Effect of petroleum chemical fraction and residual oil content in saline lacustrine organic-rich shale: A case study from the Paleogene Dongpu Depression of North China

Halite and gypsum minerals in saline shale make the retention mechanism and chemical fractionation of residual oil unique. The Dongpu Depression in North China is a typically saline lacustrine basin with developing halite and gypsum. The effect of gypsum minerals on residual oil content and chemical fractionation remains unclear. In this study, shale samples with different gypsum contents were used in organic geochemical experiments, showing that the high total organic matter (TOC) content and type II kerogen leads to a high residual oil content, as shown by high values of volatile hydrocarbon (S1) and extractable organic matter (EOM). XRD and FE-SEM result indicate that the existence of gypsum in saline shale contributes to an enhanced pore space and a higher residual oil content in comparison to non-gypsum shale. Additionally, the increase in the gypsum mineral content leads to an increase in the saturated hydrocarbon percentage and a decrease in polar components percentage (resins and asphaltene). Furthermore, thermal simulation experiments on low-mature saline shale show that the percentage of saturated hydrocarbons in the residual oil is high and remains stable and that the storage space is mainly mesoporous (> 20 nm) in the oil expulsion stage. However, the saturated hydrocarbons percentage decreases rapidly, and oil exists in mesopores (> 20 nm and < 5 nm) in the gas expulsion stage. In general, gypsum is conducive to the development of pore space, the adsorption of hydrocarbons and the occurrence of saturated hydrocarbon, leading to large quantities of residual oil. The data in this paper should prove to be reliable for shale oil exploration in saline lacustrine basins.

Hydrocarbon charge history of the Paleogene reservoir in the northern Dongpu Depression,Bohai Bay Basin,China

The hydrocarbon charge history of the Paleogene in the northern Dongpu Depression was analyzed in detail based on a comprehensive analysis of the generation and expulsion history of the major hydrocarbon source rocks, fluorescence microscopic features and fluid inclusion petrography. There were two main stages of hydrocarbon generation and expulsion of oil from the major hydrocarbon source rocks. The first stage was the main hydrocarbon expulsion stage. The fluorescence microscopic features also indicated two stages of hydrocarbon accumulation. Carbonaceous bitumen, asphaltene bitumen and colloidal bitumen reflected an early hydrocarbon charge, whereas the oil bitumen reflected a second hydrocarbon charge. Hydrocarbon inclusions also indicate two distinct charges according to the diagenetic evolution sequence, inclusion petrography features combined with the homogenization temperature and reservoir burial history analysis. According to these comprehensive analysis results, the hydrocarbon charge history of the Paleogene reservoir in the northern Dongpu Depression was divided into two phases. The first phase was from the late Dongying depositional period of the Oligocene to the early uplift stages of the late Paleogene. The second phase was from the late Minghuazhen period of the Pliocene to the Quaternary. Reservoirs formed during the first period were widely distributed covering the entire area. In contrast,reservoirs formed during the second period were mainly distributed near the hydrocarbon generation sags. Vertically, it was characterized by a single phase in the upper layers and two phases in the lower layers of the Paleogene.

Present Geothermal Fields of the Dongpu Sag in the Bohai Bay Basin

The Dongpu sag is located in the south of the Bohai Bay basin,China,and has abundant oil and gas reserves.To date,there has been no systematic documentation of its geothermal fields.This study measured the rock thermal conductivity of 324 cores from 47 wells,and calculated rock thermal conductivity for different formations.The geothermal gradient and terrestrial heat flow were calculated for 192 wells on basis of 892 formation-testing data from 523 wells.The results show that the Dongpu sag is characterized by a medium-temperature geothermal field between stable and active tectonic areas,with an average geothermal gradient of 32.0℃/km and terrestrial heat flow of 65.6 mW/m2.The geothermal fields in the Dongpu sag is significantly controlled by the Changyuan,Yellow River,and Lanliao basement faults.They developed in the Paleogene and the Dongying movement occurred at the Dongying Formation depositional period.The geothermal fields distribution has a similar characteristic to the tectonic framework of the Dongpu sag,namely two subsags,one uplift,one steep slope and one gentle slope.The oil and gas distribution is closely associated with the present geothermal fields.The work may provide constraints for reconstructing the thermal history and modeling source rock maturation evolution in the Dongpu sag.

