准噶尔盆地南缘齐古背斜复杂构造建模技术应用

齐古背斜构造复杂,变形强烈,地震资料相对较差,构造样式建立存在多解性。为准确落实该区构造特征,从地质“戴帽”、倾角标定及平衡恢复与几何变形正演等关键技术出发,对齐古背斜进行精细构造解析,确立齐古背斜为早期构造三角楔与晚期冲断褶皱复合叠加的构造样式。该背斜主体部位具分层、分块构造特征,西段以南倾冲断断裂为主,东段以北倾反冲断裂为主。复杂构造建模技术的应用将有助于建立更为合理的构造解释方案,大大降低油气勘探风险。     

Prediction Model of Coal Reservoir Pressure and its Implication for the Law of Coal Reservoir Depressurization

The main methods of coalbed methane(CBM) development are drainage and depressurization, and a precise prediction of coal reservoir pressure is thus crucial for the evaluation of reservoir potentials and the formulation of reasonable development plans. This work established a new reservoir pressure prediction model based on the material balance equation(MBE) of coal reservoir, which considers the self-regulating effects of coal reservoirs and the dynamic change of equivalent drainage area(EDA). According to the proposed model, the reservoir pressure can be predicted based on reservoir condition data and the actual production data of a single well. Compared with traditional reservoir pressure prediction models which regard EDA as a fixed value, the proposed model can better predict the average pressure of reservoirs. Moreover, orthogonal experiments were designed to evaluate the sensitivity of reservoir parameters on the reservoir pressure prediction results of this proposed model. The results show that the saturation of irreducible water is the most sensitive parameter, followed by Langmuir volume and reservoir porosity, and Langmuir pressure is the least sensitive parameter. In addition, the pressure drop of reservoirs is negatively correlated with the saturation of irreducible water and the Langmuir volume, while it is positively correlated with porosity. This work analyzed the reservoir pressure drop characteristics of the CBM wells in the Shizhuangnan Block of the Qinshui Basin, and the results show that the CBM reservoir depressurization can be divided into three types, i.e., rapidly drop type, medium-term stability type, and slowly drop type. The drainage features of wells were reasonably interpreted based on the comprehensive analysis of the reservoir depressurization type; the latter was coupled to the corresponding permeability dynamic change characteristics, eventually proving the applicability of the proposed model.     

Geochemistry,Paleoenvironment and Mechanism of Organic-Matter Enrichment in the Lower Silurian Longmaxi Formation Shale in the Sichuan Basin,China

To investigate the mechanism of the organic-matter enrichment in the Lower Longmaxi Formation shale, the geochemistry and total organic carbon(TOC) of the Longmaxi Formation black shales in the Jiaoshiba, Zhaotong, and Weiyuan areas of the Sichuan Basin were analyzed. Paleoproductivity proxy parameters(Babio, Siex, and Ni/Al), clastic influx proxies(TiO_2 and Ti/Al), redox indices(V/Cr, Ni/Co, V/(V+Ni), and U/Th), and hydrothermal indicators(Fe, Mn,and Y concentrations; Fe/Ti ratio and a Ni-Zn-Co diagram) were employed to decipher the paleoenvironment of the Lower Longmaxi Formation shales. TiO_2 and Ti/Al indicated low terrigenous detrital influx in all three areas. However, Babio, Siex,and Ni/Al indicated high productivity in the Jiaoshiba area. V/Cr, Ni/Co, and U/Th indicated higher oxygen content with larger fluctuations in the Zhaotong and Weiyuan areas. Fe, Mn, and Y concentrations and the Fe/Ti ratio implied greater active hydrothermal activity in the Weiyuan area. These heterogeneities were considered to be closely related to the paleoenvironment and paleogeography, and the large basement faults that developed during the Chuanzhong paleo-uplift could have provided vents for deep-hydrothermal-fluid upwelling. The redox indices(V/Cr, Ni/Co, and U/Th) and a paleoproductivity proxy(Ni/Al) displayed a significant correlation with the TOC, suggesting that both excellent preservation conditions and high paleoproductivity were the controlling factors for the enrichment of organic matter in the Longmaxi Formation shale. There was no obvious correlation between the clastic influx proxy(Ti/Al) and the TOC due to the extremely low supply of terrigenous debris. The hydrothermal indicator(Fe/Ti) was negatively correlated with the TOC in the Weiyuan area, indicating that hydrothermal activity may have played a negative role in the accumulation of organic matter. This study suggests that the enrichment of organic matter in the Longmaxi Formation marine shale varied according to the paleogeography and sedimentary environment.     

