivity in their proximal and distal areas, respectively. Lower‐amplitude base level changes, representative of greenhouse periods during which the shelf break is not exposed, increase the magnitude of delta‐lobe switching and favour the development of system‐wide abandonment surfaces, whose expression in real‐world stratigraphy is likely to reflect the intertwined effects of high‐frequency allogenic forcing and differential subsidence.     

Detrital zircon age spectra of middle and upper Eocene outcrop belts,U.S. Gulf Coast region

Recently reported detrital zircon (DZ) data help to associate the Paleogene strata of the Gulf of Mexico region to various provenance areas. By far, recent work has emphasised upper Paleocene‐lower Eocene and upper Oligocene strata that were deposited during the two episodes of the highest sediment supply in the Paleogene. The data reveal a dynamic drainage history, including (1) initial routing of western Cordilleran drainages towards the Gulf of Mexico in the Paleocene, (2) an eastward shift of the western continental divide, from the Jura‐Cretaceous cordilleran arc to the eastern edge of the Laramide province after the Paleocene and (3) a southward shift, along the eastern Laramide province, of the headwaters of river systems draining to the Mississippi and Houston embayments at some time between the early Eocene and Oligocene. However, DZ characterisation of most (~20 Myr) of the middle Eocene‐lower Oligocene section remains limited. We present 60 DZ age spectra, most of which are from the middle or upper Eocene outcrop belts, with 50–200‐km spacing. We define six to eight distinct groups of DZ age spectra for middle and upper Eocene strata. Data from this and other studies resolve at least six substantial temporal changes in age spectra at various positions along the continental margin. The evolving age spectra constrain the middle and upper Eocene drainage patterns of large parts of interior North America. The most well‐resolved aspects of these drainage patterns include (1) persistent rivers that flowed from erosional landscapes across the Paleozoic Appalachian orogen either into the low‐lying Mississippi embayment or directly into the eastern Gulf; (2) at least during marine regressions, a trunk channel that likely flowed southward along the axial part of Mississippi Embayment and integrated tributaries from the east and west; and (3) rivers that flowed to the Houston embayment in the middle Eocene that likely originated in the Laramide province in central Colorado and southern Wyoming, as Precambrian basement highs in those source areas were being unroofed.     

Low‐accommodation and backwater effects on sequence stratigraphic surfaces and depositional architecture of fluvio‐deltaic settings (Cretaceous Mesa Rica Sandstone,Dakota Group,USA)

The adequate documentation and interpretation of regional‐scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. However, this is often challenged by the amalgamated nature of low‐accommodation settings and control of backwater hydraulics on fluvio‐deltaic stratigraphy. Exhumed examples of full‐transect depositional profiles across river‐to‐delta systems are key to improve our understanding about interacting controlling factors and resultant stratigraphy. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA), which allows mapping of down‐dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio‐deltaic deposition in the Tucumcari sub‐basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down‐dip into single‐story channel sandstones and eventually into contemporaneous distributary channels and delta‐front strata. Down‐dip changes reflect accommodation decrease towards the paleoshoreline at the Tucumcari basin rim, and subsequent expansion into the basin. Additionally, multi‐storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised‐valley fill deposits, based on their regional occurrence, estimated channel tops below the surrounding topographic surface and coeval downstepping delta‐front geometries. This opposes criteria offered to differentiate incised valleys from flood‐induced backwater scours. As the incised valleys evidence relative sea‐level fall and flood‐induced backwater scours do not, the interpretation of incised valleys impacts sequence stratigraphic interpretations. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS). The RCS’ diachronous nature demonstrates that its down‐dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. Formation of a regional composite scour in the fluvial realm throughout a relative sea‐level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low‐accommodation settings to dominantly promote bypass, especially during forced regressions. Source‐to‐sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea‐level cycle.