Geological and Engineering‘Sweet Spots'in the Permian Lucaogou Formation,Jimusar Sag,Junggar Basin

Unconventional oil and gas resources require petrophysical logs to answer the question of how best to optimize geological and engineering‘sweet spots'.Therefore,the establishment of a key well with comprehensive descriptions of lithology,reservoir properties,hydrocarbon-bearing properties,electronic well log responses,source rock properties,brittleness,and in situ stress magnitude and direction is important for the effective exploration and production of unconventional hydrocarbon resources.Cores,thin sections,scanning electron microscopy(SEM)and comprehensive well log suites are used to build a key well for the Permian Lucaogou Formation,Jimusar Sag of the Junggar Basin.The results show that there are three main types of lithologies,including siltstone,mudstone and dolostone.Lithologies can be predicted using the combination of conventional well and image logs.The pore spaces consist of interparticle pores,intragranular dissolution pores and micropores.Nuclear Magnetic Resonance(NMR)T_(2)components longer than 1.7 ms are superposed as effective porosity.Permeability is calculated using the Coates model from NMR T_(2)spectra.The ratio of T_(2)components>7.0 ms to T_(2)components>0.3 ms is used to calculate oil saturation.TOC is calculated using theΔlog R method.Brittleness index is calculated using Poisson-Young's method,ranging from 13.42%-70.53%.In situ stress direction is determined,and in situ stress magnitudes(maximum horizontal stress SH_(max),minimum horizontal stress Sh_(min),vertical stress S_(v))are calculated using density and sonic logs.The strike-slip stress type(SH_(max)>S_(v)>Sh_(min))is encountered.The key well which comprehensively includes the above seven properties is established.Geological and engineering(geomechanical)‘sweet spots'are then optimized from the key well by fully analyzing lithology,reservoir property,oilbearing potential,in situ stress magnitude and brittleness.It is hoped that the results support engineers'and geologists'decisions for the future exploitation of unconventional hydrocarbon resources.

Control of micro-wettability of pore-throat on shale oil occurrence:A case study of laminated shale of Permian Lucaogou Formation in Jimusar Sag,Junggar Basin,NW China

The control of micro-wettability of pore-throat on shale oil occurrence in different types of reservoir spaces remains unclear.Take the shale oil reservoir of the Permian Lucaogou Formation in the Jimusar Sag,Junggar Basin as an example,the reservoir space in laminated shale and the control of micro-wettability of pore-throat on shale oil occurrence were studied by using scanning electron microscope(SEM),multi-stage pyrolysis,quantitative fluorescence,nuclear magnetic resonance(NMR)and other techniques.The results show that there are mainly two types of laminated shale in the Lucaogou Formation,namely laminated shale rich in volcanic materials+terrigenous felsic,and laminated shale rich in volcanic materials+carbonate.The former type contains feldspar dissolution pores and intergranular pores,mainly with felsic mineral components around the pore-throats,which are water-wet and control the free shale oil.The latter type contains carbonate intercrystalline pores and organic pores,mainly with oil-wet mineral components around the pore-throats,which control the adsorbed shale oil.The oil-wet mineral components around the pore-throats are conducive to oil accumulation,but reduce the proportion of free oil.In the Lucaogou Formation,free oil,with high maturity and light quality,mainly occurs in the laminated shale rich in volcanic materials+terrigenous felsic.

Biodegradation of occluded hydrocarbons and kerogen macromolecules of the Permian Lucaogou shales,Junggar Basin,NW China