Key factors controlling shale oil enrichment in saline lacustrine rift basin:implications from two shale oil wells in Dongpu Depression,Bohai Bay Basin

Comparative analyses of petroleum generation potential,reservoir volume,frackability,and oil mobility were conducted on 102 shale cores from the Dongpu Depression.Results show the shale has high organic matter contents composed of oil-prone type I and type II kerogens within the oil window.Various types of pores and fractures exist in the shale,with a porosity of up to 14.9%.The shale has high brittle mineral contents,extensive fractures,and high potential for oil mobility due to high seepage capacity and overpressure.Although the petroleum generation potential of the shale at Well PS18-8 is relatively greater than that at Well PS18-1,oil content of the latter is greater due to the greater TOC.The porosity and fracture density observed in Well PS18-1 are greater and more conducive to shale oil enrichment.Although the shales in Wells PS18-1 and PS18-8 have similar brittle mineral contents,the former is more favorable for anthropogenic fracturing due to a higher preexisting fracture density.Besides,the shale at Well PS18-1 has a higher seepage capacity and overpressure and therefore a higher oil mobility.The fracture density and overpressure play key roles in shale oil enrichment.

Hydrocarbon generation history constrained by thermal history and hydrocarbon generation kinetics:A case study of the Dongpu Depression,Bohai Bay Basin,China

With the increasing exploration and development of typical hydrocarbon-rich depressions,such as the Dongpu Depression,the exploitation difficulty of shallow formations is increasing.There is an urgent need to clarify the hydrocarbon generation mode and hydrocarbon generation histories in deep formations.In this study,a gold tube-autoclave closed system was used to simulate the hydrocarbon generation processes and establish the hydrocarbon generation mode of different types of kerogen.Then,constrained by the thermal history and hydrocarbon generation kinetics,hydrocarbon generation histories were modeled.The results show that hydrocarbon generation evolution can be divided into five stages,and the maturity of each stage is different.The hydrocarbon generation history of the source rocks of the Shahejie 3 Formation mainly dates from the early depositional period of the Shahejie 1 Formation to the middle depositional period of the Dongying Formation.Hydrocarbon generation history constrained by thermal history and hydrocarbon generation kinetics is more in line with actual geological conditions.Moreover,this research can provide important hydrocarbon generation parameters for deep oil and gas exploration and exploitation of the Shahejie 3 Formation in the Dongpu Depression.

Formation of inter-salt overpressure fractures and their significances to shale oil and gas: A case study of the third member of Paleogene Shahejie Formation in Dongpu sag, Bohai Bay Basin

Taking the inter-salt organic-rich shales in the third member of Paleogene Shahejie Formation(Es3)of Dongpu sag in Bohai Bay Basin as an example,the origin of overpressure,development characteristics,formation and evolution mechanism,formation stages and geological significance on shale oil and gas of overpressure fractures in the inter-salt shale reservoir were investigated by means of thin section identification,scanning electron microscopy observation,analysis of fluid inclusions,logging data analysis,and formation pressure inversion.The results show that overpressure is universal in the salt-lake basin of Dongpu sag,and under-compaction caused by the sealing of salt-gypsum layer,pressurization due to hydrocarbon generation,transformation and dehydration of clay minerals,and fault sealing are the 4 main factors leading to the occurrence of overpressure.The overpressure fractures are small in scale,with an average length of 356.2μm and an average underground opening of 11.6μm.But they are densely developed,with an average surface density of 0.76 cm/cm2.Moreover,they are often accompanied by oil and gas charging,and thus high in effectiveness.Overpressure fractures were mainly formed during two periods of large-scale oil and gas charging,approximately 25-30 Ma ago and 0-5 Ma ago.Inter-salt overpressure fractures play dual roles as the storage space and migration paths of shale oil and gas.They contribute 22.3%to the porosity of shale reservoir and 51.4%to the permeability.They can connect fracture systems of multiple scales,greatly improving the quality of shale reservoir.During the development of shale oil and gas,inter-salt overpressure fractures can affect the extension and morphology of hydraulic fractures,giving rise to complex and highly permeable volumetric fracture networks,improving hydraulic fracturing effect and enhancing shale oil and gas productivity.

