Action mechanisms of abnormal fluid pressure on physical properties of deep reservoirs: A case study on Jurassic Toutunhe Formation in the southern margin of Junggar Basin, NW China

Considering the action mechanisms of overpressure on physical changes in skeleton particles of deep reservoir rocks and the differences in physical changes of skeleton particles under overpressure and hydrostatic pressure, the sandstone of the Jurassic Toutunhe Formation in the southern margin of Junggar Basin was taken as an example for physical modeling experiment to analyze the action mechanisms of overpressure on the physical properties of deep reservoirs. (1) In the simulated ultra-deep layer with a burial depth of 6000-8000 m, the mechanical compaction under overpressure reduces the remaining primary pores by about a half that under hydrostatic pressure. Overpressure can effectively suppress the mechanical compaction to allow the preservation of intergranular primary pores. (2) The linear contact length ratio under overpressure is always smaller than the linear contact length ratio under hydrostatic pressure at the same depth. In deep reservoirs, the difference between the mechanical compaction degree under overpressure and hydrostatic pressure shows a decreasing trend, the effect of abnormally high pressure to resist the increase of effective stress is weakened, and the degree of mechanical compaction is gradually close to that under hydrostatic pressure. (3) The microfractures in skeleton particles of deep reservoirs under overpressure are thin and long, while the microfractures in skeleton particles of deep reservoirs under hydrostatic pressure are short and wide. This difference is attributed to the probable presence of tension fractures in the rocks containing abnormally high pressure fluid. (4) The microfractures in skeleton particles under overpressure were mainly formed later than that under hydrostatic pressure, and the development degree and length of microfractures both extend deeper. (5) The development stages of microfractures under overpressure are mainly controlled by the development stages of abnormally high pressure and the magnitude of effective stress acting on the skeleton particles. Moreover, the development stages of microfractures in skeleton particles are more than those under hydrostatic pressure in deep reservoir. The multi-stage abnormally high pressure plays an important role in improving the physical properties of deep reservoirs.

Genetic type and source of natural gas in the southern margin of Junggar Basin, NW China

Natural gas has been discovered in many anticlines in the southern margin of the Junggar Basin. However, the geochemical characteristics of natural gas in different anticlines haven’t been compared systematically, particularly, the type and source of natural gas discovered recently in Well Gaotan-1 at the Gaoquan anticline remain unclear. The gas composition characteristics and carbon and hydrogen isotope compositions in different anticlines were compared and sorted systematically to identify genetic types and source of the natural gas. The results show that most of the gas samples are wet gas, and a few are dry gas;the gas samples from the western and middle parts have relatively heavier carbon isotope composition and lighter hydrogen isotope composition, while the gas samples from the eastern part of southern basin have lighter carbon and hydrogen isotope compositions. The natural gas in the southern margin is thermogenic gas generated by freshwater-brackish water sedimentary organic matter, which can be divided into three types, coal-derived gas, mixed gas and oil-associated gas, in which coal-derived gas and mixed gas take dominance. The Jurassic coal measures is the main natural gas source rock in the southern margin, and the Permian lacustrine and the Upper Triassic lacustrine-limnetic facies source rocks are also important natural gas source rocks. The natural gas in the western part of the southern margin is derived from the Jurassic coal measures and the Permian lacustrine source rock, while the natural gas in the middle part of the southern margin is mainly derived from the Jurassic coal measures, partly from the Permian and/or the Upper Triassic source rocks, and the natural gas in the eastern part of the southern margin is originated from the Permian lacustrine source rock. The natural gas in the Qingshuihe oil and gas reservoir of Well Gaotan-1 is a mixture of coal-derived gas and oil-associated gas, of which the Jurassic and Permian source rocks contribute about half each.

Influences of burial process on diagenesis and high-quality reservoir development of deep-ultra-deep clastic rocks:A case study of Lower Cretaceous Qingshuihe Formation in southern margin of Junggar Basin,NW China