Three kerogen samples(JJZG-1,JJZG-2 and JJZG-3)isolated from the Permian Lucaogou shales of varying biodegradation levels(BLs≈0,3 and 7,respectively)were subjected to sequential stepwise pyrolysis combined with on-line detection of gas chromatography-mass spectrometry(GC-MS).Occluded fractions(bitumenⅡ)released at low-temperature steps(≥410℃)show consistent biodegradative signatures with that reported for solvent-extracted fractions(bitumenⅠ)of the original shales,e.g.,broad range of abundant n-alkanes,isoprenoids and regular hopanes for the non-biodegraded JJZG-1;trace n-alkanes and abundant hopanes for the moderately biodegraded JJZG-2;and no n-alkanes but still prominent hopanes including the microbially produced 25-nohopanes for the severely biodegraded JJZG-3.This consistency between bitumenⅡand bitumenⅠfractions indicates the biodegradability of the kerogenoccluded bitumenⅡwith limited protection from host kerogen.A minor level of protection was suggested by the trace distribution of n-alkanes in the bitumenⅡof JJZG-2,whereas the bitumenⅠhad no nalkanes.The kerogen itself was more resistant to biodegradation as reflected by the persistence of high abundances of both n-alkanes and hopanes in the high temperature(≥460℃)products of all three kerogen samples.However,the relative abundances of these product groups did show some evidence of biodegradation alteration,e.g.,ratios of n-C_(15)alkene/C_(27)hop-17(21)-ene at 510℃pyrolysis decreased by order of magnitude from the non-biodegraded(JJZG-1=27.4)to highly biodegraded(0.3 for JJZG-3)samples.The reduced biodegradation impact on the kerogen fraction(Cf.bitumen fractions)was also evident by the absence of 25-norhopanes in the high-temperature analysis of the JJZG-3 kerogen.

Organic-rich rocks;Paleoenvironment;Lucaogou Formation;Jimusar Sag;Junggar Basin

The Lucaogou Formation in the Jimusar Sag of the eastern Junggar Basin is an important sedimentary stratum accumulating huge amounts of lacustrine tight oil in China, where organic-rich rocks are commonly observed. Focusing on the Lucaogou Formation, a precise analysis of the inorganic and organic petrology and the inorganic geochemistry characteristics was conducted. The paleoclimate and paleoenvironment during sedimentation of the Lucaogou Formation were established,and the key factors that were controlling the accumulation of organic matter during this time were identified. The results of this study suggest that during the sedimentation of the Lucaogou Formation, the paleoclimate periodically changed from a humid environment to an arid environment. As a result, the salinity of the water and the redox environment fluctuated.During the sedimentation period, the lake showed su cient nutrient supplies and a high primary productivity. The interval studies in the Lucaogou Formation were divided into five sedimentary cycles, where the first, second, and fifth sedimentary cycles consisted of cyclical paleoclimate fluctuations varied from a humid environment to an arid environment and shifted back to a humid environment with levels of salinity from low to high and decreased again. The third and fourth cycles have cyclical fluctuations from a humid to an arid environment and corresponding salinity variation between low and high levels.During the period when organic-rich rocks in the Lucaogou Formation deposited in the Jimusar Sag, the paleoclimate and the water body were suitable for lower aquatic organisms to flourish. As a result, its paleoproductivity was high, especially during the early period of each cycle. A quiet deep water body is likely to form an anoxic environment at the bottom and is also good for accumulation and preservation of organisms. Fine-grained sediments were accumulated at a low deposition rate, with a low dilution of organic matter. Therefore, high paleoproductivity provided a su cient volume of organisms in the studied area in a quiet deep water body with an anoxic environment and these were the key factors controlling formation of organic-rich rocks.

Prediction of multiscale laminae structure and reservoir quality in fine-grained sedimentary rocks:The Permian Lucaogou Formation in Jimusar Sag,Junggar Basin

Fine-grained sedimentary rocks have become a research focus as important reservoirs and source rocks for tight and shale oil and gas.Laminae development determines the accumulation and production of tight and shale oil and gas in fine-grained rocks.However,due to the resolution limit of conventional logs,it is challenging to recognize the features of centimeter-scale laminae.To close this gap,complementary studies,including core observation,thin section,X-ray diffraction(XRD),conventional log analysis,and slabs of image logs,were conducted to unravel the centimeter-scale laminae.The laminae recognition models were built using well logs.The fine-grained rocks can be divided into laminated rocks(lamina thickness of<0.01 m),layered rocks(0.01-0.1 m),and massive rocks(no layer or layer spacing of>0.1 m)according to the laminae scale from core observations.According to the mineral superposition assemblages from thin-section observations,the laminated rocks can be further divided into binary,ternary,and multiple structures.The typical mineral components,slabs,and T2spectrum distributions of various lamina types are unraveled.The core can identify the centimeter-millimeter-scale laminae,and the thin section can identify the millimeter-micrometer-scale laminae.Furthermore,they can detect mineral types and their superposition sequence.Conventional logs can identify the meter-scale layers,whereas image logs and related slabs can identify the laminae variations at millimeter-centimeter scales.Therefore,the slab of image logs combined with thin sections can identify laminae assemblage characteristics,including the thickness and vertical assemblage.The identification and classification of lamina structure of various scales on a single well can be predicted using conventional logs,image logs,and slabs combined with thin sections.The layered rocks have better reservoir quality and oil-bearing potential than the massive and laminated rocks.The laminated rocks’binary lamina is better than the ternary and multiple layers due to the high content of felsic minerals.The abovementioned results build the prediction model for multiscale laminae structure using well logs,helping sweet spots prediction in the Permian Lucaogou Formation in the Jimusar Sag and fine-grained sedimentary rocks worldwide.