GEOTHERMALEVOLUTIONOFDONGPUDEPRESSI

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Hydrocarbon Generation Characteristics of Source Rocks from Different Saline Environments in the Dongpu Depression,Bohai Bay Basin,China

The Dongpu Depression is a secondary salt-bearing tectonic unit in the Bohai Bay Basin,eastern China.The depositional environment of this depression regarding its Paleogene strata is clearly different in plane,including the saltwater environment(SE)in the north,the freshwater environment(FE)in the south and the brackish water environment(BE)in the middle.The result of oil and gas exploration in the Dongpu Depression shows that more than 90%of the proven oil reserves are distributed in the northern saltwater environment.Previous studies indicate that the organic geochemistry characteristics and the hydrocarbon generation capacity of the source rocks are very clearly diverse under different environments,which results in the significant differences in the proved reserves between the north and the south.In order to further explore the differences in the hydrocarbon generation capacity of the source rocks under distinct depositional environments and the mechanism of their occurrence,three samples from different depositional environments(W18-5 for SE,H7-18 for BE,CH9 for FE)were used for confined gold tube pyrolysis experiments.The results show that the CH4 yields of W18-5,H7-18 and CH9 increase with increasing temperature,the maximum yields being 405.62 mg/g TOC,388.56 mg/g TOC and 367.89 mg/g TOC,respectively.The liquid hydrocarbon yields of W18-5,H7-18 and CH9 firstly increase with increasing temperature and then decrease after the critical temperatures.The maximum yields of C6-14 are 149.54 mg/g TOC,140.18 mg/g TOC and 116.94 mg/g TOC,the maximum yields of C14+being 852.4 mg/g TOC,652.6 mg/g TOC and 596.41 mg/g TOC,respectively for W18-5,H7-18 and CH9.To summarize,the order of hydrocarbon potential from high to low is W18-5,H7-18 and CH9.On this basis,through analyzing the influencing factors of hydrocarbon differences,this paper reveals that the saltwater environment is characterized by 4 factors:higher salinity,halophilic algae,high paleo-productivity and a strongly reducing environment,which are beneficial to the enrichment of organic matter and lead to the formation of high levels of sapropelite and exinite.According to the variation of oil and gas components in the pyrolysis experiments,the hydrocarbon generation process is divided into three stages:kerogen cracking,oil cracking and C2-5 cracking.Combined with hydrocarbon generation characteristics and stages,the evolutionary model of hydrocarbon generation for source rocks under different environments is established.

INVESTIGATION OF THE PALEOGEOTHERMAL TECTONIC HISTORY ON DONGPU DEPRESSION AND OIL/GAS FORMATION BY FISSION-TRACK METHOD

Dongpu depression is a fault basin at residual-mobility period of Diwa stage, it developed on the strata of the Mesozoie and Pre-Mesozoie. It is one of the important oil/gas- bearing basin during Cenozoie era along the East China. The strueture in Dongpu geodepression is very complex. There exists a strueture pattern with east- and west-depression belts and one central swell belt, it is divided into the southern- and northern-division by Gaopingji (orMeng Ju ) -Xieheng fault.

Discovery of Early Tertiary Hydrothermal Activity and Its Significance in Oil/Gas Geology, Dongpu Depression, Henan Province, China

Data from the super-deep wells (PS10, PS14 and YS1) led to the discovery of widespread metal-bearing hydrothermal fluids (or hot brines ) related to basic magrmas in the Lower Tertiary clastic sequence in the Dongpu Depression. In terms of SEM and EDAX analyses, pore-casting thin asction examination of sandstone, the composition and forming temperature of fluld inclusions, the trace element composition of mudstone and kerogen and organic geochemical analyses, it is demonstrated that the hydrothermal fluids ekisting in the area studied are ejecting fluids, which have a close bearing on diagenesis and edimentation, rather than intrusive veins along the tectonic fractures.The main indicators of hydrothermal activity are: (1 ) abnormal alteration of kerogen, (2)high-temperature alteted mineral assemblage; (3) abnormal distribution of hydrocarbons; (4) specific assemblages and abnormal contents of heavy metals in mudstone and kerogen; (5) specific composition of complex compounds and assemblages of fluid inclusions in sandstone: (6) periodic basaltic magma activity.Results of geological observations and laboratory simuating experiments demonstrated that the hydrothermal fluids have a close bearing on hydrocarbon generation in the Dongpu Depression. Two aspects of the effect of hydrothermal fluids are noticed: hydrothermal hydrocarbon production and strong metal catalysis in oil and gas generation.

