Carbonate rocks are widely developed in the terminal Ediacaran Qigebrak Formation of the northern Tarim Basin, China, having significant reservoir potential. However, under deep to ultra-deep burial conditions, their diagenetic evolution and reservoir development remain poorly constrained. This study integrates petrography, fluid inclusion microthermometry, and geochemistry to reconstruct the diagenetic history and its reservoir implications. The results indicate that the Qigebrak carbonates experienced marine, meteoric, and burial diagenetic environments. Marine diagenesis was characterized by matrix dolomitization and early cementation, the meteoric diagenetic environment by karstification associated with subaerial exposure, and the burial diagenetic environment by progressive compaction, multi-stage cementation, hydrothermal alteration, and thermochemical sulfate reduction (TSR). Karstification is strongly facies-controlled and occurs as vertically stacked, meter-scale dissolution cycles formed during early diagenesis by meteoric fluids, as indicated by fabric-selective dissolution and nearly in-situ karst breccias. Saddle dolomite is closely associated with TSR-related calcite and associated by-products. The overlapping homogenization temperatures of fluid inclusions in saddle dolomite (162–184 °C) and calcite (150–185 °C) suggest formation under a shared high-temperature regime conducive to TSR. This thermal regime was most plausibly sustained by hydrothermal fluid influx, whereas depleted δ13C-δ18O values and LREE enrichment in calcite indicate fluid–rock interaction involving TSR-modified fluids with an external hydrothermal contribution. Early facies-controlled karstification played a key role in reservoir development, whereas compaction, cementation, hydrothermal alteration, and TSR progressively degraded pre-existing porosity. These results establish a multistage diagenetic framework for the Qigebrak Formation, offering new insights into complex diagenesis and reservoir evolution in ancient carbonate.

Hydrothermal activity serves as a critical link that records deep geological processes and transfers material and energy to shallow strata. This study focused on the Middle Cambrian strata in the Keping area of the Tarim Basin. Systematic analyses, including thin-section petrography, cathodoluminescence, fluid inclusion thermometry, carbon-oxygen isotope and rare earth element geochemistry, combined with laser in-situ U-Pb dating, were conducted. These methods led to the identification of one stage of diagenetic fluids and three stages of hydrothermal fluids. The results show that the first stage calcite veins formed in the Early Devonian (414-412 Ma) and originated from marine-derived burial fluids; the second stage calcite veins formed from the Middle Devonian to Early Carboniferous (358-335 Ma) as products of mixed marine-derived fluids and deep thermal brines; the third stage saddle dolomite veins formed in the Middle Carboniferous (327-321 Ma) and belong to medium-to hightemperature mixed hydrothermal fluids; the fourth-stage calcite veins formed in the Middle Permian (266-264 Ma) and originated from high-temperature, high-salinity brines derived from magmatic differentiation. The research reveals that the subduction-collisional orogeny of the South Tianshan Ocean and the large-scale magmatism of the Permian Tarim Large Igneous Province served as the primary factors controlling the timing and spatial distribution of deep hydrothermal activity in the study area. The evolution of shallow hydrothermal activity was directly governed by regional tectonics and deep-seated processes. This study provides important chronological and geochemical insights for understanding the coupling mechanism between deep geological processes and shallow fluid responses in the Tarim Basin.

The Ordovician platform margin belts in the Tarim Basin are key targets for deep carbonate hydrocarbon exploration. Their sequence architecture and spatial differences exert critical controls on the distribution of high-quality reservoirs. Taking the Early-Middle Ordovician platform margin belts in the Lunnan-Fuman-Gucheng area as the research object, this study systematically characterizes the sequence framework, sedimentary architecture, and segmented differential characteristics based on seismic, drilling, logging, and thin section data, using sequence stratigraphy, seismic facies analysis, and sedimentary mapping. The results show that five sequence boundaries are identified, dividing the Lower-Middle Ordovician into two second-order sequences and four third-order sequences. Seven types of mound-shoal seismic facies are developed, and three structural models are recognized from north to south: aggradation-weak retrogradation in the Lunnan section, weak aggradation-strong retrogradation in the Fuman section, and strong aggradation-weak retrogradation in the Gucheng section. It is revealed that differential subsidence caused by back-arc extension of the Altyn orogenic belt and the paleogeomorphic barrier effect of the Tadong Low Uplift collectively controlled the segmented architecture and migration evolution of the platform margin belts. The findings clarify the differential structural patterns of platform margins and provide a geological basis for hydrocarbon exploration in Ordovician platform margin reef-shoal complexes in the Tarim Basin.