Acid-base alternation diagenesis and its influence on shale reservoirs in the Permian Lucaogou Formation, Jimusar Sag, Junggar Basin, NW China

The diagenesis and diagenetic facies of shale reservoirs in Lucaogou Formation of Jimusar Sag were studied by means of microscopic observation and identification of ordinary thin sections and cast thin sections,X-ray diffraction,scanning electron microscope and electron probe tests.The results show that alkaline and acidic diagenetic processes occurred alternately during the deposition of Permian Lucaogou Formation in Jimusar Sag.The evolution of porosity in the shale reservoirs was influenced by compaction and alternate alkaline and acidic diagenetic processes jointly,and has gone through three stages,namely,stage of porosity reduction and increase caused by alkaline compaction,stage of porosity increase caused by acid dissolution,and stage of porosity increase and reduction caused by alkaline dissolution.Correspondingly,three secondary pore zones developed in Lucaogou Formation.The shale reservoirs are divided into three diagenetic facies:tuff residual intergranular pore-dissolution pore facies,tuff organic micrite dolomite mixed pore facies,and micrite alga-dolomite intercrystalline pore facies.With wide distribution,good pore structure and high oil content,the first two facies are diagenetic facies of favorable reservoirs in Lucaogou Formation.The research results provide a basis for better understanding and exploration and development of the Lucaogou Formation shale reservoirs.

The Characteristics of the Hydrothermal Exhalative Dolostone of Lucaogou Formation in Santanghu basin and its Geology Setting Indication

The NW-SE trending Santanghu basin is located in Xinjiang,NW China,between Tianshan Mountains and Altai Mountains.The tectonic evolution history of north Xinjiang has long been debated,especially the question when did that area began its intraplate rift evolution stage.This abstract discusses the features and possible origin of the hydrothermal exhalative dolostone of Lucaogou Formation in Santanghu basin,aiming to provide relevant information about this question.The target dolostone are characterized by extreme thin lamina of 0.3cm–1 cm thick.Dolomite,ankerite,potassium feldspar and analcite are dominant composition.Most dolomite is poor crystallized and is in anhedral or subhedral shapes.Ankerite is generally porphyritic,few is in irregular shapes.It has to be noted that the porphyritic ankerite commonly develop zonal textures characterized by rings with various Fe O content.Potassium feldspar and analcite（<50%）are commonly observed in dolostones.Thin sections show some analcite is tetragonal trisoctahedron with harbour–like corrosion rims.Besides,few fragments of carbonatite rocks are observed in Lucaogou Formation and they perform intermittent or scattered distribution in rock layers.Previous work done by our study team showsδ13C PDB values are 4.8‰;1.4‰,6.93‰on average.Theδ18 O PDB values are between-5‰;21.1‰,-10.94‰on average.Paleosalinity calculated byδ13C andδ18 O is between 128.35 and 136.81,134.42 on average.Sr content of dolostones in study area reaches to164×10-6;37×10-6（379.1×10-6 on average）,most dolostone in target area are between 0.70457;.706194, average at 0.705360.Considering either accompanying residual tuff or residual leucite is found via electron probe,this indicates the analcite may derive form analcime phonolite.Furthermore,fragments of carbonatite rocks proves mantle-derived magmatism exist.The rapid variation ofδ18 O indicates multiple interactions of hydrothermal fluids with lake water during Lucaogou sedimentary period.87Sr/86Sr values are much lower than that of crustal silica rocks while are more close to mantle derived rocks,which indicates diagenetic hydrothermal fluid is mantle-origin.It has been reported that dolostone does not intergrow with iron-rich dolostone in study area.According to the latest X diffraction results of cores,iron-rich dolostone distributes rather locally.Given that ankerite commonly develop zonal textures characterized by various Fe O content,we confirm it is due to multiple hydrothermal fluids activities in different hydrothermal vents.There should be abundant hydrothermal vents during Lucaogou period.Deep faults and its relevant fractures built plenty paths for mantle-origin hydrothermal fluids to run up.Different vents owned various fluid properties,so did relevant sedimentation products.Hence we inclined to believe Santanghu basin was at intraplate rift evolution stage,under regional extension condition in late Carboniferous.During early-mid Permian the basin was a starved,deep lacustrine intracontinental rift basin.Accordingly,in northern Xinjiang,ocean basin may close in late Carboniferous and started continental sedimentary development in early Permian.

