Continental Scientific Drilling Project Research Articles

Fracture network characterisation of the Balmuccia peridotite using drone-based photogrammetry, implications for active-seismic site survey for scientific drilling

The presence of discontinuities (e.g. faults, fractures, veins, layering) in crystalline rocks can be challenging for seismic interpretations because the wide range of their size, orientation, and intensity, which controls the mechanical properties of the rock and elastic wave propagation, resulting in equally varying seismic responses at different scales. The geometrical characterisation of adjacent outcrop discontinuity networks allows a better understanding of the nature of the subsurface rocks and aids seismic interpretation. In this study, we characterise the discontinuity network of the Balmuccia peridotite (BP) in the Ivrea–Verbano Zone (IVZ), northwestern Italy. This geological body is the focus of the Drilling the Ivrea–Verbano zonE (DIVE), an international continental scientific drilling project, and two active seismic surveys, SEismic imaging of the Ivrea ZonE (SEIZE) and high-resolution SEIZE (Hi-SEIZE), which aim to resolve the subsurface structure of the DIVE drilling target through high-resolution seismic imaging. For fracture characterisation, we developed two drone-based digital outcrop models (DOMs) at two different resolutions (10–3–10 m and 10–1–103 m), which allowed us to quantitatively characterise the orientation, size, and intensity of the main rock discontinuities. These properties affect the seismic velocity and consequently the interpretation of the seismic data. We found that (i) the outcropping BP discontinuity network is represented by three more sets of fractures with respect to those reported in the literature; (ii) the discontinuity sizes follow a power-law distribution, indicating similarity across scales, and (iii) discontinuity intensity is not uniformly distributed along the outcrop. Our results help to explain the seismic behaviour of the BP detected by the SEIZE survey, suggesting that the low P-wave velocities observed can be related to the discontinuity network, and provide the basic topological parameters (orientation, density, distribution, and aperture) of the fracture network unique to the BP. These, in turn, can be used for interpretation of the Hi-SEIZE seismic survey and forward modelling of the seismic response.

Planning for the Lake Izabal Basin Research Endeavor (LIBRE) continental scientific drilling project in eastern Guatemala

Abstract. As Earth's atmospheric temperatures and human populations increase, more people are becoming vulnerable to natural and human-induced disasters. This is particularly true in Central America, where the growing human population is experiencing climate extremes (droughts and floods), and the region is susceptible to geological hazards, such as earthquakes and volcanic eruptions, and environmental deterioration in many forms (soil erosion, lake eutrophication, heavy metal contamination, etc.). Instrumental and historical data from the region are insufficient to understand and document past hazards, a necessary first step for mitigating future risks. Long, continuous, well-resolved geological records can, however, provide a window into past climate and environmental changes that can be used to better predict future conditions in the region. The Lake Izabal Basin (LIB), in eastern Guatemala, contains the longest known continental records of tectonics, climate, and environmental change in the northern Neotropics. The basin is a pull-apart depression that developed along the North American and Caribbean plate boundary ∼ 12 Myr ago and contains > 4 km of sediment. The sedimentological archive in the LIB records the interplay among several Earth System processes. Consequently, exploration of sediments in the basin can provide key information concerning: (1) tectonic deformation and earthquake history along the plate boundary; (2) the timing and causes of volcanism from the Central American Volcanic Arc; and (3) hydroclimatic, ecologic, and geomicrobiological responses to different climate and environmental states. To evaluate the LIB as a potential site for scientific drilling, 65 scientists from 13 countries and 33 institutions met in Antigua, Guatemala, in August 2022 under the auspices of the International Continental Scientific Drilling Program (ICDP) and the US National Science Foundation (NSF). Several working groups developed scientific questions and overarching hypotheses that could be addressed by drilling the LIB and identified optimal coring sites and instrumentation needed to achieve the project goals. The group also discussed logistical challenges and outreach opportunities. The project is not only an outstanding opportunity to improve our scientific understanding of seismotectonic, volcanic, paleoclimatic, paleoecologic, and paleobiologic processes that operate in the tropics of Central America, but it is also an opportunity to improve understanding of multiple geological hazards and communicate that knowledge to help increase the resilience of at-risk Central American communities.

