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.

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.

Properties of Continental Margin and its Hydrocarbon Exploration Significance in Cambrian in the Southern Ordos Kratogen of North China

It is important to determine the properties of the tectonics in Cambrian period for the sake of prospecting deep hydrocarbon in the near future in the southern Ordos Kratogen of North China. Authors chose the marginal areas of the southern Ordos basin as the object of research, avoided the effects of both the Qinling Orogenic Belts （QOB） and Weihe River Graben （WRG） whose geological structures are too complicated. By surveying typical Cambrian outcrops and profdes in the basin edges and based on the cores of 57 wells which penetrated the Cambrian in the basin, combined with the seismic profiles, the field gammaray measuement results and the carbon isotope analysis, Authors conclude that the southern margin of the Ordos Kratogen during Cambrian was a passive continental margin which resulted from sea-floor spreading of the Ancient Qinling Ocean. Epicontinental sea carbonate sediments formed in the south Ordos continental margin during Cambrian, and were predominant as tidal flat and o61itic shoal. Both transgression-regression process and the change in palaeostructure have the obvious cyclicity. Using the junction between the late Nangao age of Qiandong epoch and the early Duyun age of Qiandong epoch as a boundary, each had a full transgression cycle at the upper and lower stages. The early cycle is characterized by high energy clastic littoral facies while the late cycle is characterized by carbonate ramp on which clear water and muddy water developed alternately changing to carbonate platform last. During the early stages, An aulacogen was formed in the middle section of the southern margin. The southern Ordos margin was uplifted and denudated by the Huaiyuan Movement which occurred from the late Furongian age to the middle Flolan age and the history of the passive continental margin ended and entering into a new tectonic cycle. The unconformity surface caused by the Huaiyuan Movement, along with its neighborhood areas where dissolved pores and cavities are developed, may be another important district for good hydrocarbon reservoirs （excluding the unconformity surface on the top of the Ordovician in the Ordos 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.

Relationship between joint development in rock and coal seams in the southeastern margin of the Ordos basin

To predict joint development characteristics of coal seams, joint characteristics of rock seams from 88field stations were observed and comparisons were made between joint characteristics of coal and rock seams at 10 coal outcrops. Additionally, detailed joint measurements of underground coal seams were taken at two coal mines. This study investigated the effects of seam thickness, lithology, and structure on joint development and established the relationship between joint development of coal and rock seams, which allowed predictions of predominant joint densities for the No.5 coal seam in the southeastern margin of the Ordos basin. The results show that outcrop and underground coal seams exhibit the same joint systems as rock seams. The joints are mainly upright. Predominant joints strike 55° on average, followed by joints striking 320°. The joint density of the coal seam is 18.7–22.5 times that of the sandstone seam at the same thickness. The predominant joint density of the No.5 coal seam, controlled by the structure, is 4–20 joints per meter. Joint densities exhibit high values at intersecting areas of faults and folds and decrease values in structurally stable areas. The permeability increases exponentially with increasing density of the predominant joints.

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.

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.

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.

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.

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。

鄂尔多斯盆地西缘中-上奥陶统烃源岩的形成环境、成烃生物及岩矿特征

鄂尔多斯盆地西南缘奥陶系发育与盆地本部奥陶系沉积特征截然不同的沉积层,其中西缘的中-上奥陶统烃源岩发育较好的海相烃源岩层。近期,通过对该套烃源岩形成的构造—沉积环境、成烃生物特征及烃源岩层岩矿特征等方面的分析,表明有利烃源岩的发育受多种因素的控制,其分布具有一定的规律性:1)盆地中-上奥陶统主力烃源岩主要形成于沉积水体不断加深的构造沉积背景,其中沉积水体能量较弱,陆源碎屑注入相对较慢的半深水斜坡环境最有利于富有机质烃源岩发育;2)西南缘奥陶纪虽然生物类型多样,种群繁盛,但能形成重要烃源岩层的母源生物(生烃母质)却多以浮游生物、疑源类(微体藻类)及蓝细菌为主,相对还原的介质环境和适宜的沉积埋藏速率对有机质的有效保存也起重要的控制作用;3)X-衍射物相分析及扫描电镜等微观研究显示,主力烃源层段所谓“泥页岩层”的造岩矿物类型仍以石英、长石类为主,次为伊利石类黏土矿物与碳酸盐矿物,少量黄铁矿等;黏土矿物及黄铁矿含量与有机质丰度关系密切。