Taking the Lower Cretaceous Qingshuihe Formation in the southern margin of Junggar Basin as an example,the influences of the burial process in a foreland basin on the diagenesis and the development of high-quality reservoirs of deep and ultra-deep clastic rocks were investigated using thin section,scanning electron microscope,electron probe,stable isotopic composition and fluid inclusion data.The Qingshuihe Formation went through four burial stages of slow shallow burial,tectonic uplift,progressive deep burial and rapid deep burial successively.The stages of slow shallow burial and tectonic uplift not only can alleviate the mechanical compaction of grains,but also can maintain an open diagenetic system in the reservoirs for a long time,which promotes the dissolution of soluble components by meteoric freshwater and inhibits the precipitation of dissolution products in the reservoirs.The late rapid deep burial process contributed to the development of fluid overpressure,which effectively inhibits the destruction of primary pores by compaction and cementation.The fluid overpressure promotes the development of microfractures in the reservoir,which enhances the dissolution effect of organic acids.Based on the quantitative reconstruction of porosity evolution history,it is found that the long-term slow shallow burial and tectonic uplift processes make the greatest contribution to the development of deep-ultra-deep high-quality clastic rock reservoirs,followed by the late rapid deep burial process,and the progressive deep burial process has little contribution.

Heterogeneity and differential hydrocarbon accumulation model of deep reservoirs in foreland thrust belts: A case study of deep Cretaceous Qingshuihe Formation clastic reservoirs in southern Junggar Basin, NW China

Using the data of drilling, logging, core, experiments and production, the heterogeneity and differential hydrocarbon accumulation model of deep reservoirs in Cretaceous Qingshuihe Formation(K1q) in the western section of the foreland thrust belt in southern Junggar Basin are investigated. The target reservoirs are characterized by superimposition of conglomerates, sandy conglomerates and sandstones, with high content of plastic clasts. The reservoir space is mainly composed of intergranular pores. The reservoirs are overall tight, and the sandy conglomerate has the best physical properties. The coupling of short deep burial period with low paleotemperature gradient and formation overpressure led to the relatively weak diagenetic strength of the reservoirs. Specifically, the sandy conglomerates show relatively low carbonate cementation, low compaction rate and high dissolution porosity. The special stress-strain mechanism of the anticline makes the reservoirs at the top of the anticline turning point more reformed by fractures than those at the limbs, and the formation overpressure makes the fractures in open state. Moreover, the sandy conglomerates have the highest oil saturation. Typical anticline reservoirs are developed in deep part of the thrust belt, but characterized by "big trap with small reservoir". Significantly, the sandy conglomerates at the top of anticline turning point have better quality, lower in-situ stress and higher structural position than those at the limbs,with the internal hydrocarbons most enriched, making them high-yield oil/gas layers. The exponential decline of fractures makes hydrocarbon accumulation difficult in the reservoirs at the limbs. Nonetheless, plane hydrocarbon distribution is more extensive at the gentle limb than the steep limb.

Restoration of reservoir diagenesis and hydrocarbon accumulation process by calcite in-situ U-Pb dating and fluid inclusion analysis: A case study on Cretaceous Qingshuihe Formation in Gaoquan Structure, southern Junggar Basin, NW China

The complexity of diagenesis and hydrocarbon accumulation in the deep reservoirs in southern Junggar Basin restricts hydrocarbon exploration in the lower reservoir assemblage. The lithofacies and diagenesis of reservoirs in the Cretaceous Qingshuihe Formation in the Gaoquan structure of the Sikeshu Sag, southern Junggar Basin were analyzed. On this basis, the thermal history was calibrated using calcite in-situ U-Pb dating and fluid inclusion analysis to depict the hydrocarbon accumulation process in the Gaoquan structure. The results show that the Qingshuihe reservoir experienced two phases of calcite cementation and three phases of hydrocarbon charging. The calcite cements are dated to be (122.1±6.4) Ma, (14.4±1.0) Ma - (14.2±0.3) Ma. The hydrocarbon charging events occurred at around 14.2-30.0 Ma (low-mature oil), 14.2 Ma (mature oil), and 2 Ma (high-mature gas). The latter two phases of hydrocarbon charging contributed dominantly to the formation of reservoir. Due to the S-N compressive thrust activity during the late Himalayan period since 2 Ma, the traps in the Gaoquan structure were reshaped, especially the effective traps which developed in the main reservoir-forming period were decreased significantly in scale, resulting in weak hydrocarbon shows in the middle-lower part of the structure. This indicates that the effective traps in key reservoir-forming period controlled hydrocarbon enrichment and distribution in the lower reservoir assemblage. Calcite U-Pb dating combined with fluid inclusion analysis can help effectively describe the complex diagenesis and hydrocarbon accumulation process in the central-west part of the basin.

