PALAEO‐EXPOSURE SURFACES IN CENOMANIAN – SANTONIAN CARBONATE RESERVOIRS IN THE DEZFUL EMBAYMENT,SW IRAN

Cretaceous carbonates host major hydrocarbon reserves in SW Iran and elsewhere in the Arabian Plate. Tectonic activity combined with eustatic sea‐level changes resulted in periodic exposure of these carbonates which were subsequently modified by meteoric diagenesis under a warm and humid climate. Long‐term exposure led to the formation of several disconformity surfaces within the middle Cretaceous succession which had important effects on the interval's reservoir characteristics. These disconformity surfaces in the Dezful Embayment were investigated using microfacies, diagenetic and geochemical studies at five subsurface sections. Facies differences across these boundaries, together with features such as karstification, palaeosol development and collapse‐dissolution breccias, were used to identify emergent surfaces. Stable oxygen and carbon isotope ratios and trace element profiles indicate intense meteoric diagenesis. Disconformities were dated using biostratigraphic studies. The results indicate the presence of two major erosional disconformities: one is located at the Cenomanian – Turonian boundary separating the middle Sarvak Formation from its upper part; and the other is in the mid‐Turonian at the boundary between the Sarvak and Ilam Formations. The latter disconformity is correlatable throughout the Arabian Plate.     

川东北地区长兴组-飞仙关组碳酸盐岩同位素地球化学响应及其地质意义

碳、氧同位素是碳酸盐岩研究的重要地化指标之一,在反映全球气候变化、海平面升降变化、成岩作用影响及进行地层对比等方面发挥着重要作用。基于川东北地区野外剖面考察、岩石薄片鉴定和微量元素分析,结合长兴组-飞仙关组241件碳酸盐岩样品的碳、氧同位素组成,建立同位素演化曲线,重点对碳、氧同位素地球化学响应特征进行区域性对比分析,进一步对其地质意义进行试验性探讨。研究结果表明:川东北地区长兴期碳同位素演化曲线与海平面变化呈明显的正相关关系,并可与层序内部体系域进行良好对应,该时期氧同位素组成呈相对稳定趋势;在二叠系/三叠系界线附近碳、氧同位素值均发生强烈负漂移,达到最低值;进入飞仙关期后碳同位素值进入低幅波动的恢复阶段,在飞四段内部达到极大值后降低,氧同位素组成在飞仙关期也较为稳定。碳、氧同位素值在二叠系/三叠系界线处发生强烈负漂移可能与甲烷释放及火山喷发事件有密切关系。     

CHEMOSTRATIGRAPHY OF CENOMANIAN–TURONIAN CARBONATES OF THE SARVAK FORMATION,SOUTHERN IRAN

Stable‐isotope and trace‐element analyses from five surface and subsurface sections of the mid‐Cretaceous Sarvak Formation in southern and offshore Iran confirm the presence of the regional‐scale Turonian unconformity and of a more local Cenomanian–Turonian unconformity. The geochemical results indicate the presence of previously unrecognized and/or undifferentiated subaerial exposure surfaces. Sarvak Formation carbonates at or near palaeo‐exposure surfaces show varying degrees of diagenetic modification, and more extensive alteration is associated with longer periods of exposure. The subaerial exposure and associated diagenetic processes greatly influenced reservoir quality and amplified karstification and evolution of porosity in the Upper Sarvak Formation. The palaeo‐exposure surfaces are identified by their negative δ¹³C values (as low as – 6.4%) and negative δ¹⁸O values (as low as –9.4%), together with low Sr concentrations and relatively high ⁸⁷Sr/⁸⁶Sr ratios. These geochemical characteristics are interpreted to be the result of the interaction of the Sarvak Formation carbonates with meteoric waters charged with atmospheric CO₂. The meteoric waters also caused karstification and soil formation which in some places extends a few metres below the exposure surfaces. Depleted carbon values were not recorded in areas where palaeosols are not well developed or where the uppermost layers of the Sarvak Formation have been removed by erosion.     