The lower Cambrian Yurtus Formation (Є1y) in the Tarim Basin, characterized by its high organic matter content, serves as a critical source rock for oil and gas exploration in the platform basin. This study presents a high-resolution geochemical analysis of a geological section located near the Aksu Cement Plant in the northwest margin of the Tarim Basin. The focus is on elucidating the sedimentary environment, mechanisms of organic matter enrichment, and the depositional history of the Є1y source rock. The Є1y exhibits distinctive geochemical signatures, including elevated concentrations of Mo, Ba, and U, with an average rare earth element (REE) content of 155.75 μg/g. The formation shows significant light REE enrichment (LREE/HREE = 1.74–5.57), a moderate Ce negative anomaly (δCe = 0.4–0.71), and a notable Eu positive anomaly (δEu = 0.94–2.14), indicative of a unique depositional environment influenced by hydrothermal processes. Geochemical evidence suggests that the Є1y siliceous shales were deposited in a highly reducing, anoxic, and sulfide-rich environment, promoting organic matter preservation and enhancing sedimentary productivity. The presence of hydrothermal trace elements, likely introduced by hydrothermal fluids from volcanic activity along fractures and faults, played a critical role in enriching the sedimentary system, preserving organic matter, and boosting paleoproductivity. The model of organic matter enrichment proposed in this study underscores the dynamic interplay between hydrothermal influences and high primary productivity. These findings provide important insights into the formation of high-quality source rocks and have significant implications for the exploration of deep and ultra-deep oil and gas reserves in the Tarim Basin.

In 2023, the China National Petroleum Corporation (CNPC) has successfully drilled a 10 000-m ultra-deep well - TK-1 in the Tarim Basin, NW China. This pioneering project has achieved dual breakthroughs in ten-thousand-meter ultra-deep earth science research and hydrocarbon exploration while driving technological advancements in ultra-deep well drilling engineering. The successful completion of TK-1 has yielded transformative geological discoveries. For the first time in exploration history, comprehensive data including cores, well logs, fluids, temperature and pressure were obtained from 10 000-meter depths. These findings conclusively demonstrate the existence of effective source rocks, carbonate reservoirs, and producible conventional hydrocarbons at such extreme depths - fundamentally challenging established petroleum geology paradigms. The results not only confirm the enormous hydrocarbon potential of ultra-deep formations in the Tarim Basin but also identify the most promising exploration targets. From an engineering perspective, the project has established four groundbreaking technological systems: safe drilling in complex pressure systems of ultra-deep wells, optimized and fast drilling in complex and difficult-to-drill formations of ultra-deep wells, wellbore quality control under harsh conditions in ultra-deep wells, and data acquisition in ultra-deep, ultra-high-temperature complex formations. Additionally, ten key tools for ultra-deep well drilling and completion engineering were developed, enabling the successful completion of Asia's first and the world's second-deepest vertical well. This achievement has significantly advanced the understanding of geological conditions at depths exceeding 10 000 m and positioned China as one of the few countries with core technologies for ultra-deep well drilling.

The Shajingzi fault zone in the northwest margin of Tarim Basin lies between the Wensu Uplift of Tabei Rise and the Awati Sag of the northern depression. It is a first-order fault zone in Tarim Basin, which consists of Shajingzi fault, Yingxiong fault, Wensu fault and Shanan fault. The Shajingzi fault is the main fracture, and the other three are its branches. The Wensu branch fault is a new discovery of this study. And we interpreted the Shanan fault as the front back-thrust fault of the Yingxiong fault, which belongs to the Shajingzi fault zone. The Shajingzi fault zone was formed from the end of Ordovician to the beginning of Silurian, and was finally formed after the Late Devonian to Carboniferous, the end Permian to the beginning of Triassic, the end Jurassic to the beginning of Cretaceous, the end Cretaceous to the beginning of Paleogene and the Neogene to Quaternary multicycle thrust. The Shajingzi fault zone is a fault-controlled oil-gas rich zone, which controls the formation and distribution of Wensu oilfield, Tuotan1, Shanan1 and Xinsudi1 oil and gas reservoirs.