Simulation for the Controlling Factors of Structural Deformation in the Southern Margin of the Junggar Basin

According to the differences of structural deformation characteristics, the southern margin of the Junggar basin can be divided into two segments from east to west. Arcnate thrust-and-fold belts that protrude to the north are developed in the eastern segment. There are three rows of en echelon thrust-and-fold belts in the western segment. Thrust and fold structures of basement-involved styles are developed in the first row, and decollement fold structures are formed from the second row to the third row. In order to study the factors controlling the deformation of structures, sand-box experiments have been devised to simulate the evolution of plane and profile deformation. The planar simulation results indicate that the orthogonal compression coming from Bogeda Mountain and the oblique compression with an angle of 75° between the stress and the boundary originating from North Tianshan were responsible for the deformation differences between the eastern part and the western part. The Miquan-Uriimqi fault in the basement is the pre-existing condition for generating fragments from east to west. The profile simulation results show that the main factors controlling the deformation in the eastern part are related to the decollement of Jurassic coal beds alone, while those controlling the deformation in the western segment are related to both the Jurassic coal beds and the Eogene clay beds. The total amount of shortening from the Yaomoshan anticline to the Gumudi anticline in the eastern part is -19.57 km as estimated from the simulation results, and the shortening rate is about 36.46%; that from the Qingshuihe anticline to the Anjihai anticline in the western part is -22.01 km as estimated by the simulation results, with a shortening rate of about 32.48%. These estimated values obtained from the model results are very close to the values calculated by means of the balanced cross section.

Formation mechanism of condensates, waxy and heavy oils in the southern margin of Junggar Basin, NW China

It is a challenge to determine the source and genetic relationship of condensate, waxy and heavy oils in one given complicated petroliferous area, where developed multiple sets of source rocks with different maturity and various chemical features.The central part of southern margin of Junggar Basin, NW China is such an example where there are condensates, light oils, normal density oils, heavy crude oils and natural gases. The formation mechanism of condensates has been seriously debated for long time;however, no study has integrated it with genetic types of waxy and heavy oils. Taking the central part of southern margin of Junggar Basin as a case, this study employs geological and geochemical methods to determine the formation mechanism of condensates,waxy and heavy oils in a complicated petroliferous area, and reveals the causes and geochemical processes of the co-occurrence of different types of crude oils in this region. Based on detailed geochemical analyses of more than 40 normal crude oils, light oils,condensates and heavy oils, it is found that the condensates are dominated by low carbon number n-alkanes and enriched in light naphthenics and aromatic hydrocarbons. Heptane values of these condensates range from 19% to 21%, isoheptane values from1.9 to 2.1, and toluene/n-heptane ratios from 1.5 to 2.0. The distribution of n-alkanes in the condensates presents a mirror image with high density waxy crude oils and heavy oils. Combined with the oil and gas-source correlations of the crude oils, condensates and natural gas, it is found that the condensates are product of evaporative fractionation and/or phase-controlled fractionation of reservoir crude oils which were derived from mature Cretaceous lacustrine source rocks in the relatively early stage. The waxy oils are the intermediate products of evaporative fractionation and/or phase-controlled fractionation of reservoir crude oils, while the heavy oils are in-situ residuals. Therefore, evaporative fractionation and/or phase-controlled fractionation would account for the formation of the condensate, light oil, waxy oil and heavy oil in the central part of southern margin of Junggar Basin, resulting in a great change of the content in terms of light alkanes, naphthenics and aromatics in condensates, followed by great uncertainties of toluene/n-heptane ratios due to migration and re-accumulation. The results suggest that the origin of the condensate cannot be simply concluded by its ratios of toluene/n-heptane and n-heptane/methylcyclohexane on the Thompson's cross-plot, it should be comprehensively determined by the aspects of geological background, thermal history of source rocks and petroleum generation,physical and chemical features of various crude oils and natural gas, vertical and lateral distribution of various crude oils in the study area.