塔里木盆地塔中隆起寒武系深层油气地球化学特征及成因

塔中隆起寒武系碳酸盐岩储层油气资源丰富,然而由于复杂的构造地质背景,油气来源和天然气类型还存在较大争议。通过详细分析ZS1井、ZS1C井和ZS5井寒武系不同层段中凝析油和天然气的组成、碳同位素等特征,并结合寒武系-下奥陶统与中、上奥陶统烃源岩地球化学特征,对其油气来源和天然气成因类型进行了判别。研究结果表明,该区天然气为典型的腐泥型干酪根裂解气,其中寒武系肖尔布拉克组天然气干燥系数大于0.98,N₂含量介于2.5%~4.0%,为过成熟干气,且凝析油族组分与和饱和烃单体烃碳同位素偏重,nC₉-nC₂₀碳同位素介于-28.8‰~-26.3‰,表明油气来源为寒武系-下奥陶统烃源岩。而寒武系阿瓦塔格组和吾松格尔组天然气干燥系数介于0.63~0.78,N₂含量介于0.2%~0.8%,为低成熟湿气,且凝析油族组分和饱和烃单体烃碳同位素相对较轻,nC₉-nC₂₃碳同位素介于-37.25‰~-32.56‰,表明油气来源为中、上奥陶统烃源岩。     

延长组砂岩中碳酸盐胶结物氧碳同位素组成特征

碳酸盐胶结物中氧碳同位素组成研究有助于阐明成岩过程中流体-岩石相互作用的机理。为此，综合运用岩石学、矿物学和地球化学方法，对鄂尔多斯盆地三叠系延长组砂岩中普遍存在的不同期次碳酸盐胶结物的成因机理和物质来源进行了系统研究。结果表明，研究区早期碳酸盐胶结物主要为方解石，其碳同位素值相对较重，为-0.3‰～-0.1‰，氧同位素值较轻，分布范围为-22.1‰～-19.5‰，与碱性湖水中碳酸钙发生过饱和沉淀有关。铁方解石的碳同位素值相对较轻，为-8.02‰～-3.23‰，氧同位素值也较轻，分布范围为-22.9‰～-19.7‰，它的形成明显与早成岩阶段晚期-晚成岩阶段早期的有机质脱羧基作用有关，属于成岩阶段中晚期产物，可以作为指示烃类在油气储层中正在发生显著运移的标型自生矿物。晚期铁白云石的碳同位素值相对较重，为-1.92‰～-0.84‰，氧同位素值变化较大，分布范围为-20.5‰～-12.6‰，它的形成与晚成岩阶段中晚期形成的碱性成岩环境及古代海相碳酸盐岩岩屑提供的碳有关。     

川东卧新双地区天然气特征及上三叠统须家河组天然气来源

天然气来源分析是一个重要的石油地质问题,直接关系到勘探决策。四川盆地川东地区须家河组勘探和开发相对滞后,基础地质研究的欠缺导致卧新双地区须家河组天然气的来源一直存在争议。天然气组分及碳同位素分析结果表明：卧新双地区须家河组天然气具有甲烷含量较低、重烃含量较高、干燥系数较低等特点;天然气中甲烷碳同位素值δ¹³C₁<-40‰,具有δ¹³C₃ > δ¹³C₂ > δ¹³C₁的特征;须家河组天然气为干酪根初次裂解的陆相油型气和混合气;须家河组天然气目前主要处于成熟-高成熟的湿气阶段。卧新双地区须家河组暗色泥岩较为发育,有机地球化学分析结果表明：须家河组泥岩主要以Ⅱ₁和Ⅱ₂型干酪根为主,具有较高的有机碳含量和氯仿沥青“A”含量,总体具有较好的生烃能力,泥岩中有机质处于成熟-高成熟的湿气阶段。卧新双地区须家河组天然气成熟度与烃源岩成熟度相当,结合须家河组天然气组分特征、同位素特征及成因类型等与下伏石炭系、茅口组、龙潭组、长兴组、飞仙关组、嘉陵江组及雷口坡组天然气存在明显区别,推测该区须家河组天然气主要为自生气。     