The deeply buried Ordovician Lianglitage Formation (>6500 m) in the Halahatang area, Tarim Basin, is characterized by a paleokarst topography and subsurface, collapsed paleokarstsystems. Based on core and thin-section observation and wireline-log interpretation, this study analyzed basic features of collapsed karst systems and mapped the pattern of collapsed and original karst systems through root mean square (RMS) amplitude and variance attribute fusion. Employment of production data revealed the general rule of these ultra-deep, buried, collapsed systems as reservoirs for oil and gas. This study showed that epigenic subsurface karst systems in the Lianglitage Formation experienced full collapse, filling, and subsequent strong compaction. Passages of subsurface karst systems have a dendritic pattern These ultra-deep and strongly compacted collapsed systems are not favorable for oil and gas production owing to poor reservoir qualities. Factors controlling original subsurface karst development in this area are extensive subaerial exposure during the Falling-Stage Systems Tract (FSST) and Lowstand Systems Tract (LST) periods following deposition of the Lianglitage Formation, faults and fractures formed before or during karstification, and surface drainage systems on top of the Lianglitage unconformity. This study provides a method to comprehensively characterize the features, distribution and mechanism of the ultra-deep buried epigenic karst reservoirs and clarified their low potential as reservoirs for oil/gas exploration and development. It also helps clarify that the true oil pay reservoirs in this reservoir resulted from hypogene dissolution rather than epigenic karst.

Integrated geochemical analysis was conducted on oil and gas samples from the LG7 block, Tarim Basin, China, to investigate the causal mechanisms for the complex petroleum phase. Consistency in biomarker derived parameters suggest that heavy oil, black oil, and condensate, though vary in physical properties and phase state, share a genetic affinity and are all mature oil generated at peak oil window. However, mass loss and double-peaks pattern in n-paraffins of black oil and heavy oil, and much higher maturity of gas and some oil fractions (diamondoids) jointly suggest the oil samples in the study site have suffered secondary alteration process including phase fractionation and mixing. In combination with tectonic evolution analysis, the study site experienced severe uplift after primary oil accumulation and thus formed biodegraded heavy oil in local highs. Since Neogene, the introduction of oil-cracking gas from deeper strata charged early oil accumulations and caused phase fractionation, during which primary oil was fractionated into vaporized light oil and heavy oil residue. Vaporized light oil continued to migrate towards higher positions and were readily to either mix with other oil residue and heavy oil, or to be trapped to form secondary condensate in favorable reservoirs. Thus, the complex disordered distribution of heavy oil, black oil, and condensate is observed within a relatively small area. Our reconstruction of the petroleum accumulation and alteration process speculates future exploration endeavors to potential oil-cracking gas/condensate accumulations in the study area.

Reservoired liquid petroleum has limited potential to be preserved under high temperature conditions due to thermal cracking and potentially thermochemical sulfate reduction, and thus exploration targets in ultradeep strata are mainly gas and condensate gas. However, a giant ultradeep liquid petroleum accumulation, with an average depth of >6500 m, was discovered recently in the Hadexun area, Tarim Basin. In this study, integrated geochemical analyses were conducted on the black oil samples from the Hadexun area. Intact terpanes and steranes and low concentration of diamondoids were detected, indicating that these oils were generated at peak oil window and were barely altered by secondary geochemical process (thermal cracking or others) despite their depth. The associated wet gas with light isotopic profiles was classified as mature oil-derived gas co-generated with the oil. Petroleum accumulation analyses suggested that the favorable carbonate reservoir bodies in the Middle Ordovician Yijianfang Formation were attributed to karstification and weathering, and mainly distributed along the major strike-slip fault belts. Together with the thick mudstones in the overlying Upper Ordovician Sangtamu Formation, they formed a favorable reservoir-seal assemblage in the Hadexun area. Massive volumes of liquid petroleum were generated and expelled from the Lower Cambrian black shales in the Late Hercynian and migrated into the Ordovician carbonate reservoirs through the strike-slip fault system, and subsequently were exposed to stable tectonic conditions. Due to the rapid subsidence since the Neogene, insufficient temperature-time exposure eliminated the impact of thermal cracking; therefore, the petroleum accumulation was preserved in the liquid phase, and further indicates that huge petroleum resource potential remains in ultradeep strata in the Tarim Basin.