Structural Characteristics of Paleozoic and Geological Significance of Oil and Gas of Dongpu Depression

The Dongpu depression has experienced a complicated evolution of structure since Mesozoic. The Paleozoic carbonate rock has been strongly reformed and the buried hills with different characteristics of structure are developed in the depression. There exist lots of groups of fault structures with strikes of NNE(or NE),NW, near NS and EW etc., of which the faults with strikes of NNE and NW play an important controlling role on present-day structural framework of the depression. The faults with near NS-striking and EW-striking deeply affect the establishment of structural framework of basement of the depression. Although most of the fractures are filled by calcite and other minerals, under the action of later structural stress, the earlier fractures could change their features into tensional ones. Therefore, much attention should be paid to the exploration and exploitation of Paleozoic oil and gas in Dongpu depression.

渤海湾盆地东濮凹陷天然气成因及分布特征

针对东濮凹陷高热演化程度区天然气成因复杂,天然气富集规律及勘探潜力认识不清等问题,文中利用聚类分析、生烃模拟实验等手段,对天然气成因类型及分布特征进行了研究。研究结果表明:东濮凹陷存在油型气、煤成气及混合气3大类天然气。其中:油型气包括低熟油型气(Ro介于0.5%~1.2%)、中熟油型气(Ro介于1.2%~1.6%)和高熟油型气(Ro介于1.6%~2.0%),依次分布于构造顶部、斜坡带、洼陷带;煤成气Ro介于2.0%~3.0%,包括源外高熟煤成气和源内高熟煤成气;而混合气主要分布在高热演化烃源灶的大断裂周围。通过对主力生气区分析发现,油型气和煤成气对应的烃源岩主力生气深度分别介于4000~5000,5000~7000 m,空间上具有接力特征。东濮凹陷天然气富集程度与生烃洼陷的热演化程度关系密切,中、高热演化洼陷(Ro介于1.0%~3.0%)将是渤海湾盆地和东濮凹陷未来天然气勘探的重点领域。

基于人工神经网络方法预测油气资源丰度——以渤海湾盆地东濮凹陷文留地区古近系沙河街组三段为例

油气资源丰度通常受多个因素控制,其相关参数信息种类繁杂、数据量庞大,应用传统的地质统计学方法定量预测准确度不高。为了快速预测油气资源量丰度并明确其主控因素,以渤海湾盆地东濮凹陷文留地区古近系沙河街组三段为例,采用基于多层感知器神经网络(MLP)方法对油气资源丰度进行定量预测,同时采用Boosting集成学习算法优化预测模型,分别对66组样本油气资源丰度数据进行预测。结果表明,训练集数据实测值与预测值相关系数分别达0.789和0.989,验证集数据实测值与预测值相关系数分别达0.618和0.825,测试数据中实测值和预测值相关系数分别达0.689和0.845;有效厚度、平均渗透率、有效孔隙度是影响油气资源丰度最主要的3个地质因素,重要性系数分别为33.93%、20.12%和19.53%,圈闭面积、地面原油密度、生烃中心贡献等参数为次要影响因素。采用Boosting集成学习算法优化之后的多层感知器模型预测准确性得到了很大的提升,能为有利目标优选及勘探开发方案调整提供可靠依据,为凹陷内其他区块油气资源评价提供较好的参考和借鉴。