四川盆地乐山—龙女寺古隆起地区震旦系储层沥青地球化学特征及意义

通过对四川盆地乐山—龙女寺古隆起地区储层沥青样品进行全岩镜下测定,发现该区震旦系灯影组储层中存在大量储层沥青,并对样品进行沥青反射率测定、有机元素分析和碳同位素分析,结果表明:古隆起地区震旦系灯影组储层沥青等效镜质体反射率(R′_O)值分布在2.06%~3.0%之间,平均值为2.62%,储层沥青H/C原子比和O/C原子比仅为0.30~0.43和0.01~0.03,表明沥青的成熟度高,基本上处于成熟—过成熟阶段,生烃潜力较低;S/C原子比为0.03~0.06,与长兴组(P₂ch)和飞仙关组(T₁f)储层沥青S/C原子比相比偏低,表明古隆起地区灯影组储层沥青受硫酸盐热化学还原反应(TSR)影响较小;此外,储层沥青碳同位素值分布在-36.8‰~-34.5‰之间,平均值为-35.7‰,在四川盆地各层位干酪根和沥青碳同位素值中其值最低,比塔里木盆地海相原油的碳同位素值还要低。结合四川盆地地质构造背景,对比各层位烃源岩干酪根碳同位素,认为古隆起地区震旦系灯影组储层沥青主要来源于下寒武统筇竹寺组烃源岩,属古油藏深埋时在高温、高压作用下裂解成气后的热演化沥青—焦沥青。     

鄂尔多斯盆地富县地区马五段碳酸盐岩成岩作用研究

鄂尔多斯盆地富县地区马家沟组沉积了一套以蒸发潮坪相为主的白云岩、含膏云岩等碳酸盐岩沉积物。利用宏观岩心、微观常规薄片、铸体薄片、X-射线衍射、氧碳同位素等资料,并结合物性资料,系统研究了富县地区马五段碳酸盐岩的成岩作用类型和成岩环境。结果表明：马五段碳酸盐岩在成岩过程中经历了海水、混合水和大气淡水成岩环境;成岩作用复杂多样,其中溶蚀作用和回流渗透白云石化作用对储层孔隙发育有利,各种矿物的充填作用、去白云石化作用、去膏化作用和压实-压溶作用对储层孔隙发育不利。     

准噶尔盆地新光地区佳木河组天然气地球化学特征及成因

通过对二叠系烃源岩生烃潜力评价及地层孔隙生烃模拟实验,明确了准噶尔盆地二叠系佳木河组、风城组和下乌尔禾组3套烃源岩生烃潜力及生烃特征,并在天然气地球化学特征研究基础上,结合与天然气伴生凝析油正构烷烃碳同位素分析,确定了准噶尔盆地中拐凸起新光地区佳木河组致密砂岩气藏天然气的来源。结果表明,二叠系3套烃源岩生烃潜力从大到小顺序为：风城组＞下乌尔禾组＞佳木河组,风城组烃源岩类型最好,以生油为主,下乌尔禾组烃源岩倾油倾气,佳木河组烃源岩倾气。新光地区佳木河组致密砂岩油藏天然气C₇轻烃组成以正庚烷为主,含量大于40%,甲基环己烷含量小于40%,乙烷碳同位素值分布在-29.0‰~-27.0‰之间,为偏腐泥型的过渡型气;与佳木河组致密砂岩天然气伴生的凝析油正构烷烃碳同位素增加呈“V”型分布,与下乌尔禾组烃源岩相一致,表明新光地区佳木河组凝析油来源于下乌尔禾组烃源岩。综合分析认为,准噶尔盆地新光地区佳木河组致密砂岩天然气主要来源于高成熟的下乌尔禾组烃源岩。     

