Scientific Drilling Research Articles

Frontier of Understanding Earth's Dynamics

Frontier of Understanding Earth's Dynamics

Machine learning algorithm optimization for intelligent prediction of rock thermal conductivity: A case study from a whole-cored scientific drilling borehole

Rock thermal conductivity (TC) is a key parameter in geothermal, petroleum geology, and basin research. Although experimental analysis relying on core samples is currently an effective way to obtain the TC of rocks, it is not always feasible as most boreholes have no or limited cores, making it difficult to establish TC model of geological body efficiently and accurately. This study sheds light on how machine learning algorithms can be used to accurately predict rock TC with easily accessible and high-resolution logging data. Based on 295 measured TC data, logging data, and vertical seismic profile (VSP) data collected from the whole-cored CSDP-2 borehole, the models including random forest (RF), convolutional neural network (CNN), support vector regression (SVR), and particle swarm optimization-SVR (PSO_SVR), were applied to predict the TC of the entire borehole section. Using a confusion matrix analysis, the primary-wave velocity (PWV) from the VSP survey, measured density, and logging data, including shallow lateral resistivity (LLS), compensated neutron log (CNL), density (DEN), gamma rays (GR), spontaneous potential (SP), and acoustic transit time (AC), were used as the input variables for training models and TC prediction. The results showed that the geophysical parameters reflecting those properties related to mineral composition, porosity and reservoir fluids of geological body can be well used to predict TC through machine learning algorithms. Regardless of unconsolidated sediments or rocks, the RF model showed stronger applicability and higher accuracy in TC prediction compared to the PSO_SVR and CNN models, while the SVR model showed poor applicability in this case study. The PWV data can effectively improve the accuracy of TC prediction of all models, and the RF model finally yielded the excellent performance with a correlation coefficient (> 0.86) and root mean squared error (8%) between the predicted and measured values. Future research should focus on studying the weighted analysis for the correlation between geophysical parameters and TC and developing more accurate predictive models for wider applications.

East Asian summer monsoon evolution recorded by the middle Miocene pelagic reddish clay, South China Sea

The East Asian summer monsoon (EASM) is essential for the livelihoods of billions of people in East and Southeast Asia. Its present features and evolution history of the Quaternary have been well studied, yet how did EASM operate in much older geological times, especially before the late Miocene, is relatively less constrained. Scientific drillings conducted in the South China Sea (SCS) offer excellent opportunities to resolve this issue to a certain extent considering the EASM has been prevailing in this area since at least the earliest Miocene. In this study, mineralogical and stratigraphic studies were carried out on the middle Miocene pelagic reddish clay recovered at International Ocean Discovery Program Site U1433 using clay mineralogical and natural gamma radiation data. Our results show that the smectite content and illite crystallinity of the deep SCS clay were direct consequences of the EASM intensity varying in precession rhythm and modulated by eccentricity cycles. A high-resolution temporal framework constructed with onboard age controls and cyclostratigraphic analyses demonstrates that the pelagic reddish clay from Site U1433 was accumulated from 17.17 to 12.69 Ma. During this period, deep-sea sedimentation of the SCS was controlled by the EASM and influenced by the sea-level change. Importantly, clay mineral is proved to be an efficient terrigenous standard of astronomical tuning and stratigraphic correlation for pelagic sediments. It is also verified that the EASM intensified during the Miocene Climatic Optimum and the following Middle Miocene Climate Transition, and induced higher humidity and seasonality, respectively. Then, the EASM gradually weakened since the expansion of the East Antarctic Ice Sheet.

New Research of Borehole Wall Protection Technology in Ocean Scientific Drilling

Abstract In the process of ocean scientific drilling, borehole accidents (e.g., borehole collapse, burying of drill tools, and sticking of drill tools) are often caused by borehole wall instability in loose and broken strata. It is very difficult to deal with such accidents, and the drill pipe in the borehole has to be discarded in serious cases. Therefore, the stability of the borehole wall seriously affects the drilling quality and efficiency. At present, there are three effective methods of ensuring wellbore stability: casing, drilling fluid, and agent plugging technology. Casing can effectively prevent instability of all types of unstable formations and can isolate different pressure zones. Using the proper drilling fluid can control drilling fluid loss, reduce free water infiltration into the borehole wall, and form a thin and dense mud skin, which is conducive to the stability of the borehole wall. Agent plugging technology, especially chemical gels, is mainly aimed at the broken zone. After entering the formation, it makes the entire broken zone form a single high strength unit, improves the cementation ability of the lost formation, and improves the sealing and bearing capacity in order to achieve the purpose of sealing and plugging of leaks. In this paper, the present situation, technical principles, and technological processes of wall protection technology in ocean scientific drilling are summarized, and the different types of wall protection technology were researched and tested. The results of this study provide a reference for international ocean scientific drilling in the future.