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。

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。

东胜气田致密高含水气藏合采气井层间干扰影响因素

为了明确鄂尔多斯盆地北缘致密高含水气藏合采气井层间干扰及其影响因素,指导同类型气藏合采气井高效开发,以该盆地北缘东胜气田致密高含水气藏为研究对象,分析了储集层地质条件、储集层改造对合采井产层段贡献的影响,指出了该类合采气井层间干扰的主控因素。研究结果表明:(1)合采井各产层段贡献率主要受各产层段的孔隙度、渗透率及含气饱和度控制,其产层段孔隙度占主导地位;(2)储层压裂改造对于提高气井产量具有较大的作用,但对合采井各产层段的贡献率却很小;(3)对于致密高含水气藏而言,含气饱和度是合采井产层段贡献率及层间干扰的一个重要影响因子;(4)合采井各产层段之间的孔隙度级差、渗透率级差及含气饱和度级差直接影响着合采井层间干扰程度。结论认为:(1)合采井产层段的孔隙度越大、渗透性越好、含气饱和度越高,则产层段的产量贡献率越大;(2)合采井孔隙度、渗透率及含气饱和度3个参数的级差越大,层间干扰程度越大,当孔隙度级差大于1.248或渗透率级差大于2.69或含气饱和度级差大于1.22时,合采井层间干扰已经非常严重,亟需开展治理。

鄂尔多斯盆地东缘深部煤层气开发先导试验效果与启示

鄂尔多斯盆地东缘大宁-吉县区块深部煤层气勘探开发取得突破对煤层气产业带来重大影响,引起业内广泛关注和跟进。前期一些学者对深部煤层气勘探开发理论技术难点与对策开展了研究,但缺乏对典型气田开发先导试验系统总结。通过深入剖析深部煤层气地质特征与效益开发难点,总结大宁-吉县区块开发先导试验项目取得的进展和成效,明确开发规律并提出效益开发对策。结果表明:(1)深部煤层具有广覆式发育、含气性好、游离气含量高、保存条件好、煤体结构好、脆性指数高、顶底板封盖性强等地质特征,但微构造发育、渗透性极差、矿化度高等因素制约了深部煤层气效益开发;(2)不同地质条件下气井生产特征差异较大,通过先导试验落实气井产能和适应性开发技术对策,采用滚动开发模式可有效降低煤层强非均质性带来的开发风险;(3)开展地质-工程一体化井网优化设计,构建井网与缝网高度弥合的人造气藏,可实现资源动用和采收率最大化;(4)“长水平段+多段多簇+大砂量”的大规模、大排量极限体积压裂技术可增大有效改造体积和井控储量,大幅提高单井产量;(5)深部煤层气井具有“见气时间短、上产速度快、初期产量高、递减快”的生产特征,可实现短期快速规模上产,但气田长期稳产需持续新井投入;(6)前期开发成本偏高,实现效益开发需不断提高工程作业效率、降低开发成本。综合认为,深部煤层气资源品质好,可动用性强,具备快速推广复制条件,大宁-吉县区块深部煤层气开发实践可为国内其他区块深部煤层气规模动用提供技术借鉴,对加快深部煤层气规模勘探开发具有重要意义。

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.