川东北元坝—通南巴地区二叠系—三叠系天然气地球化学特征及成因

依据天然气组分、碳同位素和稀有气体等资料对川东北元坝—通南巴地区二叠系—三叠系天然气地球化学特征及成因进行了系统研究。结果表明,(H_2S+CO_2)与(H_2S+CO_2+∑C_n)比值可以作为表征热化学硫酸盐还原作用(TSR)程度的参数。元坝地区长兴组至须家河组二段、通南巴地区飞仙关组至须家河组四段天然气δ~(13)C_2变化幅度大于δ~(13)C_1,且δ~(13)C_2值介于-24.4%。~-36.7‰,表明存在油型气和煤型气混合,理论上各层系天然气碳同位素均应呈倒序分布,但元坝地区长兴组、飞仙关组和通南巴地区嘉陵江组天然气受TSR影响,仍表现为δ~(13)C_1δ~(13)C_2或δ~(13)C_1δ~(13)C_2δ~(13)C_3的正序分布。元坝地区须家河组三段、四段天然气δ~(13)C_2值大多重于-28%。,以煤型气为主,表现为δ~(13)C_1δ~(13)C_2δ~(13)C_3的正序分布。天然气稀有气体氦同位素R/R_a值分布于0.00881~0.02510,表现出典型的壳源特征,源于TSR的酸性气体和源于烃源岩热演化的有机酸对碳酸盐岩的溶蚀是该地区二氧化碳形成以及δ~(13)C_(CO_2)变重的主要原因。气-气及气-源综合对比表明,元坝—通南巴地区天然气成因类型可以划分为龙潭型(A1型)、混合型(A2型)和须家河型(B型),龙潭型和混合型主要来源于上二叠统龙潭组烃源岩,其中混合型混有少量须家河组来源气,须家河型主要来源于其自身层系的烃源岩。     

ORIGIN OF CRUDE OILS IN OMAN

The petroleum geochemistry of Oman provides a picture of considerable variey, since crude oils and their source rocks are found both throughout the country and throughout the stratigraphic column from the Infra-Cambrian to the Tertiary. This paper reviews the geological history history of the area and places the petroleum geochemistry within the geological context. The oils can be geochemically classified into five groups. Three groups can be related to god oil source rocks found in the pre-Cambrian Huqf Group, the Silurian Safiq and the Cretaceous Natin Formation. Another group of oils probably originates from the Upper Jurassic Diyab Formations, while the fifth group of crudes (named ‘Q’) cannot be correlated to a known source rock, but is inferred to have originated from an unsampled Huqf level. The “Huqf oils” are those that have been correlated to known Infra-Cambrian Huaf source rocks, and are characterized by a strong C₂₉ sterane predonominance and very light carbon isotope values of around-36.0%. In contrast, the ‘Q’ crudes, drived from the unknown source are characterized by a C₂₇ strerane predominance and carbon istope ratios of around -30.5%. Both the Huaf and ‘Q’ crudes also contain a series of characteristic compounds referred to as the ‘X’ compounds (all isomers of methyle and dimethyl alkanes). Oils reasoned to originate from Silurian Safiq source rocks have a week C₂₉ sterane precominance, a significant content of rearranged steranes and carbon isotope ratios of -30.5%. The oils thought to originate from the Jurassic Diyab Formation have a similar sterane distribution but heavier carbon isotope values of around -26.5%. Finally, the crude oils from the mid-Cretaceous Naith Formation source rocks are characteirzed by steranes with an equivalent distribution of C₂₇, C₂₈ and C₂₉ isomers, and carbon isotope values of around -26.9%. These variations in biomarker distributions and carbon isotope values are sufficiently distinct to ensure a high degree of certainty in the grouping of the crude oils.     

HYDROCARBONS IN THE MIDDLE MIOCENE JERIBE FORMATION,DYALA REGION,NE IRAQ

The Lower Miocene Jeribe Formation in northern and NE Iraq is composed principally of dolomitic limestones with typical porosity in the range of 10–24% and mean permeability of 30 mD. The formation serves as a reservoir for oil and gas at the East Baghdad field, gas at Mansuriya, Khashim Ahmar, Pulkhana and Chia Surkh fields, and oil at Injana, Gillabat, Qumar and Jambur. A regional seal is provided by the anhydrites of the Lower Fars (Fat'ha) Formation. For this study, oil samples from the Jeribe Formation at Jambur oilfield, Oligocene Baba Formation at Baba Dome (Kirkuk field) and Late Cretaceous Tanuma and Khasib Formations at East Baghdad field were analysed in order to investigate their genetic relationships. Graphical presentation of the analytical results (including plots of pristane/nC₁₇ versus phytane/nC_l8, triangular plots of steranes, tricyclic terpane scatter plots, and graphs of pristanelphytane versus carbon isotope ratio) indicated that the oils belong to a single oil family and are derived from kerogen Types II and III. The oils have undergone minor biodegradation and are of high maturity. They were derived from marine organic matter deposited with carbonate‐rich source rocks in suboxic‐anoxic settings. A range of biomarker ratios and parameters including a C₂₈/ C₂₉ sterane ratio of 0.9, an oleanane index of 0.2 and low tricyclic terpane values indicate a Late Jurassic or Early Cretaceous age for the source rocks, and this age is consistent with palynomorph analyses. Potential source rocks are present in the Upper Jurassic – Lower Cretaceous Chia Gara Formation and the Middle Jurassic Sargelu Formation at the Jambur, Pulkhana, Qumar and Mansuriya fields; minor source rock intervals occur in the Balambo and Sarmord Formations. Hydrocarbon generation and expulsion from the Chia Gara Formation was indicated by pyrolysate organic matter, palynofacies type (A), and the maturity of Gleichenidites spores. Oil migration from the Chia Gara Formation source rocks (and minor oil migration from the Sargelu Formation) into the Jeribe Formation reservoirs took place along steeply‐dipping faults which are observed on seismic sections and which cut through the Upper Jurassic Gotnia Anhydrite seal. Migration is confirmed by the presence of asphalt residues in the Upper Cretaceous Shiranish Formation and by a high migration index (Rock Eval SI / TOC) in the Chia Gara Formation. These processes and elements together form a Jurassic/Cretaceous – Tertiary petroleum system whose top‐seal is the Lower Fars (Fat'ha) Formation anhydrite.     