Volcanosedimentary fill of the early Cretaceous Yingcheng formation and response to the end of continental rifting in the Songliao Basin: Constraints from well SK-2, northern Xujiaweizi fault depression

Well SK-2 of the International Continental Scientific Drilling Project (ICDP) obtained continuous core samples with a length of 365.32 m in the Early Cretaceous Yingcheng Formation, showing a stratigraphy of interbedded rhyolites and coarse clastic rocks in the Xujiaweizi fault depression. The Yingcheng Formation in well SK-2 is divided into three sequences. Sequences 1 (S1) and 3 (S3) consist of coarse clastic rocks, and four types of conglomerate lithofacies are identified. The conglomerate lithofacies of S1 is characterized by gravity flows. In comparison, the conglomerate lithofacies of S3 is characterized by a progradational braided channel, reflecting a proximal provenance and a shallowing upward setting. Sequence 2 (S2) rocks are rhyolites, and geochemical analysis shows these to have mainly originated from the middle-upper crust. On the basis of volcanic rocks in wells Shengshen 2–1 and Shengshen 203 and seismic profiles crossing these wells, we identify two types of volcanic edifices: stratovolcanoes in the east and shield volcanoes in the west. The Early Cretaceous strike-slip faults, including the Xuzhong and Xudong faults, play an important role in controlling this area. In comparison with extensive, dark, and fine-grained clastic rocks of the Shahezi Formation, the felsic and coarse clastic rocks of the Yingcheng Formation in well SK-2 mark a sedimentary response to strike-slip tectonics and indicate the ending fault movement of the Xujiaweizi fault depression, and perhaps even the end of the Early Cretaceous Songliao Basin rifting stage.

In Situ High-Pressure Raman Spectroscopic, Single-Crystal X-ray Diffraction, and FTIR Investigations of Rutile and TiO2II

In ultrahigh-pressure (UHP) metamorphic rocks, rutile is an important accessory mineral. Its high-pressure polymorph TiO2II can be a significant indicator of pressure in the diamond stability field. In the present study, in situ high-pressure Raman spectroscopic measurements of natural rutile in UHP eclogite from the main hole of the Chinese Continental Scientific Drilling Project (CCSD) have been conducted up to ~16 GPa. Rutile and recovered TiO2II have also been analyzed via single-crystal X-ray diffraction and FTIR spectroscopy. The results indicate that (1) the phase transition from rutile to baddeleyite-type TiO2 terminates at about 16 GPa under compression at ambient temperature; (2) the metastable TiO2II in the exhumated UHP rocks formed during deep continental subduction can be characterized by a highly distorted octahedral site in the crystal structure. X-ray powder diffraction analyses (with Cu Kα radiation) at ambient conditions are sufficient for identifying the lamellae of TiO2II within natural rutile based on the angles (2θ) of two strong peaks at 25.5° and 31.5°; (3) rutile and recovered TiO2II in the continental slabs can contain certain amounts of water during deep subduction and exhumation. The estimated water contents of rutile in the present study range from 1590 to 1780 ppm of H2O by weight. In the crystal structure of TiO2II, hydrogen can be incorporated close to the long O-O edges (>2.5143 Å) of the TiO6 octahedra. Further studies on the pressure–temperature stability of hydroxyls in rutile and TiO2II may help to understand the transportation and release of water in subducted continental slabs.