Bed type and flow mechanism of deep water sub-lacustrine fan fringe facies:an example from the Middle Permian Lucaogou Formation in Southern Junggar Basin of NW China

Submarine or sub-lacustrine lobe deposits are important reservoirs,but the fan fringe deposits form heterogeneities within deep water fan deposits.Fan fringe facies records the complex sediment gravity flow types.By understanding of the bed types and flow mechanisms,we can identify the fan fringe deposit,which aids in the reconstruction of deep water fan and reservoir evaluations.The Jiucaiyuanzi and Dalongkou sections in the West Bogda Mountains preserve well-exposed 536-m and 171-m thick successions,respectively,of a deep water lacustrine depositional system from the Middle Permian Lucaogou Formation.Bed types of the Lucaogou Formation include high-density turbidite,low-density turbidite,incomplete Bouma-type turbidite,hybrid event beds,and slump deposits.The Lucaogou Formation is interpreted here as a fan fringe facies due to the thin bed thickness that characterize turbidites and hybrid event beds,as well as the predominance of the isolated sheet architecture.Previous studies suggest that these deposits were considered as deposited in a deep water setting due to the absence of wave-related structures.The presence of abundant mud clasts in massive medium-coarse grained sandstone beds reflects the significant erosional capability and interactions between high-density turbidity currents and lake floor.The fan fringe facies here contains amalgamated and thick-bedded homolithic facies(~30%)and thin-bedded heterolithic facies(~70%).The examination of the bed type is of wider significance for facies prediction and reservoir heterogeneity in the sub-lacustrine fan fringe facies.

基于核磁共振测井的页岩油产能分析及甜点评价

吉木萨尔凹陷芦草沟组页岩油水平井产能差异大,各井产水率区别明显,其主控因素尚不清楚,现有甜点分类标准无法满足该区页岩油精细开发的需要,基于核磁共振测井截止值的含油性及可动性解释难以精细识别页岩油甜点。以核磁共振测井和实验室核磁共振测试为基础,基于分频处理、分流体核磁共振测井孔隙结构表征、弹性能排油模拟等技术,精细表征页岩油层中不同类型流体分布;分别刻画油水赋存孔径,建立可动油量评价模型,对流体赋存、孔径分布、可动油量等进行定量表征;结合单井试油和生产数据,明确水平井产能控制因素。研究表明:大孔轻质组分占比、可动油孔隙度与水平井产能的相关性明显优于孔隙度、含油饱和度和核磁可动油孔隙度;水影响指数则反映地层水对页岩油流动的影响程度,该值越小,相同可动油孔隙度下水平井产能越高、含水率越低。以大孔轻质组分占比、水影响指数和可动油孔隙度为指标,将页岩油油层划分为3类,由Ⅰ类至Ⅲ类油层,日产油量快速减小,含水率明显升高,可作为芦草沟组页岩油甜点精细评价的依据。

吉木萨尔页岩油水平井体积压裂技术实践与认识

针对吉木萨尔页岩油储层,围绕提升缝控储量目标,从缝网设计、缝网构建、有效支撑和提升基质内原油动用能力四个方面开展了理论研究与技术实践,完成了三代技术革新,攻克了薄互层裂缝有效扩展等基础理论和段内多簇工艺、低成本材料等关键技术,集成了以缝藏匹配、精准改造、多尺度支撑、CO_(2)前置为核心的水平井体积压裂技术体系,压裂关键技术指标达到国内先进水平,支撑了吉木萨尔页岩油的规模效益开发。2023年吉木萨尔页岩油产油量突破60×10^(4) t,连续三年区块年产量增幅超过10×10^(4) t,为2025年我国首个国家级陆相页岩油示范区的高效建成提供了坚实的技术支撑,也为我国其它页岩油开发技术优化提供借鉴。