GEOCHEMICAL CHARACTERIZATION OF THE PERMIAN–TRIASSIC TRANSITION AT OUTCROP,CENTRAL SAUDI ARABIA

This study presents the results of chemostratigraphic analyses and spectral gamma‐ray logging integrated with sedimentological data across the Permian‐Triassic boundary at a measured outcrop section in central Saudi Arabia. The studied section encompasses the uppermost part of the Midhnab Member and the Lower and Upper Khartam Members of the Khuff Formation. Lithofacies were interpreted to have been deposited in subtidal, tidal to supratidal, lacustrine and meandering fluvial / flood plain, marginal marine and lagoonal depositional environments. Integration of bulk geochemical and carbon isotope (δ¹³C) data allowed the identification of a stratigraphic interval with a negative shift in δ¹³C ratio values, which was interpreted to correspond to the end‐Permian mass extinction event. The end of this “first negative shift in δ¹³C values” is taken to mark the Permian‐Triassic boundary. Above this boundary and just below an interval containing scattered thrombolites, a second negative shift in δ¹³C ratios was observed, and corresponds to an interval with long‐term uranium depletion as indicated by the bulk sediment geochemical and spectral gamma‐ray uranium data. The Permian‐Triassic boundary (PTrB) was placed at the transition between marginal‐marine and subtidal deposits. This stratigraphic position corresponds to the end of the “first negative δ¹³C shift” and the point of greatest uranium depletion. Although previous studies on outcrops of the Khuff Formation in Saudi Arabia identified a major sequence boundary between the Lower and Upper Khartam Members and interpreted it as the P TrB, no evidence is presented in this study for exposure and dissolution at this surface. Accordingly, the Permian‐Triassic transition is placed in the transgressive portion of the Upper Khartam Member, while the sequence boundary below is interpreted to correspond to the end‐Permian extinction. Correlation of Khuff time‐equivalent units in the Arabian Plate is challenging, and this study will contribute to an improved understanding of this important stratigraphic unit, which contains prolific non‐associated gas reservoirs. The identification of the Permian‐Triassic boundary in central Saudi Arabia will help in the construction of a sequence‐stratigraphic scheme for the Khuff, and with the correlation of lithofacies within this heterogeneous reservoir unit.     

焦石坝地区龙马溪组页岩解吸气地球化学特征及地质意义

通过对焦石坝地区龙马溪组页岩岩心进行解吸以分析其气体组分和碳同位素组成,研究了四川盆地志留系龙马溪组页岩气碳同位素倒转现象。结果表明,解吸气相对井口气组分明显偏湿、碳同位素值明显偏重;各组分碳同位素值随解吸时间变重：不同样品δ¹³C₁值最大变重幅度12.3 ‰ ~23.9 ‰ ,而不同样品δ¹³C₂值最大变重幅度仅0.8 ‰ ~2.3 ‰ ,即甲烷碳同位素值相对重烃变化更明显,与前人页岩岩心解吸实验结果一致。研究结果认为：地层状态下页岩气可能并未发生碳同位素倒转,岩心解吸过程中观察到的δ¹³C₁值比δ¹³C₂值变化更明显,不是不同组分扩散速率差异造成,而主要是由于甲烷与乙烷处于不同解吸阶段导致,即乙烷处于其解吸早期阶段而甲烷处于其解吸较晚阶段;生产过程中吸附作用引起的烷烃气不同组分相态差异与所处解吸阶段差异可能是导致四川盆地龙马溪组页岩气碳同位素完全倒转的主要原因,但不能否认干酪根裂解气与原油裂解气的混合对页岩气碳同位素倒转做出的部分甚至大部分贡献。     