Orbitally forced chemical weathering in the Late Cretaceous northeastern China: Implications for paleoclimate change

The International Continental Scientific Drilling Project of Cretaceous Songliao Basin has recovered a complete Cretaceous terrestrial sedimentary record in northeastern China, providing a unique opportunity to understand the terrestrial climate change during the Cretaceous period. In this study, we present high-resolution geochemical records from Members 3 and 4 of the Quantou Formation in the SK-1 South borehole. The findings show that samples from Members 3 and 4 of the Quantou Formation originated from a source area of a homogeneous composition. Most of the samples were sediments that underwent the first round of weathering. The geochemical proxies (Th, CIA, CIW, τ Na ) and average value of the CIA proxy indicate that the strata have been subjected to moderate chemical weathering. The weathering intensity trend was divided into four evolutionary stages based on the CIA proxy: the steady lower part (1915–1878 m), the slowly rising lower and middle part (1878–1815 m), the middle and upper part (1815–1800 m) showing the highest values, and the gently fluctuating upper part (1800–1783 m). Precession, obliquity, and short-eccentricity signals were recognized in the proxies of Th, τ Na , corrected CIA, and corrected CIW from Members 3 and 4 of the Quantou Formation, including about seven short-eccentricity cycle periods with a duration of ∼700 ka. The high peaks in short-eccentricity correspond to the high values of Th, corrected CIA, and corrected CIW proxies, and are consistent with the amplitudes of precession signals preserved in τ Na during humid periods. During strong precession, the enhanced seasonal contrasts increased humidity, which intensified chemical weathering. The paleoclimatic pattern of interaction between the monsoon-like system and westerlies in the Cretaceous Songliao Basin may be the underlying interpretation that causes cyclic variation in the chemical weathering proxies in Members 3 and 4 of the Quantou Formation. • Reconstruction of historical chemical weathering using multiple weathering proxies. • Humid climate derived from a non-linear response of the climate system to precession. • Interaction between the monsoon-like system and westerlies may be the interpretation causing cyclic variation.

COSC-2 – drilling the basal décollement and underlying margin of palaeocontinent Baltica in the Paleozoic Caledonide Orogen of Scandinavia

Abstract. The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project aims to characterise the structure and orogenic processes involved in a major collisional mountain belt by multidisciplinary geoscientific research. Located in western central Sweden, the project has drilled two fully cored deep boreholes into the bedrock of the deeply eroded Early Paleozoic Caledonide Orogen. COSC-1 (2014) drilled a subduction-related allochthon and the associated thrust zone. COSC-2 (2020, this paper) extends this section deeper through the underlying nappes (Lower Allochthon), the main Caledonian décollement, and the upper kilometre of basement rocks. COSC-2 targets include the characterisation of orogen-scale detachments, the impact of orogenesis on the basement below the detachment, and the Early Paleozoic palaeoenvironment on the outer margin of palaeocontinent Baltica. This is complemented by research on heat flow, groundwater flow, and the characterisation of the microbial community in the present hard rock environment of the relict mountain belt. COSC-2 successfully, and within budget, recovered a continuous drill core to 2276 m depth. The retrieved geological section is partially different from the expected geological section with respect to the depth to the main décollement and the expected rock types. Although the intensity of synsedimentary deformation in the rocks in the upper part of the drill core might impede the analysis of the Early Paleozoic palaeoenvironment, the superb quality of the drill core and the borehole will facilitate research on the remaining targets and beyond. Protocols for sampling in the hard rock environment and subsequent sample preservation were established for geomicrobiological research and rock mechanical testing. For the former, a sparse sample series along the entire drill core was taken, while the target of the latter was the décollement. COSC-2 was surveyed by a comprehensive post-drilling downhole logging campaign and a combined borehole/land seismic survey in autumn 2021. This paper provides an overview of the COSC-2 (International Continental Scientific Drilling Project – ICDP 5054_2_A and 5054_2_B boreholes) operations and preliminary results. It will be complemented by a detailed operational report and data publication.