东濮凹陷多断多凸多洼构造特征及成因

从渤海湾盆地入手研究东濮凹陷的构造特征,利用地震剖面、钻井、测井等资料对东濮凹陷进行分区、分带、全层系构造解析。研究表明:1)东濮凹陷印支期挤压南北分区,燕山期弱挤压、古近纪沙四段-沙三段沉积期强烈拉张东西分带,古近纪晚期开始强走滑-弱拉张错断成块,具有多应力叠合时空演化的构造特征,呈现平面上隆洼相间、垂向上洼中有隆、断裂棋盘式交错的构造格局。2)东濮凹陷宏观上经历了四期构造演化,发育逆冲-拉张-走滑断裂系统,根据构造变形应力期次叠合特征,将中-古生界构造样式分为两类九种,古近系构造样式主要分为背斜、断阶和背形三大类共十四种。3)板块构造活动引起的地幔上拱和深断裂右旋走滑位移是东濮凹陷新生代形成的根本动力学原因;古近系基底横向构造的存在、兰聊断层活动分期分段性差异及控洼断层大量发育,单断大洼向多断多凸多洼转变;古近纪晚期浅层发育大量的四五级断层对洼陷和凸起进行调节改造,走滑构造应力逐步加强,断层在平面上分布形态从侧列变为羽列,导致多断多凸多洼格局发生扭动构造变形,复杂的断块群构造定型,早期形成的油气藏被调整改造,为东濮凹陷精细勘探和开发提供重要支撑。

东濮凹陷前梨园洼陷南部深盆气有利目标评价

依据烃源岩品质、盐岩分布以及烃源岩热演化程度的分析,认为东濮凹陷沙三下亚段是深盆气有利勘探区面积最大的区域,为深盆气风险勘探的首选层系。根据储集条件、盖层与保存条件优选勘探区带。前梨园洼陷南部沙三下亚段可细分为两套储盖组合,其特点在于断层较少、封堵性良好,被选定为深盆气的勘探区带。针对前梨园洼陷南部沙三下亚段的3砂组、5砂组、6砂组和7砂组这四套湖底扇储层,采用井控拓频技术以提高砂体纵向分辨能力。在优选勘探目标时,优选杜寨断层下降盘靠近物源区、储层厚度最大的构造-岩性圈闭进行风险勘探。这一策略为东濮老区天然气增储建产接替阵地指明了明确的方向。

致密油运聚动力研究——以渤海湾盆地东濮凹陷Wg4井沙三中致密油为例

以东濮凹陷中央隆起带北部的文、卫、濮结合部Wg4井沙三中亚段致密油为例,开展流体包裹体古温压分析,结合盆地模拟技术,动态展现其致密油的运聚动力——烃源岩生烃增压作用。沙三中亚段致密储层于东营期构造抬升时,烃类发生幕式充注,烃包裹体Ⅰ,Ⅱ先后被捕获。致密油充注时期为古近纪末期(约19.5~17.5 Ma);基于烃包裹体捕获压力、深度可知致密油充注为超压充注,超压系数分别为1.54,1.26。通过生物标志化合物谱图及参数对比追溯的下伏烃源岩,在古近纪末期达到成熟阶段,保留有大量生烃所形成的高压。烃类超压充注与邻近下伏烃源岩生烃增压史具有良好的匹配性,有力地证实了致密油的运聚动力主要为烃源岩生烃增压作用,这对于致密油层段优选具有积极的意义,需聚焦优质烃源岩的发育规模、生烃史以及近源型油气聚集。

东濮凹陷古近系沙河街组页岩油储层岩石学及微观孔隙结构特征

泥页岩的岩石学及微观孔隙结构特征是评价页岩油气储集性能的关键指标。通过岩心观察、薄片鉴定、扫描电镜、压汞-液氮吸附联合测定及微米CT三维重构等实验分析,对东濮凹陷沙河街组页岩油储层的岩石学特征、岩相类型、孔缝类型、孔喉分布及含油性特征等进行研究。实验分析结果表明,东濮页岩油储层矿物组分主要为黏土矿物、碳酸盐矿物,含有少量长英质矿物,主要的岩相类型包括纹层状灰岩相、纹层状黏土岩相、纹层状灰质细粒混合岩相、纹层状黏土质细粒混合岩相、块状黏土岩相和块状白云岩相;储集空间包括晶间孔、粒内溶蚀孔、黏土矿物晶间孔及有机质孔,微裂缝可分为成岩缝和构造缝,纹层状灰岩相和纹层状灰质细粒混合岩相的储集空间类型多样,储集空间相对较大。岩相和层理构造是影响储层孔隙发育及优劣的重要因素,纹层状灰质细粒混合岩、纹层状灰岩相及纹层状黏土质细粒混合相孔隙尺寸大,孔喉连通性较好,裂缝较为发育,同时具有好的含油性及可动性,其中以纹层状灰岩相最优,它们是东濮凹陷页岩油重点勘探对象。

