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Previous scientific research on reservoirs of the Deng IV Member in Gaoshiti-Moxi area, the main production area of Anyue gas field with tens of billions of cubic meters reserves, concerns on karst paleogeomorphology reconstruction, facies distribution on platform margin and their effects on favorable reservoirs. However, the quality of microbial carbonate reservoirs is also closely related with their original depositional environments on the whole platform, which is significant for further petroleum exploration and exploitation of ultra-deep carbonate reservoirs in this area. Therefore, this paper attempts to reveal favorable microbial carbonate reservoir characteristics and sedimentary effects on their distribution and prediction, based dominantly on synthetic analysis of depositional characteristics, including both sequence stratigraphy and facies, such as seismic facies, microfacies and microfacies associations. The results show that favorable reservoirs of the Deng IV Member are classified into three types according to their space types, namely, fracture-cavity reservoir, pore-cavity reservoir and pore. Secondary dissolution pores and cavities are primary reservoir spaces developed mainly in non-skeletal grain dolomites with sparry cements, thrombolites, and stromatolites in microfacies association 1 (MA1), MA2, MA5, and MA7. Physical property of fracture-cavity type of reservoir is better in the upper and lower parasequence sets with a porosity between 1% and 5%, a permeability between 0.01 × 10− 3 µm2 and 1 × 10− 3 µm2; physical property of pore-cavity reservoir is fine throughout all the parasequence sets with a porosity between 2% and 4%, a permeability between 0.01 × 10− 3 µm2 and 1 × 10− 3 µm2; physical property of pore-cavity reservoir is the worst. In vertical, the favorable reservoirs are developed mainly in parasequence set 6 (PSS6) and PSS7 in vertical. On planar, they are distributed in well zone MX9-MX19-MX1 for the fracture-cavity type, MX105-MX110-GS20 for the pore-cavity type and MX17-MX107-MX41-MX102-GS102 for the pore type. What’s more, effects of depositional sequences, seismic facies, microfacies and microfacies associations on reservoir distribution indicate that to some extent, fracture-cavity type of reservoir is constrained by the top boundaries of PSS7, PSS2, parasequence 17 (PS17) and PS14; pore-cavity type of reservoir by the top boundaries of PSS7, PSS4, PS18 and PS12; pore type of reservoir by the top boundaries of PSS7, PSS6, PSS3, PSS2, PS18, PS17, PS14, and PS12. Seismic facies associated with shoals and of mound-flat complex are related with facies distributions of pore cavity and pore reservoirs. MA1, MA3, MA7, MA8 are predominant microfacies associations of favorable reservoirs of the Deng IV Member in Gaoshiti-Moxi area.

By analyzing the structural background, petroleum geological conditions, and typical regional (paleo) oil and gas reservoirs in marine ultra-deep oil and gas regions in China, this paper reveals the evolution processes of the marine ultra-deep oil and gas reservoirs and the key controlling factors of accumulation. The marine ultra-deep oil and gas resources in China are buried at depth of greater than 6000 m, and are mainly distributed in the Precambrian and Lower Paleozoic strata in the Sichuan, Tarim and Ordos cratonic basins. The development of marine ultra-deep source rocks in China is controlled by cratonic rifts and cratonic depressions with the background of global supercontinent breakup-convergence cycles. The source rocks in Sichuan Basin have the most developed strata, followed by Tarim Basin, and the development strata and scale of Ordos Basin needs to be further confirmed. The marine ultra-deep reservoir in China is dominated by carbonate rocks, and the reservoir performance is controlled by high-energy sedimentary environment in the early stage, superimposed corrosion and fracture in the later stage. The regional caprocks are dominated by gypsum salt rocks, shale, and tight carbonate rock. The ultra-deep oil and gas fields in China have generally experienced two stages of oil-reservoir forming, cracking (or partial cracking) of paleo-oil reservoirs, and late finalization of cracked gas (or highly mature to over mature oil and gas). The oil and gas accumulation is controlled by static and dynamic geological elements jointly. Major hydrocarbon generation center, high quality and large-scale reservoir resulted from karstification of high energy facies belt, thick gypsum rock or shale caprock, and stable trapping and preservation conditions are the key factors for accumulation of ultra-deep oil and gas. We propose three favorable exploration directions, i.e. the areas around intracratonic rift and intracratonic depression, and craton margin.