Hydrogen-rich gas discovery in continental scientific drilling project of Songliao Basin, Northeast China: new insights into deep Earth exploration

Hydrogen-rich gas discovery in continental scientific drilling project of Songliao Basin, Northeast China: new insights into deep Earth exploration

Discing behavior and mechanism of cores extracted from Songke-2 well at depths below 4,500 m

Understanding in-situ stresses is the foundation for investigating deep rock mechanics. In practice, the fracture morphology of a disced core can often reflect its in-situ environment and disturbance-induced fracture process to some extent. In this study, three-dimensional dynamic scanning technology is used to reconstruct the fracture morphology of the disced cores extracted from Songke-2 as well as part of the Chinese Continental Scientific Drilling Project . The roughness of various regions of the fracture surfaces of the cores is investigated. Additionally, a parametric system is developed for the quantitative study of the integrity coefficient of the disced rock samples. Furthermore, the mechanisms and characteristics of the fractures along the stress paths are investigated. According to the findings, when shallow cores undergo discing, they have notable saddle-shaped coarse fractures, which may be related to the properties of the cores at these depths. Deep cores demonstrate discing behavior, but the generated discs are relatively thick. Deep core fracture surfaces are mostly smooth and straight, possibly propagating from the outside to the inside. Under excavation disturbance in the hydrostatic state, the extreme values of the maximum tensile stress at the core stubs show a saddle-shaped distribution. In general, the results of this study can serve as a theoretical foundation for the quantitative assessment of the intactness of disced cores. Furthermore, because disc patterns and characteristics are associated with stress states, this approach can be used to evaluate in-situ stress environments.

Major Mineral Fraction and Physical Properties of Carbonated Peridotite (Listvenite) From ICDP Oman Drilling Project Hole BT1B Inferred From X‐Ray CT Core Images

AbstractWe quantified mineral proportions in listvenite (completely carbonated peridotite) in Hole BT1B drilled across the basal thrust of the Samail ophiolite by the International Continental Scientific Drilling Project Oman Drilling Project using 3D X‐ray Computed Tomography (XCT). We analyzed >250,000 XCT images from a continuous ∼200 m listvenite core. Histograms of the intensity of X‐ray attenuation of each XCT core‐slice image were fitted assuming that the listvenites are composed of magnesite, quartz, and dolomite. The XCT mineral peaks were confirmed by comparison with chemical mapping data obtained using an X‐ray fluorescence (XRF) core scanner. Listvenite matrix is composed almost entirely of magnesite and quartz, consistent with discrete XRD and XRF data. Veins are composed mostly of dolomite. The mean abundance of dolomite in listvenite from BT1B is 11 vol.%, whereas that in core sections within 15 m of the basal thrust is >50 vol.%, suggesting the basal thrust acted as a source of Ca‐ and CO2‐rich fluids. The SiO2:MgO:CaO molar ratio in the entire core from BT1B is 42:52:6, similar to that of onboard XRF data for discrete samples (41:54:5), whereas average Oman peridotites have ratios of (39:60:1), indicating Ca addition perhaps during carbonation. P‐ and S‐wave velocities and density of listvenite are close to those of peridotite and are higher than those of serpentinites. These results suggest that limited material transfer during carbonation and hydration of the Samail ophiolite, except for Ca, CO2, and H2O. Listvenites formed in the mantle wedge above subduction zones may be an overlooked reservoir for carbon in the Earth's interior.

Detection of the deep biosphere in metamorphic rocks from the Chinese continental scientific drilling.

It is generally accepted that there is a vast, well-populated biosphere in the subsurface, but the depth limit of the terrestrial biosphere has yet to be determined, largely because of the lack of access to the subsurface. Here as part of the Chinese Continental Scientific Drilling (CCSD) project in eastern China, we acquired continuous rock cores and endeavored to probe the depth limit of the biosphere and the depth-dependent distribution of microorganisms at a geologically unique site, that is, a convergent plate boundary. Microbiological analyses of ultra-high-pressure metamorphic rock cores taken from the ground surface to 5,158-meter reveal that microbial distribution was continuous up to a depth of ~4,850m, where temperature was estimated to be ~137°C. The metabolic state of these organisms at such great depth remains to be determined. Microbial abundance, ranging from 103 to 108 cells/g, was also related to porosity, but not to the depth and rock composition. In addition, microbial diversity systematically decreased with depth. Our results support the notion that temperature is a key factor in determining the lower limit of the biosphere in the continental subsurface.