吉木萨尔凹陷二叠系芦草沟组一段沉积期古地貌特征及有利储层分布

依据岩心、测井及地震等资料,对吉木萨尔凹陷二叠系芦草沟组一段沉积期古地貌进行了恢复,并预测了其有利储层分布。研究结果表明:①吉木萨尔凹陷芦草沟组一段发育丰富的粒序层理、块状层理、爬升沙纹层理及植物碎片,频繁出现的对偶粒序及内部侵蚀面沉积构造为湖泊异重流成因,进一步识别出水道、水下天然堤、朵叶体及侧缘4种微相类型,其中水道和朵叶体为有利储集微相。②芦草沟组一段沉积期,吉木萨尔凹陷古地貌整体呈“南低北高、中部低东西高”的沉积格局,低部位发育古沟槽、古低凸起及古低洼3类微古地貌单元。古沟槽内水道储层为加积叠置、厚层状充填,古低洼区内朵叶体为进积—侧积叠置、薄层席状披覆,古低凸起分割异重流沉积;古斜坡区异重流欠发育。③吉木萨尔凹陷南部发育3个异重流供给水道区。异重流水道向北进积,主水流线分散成多支,在水道末端形成多个连片叠置的朵叶体。

吉木萨尔凹陷芦草沟组页岩油生烃母质及其生烃机理

为明确吉木萨尔凹陷芦草沟组上、下甜点段页岩油生烃母质差异和生烃机理,采用场发射扫描电镜、电子探针和傅里叶红外光谱实验,对芦草沟组烃源岩超微生物特征进行研究。上甜点段页岩油主要生烃生物为层状藻(微囊藻),母质以直链脂肪族为主;下甜点段以结构藻(塔斯马尼亚藻)为主,生烃母质富集富支链脂肪族、芳香族和亚砜官能团。由于长直链饱和烃断裂所需的活化能远高于分支链及碳硫和碳氮低键能,因此,下甜点段页岩油的生烃母质活化能低于上甜点段,发生早期生烃,在低成熟度下形成高非烃沥青质的高密度原油,是下甜点段原油性质偏重偏稠的主要原因。

古生代陆相盆地中的17万年天文周期

【目的】米兰科维奇周期通过调控地球天文轨道参数来影响地球气候系统和有机碳埋藏。除通过线性过程调控气候系统的常规周期外,还存在通过一系列“非线性”正负反馈进程调控气候系统的“非常规”天文周期,如17万年斜率振幅调制周期。先前研究已证明17万年天文周期对中新生代地球中高纬度有机碳埋藏具有调控作用,然而由于缺乏准确的天文解和高分辨率的地质记录,17万年信号在古生代鲜有报道。【方法】对准噶尔盆地早二叠世芦草沟组的总有机碳含量和自然伽马测井数据进行旋回地层学分析,认为芦草沟组保存了短偏心率、斜率、岁差周期信号。【结果】根据短偏心率周期进行了天文调谐,结果显示芦草沟组沉积持续时间约为2.8 Myr,沉积速率估算为9.1 cm/kyr。除常规周期外,17万年周期信号也在去趋势数据序列和斜率振幅调制曲线中被发现。【结论】对古生代陆相地层中的17万年天文周期进行系统探讨,基于强烈的斜率信号,推测该17万年周期信号来源于斜率振幅调制周期s3-s6。它通过调控早二叠世地球中高纬度水循环过程影响有机碳埋藏,而沉积盆地中的阈值响应效应将高频的斜率周期中的较低频17万年振幅调制周期放大,并出现在地质记录中。