塔里木盆地台盆区深层海相碳酸盐岩在7000 m以深持续发现大型油气聚集,但由于其复杂的地质结构与演化特征,仍需进一步加强油气成藏研究.位于塔北隆起西南部围斜的跃满地区发现了埋深在7100～7600 m之间的超深油藏,通过对该油藏的地质—地球化学综合分析,厘定了超深油藏成藏的有利条件:深大断裂一方面控制了岩溶作用的发生,导致一间房组大规模层间岩溶的发育与断溶体圈闭的形成、并与上覆吐木休克组和桑塔木组有效盖层组成了有利的储盖组合;另一方面作为流体运移的优势通道,为来自寒武系—奥陶系烃源的油气运移提供了便利条件;油气成藏后在低地温梯度和晚期快速深埋条件下,由于时间与温度的补偿效应不足,原油未发生裂解,以单一油相保存.跃满地区超深油藏成藏演化过程揭示了深层仍具有巨大的液态石油勘探潜力,勘探目标以具有串珠状强反射的断溶体油气藏为主.

塔里木盆地阿克苏地区寒武系第二统第三阶肖尔布拉克组主要由微生物白云岩组成,代表性的剖面在阿克苏市西南90 km处的苏盖特布拉克.由于成岩作用改造严重,对这套微生物碳酸盐岩的特征和形成环境的认识还存在很多分歧,制约了勘探工作.通过详细野外勘察和室内研究,将肖尔布拉克组微生物岩分为4种结构类型:凝块结构、纹层结构、砂屑结构和骨架结构.首次对凝块结构和纹层结构进行了亚类型的划分,其中凝块结构可划分为蠕虫状、网状和斑点状3种亚类型,纹层结构可划分为致密纹层、短薄纹层、颗粒纹层以及单纹层、纹层组、复合纹层.肖Ⅰ段—肖Ⅲ段发育凝块石白云岩、凝块—层纹石白云岩和层纹石白云岩,肖Ⅳ段发育凝块石微生物丘,肖V段下部发育网状结构凝块石白云岩,肖V段上部发育砂屑白云岩和肾形菌骨架岩.白云石化作用、溶蚀作用、重结晶作用是改变肖尔布拉克组微生物岩结构最重要的成岩作用,且该组下部比上部遭受了更强的成岩作用改造;微生物岩结构对成岩作用改造的抵抗能力为:砂屑结构>纹层结构>凝块结构.根据微生物岩结构,推测肖Ⅰ段—肖Ⅲ段形成于潮坪环境,肖Ⅳ段和肖V段下部形成于深水潮下环境,肖V段上部形成于浅水潮下环境.以上成果为认识塔里木盆地肖尔布拉克组微生物岩的平面分布规律和今后开展被成岩作用强烈改造的白云岩型微生物岩的研究提供了一个重要参考.

随着油气勘探向深层发展,7 000 m以深的超深层成为勘探重点.超深层古老碳酸盐岩储层的形成、保存和预测是关键难题.通过分析中国塔里木盆地奥陶系7 000 m以深已钻井资料,表征超深层碳酸盐岩储层发育特征及形成演化过程,发现高能沉积相带、准同生期暴露岩溶作用和断裂改造等控制了超深层碳酸盐岩储层的形成.通过地震属性提取,发现“串珠”状反射,提出了沿断裂带顺岩溶层钻探的方法,钻井成功率提高到了75％.建立了缝洞体定量雕刻与表征技术,形成了缝洞型油藏油气富集规律与井点优选方法.建立断层与缝洞型碳酸盐岩储层中孔洞的力学模型,开展数值模拟和理论分析,结果表明:随与断层面距离的增加,裂缝发育能力减弱;8 500 m以浅为碳酸盐岩储层优势分布区,8 500～9 200 m为有效分布区,9 200～9 500 m为一般分布区,11 000 m以深大型孔洞逐渐消亡;台盆区超深碳酸盐岩储层中古溶洞顶部形成抛物面型压力拱,阻碍溶洞的完全垮塌,以高跨比为1、矢高为8m的抛物面型溶洞为例,其完全闭合深度在50 000 m以深.因此,碳酸盐岩洞穴储层勘探深度下限远远超过目前可钻深度.