Timing of deformation, metamorphism and leucogranite intrusion in the lower part of the Seve Nappe Complex in central Jämtland, Swedish Caledonides

ABSTRACT Recent studies in the context of the International Continental Scientific Drilling Project “Collisional Orogeny in the Scandinavian Caledonides” have focused on the importance of the Seve Nappe Complex (SNC) for understanding the subduction history of the Baltoscandian margin during closure of the Iapetus Ocean. In the classical Åre area of western central Jämtland, granulite facies migmatites and leucogranites of the Åreskutan Nappe provide evidence of Early Silurian (c. 440 Ma) high temperature metamorphism and a previous prograde, ultra-high pressure history, with microdiamonds. New LA-ICPMS zircon isotope age investigations of the underlying amphibolite facies Lower Seve Nappes, reported here, have also identified an Early Silurian tectonothermal history with pegmatitic leucogranite (c. 443 Ma) and, at lower structural levels, another felsic intrusion of earliest Middle Ordovician age (c. 469 Ma). The latter intrudes isoclinally folded host rock amphibolites and calcareous psammitic paragneisses and is itself tightly folded. Zircons in an amphibolite proved to be highly discordant but indicate Early Silurian metamorphism during isoclinal folding. Detrital zircons in a paragneiss are dominated by Sveconorwegian populations, but also include a range of younger Neoproterozoic grains down to the Early Ediacaran (c. 600 Ma). This new evidence of early Caledonian deformation and metamorphism indicates that, as farther north in the orogen, the Seve tectonothermal history in central Jämtland probably started early in the Ordovician, or before. Subduction and accretion along the Baltoscandian outer margin occurred prior to Scandian continent-continent collision, with Siluro-Devonian emplacement of the SNC across the foreland basins onto the Baltoscandian platform.

Scientific Drilling ‐ to Construct the Telescopes that Inserting to the Earth Interior

AbstractMankind live in the earth for countless years, but until now; people do not really understand the connotation of the Earth. We know that the earth composition including the lithosphere, the asthenosphere, mantle and core. Of course, the lithosphere supports all the life on Earth. For a long time, geoscientists trying to use all kind of methods such as geological, geophysical and geochemical methods to detect and study the earth, but the knowledge about earth are mostly indirect. Through the direct observation to the lithosphere, people can understand and recognize the plate movement of ocean and the mainland, crustal stress, earthquakes, volcanic processes, deep resources, the origins of life, global climate change and biodiversity. They are all the basis of a series of geosciences problems (Su and Yang, 2010).Geological specimens, especially the true samples from deep of the Earth, are the most directly study subjects for geologists. But the only way to access the true samples from deep of the earth is drilling. The most directly relevant evidence always originated from the deep of the earth, such as core, cuttings, fluid samples and other physical samples.Continental scientific drilling has been demonstrated which is an efficient technique for directly obtaining information from the Earth's surface to the deep crust, and is acknowledged as “to build a telescope inserting to the interior of the Earth”, as well as “a key for opening the door of the Earth”. Over the last four decades, continental scientific drilling has achieved great success in enhancing our knowledge of the Earth, and in providing information on mineral resources, large engineering projects and global change. SinoProbe‐05 is a new scientific drilling venture, which builds on the success of the Chinese Continental Scientific Drilling Project (CCSD), and is similar to the current major scientific drilling project on the Wenchuan earthquake fault. SinoProbe‐05 will focus on 6 critical tectonic and mineral resource regions, including the Jinchuan Cu‐Ni sulphide deposits in Gansu, the Luobusa chromite deposits in Tibet, the Tengchong volcano‐thermal tectonic zone in Yunnan, the Yudu‐Ganxian polymetallic deposits in South China, the Tongling polymetallic deposit and the Luzong volcanic basin and mineral deposit district in Anhui. As of the end of 2013, all of these pilot holes have been completed, all of them have achieved the desired scientific objectives.The construction of another ICDP project, Songke No.2 well, has come to an end. Current well depth is 5929m. Drilling throughout the Cretaceous strata is just around the corner (The design well depth is 6400m.). This will be the first complete Cretaceous stratigraphic profile in the world.The deep exploration project which will be stared soon will build a large number of different depths of scientific drilling holes. The deepest hole depth will reach to 13000m. We believe that the construction of these scientific coring drilling holes will provide geologists with a lot of real core samples. These cores can meet the needs for different geoscience research areas. No doubt, the research results based on these cores will promote China's geological science research to a new height, of course; will also contribute to the progress of the world's earth science. This is also a good opportunity to promote China's drilling technology.So, we know that no advanced drilling technology, no enough high quality samples from the deep of the Earth, the in‐depth studies for geosciences will be restricted of course (Zhang et al., 2013).