吉木萨尔凹陷二叠系芦草沟组页岩油储层天然裂缝特征与压裂模拟

综合利用岩心、地震、测井和微地震监测等资料,在天然裂缝模型和地应力模型的约束下,运用页岩储层压裂缝网模拟研究了吉木萨尔凹陷二叠系芦草沟组天然裂缝特征及其对压裂缝网扩展的影响。研究结果表明:(1)吉木萨尔凹陷二叠系芦草沟组天然裂缝包括层理缝和构造缝,以层理缝为主,数量多、倾角小,裂缝数量平均为251条,裂缝面密度为0.58~1.34条/m,平均为0.93条/m。构造缝倾角为70°~95°,裂缝数量明显少于层理缝,根据形成时间及产状,构造缝可分为Ⅰ类和Ⅱ类构造缝。(2)研究区最小水平主应力为50.41~55.22 MPa,最大水平主应力为53.52~74.43 MPa,有利于水力压裂缝网的延伸,芦草沟组纵向存在应力隔层,最大层间应力差可达12 MPa,水力压裂时人工裂缝不易穿层。(3)研究区芦草沟组页岩压裂改造以激活高角度构造缝为主,96.45%的压裂缝为“T形”裂缝,而“十字形”和“一字形”压裂缝仅占2.24%和1.21%,芦草沟组压裂缝半缝长度为70~100 m,高度为10~30 m,邻近断层时由于缝长过大,易发生井窜。

准噶尔盆地阜康凹陷东部深层二叠系超压形成机制及演化特征

利用钻井、录井、测井以及实测地层压力等资料,采用考虑多种超压机制的盆地模拟技术,综合判识了准噶尔盆地阜康凹陷东部二叠系地层超压的成因机制,定量恢复了各成因类型的超压演化特征。研究结果表明:(1)准噶尔盆地阜康凹陷东部二叠系发育弱超压—强超压,地层压力系数为1.36~1.88,过剩压力为12~49 MPa,不同构造部位发育的超压存在明显差异。凹陷区超压最强,地层压力系数为1.50~1.88,过剩压力为23~49 MPa;斜坡带次之,地层压力系数为1.52~1.79,过剩压力为24~37 MPa;凸起区相对最弱,地层压力系数为1.36~1.59,过剩压力为12~23 MPa。(2)研究区不同岩性的地层超压成因不同,芦草沟组烃源岩超压成因为生烃和欠压实作用;上乌尔禾组储层超压成因为超压传递和欠压实作用;上乌尔禾组泥岩盖层超压成因为欠压实作用。(3)研究区芦草沟组烃源岩和上乌尔禾组泥岩盖层的超压具有持续增大的特征,芦草沟组烃源岩生烃增压贡献率沿凸起区、斜坡带至凹陷区逐步增大,上乌尔禾组泥岩盖层欠压实增压量也具有相同变化趋势;上乌尔禾组储层超压经历了晚三叠世至晚侏罗世缓慢增大、晚侏罗世末期至早白垩世快速增大、早白垩世末期至现今缓慢增大3个阶段,其中超压传递增压对现今储层超压的贡献率为58.46%~78.86%。

三塘湖盆地中二叠统芦草沟组油页岩热重特性及影响因素

为了研究油页岩加热过程中的热重特性和热解过程及其影响因素,对三塘湖盆地芦草沟组油页岩的含油率、总有机碳、热解、主量元素和热重分析等进行测试。结果显示,三塘湖盆地芦草沟组油页岩为具有较高有机质丰度、高灰分和中等发热量的中等品质油页岩,且灰分主要元素组成为SiO_(2)、Al_(2)O_(3)、CaO,属于高熔灰分。油页岩热重分析显示其热解过程主要为低温、中温和高温失重段3个阶段,中温失重段为油页岩主要失重段和油页岩热解反应阶段,温度范围为300~580℃。其中油页岩热解过程中油气大量生成阶段的温度范围为430~500℃,为油页岩热解过程中生油关键阶段,而500~580℃为页岩气生成阶段,可以形成一定量的页岩气。

基于改进型随机森林算法的页岩岩性识别——以准噶尔盆地芦草沟组为例

在储集层岩性识别的应用中,特别是对页岩等非均质性较强的非常规储集层的岩性识别,机器学习算法的高效性、准确性和有效信息整合能力已经得到了充分验证。考虑到岩性识别的特征参数优选问题,优选自然伽马、T2几何平均值、结构指数、骨架密度指数、密度和深侧向电阻率,采用结合递归特征消除的随机森林算法,对准噶尔盆地中二叠统芦草沟组页岩储集层的主要岩性进行识别;利用传统的随机森林算法和支持向量机法,对同一套资料进行岩性预测,并与岩石薄片鉴定结果对比。结合递归特征消除的随机森林算法只需选择一半的测井参数,便能够达到更好的效果,而且通过优选特征参数,缩短了算法的运行时间。因此,结合递归特征消除的随机森林算法能够实现测井特征参数的优选,提高页岩岩性识别的准确率,缩短运行时间,为复杂岩性识别和多参数选择提供了新的思路。