大宁–吉县区块深部煤层气多轮次转向压裂技术及应用

鄂尔多斯盆地东缘大宁-吉县区块深部煤层气资源丰度高,煤储层天然裂缝与煤自身割理裂隙发育、煤体结构好、机械强度高、顶底板封盖能力强,为大规模体积压裂缝网的形成提供了有利条件。超大规模压裂改造工艺使深部煤层气单井产量获得重大突破,但示踪剂监测结果显示,水平井各压裂段产气效果贡献不均一、资源动用存在盲区、综合效益未达预期。指出深部煤储层形成超大规模有效缝网面临两类主要挑战:(1)深部煤层裂缝扩展规律认识不清;(2)现有压裂技术存在过度改造及改造不充分区域。基于此问题,提出适合深部煤储层改造的多轮次转向缝网弥合压裂技术。首先,分析深部煤层超大规模缝网形成的可行性;其次结合现场压裂数据与微地震监测结果,分析地层曲率、倾角等对压裂裂缝扩展的影响;最后建立应力场计算方法,以此为依据,进行多轮次转向工艺优化及现场试验。在大宁-吉县区块现场进行试验验证,井周微应力场非均匀区域水力裂缝实现了较为均匀的扩展,增大了裂缝整体改造体积,单井产气效果较周边井有明显提升,其中DJ55井5轮次压裂,储层改造体积达到243.6×10^(4)m^(3),生产340 d累产气量970.5×10^(4)m^(3),平均日产气量2.85×10^(4)m^(3),日产量和压力均保持稳定,改造效果较好,预计采收储量(EUR)大于3000×10^(4)m^(3),产气潜力较大;JS8-6P05井第1-7段采用2~3轮次压裂,压后日产气量8.59×10^(4)m^(3),相比各段均采用单轮次压裂的JS8-6P04井加砂规模降低41.9%、压裂费用降低21%,但2口井水平段千米日产气量相当。试验效果表明,多轮次压裂工艺在一定程度上解决了水平井两侧应力差异而导致的裂缝单侧扩展问题,促进井筒两侧压裂裂缝趋于均匀扩展,极大程度上保障了深部煤储层资源动用程度和压后产量,是深部煤层气压裂工艺降本增效的主要技术途径。

准噶尔盆地南缘下侏罗统三工河组地球化学、沉积环境及源区特征分析

准噶尔盆地南缘是重要的油气勘探地区,也是研究盆地构造属性、沉积环境演化的重要区域。南缘下侏罗统三工河组由上部主体浅青灰色-灰绿色长石岩屑砂岩、粉砂质泥岩、泥质粉砂岩和下部土黄色长石岩屑砂岩、含砾粗砂岩、砾岩组成,对上部样品进行岩石学、岩相学和地球化学研究显示:样品化学蚀变指数(CIA)为77.57,反映物源区经历中等风化作用;碎屑物质磨圆和分选较差,表明沉积物搬运距离短,成分成熟度低;Cu/Zn、V/Cr、V/(V+Ni)、Ni/Co及U/Th值指示古沉积环境为富氧的氧化环境-贫氧过渡环境;Sr/Cu、Al_(2)O_(3)/MgO值指示温暖湿润的气候特征;Li,Sr,Sr/Ba,Th/U值指示淡水环境;综合岩相学特征认为,其上部主体为浅湖亚相沉积,下部为辫状河三角洲平原亚相沉积。样品中含流纹岩岩屑,La/Th-Hf、La/Sc-Co/Th和Ni-TiO_(2)判别图指示三工河组源岩主要来自于上地壳长英质火山岩;出现少量安山岩岩屑和Th/Co、Th/Cr比值显示源岩有少量中-基性岩。通过样品与不同构造背景杂砂岩成分对比、Th-Co-Zr/10、La-Th-Sc、Th-Sc-Zr/10判别图显示物源区应为大陆岛弧构造背景。

准噶尔盆地南缘西段齐古组深层储层特征及物性控制因素

准噶尔盆地南缘西段齐古组深层碎屑岩储层油气勘探潜力巨大,但目前针对其储层特征及物性控制因素尚缺乏系统研究,制约了后期油气勘探进程。本文综合利用铸体薄片、扫描电镜、物性、压汞及包裹体等资料,并结合区域埋藏史及古地温等相关成果,对齐古组储层岩石学特征、物性特征、成岩作用特征及物性控制因素进行系统研究。结果表明,齐古组储层具有低成分成熟度、高塑性岩屑含量及中等结构成熟度的岩石学特征。尽管储层主体埋深大于3500 m,但储集空间仍以粒间孔为主,平均孔隙度为10.29%,平均渗透率为34.12×10^(-3)μm^(2),总体上属低孔低渗储层,但仍发育部分中-高孔渗储层。储层成岩作用主要有压实作用、胶结作用及溶蚀作用,成岩强度相对较弱,主体处于早成岩B期—中成岩A期,并表现为压实强度中等、胶结物含量较低且晚期发育酸性溶蚀的特征。富石英与长石、贫岩屑以及分选好等特征有利于储层物性的保存,而储层物性损失以压实减孔最为显著,但储层内部绿泥石包壳及中成岩期的酸性溶蚀作用可有效改善储层物性。此外,齐古组地层早期长期浅埋、后期短期快速深埋、地层超压及较低的古地温梯度等因素延缓了储层成岩进程,进而降低成岩作用强度,导致齐古组优质储层得以有效保存。