郯庐断裂右旋走滑活动对东濮凹陷构造演化的影响

太平洋板块俯冲方向改变,造成郯庐断裂由左旋向右旋走滑转变,渤海湾盆地东部各个凹陷对该构造事件响应明显,盆地西部的东濮凹陷是否受其影响以及影响程度如何直接影响东濮地震解释方案的制定。结合三维地震和深部地球物理资料,分析兰聊断层的控盆特征;根据雁列断层组合演化与区域年代资料,探讨雁列组合与区域构造活动的耦合关系;通过低序级断层走向统计,明确该区新生代所处的应力场特征。结果表明:兰聊断层西部分支是控制东濮凹陷整体结构的关键断层;雁列断层组合形成时间与区域右旋走滑耦合性差;东濮地区古近纪应力场稳定,未见板块俯冲方向改变前后的明显差异;拉张应力是东濮新生代构造演化主要动力,右旋扭应力对该区构造影响较小。

基于密集台阵的东濮凹陷中北段浅层速度结构

文中利用布设在东濮凹陷中北段由412个台站组成的密集台阵记录的数据,基于噪声成像技术获得了研究区0~3.5km的三维S波速度模型,所得结果显示速度结构特征与断裂的形态展布特征具有较强的关联性。主要得到的认识包括:1)东濮凹陷中北段呈低速,两侧的内黄隆起和鲁西隆起为高速特征,隆起和凹陷的速度差异至少持续到3.5km深度处。2)东濮凹陷和鲁西隆起高、低速的分界位置与兰聊断裂一致。3)在1~3.5km深度处,东濮凹陷中北段表现出了明显的低速特征,说明古近纪兰聊断裂的活动强烈,影响了东濮凹陷中北段的沉积特征;在0~1km深度处,凹陷和隆起的速度差异减小,说明兰聊断裂在新近纪和第四纪的活动变弱,该时期的沉积构造受兰聊断裂的影响减小。

挥发性致密油藏孔隙结构及高温高压三相相渗实验

东濮凹陷文南地区古近系沙三中段油藏属于典型的深层、高温、高压挥发性油藏,存在注水见效差的问题。通过应用恒速压汞、高温高压相渗测试及Stone1模型对东濮凹陷深层致密砂岩储层的孔隙结构特征、不同渗透率样品在高温、高压及不同驱替流体(原始油样/贫气原油/富气原油)条件下的可动流体特征进行了系统研究。研究结果显示,样品喉道半径分布在0.745~5.042μm;孔隙半径分布在16.970~171.035μm;孔喉半径比分布在40~278,最大连通喉道半径分布在1.041~12.672。不同样品喉道呈“多峰”分布且喉道半径普遍低于10μm。不同样品孔隙半径分布一致,存在135μm和165μm两个峰值。样品孔喉半径比也具有“双峰”特征,两个峰值分别为60和130。孔喉半径比越大,样品的渗透率越低。当喉道半径值大于1μm时,喉道对渗透率有明显的贡献。基于Stone1模型构建了致密储层三相渗透率曲线,油、气、水各自的相对渗透率都随着饱和度的增加而增加;油的相对渗透率是油、气、水三相饱和度的函数。最终,计算并绘制了样品在140℃及不同测试压力条件下的相渗三角图。结果显示,每一种原油存在一个最佳驱替压力时,可动流体空间最大。此外,当原油中含气量较少时,可动流体空间会随压力的增大而增大;当原油中含气量较多时,压力对低渗油藏的可动流体空间的影响不明显。当驱替流体为富气原油时,可动流体空间最大。这是由于,气体的加入占据了原来是束缚水或束缚油的一部分空间,气体的可流动性更强,因此其可动流体空间增加。