The TZ-N degrees 1 gas field in the Tarim Basin is the largest condensate field in China; however, it has not developed efficiently because of low and unpredictable production during the past 20 yr. Cores, logging interpretation, seismic descriptions, fluid properties, and production data indicate that this Ordovician carbonate field is different from conventional stratigraphic oil and gas fields as follows: (1) the hydrocarbon-bearing area covers a large region of 2000 km(2); (2) matrix reservoirs have low porosity (<6%) and low permeability (<1 md) and small throat radii (<1 mu m), but superimposed fracture caves with high porosity and permeability are present, resulting in strong lateral poroperm heterogeneity; (3) significant variations in fluid properties and phases as well as the absence of a uniform oil-water contact; (4) except for some "sweet spots" in large fracture caves, economic production requires acid fracturing and horizontal drilling, yet there are many poorly performing wells with complex output of oil, gas, and water; and (5) more than 70% of the production come from fracture-cave sweet spots but with a high decline of production rates (>20% per year). An examination of the carbonate reservoir and hydrocarbon accumulation history suggests that this large-scale stratigraphic accumulation formed during hydrocarbon emplacement in the early Paleozoic, with the reservoirs gradually evolving into tight reservoirs as a result of intense diagenesis. Variable amounts of Neogene gas charged the tight carbonate reservoirs and formed unconventional accumulations. The TZ-N degrees 1 gas field is characterized by a strongly heterogeneous tight matrix reservoir with a superimposed fracture-cave reservoir and a complicated unconventional fluid distribution, which provides insights into the exploitation challenges of unconventional carbonate resources.

Giant petroleum accumulations worldwide with burial depths more than 7000 m (>23,000 ft) occur mostly in Mesozoic and Cenozoic reservoirs and yield predominantly natural gas. Recently, however, a giant oil accumulation with reservoir depths between 7000 m (23,000 ft) and 8000 m (26,000 ft) was discovered in the lower Paleozoic section in the southern part of the Halahatang region in the Tarim Basin, China. Petroleum sourced from lower Paleozoic rocks is contained in Ordovician karst fracture-cave reservoirs and sealed by Middle-Upper Ordovician limestones and mudstones. The newly discovered superdeep accumulation is among the deepest black single-phase oil accumulations worldwide and opens up new avenues for petroleum exploration in deep-marine carbonate reservoirs. Reservoir pressures are between 75 MPa (10,878 psi) and 85 MPa (12,328 psi), with pressure coefficients between 1.2 and 1.7 and temperatures ranging between 140 degrees C (284 degrees F) and 172 degrees C (342 degrees F). Charging and accumulation of petroleum occurred during the late Hercynian orogeny, followed by subsequent gradual deep burial, which took place before rapid subsidence beginning circa 5 Ma. Following subsidence, the thickness of overlying strata increased by more than 2000 m (>6600 ft) before finally attaining current depth. Therefore, this oil accumulation represents a well-preserved ancient petroleum system. Based on the geochemical features of oils and gases, the crude oils can be classified as mature, sourced from mixed marine organofacies of shale, marl, and carbonate, whereas the gases were cogenerated with oils. Despite very high present-clay reservoir temperatures, no oil cracking has occurred because of the relatively short exposure of oils to high temperatures in a low geothermal gradient regime. Thus, there is significant exploration potential under similar conditions for liquid petroleum in superdeep strata. Faults and reservoirs are major factors controlling petroleum accumulation. Interlayer karsts with excellent fracture-cavity connectivity developed adjacent to faults, generally resulting in the enrichment of oil and gas along fault zones. High-quality reservoirs in this area are easy to identify because they exhibit strong bead-like amplitude features in seismic sections. Wells located near faults produce relatively large amounts of oil and gas. Effective karst fracture-cave reservoirs with noncracked oil may exist below 8000 m (26,000 ft) in the Tarim Basin and represent a significant exploration target in China.