Lithofacies paleogeography restoration and its significance of Jurassic to Lower Cretaceous in southern margin of Junggar Basin,NW China

In view of the difficulties in the study of lithofacies paleogeography and the low reliability of the distribution range of sedimentary sand bodies in the prototype basin caused by less deep drilling, complex seismic imaging and low degree of exploration in the southern margin of Junggar Basin, NW China. A new method based on the source to sink idea was used to restore lithofacies paleogeography and predict glutenite distribution. In the restoration, apatite fission track age was used to define range and uplift time of macro-provenance;the range of provenance area and the migration process of lake shoreline were restored based on the quantitative relationship between gravel diameter and transportation distance, tectonic shortening and other geological parameters;drilling cores and field outcrop sedimentary structures were analyzed, and a series of maps of lithofacies paleogeographic evolution and distribution range of glutenite bodies were compiled. It is concluded that from Early Jurassic to Early Cretaceous, in the southern margin of Junggar Basin, the provenance area gradually expanded from south to north, the lake basin expanded, shrunk and expanded, and the paleoclimate changed from humid to drought to humid. The western section always had proximal fan delta deposits from the southern ancient Tianshan provenance developed, and in the middle and eastern sections, the provenance areas evolved from far source to near source, mainly river-delta, braided delta, fan delta and other sediments developed. The boundary between provenance areas of the western and middle sections is speculated to be Hongche fault zone. In an angle open to the northwest with the current basin edge line, the restored ancient lake shoreline controlled the heterogeneity of reservoirs in the delta plain belt and delta front belt on its both sides. The ancient lake shoreline, current stratigraphic denudation line and current basin margin line limit the types and scope of favorable reservoirs.This understanding provides an important geological basis for oil and gas exploration in the deep lower source-reservoir assemblage at the southern margin of Junggar Basin.

Major breakthrough of Well Gaotan 1 and exploration prospects of lower assemblage in southern margin of Junggar Basin, NW China

Well Gaotan 1 was tested a high yield oil and gas flow of more than 1 000 m^3 a day in the Cretaceous Qingshuihe Formation,marking a major breakthrough in the lower assemblage of the southern margin of Junggar Basin. The lower assemblage in the southern margin of the Junggar Basin has favorable geological conditions for forming large Petroleum fields, including:(1) Multiple sets of source rocks, of which the Jurassic and Permian are the main source rocks, with a large source kitchen.(2) Multiple sets of effective reservoirs,namely Cretaceous Qingshuihe Formation, Jurassic Toutunhe Formation and the Khalza Formation etc.(3) Regional thick mudstone caprock of Cretaceous Tugulu Group, generally with abnormally high pressure and good sealing ability.(4) Giant structural traps and litho-stratigraphic traps are developed. The northern slope also has the conditions for large-scale litho-stratigraphic traps.(5) Static elements such as source rocks, reservoirs and caprocks are well matched, and the dynamic evolution is suitable for large oil and gas accumulation. The lower assemblage of the southern margin of the Junggar Basin has three favorable exploration directions, the Sikeshu Sag in the west part, the large structures in the middle and eastern part, and the northern slope.

Coalbed Methane Enrichment Regularity and Major Control Factors in the Xishanyao Formation in the Western Part of the Southern Junggar Basin

There are abundant coal and coalbed methane(CBM)resources in the Xishanyao Formation in the western region of the southern Junggar Basin,and the prospects for CBM exploration and development are promising.To promote the exploration and development of the CBM resources of the Xishanyao Formation in this area,we studied previous coalfield survey data and CBM geological exploration data.Then,we analyzed the relationships between the gas content and methane concentration vs.coal seam thickness,burial depth,coal reservoir physical characteristics,hydrogeological conditions,and roof and floor lithology.In addition,we briefly discuss the main factors influencing CBM accumulation.First,we found that the coal strata of the Xishanyao Formation in the study area are relatively simple in structure,and the coal seam has a large thickness and burial depth,as well as moderately good roof and floor conditions.The hydrogeological conditions and coal reservoir physical characteristics are also conducive to the enrichment and a high yield of CBM.We believe that the preservation of CBM resources in the study area is mainly controlled by the structure,burial depth,and hydrogeological conditions.Furthermore,on the basis of the above results,the coal seam of the Xishanyao Formation in the synclinal shaft and buried at depths of 700-1000 m should be the first considered for development.

