The genesis of H2S associated with heavy oils in Hendijan and Bahregansar oilfields,Sarvak reservoir

Bahregansar and Hendijan oilfields are located in the northwest of the Persian Gulf. Ghar/Asmari and Sarvak Formations are the main productive reservoirs, which contain sweet and sour gas, respectively. The oilfields are considered as a component of a petroleum system due to proximity and large number of geochemical similarities between them. Four gas samples, as well as oil and water samples, were collected in order to study and determine the hydrogen sulfide production mechanisms in the Sarvak reservoir. The prevalent mechanism of sourness in the reservoir, such as thermal sulfate reduction, thermal cracking, bacterial sulfate reduction, and migration from deeper intervals, have been investigated by studying relevant parameters, such as temperature, oil and water composition, lithology, and stable isotope of sulfur and carbon in hydrogen sulfide, asphaltene, and methane. Reservoir temperature as well as isotopic signature and geological data negate the possibility of thermal sulfate reduction, thermal cracking of oil, and migration from deeper intervals as the main reason of sourness. Bacterial sulfate reduction, by contrast, is considered as the main mechanism for hydrogen sulfide production in Sarvak reservoir of Bahregansar and Hendijan oilfields supported by reservoir temperature, water composition, and sulfur isotope ratio.     

中国烃源岩研究进展、挑战与展望

新中国油气工业发展60年历经两次大飞跃:第一次是在20世纪50年代初至80年代初,实现了陆相油气勘探重大发现并建立了陆相石油地质理论;第二次是在上世纪80年代初至今,实现了海相碳酸盐岩层油气勘探的重大突破并形成了中国特色海相石油地质理论。这些成果基于从中元古界到新近系均有发育的丰厚烃源岩基础,其中新生界陆相烃源岩和下古生界海相烃源岩生成了主要的石油储量,发现了大庆油田、渤海湾富油区和塔河等大油田;石炭—二叠系和侏罗系烃源岩构成了天然气储量主体,探明了苏里格、克拉2和普光等大气田。进入21世纪以来,中国油气勘探更呈现出"三海一陆"并进、石油稳定发展、天然气快速发展的良好态势,继上世纪60年代大庆和渤海湾油气大发现以后,全国年均新增探明石油地质储量再次突破10×108t大关,新增探明天然气储量也以年均5000×108m3的速度增长。该成果的取得与优质烃源岩、多元生烃的认识及陆相岩性地层油气藏、海相碳酸盐岩油气藏理论的提出等理论认识的重大突破,以及不断进步的钻探、物探和有机地球化学等勘探技术密不可分。目前,我国烃源岩研究仍面临着找到了大油气田主力烃源岩尚未明确、深层油气生成及其保存机制尚不清楚和资源潜力预测仍存在不确定性等亟待解决的众多挑战,其未来发展必须借助于油气勘探稳定发展的良好时机,把握生烃成藏的核心问题和勘探开发实际需求,切实将成烃与成盆、成藏作为一个含油气系统来动态研究烃源岩问题。     

Geochemical correlation of Asmari/Jahrum reservoir of Nargesi oilfield with seeps nearby

In case of maintaining the reservoir pressure by gas injection, connection between the reservoir and oil seeps around the oilfield should be investigated. Existence of probable conduits from reservoir to surface would cause problems such as environmental issues and capital losses. Comprehensive geochemical analyses were performed on Nargesi oilfield and nearby seep samples in order to investigate their geochemical correlation. Biomarker and diamondoid distributions as well as stable carbon isotope analysis on selected samples were determined by GC-MS and Finnigan Delta Plus mass spectrometer, respectively. Two active petroleum systems were identified in the region. A Jurassic petroleum system charged Nargesi oilfield, whereas the seeps appear to be charged by an older petroleum system. Higher maturity of seep samples identified by methylnaphthalenes, trisnorhopanes, and triaromatic steroid ratios implied that the second petroleum system should be older than Jurassic. Biomarker ratios confirmed that Marl-Carbonate source rocks deposited under anoxic to dysoxic conditions in open marine environment were the main oil-generating facies for the oilfield. Diamondoid indexes further support the concept developed by biomarker data and reveal that the seeps should be probably charged by shaly source rock. The negative correlation implies that gas injection would be effective.     