白云岩储层成因的激光原位U-Pb定年和同位素地球化学新证据——以四川盆地西北部中二叠统栖霞组白云岩储层为例

以四川盆地西北部中二叠统栖霞组白云岩储层为例,采用激光原位U-Pb定年和碳、氧、锶同位素地球化学分析手段对白云岩中的孔洞和晶间孔成因进行了研究.白云岩的围岩与孔洞中的第1期白云石胶结物具有相近的U-Pb年龄和相似的碳、氧、锶同位素组成,表明孔洞在白云石化作用之前就已存在,孔洞为白云石胶结物从白云石化流体中沉淀提供了空间...     

四川盆地东北部马路背地区上三叠统须家河组天然气地球化学特征及气源

依据天然气化学组分及碳、氢同位素等地球化学资料,分析了四川盆地东北部马路背地区上三叠统须家河组天然气地球化学特征、天然气成因及来源。研究表明,马路背地区须家河组天然气组分以甲烷为主,含量介于92.60%~99.04%,平均为97.59%,干燥系数普遍高于0.990 0,平均为0.992 2,热演化程度较高;与邻区须家河组天然气对比,马路背地区须家河组天然气碳同位素明显具有甲烷碳同位素偏重、乙烷碳同位素偏轻的特征,δ¹³C₁值介于-33.70‰~-28.60‰,平均为-30.88‰,δ¹³C₂值介于-36.40‰~-28.90‰,平均为-33.11‰,甲烷和乙烷碳同位素多表现为倒转分布。天然气成因鉴别及气-源对比研究表明,马路背地区须家河组天然气为Ⅲ型和Ⅱ型干酪根生成的煤型气和油型气的混合热成因气,天然气主要来源于上三叠统须家河组煤系烃源岩及上二叠统吴家坪组海相烃源岩,甲烷和乙烷碳同位素倒转正是煤型气及油型气混合所致。马路背地区须家河组天然气高产富集与该区海相、陆相烃源岩双源供烃及深大断裂有效沟通海相、陆相多套优质烃源岩关系密切,沟通海相、陆相烃源岩的通源断裂在该区天然气成藏富集及后期调整改造方面具有重要作用。     

SOURCE‐ROCK MATURITY,HYDROCARBON POTENTIAL AND OIL – SOURCE‐ROCK CORRELATION IN WELL SHORISH‐1, ERBIL PROVINCE,KURDISTAN REGION,IRAQ

The Shorish‐1 exploration well is located in Erbil Province in the Kurdistan region of Iraq, on the outskirts of Erbil City near the dividing line between the Low Folded and High Folded Zones of the Zagros foldbelt. The well penetrated rocks which are between Miocene and Late Triassic in age. The depositional environment, source potential and maturity of organic‐rich intervals within the well succession were investigated using 38 cuttings samples. All samples were analysed for bulk geochemical parameters (i.e. total organic carbon, total carbon, sulphur, Rock‐Eval). A subset of 13 samples was selected for biomarker analysis, pyrolysis – gas chromatography and isotope investigations. In addition non‐commercial oil and oil impregnations were investigated for oil‐source correlations. Source rocks occur in the Jurassic Sargelu and Naokelekan Formations and the lowermost Cretaceous Chia Gara Formation. Analytical results suggest that these source rocks were deposited in a carbonate‐rich, anoxic environment in an intrashelf basin setting with free H₂S in the water column. Oxygen‐depleted conditions were favoured by salinity stratification. The average preserved TOC contents of the 100 m thick Sargelu Formation and the 25 m thick Naokelekan Formation are 2.2% and 4.6%, respectively. The TOC content of the Chia Gara Formation decreases upwards and averages 3.2% within its lower 40 m. Very high sulphur contents suggest the presence of kerogen Type II‐S, and that all the formations have generated sulphur‐rich hydrocarbons at relatively low maturities. In contrast to the oil impregnations within Jurassic strata, the oil and the oil impregnations within Cretaceous rocks are heavily biodegraded. Oil biomarker and isotope data indicate generation from the above‐mentioned Jurassic and Cretaceous source rock formations. As a result, generation from Triassic and Paleogene rocks can be excluded or is of negligible significance. Numerical models show that hydrocarbon generation rates from the Sargelu, Naokelekan and Chia Gara Formations peaked firstly at about 55 Ma (Paleocene/Eocene) and then again at 5 Ma before present (late Miocene/Pliocene). The first peak resulted from increased Paleocene subsidence, and the second peak was related to deep late Miocene/Pliocene burial. Hydrocarbon generation ceased during Recent uplift, during which ～2000 m of the Late Neogene succession was eroded.     

