川西中三叠统雷口坡组三段-四段白云岩特征与成因——来自于岩相学及地球化学的约束

白云岩化是影响储层发育是否的重要沉积-成岩过程。作者通过在对川西地区的中三叠统雷口坡组的雷三至雷四段的岩相学,碳、氧、锶、镁同位素以及元素地球化学等综合研究,划分出含膏的泥晶云岩AD0、泥晶云岩D0、泥粉晶云岩D1、粉细晶云岩D2、微生物云岩MD、含灰质藻云岩CD(交代结构)以及去云化的泥粉晶云岩(CD0CD1)等七类白云岩。白云石有序度及铁、锰含量较低。阴极发光以暗紫、暗紫红、蓝紫为主;次为玫瑰红、橙红及橙黄红色。δ~(13)CPDB=1. 95‰～2. 46‰,δ~(18)OPDB=-4. 05‰～2. 70‰;~(87)Sr/~(86)Sr=0. 70778～0. 70807,δ~(26)Mg=-1. 872‰～-2. 124‰,其中δ~(13)C_(PDB)、~(87)Sr/~(86)Sr的平均值与中三叠世全球海水相似;δ~(18)O_(PDB)为弱负漂及正偏移。从D2、D1至D0、AD0,Sr、Na和大部分微量元素含量及比值和δ~(18)O_(PDB)逐渐增加; AD0、少量D0或MD相对富含硅、铝,并与高(低镁)方解石、黏土、有机质等共生。离子组成反映出白云石的前驱物以方解石型为主,少量为文石、原白云石结构。存在广盐、稍咸和超盐度的碱性等沉积环境。白云岩形成主要受向上变浅米级旋回序列,干燥、炎热为主、偶夹潮湿古气候以及古地貌-古水文条件等因素影响。存在浅潟湖的萨勃哈(AD0或D0)、环潮缘至局限台地(D0-D1、微生物诱导MD)、潮间-潮下的微生物礁(席)构成的障壁的台缘带(MD-CD1-CD)、潮坪-开阔台地(D0-D2-CD1、MD)等环境,以萨勃哈和受蒸发泵-密度差驱动的"渗透-回流白云石化"模式为主。     

姬塬北地区延长组长7-长8油层组泥岩地球化学特征与地质意义

基于对鄂尔多斯盆地姬塬北地区上三叠统延长组长7、长8油层组泥岩样品微量元素和稀土元素的测试分析发现,长7、长8油层组泥岩REE富集,Eu总体上呈明显的负异常;REE分布模式图显示轻、重稀土元素分异明显,曲线在La-Eu段表现为斜率较大的"右倾型",在Gd-Lu段表现为斜率较小的"平缓型"。结合Sr/Cu、Sr/Ba、V/(V+Ni)、Ceanom等特征参数的分析发现,长7、长8油层组泥岩形成于温湿、微咸水、还原水体的沉积环境。泥岩(La/Yb)N地化指标显示悬浮物颗粒总体表现为沉降缓慢,沉积速率低,由下至上泥岩悬浮物沉积速率表现为由高到低的变化趋势。同时,δCe、δEu及La/Lb-∑REE判别图解,指示长7、长8油层组泥岩母岩以花岗岩为主,同时有少量碱性玄武岩的混入,源区构造背景为大陆边缘环境。     

鄂尔多斯盆地南缘上二叠统——中下三叠统地球化学特征及其古气候、古环境指示意义

为探索陆相湖泊环境记录中二叠纪—三叠纪之交古气候演化的信息,以鄂尔多斯盆地南缘陕西铜川石川河剖面上二叠统石千峰组(P3s)和三叠系的刘家沟组(T1l)、和尚沟组(T1h)、纸坊组(T2z)为研究对象,对界面上下地层开展了系统的矿物学、岩石学和地球化学研究。通过主量和微量元素、碳氧同位素以及TOC测试对古盐度、古氧化还原环境和古气候演化规律进行分析。测试结果显示在二叠系—三叠系(P/T)界线附近主、微量元素和碳、氧同位素发生较明显的变化,气候环境代用化学指标的波动指示了从晚二叠世至早中三叠世鄂尔多斯盆地的古气候、古环境的变化。研究结果表明上二叠统石千峰组形成于河流-三角洲沉积环境,氧化程度相对低,古气候相对温暖湿润;下三叠统刘家沟组与和尚沟组的紫红色砂泥岩代表水体较浅的河流-三角洲相,强氧化环境,气候干旱炎热;而到中三叠统纸坊组沉积期,湖平面上升,元素的迁移作用加强,氧化程度变弱,气温降低,气候转为半干旱半湿润气候。碳同位素分析结果显示,鄂尔多斯盆地陆相P/T界线上δ^13CPDB存在显著负偏,与全球范围内的海相P/T界线具有一致性,说明在华北地台陆相P/T界线上同样存在气候突变和生物灭绝等重大地质事件的沉积记录,与海相地层可对比。     

准噶尔盆地浅覆盖区浅钻化探找矿方法探索

通过拉伊克勒克典型浅覆盖区浅钻化探成果,介绍了浅钻化探工作方法和取得的试验研究成果,显示该方法有效,经济可行,效率较高,操作简便,充分证明了浅钻化探技术在准噶尔干旱荒漠浅覆盖区是有效的找矿手段。     

特殊测井在准南地区乌鲁木齐一带芦草沟组页岩油气层评价中运用

以地表地质调查成果为基础,以钻探、地质综合录井、核磁共振测井、电成像测井、正交多极子阵列声波等测井方法为手段,以岩石学特征、储层物性、储集空间类型和储集性能研究为重点,开展准南冲段带东段乌鲁木齐一带二叠系芦草沟组页岩油气评价。研究结果表明:该区带芦草沟组页岩含油气7层,其中优质含油层2层(64和66层);页岩储层矿物成分以高脆性矿物为主,物性特征表现为天然高导裂缝发育和低孔特低渗;油气藏表现为具中等含油饱和度的典型裂缝型油气藏特征。页岩储层各向异性较强,总体最大水平主应力为NWW向。     

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.