Source rock potentiality of Middle Jurassic–Lower Cretaceous of wells,North Western Desert,Egypt

The source rock potentiality of Middle Jurassic–Lower Cretaceous source rocks in Meleiha area was investigated through total organic carbon (TOC), R_o%, and pyrolysis analysis for 38 cutting samples collected from six wells. Also, the geochemical burial history profile to estimate the timing of hydrocarbon generation and expulsion of source rocks was constructed. The result revealed that the main hydrocarbon of source rocks, for the Middle Jurassic (Khatatba Fm.), is mainly mature, and has good capability for producing oil till present time. Lower Cretaceous source rocks (Alam El Bueib Fm.) are mature, derived from mixed organic sources, and have fair to good capability to generate gas and oil. Kharita Formations immature source rocks originating from terrestrial origin and have poor to fair potential to produce gas.     

Thermal and geochemical characterization of Lokpanta oil shales,Nigeria

Thermal decomposition of Lokpanta oil shale from Nigeria was studied by non-isothermal thermogravimetry (TG) and differential thermal analysis (DTA). The experiments were performed in an inert environment with a temperature range of 25 to 600 °C. The geochemical characteristics of the oil shale were also investigated by Rock Eval. pyrolysis. Thermal breakdown of the kerogen content of the oil shale takes place mainly at the temperature range of 300 to 570 °C. The estimated decomposable kerogen content of the oil shale ranges from 4.55 to 9.64 wt.%. The activation energies of the pyrolysis process vary from 73.2 to 75.0 kJ/mol. The DTA data reveals the exothermic nature of the decomposition process. The results from the geochemical analysis indicate that the oil shale contains sufficient, good quality kerogen to generate both oil and gas upon pyrolysis.     

Oil and Gas Occurrences in Southwest Turkey

Abstract

In SW Turkey, on both sides of the Antalya basin, two continental micro-plates can be distinguished: the Anatolian micro-plate to the NE and Bey Da?lar[idot] micro-plate to the W. These micro-plates are composed of a Paleozoic basement of Gondwana type, surrounded by Mesozoic carbonate platforms. From south to north the Bey Da?lar[idot] platforms are made of shallow marine carbonates from Triassic time up to Cenomanian. The southern part of this carbonate platform remained under shallow marine conditions up to the Eocene. On the contrary, the northern part subsided during Late Cretaceous time. In the Bey Da?lar[idot] platform, occurrences of organic materials are known in the Triassic and in the Early Cretaceous-Cenomanian carbonates. Rock-eval analysis indicate 0.25 to 1.46% total organic carbon (TOC). These facies could have represented a source rock for oil and gas. In the same area the uncomformable Early Miocene carbonates are made of bioclastic calcarenites. In some areas these calcarenites are dark colored and contain oil. These carbonates represent a reservoir rock The Anatolian micro- plate is also composed of shallow marine carbonates from Triassic time up to Eocene. Organic materials are known in the Akkuyu formation, Late Jurassic in age. According to organic geochemical characteristics, this unit is a good source rock. The total organic carbon (TOC) content of this unit is up to 12%. In the same area, other occurrences of oil and gas are known in two locations, Çirali to the SW of Antalya Bay and the Kizildag to the NE of Antalya. The Çirali location is known since the ancient civilizations as Chimera. Gas of this area is pouring out from a complex tectonic imbricate structure including ultrabasic rocks. The source rock and the reservoir are poorly known. The Kizildag is a large klippen of peridotites in the Antalya nappes complex. Liquid petroleum seepage is observed in this ophiolitic unit.     

Oil-source rock correlations of Jurassic and Cretaceous oils in the West Khalda area,North Western Desert,Egypt

Oil-source rock correlations are used in this study in order to achieve their relationship, depositional environments, and diagenetic processes in the source rocks. For this purpose many parameters are used, e.g., gross composition of oil and source rock extracts, and biomarker analyses. Ten representative oil samples and seven source rock hydrocarbon extracts were analyzed using relative geochemical analyses, and gas chromatography-mass spectrometry. The results revealed a genetic close relation between them and supported the indigenous mixed source of Alam El Bueib oil, which related to different sources, including Khatatba, Alam El Bueib, and Bahariya formations. Accordingly, Alam El Bueib formation can be considered as an important source for petroleum generation in that area.     