川西地区须家河组二段成岩作用及其对储层发育的影响

川西地区须家河组二段砂岩的孔隙类型主要以次生孔隙为主,其原生孔隙几乎全部被成岩作用所破坏,其中对储层孔隙发育影响最大的是压实作用、溶蚀作用、胶结作用和破裂作用等。通过对岩心、普通薄片、铸体薄片、阴极发光、碳和氧同位素、微量元素、流体包裹体等多种资料进行综合研究,阐述了主要成岩作用的形成机理和对储层孔隙发育的影响：压实作用和胶结作用是储层原生孔隙的主要破坏者,胶结作用以硅质胶结和碳酸盐胶结为主,不同成岩阶段胶结物类型不同;溶蚀作用下储层的主要储集空间为次生溶蚀孔,以长石颗粒被溶为主;破裂作用产生的裂缝能提高储层的渗透能力。      

沉积条件下白云石与伴生方解石碳氧同位素组成的差别及影响因素

以岩石学为基础,运用元素、X射线衍射和碳氧同位素分析等方法,在手标本中观尺度上探讨同一样品中白云石与伴生方解石的碳氧同位素组成及影响因素。研究表明,白云石比伴生方解石具有更高的δ13C和δ18O值。白云石的δ18O值高于伴生方解石可能与如下2种因素有关:（1）在白云石-水和方解石-水系统中,前者的氧同位素分馏系数大于后者,因此在白云石-方解石系统中,氧同位素分馏系数大于1;（2）白云石沉淀于比方解石盐度更高、更富18O的水体中。白云石的δ13C值高于伴生方解石可能与如下因素有关:在白云石-CO₂和方解石-CO₂系统中,前者的碳同位素分馏系数大于后者,因而对交代过程的白云石-方解石系统而言,碳同位素分馏系数大于1。准同生白云石与伴生方解石的氧同位素组成差值较大,而热液/深埋藏白云石与伴生方解石的氧同位素组成差值较小。      

伊朗Zagros盆地西南部白垩系Sarvak组碳酸盐岩储层特征

为了阐明伊朗Zagros盆地西南部白垩系Sarvak组碳酸盐岩储层特征,利用岩心、薄片、录井、试油及测井资料,通过储层岩性类型、储集空间、物性、电性特征及孔隙发育的影响因素分析,指出Zagros盆地西南部白垩系Sarvak组碳酸盐岩储层岩性类型有白垩质灰岩、云质灰岩、颗粒灰岩,储集空间类型多,主要为次生溶孔、铸模孔,其中颗粒灰岩的物性最好,白垩质灰岩中白垩质主要为浮游有孔虫,孔隙较发育,一般随物性增加,含油性级别升高。成岩作用对储层物性影响也较大,起建设性的成岩作用有溶蚀作用、白云化作用、生物扰动及压溶产生缝合线、缝合面。泥粒灰岩、粒泥灰岩在这些成岩作用的影响下,物性有较大改善。储层孔隙发育微观上主要受控于岩相、成岩作用,平面上还和构造位置及沉积环境有关,位于构造高部位的台地浅滩微相往往物性较好。利用垂向上测井响应及平面上小层物性分布特征,明确了物性较好、含油丰度较高的层段,为寻找高产有利储层提供了依据。