The dendrolites composed of light gray massive micrite limestone occur at the top of the Cambrian Zhangxia Formation in Houziyu Section, Zibo, Shandong Province. Because it is very difficult to study the genesis of microbial rocks through “the function of diagenesis filter,” this paper analyzes its genetic mechanism by characterizing the sedimentary fabric and formation environment of dendrolites and it is of great significance to study microbial carbonate deposited in geological history in oil exploration. The Cambrian Zhangxia Formation in the Houziyu section is a marine deposit. The macroscopic shrub-like fabric of centimeter scale can be seen on the surface of the tree-shaped stone, with small biological burrows and remnants of calcareous mud components after filling. The microstructure observation shows that the main fabric of the dendrolites is a dark micrite matrix, bright calcite cement, clastic particles, and a calcified cyanobacteria biological community. Detailed supplementary information on the diversity of calcified microorganisms in dendrolites has been made through the study of various types of calcified cyanobacteria and calcified residual substances in the microbial membrane of calcified cyanobacteria in the dendrolites of the study area. It is clear that dendrolites are the product of the calcification of biofilms or microbial mats dominated by cyanobacteria. With the deepening of this kind of research, it is bound to raise the research of microbial carbonate to a new level in China and provide great help to find oil and gas resources in marine strata of microbial origin in China.

Ordos Basin is rich in shale oil resources. Fuxian area in the southern Ordos Basin is an important area where Sinopec is expected to make a breakthrough in the exploration and development of lacustrine shale oil. To further identify the exploration target of shale oil in Chang 7 Member of Fuxian area, Ordos Basin, this study systematically analyzed the sedimentary characteristics, source rock characteristics, reservoir characteristics, oil-bearing characteristics, fracability and preservation conditions of Chang 7 Member in this area. The results show that: (1) the organic matter abundance of shale in the Chang 7 Member is high, and its type is dominated by type I-II1; the maturity is also relatively high, with Ro generally greater than 0.8% in the central and western parts, which is favorable for the generation and accumulation of shale oil. The development of fractures is pretty low, and thus the structure preservation conditions are relatively favorable. Delta front deposits are mainly developed in the northeastern part, while deep lake - semi-deep lake mudstone and gravity-flow deposits are developed in the western part, and the shale oil types are mainly type II and III. (2) Comparing with the western Ordos Basin, the reservoir in Fuxian area has rapid lateral variation and relatively thin cumulative thickness; the thickness of high-quality shale and maturity are low, resulting in low intensity of hydrocarbon generation and low mobility of oil-bearing saturation. Therefore, there is still a need for further improvement and refinement in the exploration evaluation, effective development and engineering techniques. (3) Integrating sedimentary characteristics with shale oil types, source conditions, oil-bearing properties, mobility, fracability and preservation conditions, it is clarified that the Type II shale oil of Chang 72 sub-,Member in Fuxian area is the current realistic exploration type of shale oil, and its favorable target is located in the development area of delta front in the central part and gravity flow in the western part.

Fine-grained sedimentary rock (FGSR) reservoirs in a deep-water sedimentary environment from the Late Triassic Yanchang Formation in the Ordos Basin in central China have huge potential for tight oil production. According to the comprehensive research of fluid inclusion experiment, scanning electron microscopy, cathodoluminescence, thin section identification, and whole rock analysis, the petrographic characteristics, fluorescence spectrum parameters, and the homogenization temperature of oil inclusions and associated brine inclusions in the FGSR reservoir were analyzed to explore the coupling relationship between densification characteristics and tight oil accumulation of the FGSR reservoir. The results show the FGSR reservoir diagenesis has experienced compaction, cementation, and multiple stages of dissolution. A comprehensive analysis of burial history shows that the Chang 7 Member FGSR reservoir in the study area has three phases of oil charging, corresponding to the geologic time range of 132–124, 120–102, and 98–97 Ma. The organic acid produced by the first-stage oil charging accelerated the dissolution of feldspar and cuttings, and the dissolution pores increased significantly. Then, the organic acid in the second-stage oil charging accelerated the dissolution, and the abnormally high hydrocarbon expulsion pressure inhibited the damage of compaction on the pores of FGSR reservoir. Finally, the thermal evolution degree of source rocks reached the highest in the third-stage oil charging. The constructive effect of large-scale organic acids on pores and the protective effect of the chlorite membrane on pores inhibited the densification process of the FGSR reservoir. In short, the FGSR reservoir has experienced a cyclical reservoir densification process of “reducing porosity–increasing porosity–preserving porosity.” The coupling of pore evolution and oil charging of the FGSR reservoir is the key to the extensive accumulation and large-scale reservoir formation of tight oil in the Chang 7 Member of the Yanchang Formation in the Zhenyuan area, southwest Ordos Basin. The significance of the study may help to understand the process of the tight oil accumulation and predict the tight oil of the FGSR reservoir distribution.