Source input and maturation assessments of oil families depending on specific and gross geochemical aspects of crude oils from Bakr oilfields in the central Gulf of Suez,Egypt

Different analytical techniques, including API gravity; sulfur–nickel–vanadium contents; liquid chromatographic separation; and gas chromatography, were utilized to investigate oil families of three crude oils collected from Bakr oilfield of middle-lower Miocene age and characterized by limestone facies at various depth locations in the central Gulf of Suez. These geochemical aspects were used to assess source input and maturation of oil families. The results showed that the studied oils indicate a close genetic relationship between studied crude oils, and classified as aromatic intermediate oils. These types of oils are characterized by mature sources derived mainly from marine inputs such as biomass from algae and plankton from different saline environments.     

Timing of petroleum generation and source maturity of selected wells in Abu Gharadig Basin,North Western Desert,Egypt

The timing of petroleum generation of source rocks is recognized to investigate the maturation level of the proven potential source formations for oil preservation dead lines, and predict the levels of thermal maturity of the studied sequences in terms of hydrocarbon generation and expulsion. For theses purposes four thermal burial history and maturity profiles were constructed of the Abu Gharaig-1 SW Umbaraka-1, GPZ-1, and GPX-1 wells. The results showed Abu Roash and Bahariya formations are immature to mature source rocks and have poor to fair potential to generate both oil and gas and still are within the early stage of hydrocarbon generation till the present time. Alam El Bueib and Masajid formations bear mature source rocks and have good generating capability for generating both oil and gas and entered the oil window since Cretaceous to Miocene times and lies within oil and gas windows at present time. Khatatba Formation bears a mature source rock and has good generating capability for both oil and gas and entered the oil window during Late Cretaceous to Eocene times.     

Utilizing the Rock-eval pyrolysis and biomarkers parameters to characterize the organic matters of selected wells in the Central Gulf of Suez,Egypt

Organic matters from the KK 85-1and HH 83-1wells in the Central Gulf of Suez were analyzed by two well-proven organic geochemical methods: Rock-Eval pyrolysis and gas chromatography–mass spectrometry (GC–MS) analyses. These techniques were used to obtain independent parameters of organic matter composition, thermal maturity, and environment of deposition. The study reveals a close concordance between Rock-Eval pyrolysis data and biomarkers parameters such as steranes and triterpanes. Rock-Eval pyrolysis in conjunction with GC–MS analyses shows that the organic matters contain two types of kerogen (Type-II/III and Type III), which lie dominantly prior to the peak stage of the conventional oil window (end of diagensis–beginning of catagensis). The case study shows that these methods are suitable for a proper assessment of the petroleum potential of source rocks and the rapid geochemical characterization of sedimentary organic matter.     

影响元坝气田超深井钻井提速的工程地质因素及技术对策

元坝气田工程地质特征异常复杂,钻井难度大,存在井漏、井涌、卡钻、井塌、高含硫化氢、高压水层等工程地质复杂问题,钻井效率低,周期长,建井成本高.从油气藏的基本地质特征、岩石力学性质、井壁稳定性等方面,分析认为,储层埋藏超深,钻遇地层岩性复杂、储层特征多样、油气立体成藏、油气水分布复杂、各油气藏特征差异大,岩石致密、强度大、可钻性差,异常高压-超高压、纵向多压力系统、井壁力学稳定性差、安全钻井液密度窗口窄,是钻井提速的工程地质影响因素.结合工程地质特征,提出了优化井身结构设计,优选空气钻井、泡沫钻井、液体欠平衡钻井、“螺杆+PDC钻头”和“涡轮+孕镶金刚石钻头”复合钻井、旋转导向钻井等钻井技术,以及优选高效钻头,优选钻井液体系等钻井提速技术对策,能够满足元坝气田海相超深井安全、快速钻井的需要.     

Hydrocarbon potential of cretaceous sediments from lower Indus Basin,Pakistan

In previous studies, Patala-Nammal Composite Total Petroleum System (TPS) was recognized as a potential source of hydrocarbon in the Upper Indus Basin, and Sembar-Goru Composite TPS in the Lower Indus Basin. However, petroleum source-rock potential of Cretaceous strata in the Indus Basin is poorly known. In the current study, Rock Eval and total organic carbon (TOC) analyses were conducted to investigate the thermal maturity and source-rock potential of Cretaceous unit in the Lower Indus Basin. The Parh Formation of the Lower Indus Basin is lean in organic contents (TOC < 0.73%) and consistent with immature type-III/IV kerogen. The Upper Goru Formation is fair in organic contents and presents similar characteristics to the Parh Formation with respect to the hydrocarbon generation zone. The Lower Goru Formation presents fair to very good organic contents. The members of Lower Goru Formation have enough organic matter (OM) and are mature, with the exception of Badin shales. The OM, throughout the formation, is predominantly gas prone. The Sembar Formation is fair in organic contents and mature with respect to hydrocarbons generation. These results support that the Lower Goru rocks are comparatively more prospective with respect to hydrocarbons.     