Petroleum exploration of shallow marine deposit Carboniferous volcanic tuff reservoir in the western margin of Junggar Basin

In 2011,petroleum exploration of shallow marine deposits Carboniferous and volcanic tuff reservoir realized breakthroughs at Chepaizi slope in the western margin of Junggar Basin. Pai 61 well,with 855.7 ~ 949.6 m section,in the conventional test oil obtained 6 t/d industrial oil flow. The surface viscosity is 390 mPa· s(50℃). The marine deposit of Carboniferous are deep oil source rocks and high-quality reservoir. Magma volcanic activity provides the basis for volcanic reservoir development and distribution. The weathering crust and secondary cracks developed volcanic tuff by strong rock weathering and dissolution of organic acids which has become top quality reservoir. Deep Permian oil- gas migrated and accumulated to high parts along Hong- Che fault belt and stratigraphic unconformity stripping. Permian and Triassic volcanic rocks or dense mudstone sedimentary cover as a regional seal for the late Carboniferous oil-gas to save critically. The seismic pre-stack time migration processing technologies for the problem of poor inner structures of Carboniferous were developed. Response of volcanic rock seismic and logging are obvious. The application imaging logging and nuclear magnetic technology achieved the qualitative identification and quantification of fracture description.

New insights into multiple provenances evolution of the Jurassic from heavy minerals characteristics in southern Junggar Basin, NW China

The method of random forest was used to classify the heavy mineral assemblages of 2 418 Jurassic samples in the southern Junggar Basin, and determine the distribution of the heavy mineral assemblages from the same provenance systems. Based on the analysis of heavy minerals assemblages, ZTR index, sedimentary characteristics, U-Pb zircon ages, whole-rock geochemical and paleocurrent direction analysis, the study reveals that five important provenances were providing sediments to the southern Junggar Basin in the Jurassic period: The North Tianshan(NTS), Central Tianshan(CTS), Bogda Mountains, Zhayier Mountains and Kalamaili Mountains. During the Early Jurassic, NTS-CTS, Kalamaili Mountains and Zhayier Mountains are primary provenances, Bogda Mountains started to uplift and supply clastic materials in the Middle Jurassic. There are three sedimentary area in the Jurassic of southern Junggar Basin: the western part, the central part and the eastern part. In the western part, the clastic materials of the Early Jurassic was mainly from NTS blocks and Zhayier Mountains, and the sediments were dominantly derived from the Zhayier Mountains during the Middle–Late Jurassic. In the central part, the main provenance of the Early Jurassic switched from NTS to CTS. In the Xishanyao Formation, the main source went back to NTS again. The NTS was the primary provenance during the sedimentary periods of Toutunhe Formation and Qigu Formation. In the eastern part, the contribution of CTS and Kalamaili Mountains were considered as major provenances in the Early Jurassic-Xishanyao Formation, small proportion of sediments were from NTS. The Bogda mountains uplifted and started to provide sediments to the Junggar Basin in the sedimentary period of Xishanyao Formation, and became the major source during the Toutunhe Formation period, with small amount of sediments from CTS. The provenance from CTS was hindered during the sedimentary period of Qigu Formation owing to the uplifting of the Bogda mountains, and the sediments were mainly from the Bogda mountains and NTS.

THE SEQUENCE OF PALEOENVIRONMENTAL CHANGES SINCE ABOUT 4KA B.P., RECORDED BY NIYA SECTION IN SOUTHERN MARGIN OF TARIM BASIN

Through synthetic researches of multi-index geological records of Niya section, which are of high resolution in southern margin of Tarim Basin, this paper has reconstructed the sequences of paleoclimate in this region during historical times (since about 4000a B.P.). During the last 4000 years, the area has experienced alternations of relative cold-moisture and relative warm-dry periods. Three evident cold-moisture periods and three warm-dry periods are identifing. The study shows that the human activities have an intimate relation with the evolution of paleoclimate in the southern Xinjiang. Paleoclimate has played very important role in influencing human being′s agricultural activities.

Formation conditions and exploration direction of large and medium gas reservoirs in the Junggar Basin, NW China

The Junggar Basin is rich in oil but lacks natural gas, which is inconsistent with its geological background of natural gas. Based on the analysis of main source kitchens, and the evaluation of geological setting and controlling factors of gas accumulation, it is proposed that three significant fields for gas exploration should be emphasized. The first field is the Carboniferous volcanic rocks. The Carboniferous residual sags and large-scale reservoirs were developed in three active continental margins, i.e., the southeastern, northeastern and northwestern active continental margins. Gas accumulation is controlled by the favorable reservoir-caprock combinations composed of volcanic rocks and their superimposed lacustrine mudstones in the Upper Wuerhe Formation. Dinan, Eastern and Zhongguai uplifts are three favorable directions for natural gas exploration. The second field is the Lower combinations in the southern margin of Junggar Basin. Rows of structural traps were developed in this area with ideal preservation conditions and space-time configuration for trap-source combinations. Sets of clastic reservoirs and overpressured mudstones formed perfect reservoir-caprock combinations which are the main exploration direction for Jurassic coal-type gas reservoirs in this area. The seven large structural traps in the middle-east section are recently the most significant targets. The last field is the Central Depression. Large hydrocarbon generating centers, i.e., Mahu, Fukang and Shawan sags, were developed in this area, their source rocks were deeply buried and at highly-mature stage. Thus the Central Depression is a favorable exploration direction for Permian high-over mature gas fields(reservoirs). Great attentions should be paid to two types of targets, the deeply–buried structures and structural-lithologic traps. Based on three main gas systems, gas exploration is suggested be strengthened within three fields and on three levels.