Understanding the relationship between petroleum recovery and characteristics of hydraulic fracture network is a key component of economic development of tight reservoirs. Owing to the limitations inherent in current reservoir simulators, optimization of fracture network has been simply focused on the parameters of fracture conductivity, fracture number, aperture, and so on. Deeper insight into the effect of decisive parameters, such as fracture density and fracture connectivity on the well production in tight reservoirs, is now required to maximize the petroleum recovery. In this work, a newly developed discrete fracture simulator is applied to comprehensively study the effect of fracture density and fracture connectivity in tight reservoirs. Conceptual models with different fracture densities and different fracture connectivity are firstly designed and simulated to explore how these two parameters affect the reservoir behavior and establish the equations for effect measurement. Then, we simulate models with different well placement strategies and a fixed set of natural fractures to determine the optimal strategy. Finally, simulations are performed on a field-scale reservoir with three long fractured horizontal wells. Results demonstrate that increases in either fracture density or fracture connectivity can significantly improve well production. However, an optimal value exists considering the economic profit. Compared to the fracture density, fracture connectivity plays a more important role in affecting the well production. In a tight reservoir with abundant natural fractures, making the horizontal well parallel to the direction of natural fractures is determined to be the optimal well placement strategy. The heterogeneous distribution of remaining oil in real tight oil reservoirs is mainly caused by the heterogeneous distribution of fracture density and fracture connectivity.

为了研究鄂尔多斯盆地长7油层组沉积物变形构造时空展布规律,对盆地西南部镇原地区20口井的岩心进行了精细观察与描述,综合分析了沉积物变形构造的形态特征和形成机制,共识别出7种常见的沉积物变形构造类型,即滑塌变形、液化卷曲变形、泥质撕裂屑、液化砂岩脉、球枕构造、火焰构造和重荷模等.垂向上,沉积物变形构造在长72小层最为发育,长71小层次之,长73小层较少;平面上,在镇原地区中部集中发育,西部和东部局部发育.斜坡背景下沉积物变形构造的形成机制和展布规律为:①盆山耦合激活了沉积物变形构造的触发因素;②湖进与湖退转换期是沉积物变形构造最为集中发育的阶段;③不同类型沉积物变形构造的分布与坡折带的发育关系密切,随着向半深湖—深湖沉积区推进,其类型发生规律性演化.该研究成果对于探讨沉积物变形构造的分布模式、重力流砂体分布预测及事件沉积等研究具有参考价值.

The source of the Chang 7 Member of the Upper Triassic Yanchang Formation in the Zhenyuan area in the southwestern Ordos Basin has been a key issue in sedimentology and reservoir geology. In this paper, we sampled the key wells of the Chang 7 Member of this area and systematically studied the rock type, mineral maturity, source index of debris components, quartz content, rock debris type and heavy mineral assemblages characteristics. By comparing the planar distribution characteristics of each factor, the partition result of the source of the target layer is obtained. The study shows that there are three sources of supply in the Chang 7 Member of the study area, which are the southwestern source of the southeast part of the Longxi ancient land, the western source of the northern part of the Longxi ancient land, and the northwestern source of the northern part of the Alxa ancient land. Among them, the southwestern source is the main source, while the western source and the northwest source are secondary sources. These three sources intersect in the northeastern part of the study area.

基于目标的随机建模方法能够较好地刻画地质体展布规模和几何形态,在河流相储层建模中得到了广泛应用.在商业化建模软件中,基于目标的河流相建模方法默认是贯穿整个研究区的.在N气田存在某一物源方向的河道在研究区内部终止的情况,此前为了对此类河道建模,常采用一些约束方法,但经过多种尝试,效果并不理想.因此,提出了一种基于目标的河道在研究区内终止的建模方法.具体的做法是:根据地质认识确定的河道分布范围,对于非贯穿型河道在研究区内设置相应的终止边界;对河流相储层建模方法Fluvsim进行改写,令河道延伸到边界时终止,并且厚度逐渐减薄;对于贯穿型河道,则不做改变.实例研究表明,该方法较好解决了同时存在贯穿型和非贯穿型河道的建模问题.

辫状河具有较多的沉积类型和复杂的形成机理,易形成优质储集沙体.为研究不同类型辫状河心滩坝发育特征及其主要控制因素,结合不同地区的辫状河类型,以底形坡度、河道宽度及河岸类型为地质变量,基于水槽沉积模拟实验,设计3种类型辫状河,即开阔型辫状河、限制—开阔型辫状河和限制型辫状河;控制不同水流大小和加沙量,根据水槽沉积模拟实验结果,分析不同类型辫状河心滩坝沉积特征及定量表征参数.结果表明:开阔型辫状河心滩坝长宽比介于3～11,平均为6,以纵向沙坝为主;限制—开阔型辫状河心滩坝长宽比介于2～5,平均为3,以纵向沙坝和侧向沙坝为主;限制型辫状河心滩坝长宽比介于1～3,平均为2,以侧向沙坝和横向沙坝为主.底形坡度、水流强度与河岸类型是影响不同类型辫状河心滩坝沉积差异的主要因素,其中,不同因素引起辫状河心滩坝形态特征及几何规模的差异,可为古辫状河心滩坝沉积的精细表征提供定量参数和理论依据.