Organic richness,hydrocarbon potentiality,maturity, and timing of petroleum generation of the Cretaceous and Miocene source rocks in the central Gulf of Suez,Egypt

Total organic carbon (TOC) and pyrolysis analysis of the Cretaceous and Miocene source rocks in the central Gulf of Suez were evaluated throughout the 25 rock samples collected from 6 formations, namely Wata, Raha, Nubia “A” (Cretaceous source rocks); and Nukhul, Zeit, and Belayim (Miocene source rocks) from Gharib-252, Gharib-153, Gharib-163, Gharib-164, Gharib-167, and Gharib-165 wells. These data are used to study the probabilities of the source rock in the Cretaceous and Miocene source rocks in the central Gulf of Suez for the hydrocarbon generation through identifying the organic richness, type of organic matters, and thermal maturation of these organic materials. The results revealed that the Cretaceous formations are immature source rocks, ranging from fair to good source rocks and have kerogen of type III and type III/II. Meanwhile, Miocene source rocks, ranging from immature to marginally mature source rocks, are considered to range from good to very good source rocks for potential generation of both oil and gas and are characterized by kerogen of type III/II and type II.     

重油储层流体非均质性成因及流体物性预测

绝大部分重油和油砂都是由生物降解作用所形成,准确预测生物降解作用程度,能大大降低勘探风险并优化石油开发。由于微生物仅生活在水中,所以生物降解主要发生在油水界面附近。控制生物降解程度及速度的主要因素是油藏热史、地层水进入油藏的难易程度、养分供给、油藏充注史、降解与未降解油的混合作用及油水界面大小与油藏体积的关系。温度是油藏生物降解作用的最关键控制因素,生物降解的终止温度大约为80℃,但油藏温度低于约30℃后,降解通量会大大降低。养分是原油生物降解的最终控制因素,在没有明显地层水活动的区带,底水存在与否及底水层厚度大小就成了生物降解的另一个重要控制因素。由生物降解和充注混合造成原油组成和物性在盆地范围内大规模侧向梯度及油藏范围内小规模垂向梯度变化在重油区非常普遍,在一个连续充注的油柱上,原油所遭受的生物降解程度差异非常大,底部和顶部原油的组成和性质完全不同,这主要是因为未降解油向油柱顶部充注,而生物降解发生在油柱底部,充注强度与生物降解速度的相对大小决定了原油的最终组成面貌,原油物性变化与油藏温度(史)密不可分。通过地质因素对流体物性变化控制的定量描述,根据岩心或岩屑抽提物的地球化学分析获取高分辨率地球化学信息,根据统计方法可以建立地球化学参数与实测黏度间的对比关系,快速获取原油黏度或API重度,并将结果运用到油藏描述和定量模拟中,为产能预测和优化管理提供更有效的工具。     

Source rocks evaluation and timing of petroleum generation of selected wells in Meleiha Area,North Western Desert,Egypt

Fifteen rock samples were subjected to comprehensive organic geochemical studies aiming to evaluate potential source rocks as well as to predict the time of petroleum generation and expulsion of Kharita, Alam El Bueib, and Khataba Fms. in some wells in Meleiha area. The study revealed the Kharita Fm. is immature and has fair potential to produce gas. The organic matter is derived from terrestrial origin. Alam El Bueib Fm. is mature with fair to good capability of producing mixed oil and gas. The organic matter is originated mainly from mixed organic sources. Khatatba Fm. is mature and has good potentiality for generating oil. The organic matter is derived mainly from marine origin. The geothermal profile revealed that Kharita Fm. reached only the early stage of hydrocarbon generation and did not enter the oil widow till the present time. Alam El Bueib Fm. entered the oil window during Late Eocene time. Khatatba Fm. entered the oil window during Late Cretaceous. Consequently, Khatatba Fm. in Meleiha area can be considered as effective source rocks for generating both oil and gas.     