陆相混合细粒岩沉积微相及其对甜点的控制作用——以吉木萨尔凹陷芦草沟组为例

【目的】吉木萨尔凹陷二叠系芦草沟组发育了一套陆相混积沉积体系,混积细粒岩沉积微相类型及甜点储层分布规律等研究的不足制约了该区页岩油高效开发。【方法】综合岩心、露头、测井、X射线荧光光谱(X-Ray Fluorescence,XRF)元素录井、分析化验和试油试采等资料,采用岩相构型、沉积微相耦合分析和动静结合等方法,开展了沉积微环境及微相类型划分、沉积模式及其对甜点的控制作用等研究。【结果】(1)研究区主要发育浪成交错层理、水平层理、同生变形构造、黄铁矿、方解石条带、鸟眼构造和结核、缝合线构造、含生物化石和白云岩溶蚀孔8类沉积构造。研究区分为半深湖—深湖、混合浅湖和碎屑浅湖亚相,细分为半深湖泥、云坪、混合滩坝、混合浅湖泥、浅湖砂坝和碎屑浅湖泥等6种微相,不同微相沉积特征及其沉积机制差异明显。(2)建立了咸化湖泊相混积细粒岩沉积微相模式。芦一段自下而上从深湖—半深湖—浅湖演化过程,发育了浅湖砂坝、混合滩坝与云坪微相。其中,云坪呈连片状大范围分布,混合滩坝呈土豆状分布,发育程度较高,不同层规模有差异,浅湖砂坝发育程度一般,呈断续状局限分布,垂向上呈薄储集层与厚层泥岩叠置状。芦二段以浅湖为主,微相类型与芦一段类似,但形态、规模与叠置样式差异较大。云坪和混合滩坝发育数量和规模大大减小,浅湖砂坝则发育程度较高,呈大规模分散土豆状发育,垂向上呈厚层叠置状。不同位置剖面微相的叠置样式不同。(3)甜点段XRF元素分析显示,目的层沉积时为干燥炎热的半咸水环境到咸水过渡环境,古生产力水平较高;下甜点段为富氧环境,上甜点段则为厌氧亚还原到还原环境。(4)沉积微相控制了甜点分布和开发对策。混合滩坝微相Ⅰ类甜点发育程度高,非均质性弱,开发效果最好,采用大规模部署水平井平台化作业进行效益开发。云坪微相Ⅲ类甜点发育,非均质性强,开发效果一般,是后续接替区域。浅湖砂坝Ⅱ类甜点发育,整体分散状,连续性较差,非均质性强,开发效果较好。【结论】后续应在沉积微相空间分布精细研究基础上,参考核磁曲线参数部署水平井开发。

吉木萨尔凹陷芦草沟组层理页岩渗吸置换规律

为研究吉木萨尔凹陷二叠系芦草沟组层理页岩储集层压裂后渗吸期间原油的动用规律,采用岩心渗吸置换实验结合核磁共振技术,定量描述不同孔隙内原油的相对含量。采用吉木萨尔地区上甜点的岩心开展渗吸实验,研究重力作用、各向异性、重力分异和水力压裂裂缝宽度对渗吸置换影响,并进行定量表征。结果表明:层理页岩自发渗吸的过程中,重力作用在渗吸中起到了动力作用,顶部渗吸的采收率高于水平渗吸;各向异性对层理页岩渗吸的影响较大,压裂液进入平行于层理的渗吸置换量大,达到渗吸平衡的时间较垂直于层理短,平行于层理渗吸采收率高于垂直于层理;重力分异是指在岩心底部渗吸时,渗吸置换出原油而停留在岩层表面形成油膜,阻止压裂液继续进入基质,导致渗吸效果变差,底部渗吸采收率与顶部渗吸采收率相差14.12%;模拟水力压裂裂缝宽度为2 mm的条件下发生渗吸置换的液量有限,导致模拟裂缝内含水饱和度下降快,限制了渗吸的进一步进行。因此,裂缝的缝高方向应尽量穿过平行层理,增大裂缝宽度,增加裂缝改造体积。