Design and applications of drilling trajectory measurement instrumentation in an ultra-deep borehole based on a fiber-optic gyro

Abstract. The working environment in hot dry rock boreholes, encountered in deep geothermal investigation drilling and ultra-deep geological drilling (up to 5000 m), is very difficult at the present stage. We have developed a drilling trajectory measuring instrumentation (DTMI), which is based on the interference fiber-optic gyro (FOG). This can work continuously, for 4 h, in an environment where the ambient temperature does not exceed 270 ∘C and the pressure does not exceed 120 MPa. The DTMI is mainly divided into three parts: an external confining tube, a metal vacuum flask, and a FOG measurement probe. Here, we focus on the mechanical design, strength, and pressure field simulation analysis for the external tube, the structural design and temperature field simulation analysis for the vacuum flask, and the FOG Shupe error analysis and compensation in the temperature field. Finally, through the engineering applications of the SK-2 east borehole of the China Continental Scientific Drilling (CCSD) project and the geothermal well of Xingreguan-2, the data measurements of the drilling trajectory were used to analyze the stability of the DTMI. The instrument realizes long-duration, high-stability work in the process of making trajectory measurements in an ultra-deep hole. The instrument has the characteristic of anti-electromagnetic interference and enables work to be carried out in the blind zone of existing technologies and instrumentation. Therefore, DTMI has great potential in the promotion and development of geological drilling technology.

Research and application of high−temperature drilling fluid designed for the continental scientific drilling project of Songliao Basin, China

ABSTRACT Well Songke−2 is the main hole of the Continental Scientific Drilling Project of Songliao Basin, China, and its bottom hole temperature is estimated to exceed 240°C in the fourth spud at the well depth of 5800 m. To ensure that the drilling fluid could meet the demand of high temperature resistance, different components, including clay, filtration reducers and anti−collapse additives, of the high–temperature drilling fluid system were optimized through thermal stability tests. Comprehensive test results suggested that the optimal bentonite content to be 4% (w/v). Compared with other materials of the same type, polymer filtration reducers SO−1 and HLW−1, as well as sulfonation additive LOCKSEAL were demonstrated to have stronger resistance to high temperature. The proposed high temperature drilling fluid formula exhibited good thermal stability, rheological behaviour, anti−contamination capacity and shale inhibition property. Finally, a great success of the formula was practically obtained in the field application during the following−up core drilling project.

Progress on Continental Scientific Drilling Project of Cretaceous Songliao Basin (SK-1 and SK-2)

Progress on Continental Scientific Drilling Project of Cretaceous Songliao Basin (SK-1 and SK-2)

A reassessment of the stress and natural fracture orientations from analysis of image logs in the Chinese Continental Scientific Drilling Program borehole at Donghai county, Jiangsu province, China