High‐precision Dating and Geological Significance of Chang 7 Tuff Zircon of the Triassic Yanchang Formation,Ordos Basin in Central China

The Ordos Basin, as the second largest petroliferous basin of China, contains abundant oil and gas resources, oil shale, and sandstone-type uranium mineral resources. Chang 7 shale is not only the major source rock of the Mesozoic petroliferous system of the Basin, but is also crucial in determining the space-time distribution relationship of the shale section for the effective exploration and development of the Basin's oil and gas resources. To obtain a highly precise age of the shale development section, we collected tuff samples from the top and bottom profile of the Chang 7 Member, Yishi Village, Yaoqu Town, Tongchuan District, on the southern margin of the Ordos Basin and performed high-precision chemical abrasion(CA)–isotope dilution(ID)–thermal ionization mass spectrometry(TIMS) zircon U-Pb dating on the basis of extensive laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) zircon U-Pb dating data. Our results show the precise ages of the top and bottom zircon in the Chang 7 shale to be 241.06±0.12 Ma and 241.558±0.093 Ma, respectively. We first obtained Chang 7 age data with Grade 0.1-Ma precision and then determined the age of the shale development in the Chang 7 Member to be the early-Middle Triassic Ladinian. This result is supported by paleontological evidence. The deposition duration of the Chang 7 shale is 0.5 Ma with an average deposition rate of the shale section being 5.3 cm/ka. Our research results provide time scale and basic data for further investigation of the basin–mountain coupling relation of the shale section, the sedimentary environment and volcanic ash and organic-matter-rich shale development relation, and the organism break-out and organic-matter enrichment mechanism.     

Distribution Characteristics and Accumulation Model for the Coal‐formed Gas Generated from Permo‐Carboniferous Coal Measures in Bohai Bay Basin,China: A Review

Coal-formed gas generated from the Permo-Carboniferous coal measures has become one of the most important targets for deep hydrocarbon exploration in the Bohai Bay Basin, offshore eastern China. However, the proven gas reserves from this source rock remain low to date, and the distribution characteristics and accumulation model for the coal-formed gas are not clear. Here we review the coal-formed gas deposits formed from the Permo-Carboniferous coal measures in the Bohai Bay Basin. The accumulations are scattered, and dominated by middle-small sized gas fields, of which the proven reserves ranging from 0.002 to 149.4×108 m3 with an average of 44.30×108 m3 and a mid-point of 8.16×108 m3. The commercially valuable gas fields are mainly found in the central and southern parts of the basin. Vertically, the coal-formed gas is accumulated at multiple stratigraphic levels from Paleogene to Archaeozoic, among which the Paleogene and PermoCarboniferous are the main reservoir strata. According to the transporting pathway, filling mechanism and the relationship between source rocks and reservoir, the coal-formed gas accumulation model can be defined into three types: "Upward migrated, fault transported gas" accumulation model, "Laterally migrated, sandbody transported gas" accumulation model, and "Downward migrated, sub-source, fracture transported gas" accumulation model. Source rock distribution, thermal evolution and hydrocarbon generation capacity are the fundamental controlling factors for the macro distribution and enrichment of the coal-formed gas. The fault activity and the configuration of fault and caprock control the vertical enrichment pattern.     

Molecular Structure of Kerogen in the Longmaxi Shale: Insights from Solid State NMR,FT‐IR,XRD and HRTEM

Kerogen plays an important role in shale gas adsorption, desorption and diffusion. Therefore, it is necessary to characterize the molecular structure of kerogen. In this study, four kerogen samples were isolated from the organic-rich shale of the Longmaxi Formation. Raman spectroscopy was used to determine the maturity of these kerogen samples. High-resolution transmission electron microscopy (HRTEM), 13C nuclear magnetic resonance (13C NMR) , X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were conducted to characterize the molecular structure of the shale samples. The results demonstrate that VReqv of these kerogen samples vary from 2.3% to 2.8%, suggesting that all the kerogen samples are in the dry gas window. The macromolecular carbon skeleton of the Longmaxi Formation kerogen is mainly aromatic (fa’=0.56). In addition, the aromatic structural units are mainly composed of naphthalene (23%), anthracene (23%) and phenanthrene (29%). However, the aliphatic structure of the kerogen macromolecules is relatively low (fal*+falH=0.08), which is presumed to be distributed in the form of methyl and short aliphatic chains at the edge of the aromatic units. The oxygen-containing functional groups in the macromolecules are mainly present in the form of carbonyl groups (fac=0.23) and hydroxyl groups or ether groups (falO=0.13). The crystallite structural parameters of kerogen, including the stacking height (Lc=22.84 ?), average lateral size (La=29.29 ?) and interlayer spacing (d002=3.43 ?), are close to the aromatic structural parameters of anthracite or overmature kerogen. High-resolution transmission electron microscopy reveals that the aromatic structure is well oriented, and more than 65% of the diffractive aromatic layers are concentrated in the main direction. Due to the continuous deep burial, the longer aliphatic chains and oxygen-containing functional groups in the kerogen are substantially depleted. However, the ductility and stacking degree of the aromatic structure increases during thermal evolution. This study provides quantitative information on the molecular structure of kerogen samples based on multiple research methods, which may contribute to an improved understanding of the organic pores in black shale.     