Characteristics and evolution process of strike-slip fault is a key issue restricting further exploration in Halahatang area, North Tarim Basin, NW China. This paper uses the new-acquired 3D seismic data and applies fault structural analysis method to study the characteristics of Halahatang area, and discusses evolution process of the faults.The data used in this paper include 1960 km2 3D seismic data in prestack time migration in Halahatang area, and 4 wells logging data used to calibrate seismic horizon. The bin size of 3D seismic is 25 m×25 m with sampling rate of 4ms, and data length of 7000 ms. Firstly, the Eigen-structure coherency and SO semblance are used to identify the distribution of the strike-slip fault. Secondly, the segmentation of Ordovician strike-slip fault in the study area is studied and the control effect of segmentation on reservoir development and oil and gas enrichment is discussed.The slip distance of strike-slip fault is very small, the maximum is no more than 2 km. They are typical cratonic strike-slip faults which are developed inside the craton. There are four kinds of structural styles on the profile, which are vertical and steep, positive flower structure, negative flower structure and semi-flower structure. Five structural styles of linear extension, X type, braided structure, horsetail structure, and en-echelon structure are developed on the plane. There are obvious segmentation along the fault trend.According to the strata subjected to strike-slip deformation and the structural styles in different strata, it is determined that the strike-slip faults have three stages of activity in Halahatang area. In the Late Ordovician, NNE, NNW, NE, and NEE strike-slip faults are mainly developed in the study area. The faults on the seismic profile are steep and upright, with small displacements. Faults generally only break into the Ordovician, and later activities will cause faults to go up to the Silurian and even the upper Palaeozoic, which have different tectonic styles with that of the Ordovician faults. The NNE and NNW strike-slip faults form an “X”-type conjugate strike-slip fault, reflecting the conjugate strike-slip fault is generated by near north-south compression.In the Late Permian, 4 NNW transtensional strike-slip faults are generated by the activation of some Ordovician strike-slip faults. In the Late Cretaceous-Palaeocene, the study area mainly develop several groups of NNE, near SN transtensional strike-slip faults. These transtensional strike-slip faults appear as graben and horst or stepped faults on the section. These transtensional strike-slip faults are R-shear faults in the Mesozoic and Cenozoic strata formed by the Ordovician NNE faults slip dextrally under the tectonic stress.

Based on the three dimensional seismic data and drilling data in Gaoshiti–Moxi area, the structural characteristics and evolution process of strike-slip faults in the study area and their significance for gas accumulation were examined using the method of fault structure analysis. The results show that: (1) Transtensional strike-slip faults are developed in the Paleozoic in study area. On the profile, there are three types of structural styles: steep and erect, flower structures, “Y” and reversed “Y” type faults. On the plane, strike-slip faults developed in the Cambrian extending linearly and along the nearly EW, NW and NE direction. The faults are composed of multiple secondary faults in en-echelon arrangement; faults in the Permian are mainly along nearly EW and NW direction, and the Permian faults are distributed in the middle east part of the study area and they are more in the north than in the south. (2) The nearly EW and NW trending faults are dextral strike-slip faults, and the NE trending faults are sinistral strike-slip faults. The strike-slip strength of the nearly EW trending faults are the strongest and the maximum horizontal displacement is 550 m, while the strike-slip strength of the NE trending faults is the weakest. The Cambrian faults had stronger activities than the Permian faults. (3) The transtensional strike-slip faults were active in two periods, the early Caledonian period and the late Hercynian period, and were the products of oblique extension of pre-existing weak zones in Xingkai and Emei taphrogenesis, with certain inheritance in the main faults. (4) The strike-slip faults and surrounding fractures enhance the porosity and permeability of the reservoir in Cambrian Longwangmiao Formation and control the distribution of karst reservoirs in the Permian Qixia Formation–Maokou Formation, bringing about the situation of multiple gases bearing series in this area. Key words: Sichuan Basin, Gaoshiti–Moxi area, Cambrian, Permian, strike-slip fault, structural characteristics, gas accumulation

Through new 3-D seismic data, we present relationship between maximum throw and fault length and fault segment length in fault zones, and relationship among length, width, throw and separation in overlap and tip zones of a conjugate strike-slip fault system in the intracratonic Tarim Basin, NW China. The results show that: (1) the major fault zones are in range of 23–76 km in length, and compose of 3–8 segments with low maximum throw less than 140 m; (2) a good power–law-scaling relationship of throw-segment length but not of throw-fault length; (3) more mature in NNW trending faults than in NNE trending faults; (4) the hard-linked overlap zones concentrate most deformation and exceptional high throws, with better linear correlation between throw and overlap zone length rather than soft-linked segments; (5) length/width, length/throw and separation/throw ratios from the transpressional overlap zones varies in a range of 4.6–11.2, 59–130 and 6.1–12.3, which are quite larger than those from extensional settings. Our study suggest that: (1) the fault growth depends on the stages of segment linkage (maturity); (2) the linear trends of scaling relationship between fault elements are mainly controlled by mechanical properties, while the scattered distribution of data is related to the stage of fault linkage and overlapping; (3) the deformation and displacement are localized in the overlap zones after hard-linkage following fault segments interaction; (4) fault elements could be useful to understanding fault growth and evolution stages in the deep subsurface. These results provide new insight into a better understanding of fault linkage and interaction from the subsurface seismic data in strike-slip fault zones.