The Chinese Continental Scientific Drilling (CCSD) project has drilled a 5100 m deep research borehole in the Sulu ultra-high pressure (UHP) metamorphic belt, eastern China. The UHP metamorphic belt is thought to be a product of continent-continent collision and has consequently experienced very intensive structural deformation. Based on a more complete well log data set of CCSD borehole, we can have a more detailed and reliable study on the structure features of borehole wall and other rock physical properties than a previous study published in 2009. Abundant data related to borehole breakouts (BOs), drilling induced tensile fractures (DITFs) and natural fractures were collected from the image logs. The BO and DITF data indicate that the average direction of the maximum horizontal principal stress (SH) of the CCSD borehole site is about 79.2° which is consistent with the convergent direction (E-W) of the Pacific Sea Plate with respect to the Eurasian Plate. Analysis of DITFs indicated that in the case of the CCSD borehole, axial drilling induced tensile fractures (ADITFs) occur occasionally in the upper section (0–2300 m) of the borehole with low dipping angle (0–10°), while transverse drilling induced tensile fractures (TDITFs) occur significantly in the lower section (3800–5000 m) with high dipping angle (10–30°). The natural fracture distribution at depth in the metamorphic rocks of the CCSD borehole indicates that (1) the failure strength of rocks and borehole depth are two factors that affects natural fracture frequency, (2) most of the dip azimuth of natural fractures is consistent with the dip azimuth of foliations observed in the core, (3) the development of most of the natural fractures probably was dominated by the development of foliations, and both the natural fractures and foliations developed in response to the subduction and exhumation of the Sulu terrene.

Main technical innovations of Songke Well No.2 Drilling Project

ABSTRACT Songke Well No.2, one of the main part of the scientific drilling project in Songliao Basin, which was drilled 7018 m and acquired the part of cores continuously from the Low Cretaceous to the Carboniferous and the Permian from the 2843 m deep, can be considered as the deepest continental drilling project in Asia. Aiming at the features of longer well sections, larger diameters and multiple spud-ins for coring of Songke Well No.2, this project broke through the “coring in small diameter and reaming in large diameter” spud-in drilling-completion procedures which are always used in large-diameter-well coring for continental scientific drilling projects in domestic and overseas and the drilling method of short-single-cylinder roundtrip footage. At the same time, “coring in the same diameter and completing drilling at one single diameter” was achieved at all φ311 mm and φ216 mm coring sections of more than one thousand meters long, high-efficient operation with “drilling long footage with drill tools combined in multi-cylinders” was achieved at deep coring section. Four world drilling records were created which include more than a thousand meters continuous coring at φ311 mm, and the footage per roundtrip footage at φ311 mm, φ216 mm and φ152 mm is all more than 30 m, all of these breakthroughs reduced at least 300 days for this project; moreover, considering the characteristics of formations that the geothermal gradient is high in the drilled sections and the inside-well temperature is over 240°C after drilling completion, a formate-polymer water-based mud system was developed by compounding attapulgite and sodium bentonite and by adding independently developed high-temperature stabilizer, which can provide critical technical support for successful well completion at 7018 m in the super-high-temperature environment It is the first time that the water-based mud is operated at the working temperature higher than 240°C in China; Besides, considering the high-quality requirement on cores imposed by the project, the method “mechanical cored is charge” to discharge core nondestructively on the ground was worked out, and more than 4000 m scatheless cores were discharged out of the drill pipes while maintaining original stratum structures.

Pore structure characterization of the Cretaceous Quantou Formation: Results from microresistivity imaging logs in the second scientific drilling borehole (SK-2 east borehole) Songliao basin, northeast China