The reservoir characteristics and the exploration result are greatly different in different areas of Chang 8 tight sandstone reservoir of Yanchang Formation in Ordos Basin owing to the multiple reservoirforming factors.In this paper,the fluid inclusion technical method is employed to explore the oil charging history in the micro aspect.Combing with the characteristic of hydrocarbon accumulation conditions,the paper analyzes the diversity hydrocarbon reservoir forming process of Chang 8 interval of Yanchang Formation.The results indicate that there was active oil charging history in the eastern region of Chang 8 interval in Zhenyuan area,and the oil charging events mainly occurred in the early period of Early Cretaceous (133 -124 Ma),the middle period of Early Cretaceous (115 Ma) and the early period of Late Cretaceous (95 Ma).But the oil charging history was very weak in western region of Chang 8 interval in Zhenyuan area,and the oil charging events mainly occurred in the early period of Late Cretaceous (96 Ma).The different hydrocarbon accumulation process of Chang 8 interval in Zhenyuan area is impacted by the distance to the hydrocarbon generation center,the diagenesis of reservoir and the tectonic movement.

Aimed at exploration of provenance and basin-mountain coupling relationship in southwestern Ordos Basin, the authors selected detrital zircons from the first member of Shanxi Formation and the eighth member of Shihezi Formation of the late Paleozoic in southwestern Ordos Basin and conducted LA-ICP-MS detrital zircon U-Pb isotope analysis. The result reveals that the 105 analytical points of the magma-genetic detrital zircons yielded four age groups:(1) The first group which ranges from 260 to 340Ma accounting for 21.9% of the total analytical points, indicating that the provenance might have come from the North Qinling orogenic belt and the West Qinling orogenic belt;(2) The second group which ranges from 370 to 470 Ma accounting for 24.8%of the total analytical points, suggesting that the provenance was mainly derived from the North Qinling orogenic belt, the West Qinling orogenic belt and the North Qilian orogenic belt; (3) The third group which ranges from 1600 to 2000 Ma accounting for 32.4%of the total analytical points, implying that the provenance might have come from the North Qinling orogenic belt and the North Qilian orogenic belt; (4) The last group which ranges from 2300 to 2600 Ma accounting for 15.2% of the total analytical points, indicating that the provenance was derived from the North Qinling orogenic belt, the West Qinling orogenic belt, the North Qilian orogenic belt and the crystalline basement of the North China plate. This study indicates that the provenance of southwestern Ordos Basin had multiple origins:the North Qinling orogenic belt, the West Qinling orogenic belt, the North Qilian orogenic belt and the crystalline basement of the North China plate, mainly from the North Qinling orogenic belt and the North Qilian orogenic belt. The Paleozoic detrital zircons have also proved that the southwestern Ordos Basin passive continental margin was developed during the Ordovician, then it evolved into continent-continent collisional orogenic belt during the Silurian-Devonian, and finally gradually evolved into a sedimentary basin during the Carboniferous-Permian period.

为了更详细和系统地对鄂尔多斯盆地西南部演武-镇原地区延长组长7油层组储层质量进行评估和预测,运用宏观与微观研究相结合的方法,以物性、铸体薄片、阴极发光、扫描电镜及压汞等实验室数据为基础,对储层孔隙结构特征进行描述、分析和精细解剖,并讨论其对储层储渗能力的控制与影响作用.综合研究结果表明,长7油层组孔隙类型以原生粒间孔为主,其次为长石溶孔和岩屑溶孔;孔隙结构以中、小孔-细喉组合的为主,微孔-微喉型组合次之;原生孔隙、次生孔隙和微裂缝共同控制了储层的储渗能力.

In-field detailed sectional records and measurements indicate that 5 major facies have developed in Chang 7 of Yaoqu in the south Ordos basin, including deep-water autochthonous facies, tuffaceous facies, sandy clastic-flow facies, turbidite facies, and slump facies. These facies constitute four vertical combination patterns: A, B, C and D. We comprehensively analyzed the lithologic characteristics, facies combinations, sedimentary structures, and biological remains there. Based on the results, we divided the study area into two major depositional systems: the lake system and the channel-type gravity flow system. The lake system was subdivided into semi-deep lake/deep-lake subfacies, and semi-deep lake/deep-lake mud microfacies. The channel-type gravity flow system was subdivided into proximal channels, distal channels, banks, and front lobes, including 4 microfacies of sandy clastic flow deposits, turbidite deposits, slump deposits, and autochthonous deposits. Section profile analysis shows that the high-quality hydrocarbon source rocks and gravity flow sandbodies in the study area are favorable for the production of excellent lithologic oil-gas reservoirs.

鄂尔多斯盆地演武-三岔地区是多油层叠合的含油富集区,但区块开发程度低,地质条件复杂,近年来油气勘探一直未能取得较大的突破.物源分析基于长8油层组三角洲沉积体系,对区内轻矿物组分、碎屑岩特征、重矿物特征、石英阴极发光及粒度特征等进行综合分析,结果表明演武-三岔地区主要受到西南部物源控制和影响,其母岩来自于西南部陇西古陆及南部秦岭的变质岩和酸性岩浆岩组合.