Structural Evolution of Chepaizi Uplift and its Control on Stratigraphic Deposition in the Western Junggar Basin,China

Geological mapping, interpreted cross sections, structural analyses and residual thickness maps were used to characterize the evolution of stress setting, structure and stratigraphic distribution of the Chepaizi Uplift, which is a NW-SE trending structure located in the Western Junggar Basin. The NS-trending faults show an important transpressional phase during the Late Permian, as demonstrated by tectonic stress field and stratigraphic thickness variations. A major compressional thrusting and strike-slip phase during the Late Jurassic created a series of NW-SE faults that originated by the large-scale uplift event in the Northern Tianshan. Faults were reactivated as thrust and dextral strike-slip faults. In addition, the angular unconformity observed between Jurassic and Cretaceous provide evidence of this tectonic event. Lots of normal faults indicate that the area records southward tilting and regional derived extensional stress that took place during the Neogene. Before that, thick Early Cenozoic strata are widely deposited. The balanced cross-section highlights the evolution of stress setting and stratigraphic distribution of the Chepaizi Uplift.     

准噶尔盆地玛湖凹陷三叠系源上砂砾岩扇—断—压三控大面积成藏模式

准噶尔盆地玛湖富烃凹陷下三叠统百口泉组新近发现了我国首个源上大面积连续型砂砾岩油藏群,是对全球"连续型"油气藏研究的新补充,但其成藏机理和模式并不很清楚。为加强对其的理论认识,并为下步勘探提供参考,基于油气生、储、盖、圈、运、保等基础石油地质条件,并结合油气藏特征,进行了成藏条件与成藏模式的综合研究。结果表明,优质充足的下二叠统风城组碱湖油气来源、规模有效的扇三角洲前缘砂砾岩储层、多重组合的扇三角洲平原致密砾岩、泥岩和断裂封盖保存、沟通良好的高角度断裂输导体系、平缓连续的构造背景奠定了大面积连续成藏的地质基础。在此背景下,高成熟的风城组所生成油气,在切穿烃源灶和储层的高角度压扭性断裂沟通下,优先充注物性相对好的扇三角洲前缘水下河道砂岩和砂质细砾岩,并且在地层异常高压促进下,控制着油气富集程度,使得油气成藏表现为大型缓坡浅水扇三角洲沉积控制下的源上扇-断-压三控大面积"连续型"。百口泉组油气藏具有的油质轻且含气、微裂缝广泛发育,以及异常高压等,决定了砾岩储层虽总体低孔低渗,但依旧能够高产。在油源断裂沟通的斜坡区上倾方向,叠合地层异常高压以及扇三角洲前缘水下河道砂砾岩的区域是下步有利勘探方向。     

Evolution of the depositional environments of the Jurassic Walloon Coal Measures,Surat Basin,Queensland, Australia

The Jurassic Walloon Coal Measures of the Surat Basin in eastern Australia host the continent's most significant coal bed methane resources. Previous studies have interpreted the Walloon Coal Measures within a single depositional facies model encompassing a wholly terrestrial setting. Using a multidisciplinary approach (facies analysis, palynology and wireline logs), the evolution of the Walloon Coal Measures is described within a new chronostratigraphic framework defined by accurate and precise U–Pb tuff dates. Analysis of sedimentary facies indicates that the majority of the Walloon Coal Measures was deposited by relatively small (<300 m wide), low gradient rivers on a poorly‐drained floodplain with numerous small lakes and mires. However, this study also identified some marine‐influenced facies with brackish palynomorphs (notably dinoflagellate cysts) and tidal sedimentary structures. These facies appear to have been deposited in estuaries during times of transgression. The evidence for base level shifts suggests that the coals may not have coevally accumulated with at least some of the thicker sandstones. Palaeogeographic maps for eleven time intervals suggest that rivers drained towards to the south/south‐west and south‐east, as indicated by sandstone percentage and gross unit isopach maps, presumably into proximal estuarine complexes. Marine incursions into the continent probably came from the north and east during times of high eustatic sea level and as precursors to those of the more persistent and extensive transgressions of the Early Cretaceous. A similar multidisciplinary approach should help to elucidate the evolution of other fluviolacustrine systems in other basins and aid in resource prediction.     

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。