Organic petrology and hydrocarbon generation of potential source rocks in Permian formation of Junggar Basin,Northwest in China

From the outcrops in the Yaomoshan and Hongyanchi sections,oil shales,deep dark mudstones or black mudstones with better organic richness were found.Through the analysis of the samples in the organic petrology method,the microscope features of the sedimentary organic matter were studied.The results indicate that three types of kerogens present in the measured samples.Kerogen type Ⅰ consists of the laminate algainite,abundant sporinite and only little content of cutinite,which can mainly generate oil.The generation hydrocarbon components of the type Ⅱ kerogen are dominated by the sporinite,cutinite and little the exinite debris.The type Ⅲ kerogen is comprised of the sporinite and debris of the exinite with some components of gas generation.Through the analysis of the experiments,the organic kerogen of the Lucaogou formation is mostly comprised of the type Ⅰ,partially type Ⅱ,and particularly type Ⅲ.In Hongyanchi formation,the organic type is mixed by the types Ⅱ and Ⅲ.The plot of the (S1 +S2) or TOC value and the content of exinite show two trends.From the evolution of burial and the Permian source rocks in Changji Depression,the Permian formation source rock has ended the generation of hydrocarbon.A significant difference in constituents of the organic macerals among three kerogens in these samples leads to the distinction of the potential hydrocarbon generation.The Lucaogou formation for kerogen type Ⅰ has better potential hydrocarbon generation.It can reach the oil peak with Ro ratio of 0.9%.For the kerogen Ⅱ,the oil peak of the source rocks comes late with the Ro ratio of 1.0% with less quantity of the generation hydrocarbon than the kerogen Ⅰ.For type Ⅲ,it can mainly generate gas and reach the gas peak with the Ro ratio of 1.3%.In a word,the Lucaogou formation and Hongyanchi formation source rocks with high organic richness in Permian source rocks have well exploration prospects.

Double Difference Location of the Mainshock and Aftershocks of the Hutubi MS6.2 Earthquake That Occurred on December 8,2016

The mainshock and aftershocks of the Hutubi M_S6.2 earthquake on December 8,2016 were relocated by applying the double difference method, and we relocated 477 earthquakes in the Hutubi region. The earthquake relocation results show that the aftershocks are distributed in the east-west direction towards the north side of the southern margin of the Junggar Basin fault,and are mainly distributed in the western region of the mainshock. The distance between the mainshock after relocation and the southern margin of the Junggar Basin fault is obviously shortened. Combined with the focal mechanism and the spatial distribution of the mainshock and aftershocks,it is inferred that the southern margin of the Junggar Basin fault is the main seismogenic structure of the Hutubi earthquake.

准噶尔盆地南缘侏罗系八道湾组富藻类体煤系源岩的发现及其沉积背景

通过沉积有机质中生物标志化合物组合分析,并结合荧光显微组分镜检结果,本研究首次在准噶尔盆地南缘建功剖面下侏罗统八道湾组上段识别出一套富藻类有机质输入的煤系沉积。该套煤系源岩主体处于低成熟–成熟早期演化阶段,镜质组反射率为0.5%~0.6%;有机碳(TOC)含量主要介于2.0%~4.0%之间,局部发育碳质泥岩和煤线;生烃潜量(S_(1)+S_(2))值普遍为3.0~5.0 mg/g,碳质泥岩段最高达18.4 mg/g;氢指数(HI)主要为100~150 mg/g,碳质泥岩段达280 mg/g,属于Ⅱ2型有机质。沉积有机质中生物标志化合物组合表现为姥鲛烷优势,中、短链正构烷烃含量较高,C_(27)~C_(29)规则甾烷呈“V”型分布,Ts、C_(29)Ts、C_(30)H藿烷含量较高,C同位素组成较轻。全岩荧光显微镜镜检结果表明,源岩中壳质组主要为孢子体和藻类(屑)体。结合沉积背景综合判断,该套富藻类体煤系沉积形成于水体较深的湖泊沼泽化早期阶段,浮游藻类等低等水生生物对沉积有机质存在显著贡献,有望成为区域潜在的优质烃源岩。