The origin of magmatic episodes between final assembly and initial breakup of Rodinia is crucial for deciphering geodynamic transition and continental crust growth processes. However, few igneous rocks were identified during the quiescent time from 900 Ma to 830 Ma in the Tarim Craton. Along its northwestern margin, our field investigations identified abundant granitic debris in the Cryogenian Qiaoenbrak Group. Zircon U-Pb age determination revealed crystallization age at ca. 850 Ma. Detrital zircon crystals within Cryogenian to Ediacaran clastic rocks and schists of the basement Aksu Group also contain a major population having crystallized at ca. 860–840 Ma. Thus, we suggest that a hitherto unknown major magmatic event occurred ca. 850 Ma ago in northern Tarim. Granite gravels exhibit typical fractionated granite features, with high values of SiO2 (73.1–75.7 wt%), alkali oxides (Na2O + K2O = 7.8–8.7 wt%) and Na2O/K2O (avg. 1.3 wt%), and low values of P2O5 (≤0.04 wt%) and A/CNK (0.87–1.01), together with Rb, Th, U and K enrichment, and depletion in Nb, Ta, Sr, P, Ti and Eu, negative Eu anomalies (δEu = 0.21–0.74) and fairly low Ga/Al ratios. Including detrital crystals, ca. 850 Ma zircon crystals display a large range of eHf(t) values from −17.0 up to +11.6. Elemental and zircon Hf isotopes suggest that granites were derived from melting of juvenile lower crust, with addition of reworked upper crust and mantle-derived melts. We propose (1) before ca. 850 Ma, arc-continental collision setting related to southward accretionary assembly along Tarim margin, (2) progressive assembly of Tarim Craton, and (3) position of Tarim Craton within Rodinia supercontinent probably closer to North India Block than to Australia at ca. 850 Ma.

Abstract Donghe sandstone of Devonian in Halahatang-Hadexun area is typical clastic reservoir of wave-dominated coast in China. It is buried now more than 5500m.The physical property of Donghe sandstone is well, while the heterogeneity is great for the carbonate cement. Research on genesis of carbonate cement has great significance to reservoir prediction. Based on core observation, this paper indicates there are four lithologic associations of carbonate cement sandstone: biological burrow type(?), bedding - laminae type(?), thin calcareous sandstone intercalated in thick sandstone (?) and calcareous concretion(?), and different genesis of carbonate cement in different lithologic associations. Slice and cathodoluminescence analyses show the carbonate cements include more calcite, some ferrocalcite and ankerite, and few dolomite. The carbonate cement usually deposits after quartz overgrowth, and fills in intergranular dissolved pore, feldspar and lithologic fragments dissolved pore, or occurs metasomatic processes of detrital grain. The results of carbon and oxygen isotope show d13CPDB is -2.8~-7.7‰,average -4.7‰;d18OPDB is -11.8~-16.6‰,average -14.7‰. With comprehensive analysis, the genesis of carbonate cement in Donghe sandstone has four types: organic acid decarboxylation, erosion and solution genesis of Ordovician carbonate, biogenesis and exposed sedimentogenesis. According to logging analysis, there is a significant negative correlation between the content of carbonate cement and porosity and permeability of reservoir. When the content of carbonate cement is more than 10%, the sandstone cements tight with poor physical property. The dense layers of carbonate cement distribute along unconformity, slope area or structural high part, which forms safeguard as the lateral sealing layers, local floor and cap rocks of hydrocarbon trap. This paper changes the opinion of people that Donghe sandstone as beach sand is not a strongly heterogeneous reservoir and the carbonate cement has no benefit to hydrocarbon trap. Introduction Carbonate cement is a kind of authigenic diagenetic minerals, it distributes widely in clastic rock, and it is one factor influencing on reservoir physical property(Kantorowicz,1987;Boles,1998).Many previous studies consider carbonate cement have a preference for sandstones that had relatively high initial porosities and permeabilities. Thus, the flux of formation water and probably long-distance transportation of diagenetic components were more important influences on reservoir quality of sandstones than was the local availability of components(Keith et al.,1991), and the effect of carbonate cement diagenetic phases on permeability was distinct from their effect on porosity(Marco et al., 1991,1993;Sylvia et. al,2000). The carbonate cement mainly occurs within the highest permeability facies in the sandstone body, which results in carbonate cements in sandstones commonly occur as irregularly distributed concretions, which makes heterogeneity of it (Kitty,2001;Shirley et al.,2002). So, research on genesis of carbonate cement has great importance in reservoir prediction and petroleum development. This paper takes Halahatang-Hadexun area, Tarim, as an example, analyzes lithologic associations of carbonate cement sandstone;origin of carbonate cement and genetic characteristics;influences on reservoir property and hydrocarbon trap, and provides new idea to predict beneficial reservoir and find lithologic stratigraphy trap.