塔里木盆地哈拉哈塘地区走滑断裂发育类型多样,平面上表现为明显的分段性,活动期次上具有多期性与继承性发育的特点.基于地震资料,采用多种方法查明了哈拉哈塘A地区断裂平面展布特征,并结合应力性质对哈拉哈塘A区块走滑断裂的发育特征进行研究,明确了走滑断裂对油气差异富集的控制作用.研究发现,研究区共发育3条主干断裂,根据断裂组合样式、地震剖面及古地貌特征将这3条走滑断裂分为张扭、压扭、走滑等12段;深大断裂带控储控藏特征明显,走滑断裂不同应力段控制岩溶储集层发育和油气富集;走滑断裂压扭段及张扭段的构造高部位易形成大型缝洞集合体,是优质储集层发育与油气成藏的优势区域.

Most Paleozoic marine craton basins in China are rich in natural gas except the Tarim Basin, where both oil and gas are prolific. Various hydrocarbon types have been found in this basin, including deep ultra-heavy oil, heavy oil, normal oil, volatile oil, condensate and natural gas. Petroleums with diverse types even coexist within a single reservoir. Generally, the Ordovician and Cambrian reservoirs are deeply buried (5500–8000 m) and intensively altered after initial oil and gas accumulations, bringing challenges to physical property prediction before drilling and evaluation of exploration targets. Based on recent exploration discoveries and experimental data, we systematically analyzed the origin of oil and gas, demonstrated the mechanisms and processes of secondary geochemical alteration (e.g. biodegradation, gas washing fractionation, TSR and high-temperature cracking). Moreover, the preservation mechanism of ultra-deep normal oil was also clarified, and the distribution patterns of oil and gas were predicted. Tarim Basin has been uplifted and shallowly buried in the early accumulation stage, then rapidly and deeply buried in the late stage, resulting in various geochemical alteration processes at different burial stages. Through the reconstruction of complex deep-strata oil and gas accumulation histories, the spatial distribution of deep petroleum types were predicted. This review has provided detailed assessment with case studies in the Tarim Basin, and shed light on the preservation mechanisms and the alteration processes of deep liquid petroleums. In addition to massive gas accumulations, liquid oils still have great exploration potential in strata deeper than 8000 m in the Tarim Basin.

塔里木盆地塔中北斜坡奥陶系鹰山组岩溶发育规模大范围广,岩溶作用类型及岩溶期次复杂,岩溶缝洞发育.通过电成像测井结合常规测井、岩心等资料,将研究区鹰山组划分为8类成像测井相.研究认为鹰山组岩溶体系中的溶蚀洞穴相、溶蚀孔隙相、溶缝-溶沟相、溶缝+溶孔复合相为有利的油气储集空间,溶沟-溶缝、高角度溶缝+溶孔复合相是沟通岩溶体系间的流体通道.

Crude oil in reservoirs may crack to gas with increasing buried depth and temperature, resulting in natural gas as the major exploration target in deep strata. Exploration of ultradeep targets in the Tarim Basin, Northwest China, unexpectedly discovered huge accumulations of liquid oil in Ordovician carbonate reservoirs with burial depths of >7000 m. Applying comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry, this paper analyzes the chemical compounds of crude oil in these ultradeep layers and has found that these oils are slightly cracked with low conversion of oil to gas, as evidenced by limited diamondoid compound analogues and low concentrations. Gold tube pyrolysis simulation and kinetic calculation suggest that the cracking temperatures of oil are in the range of 210-220 degrees C. The temperature implies that the deepest liquid oil surviving limit is inferred as 9000 m in this basin with the increase of the temperature. The major controlling factors on preserving abundant liquid oil in ultradeep layers of the Tarim Basin include the insufficient compensation effect of a low geothermal gradient and fast deep burial during a later period. It has potential to find oil in ultradeep (>7000 m) layers.