鄂尔多斯盆地南缘麟游-淳化地区平凉组礁滩体沉积特征及分布预测

鄂尔多斯盆地南缘平凉期发育规模生物礁滩型储层,目前对该区的研究主要集中在礁滩体的类型、成因、区域演化等方面,而对礁滩体的地球物理预测尚未开展系统研究。为了提高礁滩体的预测精度,建立礁滩体储层地震预测方法,通过野外露头实地踏勘,结合岩心及分析测试等资料,对镶边台地高能环境下的生物礁滩发育特征进行研究。通过已知井的井震响应特征,建立礁滩体正演模型,同时开展流体活动性、地震纹理属性分析,形成研究区礁滩体储层的地震预测方法。结果表明:鄂尔多斯盆地南缘平凉组主要发育碳酸盐岩台地边缘-浅水陆棚沉积体系;礁滩体主要分布于台地边缘亚相,多期叠置;高亮体和纹理属性对礁滩体的预测效果最好,2种方法的联合应用大大提高了礁滩体预测精度。研究成果为台缘带礁滩体平面分布规律预测和鄂尔多斯盆地南缘平凉组礁滩体的勘探开发奠定基础。

基于核磁共振动态截止值理论的致密砂砾岩储层渗透率评价方法

准噶尔盆地南缘深层清水河组致密砂砾岩储层为该区的重要勘探领域,渗透率是评价致密砂砾岩储层的关键参数。为提高此类储层渗透率计算精度,基于核磁共振实验,分析致密砂砾岩岩心饱和水及离心核磁共振横向弛豫时间(T_(2))谱,明确致密砂砾岩孔隙中流体的赋存形态及渗流规律,提出常规核磁共振渗透率计算方法的不足,并且提出核磁共振动态截止值的概念。基于核磁共振动态截止值,将储层孔隙空间划分为3类:自由流体孔、毛细管半束缚孔、完全束缚孔;分析了渗透率与不同孔隙类型之间的相关关系:致密砂砾岩储层渗透率与自由流体孔孔隙度、核磁总孔隙度、毛细管半束缚孔的T_(2)几何平均值呈正相关关系,与完全束缚孔流体饱和度呈负相关关系。构建基于不同孔隙类型渗透率模型,计算渗透率与岩心实验渗透率之间的相对误差小于9.0%。该方法提高了致密砂砾岩储层渗透率的计算精度,且在准噶尔盆地南缘深层清水河组致密砂砾岩储层评价中具有广泛的应用前景。

新疆准噶尔盆地西北缘克拉玛依-乌尔禾断裂带推覆体上盘构造样式及影响因素

准噶尔盆地西北缘克拉玛依-乌尔禾断裂带(克-乌断裂带)及其周缘发现了大量的油气藏,尤其是推覆体上盘伴随着勘探程度及地质认识不断深化,已呈现出“百里油区”的态势。然而,受多期构造活动及断裂带内部复杂的岩性组合影响,石炭系内幕地层构造样式展现出多种类型及复杂的空间展布样式,因此需要对构造样式及成因进一步探讨。综合地震和钻井资料,结合区域构造格局,梳理了准噶尔盆地西北缘克-乌断裂带上盘构造变形特征与影响因素;根据构造样式与推覆体内的岩性组合类型,将克-乌断裂带推覆体上盘划分出南段、中段和北段3个变形单元;明确了上盘石炭系5期主要构造阶段,分段恢复了推覆体上盘构造演化期次及样式。综合上述研究,认为克-乌断裂带上、下盘原始岩性组合关系是造成上盘石炭系内幕地层原始形变差异的主要因素,上盘石炭系内幕地层岩性组合差异是造成原生构造保存的主要因素。上述因素共同造成了圈闭条件沿克-乌断裂带自南向北变化。该研究为克-乌断裂带上盘油气勘探提供指导,同时也为类似条件地区的油气勘探提供借鉴。