Evaluating the hydrogen storage potential of shut down oil and gas fields along the Norwegian continental shelf

The underground hydrogen storage (UHS) capacities of shut down oil and gas (O&G) fields along the Norwegian continental shelf (NCS) are evaluated based on the publicly available geological and hydrocarbon production data. Thermodynamic equilibrium and geochemical models are used to describe contamination of hydrogen, loss of hydrogen and changes in the mineralogy. The contamination spectrum of black oil fields and retrograde gas fields are remarkably similar. Geochemical models suggest limited reactive mineral phases and meter-scale hydrogen diffusion into the caprock. However, geochemical reactions between residual oil, reservoir brine, host rock and hydrogen are not yet studied in detail. For 23 shut down O&G fields, a theoretical maximum UHS capacity of ca. 642 TWh is estimated. We conclude with Frigg, Nordost Frigg, and Odin as the best-suited shut down fields for UHS, having a maximum UHS capacity of ca. 414 TWh. The estimates require verification by site-specific dynamic reservoir models.     

Essential Elements of the Allochthonous Taurus Petroleum System

This study has been carried out to investigate the petroleum potential of the Allochthonous Taurus units in the central Taurus Belt region. For this, essential elements of the petroleum system, such as source rock, reservoir and seal rocks, traps and critical moment of the generation and accumulation have been studied. Organic matter rich shales and carbonates of the both the Carboniferous and Permian sequences are potential source rocks, whereas the Middle-Upper Carboniferous grainstones and sandstones with the Permian carbonates including Girvanella and algae are probable reservoir rocks in the Allochthonous Taurus petroleum system. Although trap formation processes are mostly related to the thrust faults that have been formed during the Eocene, the primary or depositional stratigraphic traps are more dominant than structural ones.     

Occurrences and distributions of normal alkanes and biological markers to detections of origin,environments, and maturation of crude oils in El Hamed oilfield,Gulf of Suez,Egypt

The gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS) analyses for crude oils from Kareem reservoir in the wells El Hamed-1, 3, and 5 are used to provide information on source organic matters input, depositional environment, and maturation level. Data include normal alkane and acyclic isoprenoids distribution, terpane, and sterane aliphatic biomarkers. Pristine/phytane (Pr/Ph), Pr/nC17, and Ph/nC18 ratios indicated mixed organic sources of organic matters (kerogen type II, III) dominantly (kerogen type III) with a less effect of biodegradation and mature stage of occurrence. The diasteranes/steranes ratio showed generally low ratios as in most marine carbonate sources, while algal-bacterial organic matter contribution for the oil samples suggested dependence on the predominance of C23 tricyclic terpane relative to the C19 tricyclic terpane, and the C25 tricyclic terpane greater than C24 tricyclic terpane. The gammacerane index indicated that a low-salinity environment of deposition for the initial organic matters existed in the analyzed samples.     

涠洲油田低渗储层长岩心驱替实验研究

中海油在南海西部海域的涠西南凹陷发现低渗透油气田。目前,该油田开发面临的主要问题包括:特低渗(渗透率小于10×10-3μm2)油藏储量所占比例大,如何提高低渗透储层产能,如何有效动用储量,以及注水开发可能存在注入能力低等。由于地层原油黏度低,油质较轻,注气开发是提高低渗透油藏采收率的有效手段;此外,该油田开发过程中将产生大量伴生气,有足够的气源。因此,采用油田伴生气回注是值得探索的提高采收率的方法。为此,有必要通过长岩心驱替实验,对低渗透油气田的注入方式进行评价优选,为编制海上低渗透油田开发方案提供依据。选取涠洲某油田流沙港组低渗透储层,通过室内长岩心驱替实验研究,综合评价了衰竭、水驱、气驱、气/水交替驱替时的驱油效率和渗流特征,从而为注水、注气驱提高采收率开发方式的选择提供实验数据支持和参考。实验结果表明:衰竭式开采方式效果最差,注水比注气效果要好,注液化气前置段塞+外输气驱的方式,能够达到最好的驱替效果。     

柴达木盆地柴西与柴北缘地区凝析油气地化特征及其成因探讨

通过柴西与柴北缘地区凝析油气与烃源岩的地化特征对比,得出凝析油烃源岩为高成熟的烃源岩,柴西地区凝析气的母质成熟度要高于柴北缘地区。综合烃源岩与凝析油气的地化指标、包裹体测定温度、方解石年龄测定等因素得出：柴西凝析油气来自深层或邻近凹陷下第三系成熟-高熟的湖相烃源岩,成藏不晚于N1时期;柴北缘凝析油气来自深层或邻近凹陷下侏罗系成熟-过熟含煤湖沼相烃源岩,形成于N1初-N21初,成藏于N21时期或之后。