As the main borehole of the China Cretaceous Continental Scientific Drilling Project, the SK-2 east borehole was drilled to obtain in-situ multi-information of geophysics and investigate the paleoclimatic and environmental changes. A study based on continuous geophysical logs facilitates achievement of scientific goals, such as the establishment of the typical petrophysical properties for Songliao basin and other similar basins, analysis of sedimentary environment, resource exploration, geothermal system research, and long-term observation and fluid experiments on deep strata. Both conventional logs and microresistivity imaging logs of the Cretaceous Quantou formation have been acquired. Porosity spectra from microresistivity imaging logs are obtained by using the Archie equation. Based on analysis of porosity spectrum features, we divide the porosity spectra of K1q in the SK-2 east borehole into twelve configurations according to the location and combination of peaks to characterize different pore structure. The porosity spectra of K1q in the SK-2 east borehole are dominated by unimodal distribution indicating more primary porosity. Five layers dominated by unimodal distribution are considered for performing long-term observations and fluid experiments on aspects of depth, thickness or petrophysical properties. By comparing spectrum features, porosity spectrum can be used to reflect the heterogeneity and analyze the pore structure of clastic strata. Layered strata will produce complicated porosity spectra as secondary porosity will. It is better to combine porosity spectra with microresistivity image to study secondary porosity. The decline of the porosity heterogeneity in the SK-2 east borehole is demonstrated by two parameters, φvk and W from porosity spectra, which can indicate the sedimentary environment. Moreover, porosity spectra in clastic strata is favorable for determining lithology and sedimentary environment when combined with microresistivity images.

Fifteen years of the Chinese Continental Scientific Drilling Program

Abstract. Continental scientific drilling can be regarded as a telescope into the Earth's interior because it provides process insight and uncompromised samples of rocks, fluids, and even sampled from the deep biosphere from the Earth's surface to great depths. As one of the three founding members of the International Continental Scientific Drilling Program (ICDP), ICDP China has made great achievements in many scientific drilling-related research fields. Based on the ICDP participation it attracted global attention of scientists and set up not only the Chinese Continental Scientific Drilling (CCSD) Program in 2001 but also a growing number of ambitious drilling projects in the country. The 5158 m deep borehole of the CCSD project at Donghai County in the Sulu ultrahigh-pressure metamorphic terrain demonstrates that large amounts of crustal rocks of the South China Block have been subducted to at least 120 km, followed by rapid uplift. After successful completion of drilling at Donghai, several continental scientific drilling projects were conducted with funding of the Chinese government and partially with support of ICDP, resulting in a total drilling depth of more than 35 000 m. These projects encompass the Continental Environmental Scientific Drilling Program of China, the Scientific Drilling Project of Wenchuan Earthquake Fault Zone, the Continental Scientific Drilling Project of Cretaceous Songliao Basin, and the Program of Selected Continental Scientific Drilling and Experiments. On the occasion of the 20th anniversary of the ICDP and the 15th anniversary of the CCSD Program, this paper reviews the history and major progress of the CCSD Program.

Noble gas composition and 40Ar/39Ar age in eclogites from the main hole of the Chinese Continental Scientific Drilling project

We present the first comprehensive noble gas study on eclogites. The four eclogite samples were recovered during the Chinese Continental Scientific Drilling and are from two distinct profile depth sections differing in their degree of interaction with meteoric water, based on their δ 18O-values (surface related and of mantle-type). Hence, noble gas analyses offer the potential to further discriminate between shallow (meteoric) and deep (mantle) fluid sources. Noble gas compositions reveal typical crustal fluid compositions, characterized by a variable mixture of atmospheric gases with significant contributions of nucleogenic neon, radiogenic 4He*, radiogenic 40Ar*, fissiogenic 131–136Xe, and presumably bariogenic 131Xe, but no significant addition of mantle gases. This signature can be also considered to represent one endmember component of eclogitic diamonds. Concentrations of non-radiogenic noble gases are rather low, with depletion of light relative to the heavier noble gases. Eclogites from lower depth which experienced a higher degree of interaction with meteoric water also showed higher contributions of atmospheric gas compared with eclogites recovered from greater depth. This is interpreted to result from interaction with high-salinity fluids during ultrahigh pressure (UHP). It demonstrates that the atmospheric noble gas abundance is a proxy for interaction with surface related fluids. 40Ar/39Ar (inverse) isochron ages of two phengite separates (241.2 ± 0.4 Ma and 275.0 ± 1.8 Ma, 1σ-errors) predate the main phase of UHP metamorphism (ca. 220 Ma). Biotite yields an integrated age of about 1100 Ma. These age values are interpreted to reflect the likely addition of excess 40Ar without any chronological meaning.