The Extending Ocean Drilling Pursuits (eODP) Project: Synthesizing Scientific Ocean Drilling Data

AbstractFor over 50 years, cores recovered from ocean basins have generated fossil, lithologic, and chemical archives that have revolutionized fields within the earth sciences. Although scientific ocean drilling (SOD) data are openly available following each expedition, the formats for these data are heterogeneous. Furthermore, lithological, chronological, and paleobiological data are typically separated into different repositories, limiting researchers' abilities to discover and analyze integrated SOD data sets. Emphasis within Earth Sciences on Findable, Accessible, Interoperable, and Reusable (FAIR) Data Principles and the establishment of community‐led databases provide a pathway to unite SOD data and further harness the scientific potential of the investments made in offshore drilling. Here, we describe a workflow for compiling, cleaning, and standardizing key SOD records, and importing them into the Paleobiology Database and Macrostrat, systems with versatile, open data distribution mechanisms. These efforts are being carried out by the extending Ocean Drilling Pursuits (eODP) project. eODP has processed all of the lithological, chronological, and paleobiological data from one SOD repository, along with numerous other data sets that were never deposited in a database; these were manually transcribed from original reports. This compiled data set contains over 79,899 lithological units from 1,125 drilling holes from 422 sites. Over 26,000 fossil‐bearing samples, with 5,378 taxonomic entries from 13 biological groups, are placed within this lithologic spatiotemporal framework. All information is available via GitHub and Macrostrat's application programming interface, which renders data retrievable by a variety of parameters, including age, site, and lithology.

Incompatibility between serpentinization and epidote formation in the lower oceanic crust: Evidence from the Oman Drilling Project

AbstractIt is a general tendency that epidote, which is a typical greenschist facies mineral, is scarce in the lower oceanic crust, in spite of the widespread occurrence of the other minerals indicative of similar temperature conditions such as chlorite, actinolite, prehnite and serpentine. To find the cause of this, we carried out petrological analyses of lower crustal rocks of the Oman ophiolite sampled by the Oman Drilling Project of the International Continental Scientific Drilling Program (ICDP). Petrographic observations revealed the tendency, as expected, that the amount of epidote formed by static alteration of plagioclase decreases with depth. Because mineral assemblages indicative of a wide range of temperature conditions from amphibolite to subgreenschist facies occur throughout the cores without systematic variations of abundance, the decrease of epidote amount cannot be explained by the difference of temperature condition of alteration. Petrographic observations also revealed that epidote is absent or rare in rocks containing serpentinized olivine in contrast to prehnite showing a close association with serpentinization of olivine. In an exceptional sample containing both epidote and serpentinized olivine, epidote occurs with chlorite that cuts or replaces plagioclase, mantles adjacent olivine and is connected with chlorite + lizardite veins cutting mesh‐forming serpentine veins. The distribution and mode of occurrence of epidote suggest decoupling of its formation with the main stage of serpentinization. Serpentine veins cutting olivine to form mesh texture are typically lizardite with magnetite ribbons at vein centres and have compositions of lizardite–cronstedtite solid solution at vein margins or in magnetite‐free veins, suggesting a chemical condition with low silica and low oxygen potentials at an early stage of serpentinization. Thermodynamic modelling for olivine and plagioclase alteration at greenschist facies conditions indicates that silica potential for plagioclase alteration to form prehnite + chlorite and epidote + chlorite could be higher than for olivine serpentinization. On the other hand, oxygen potential for the prehnite + chlorite formation is lower than for the epidote + chlorite formation and is comparable with that for olivine serpentinization. From the observations and analyses, it is concluded that epidote formation is inhibited by olivine serpentinization, which maintains a reducing condition for alteration in the lower oceanic crust.

Carbon released by sill intrusion into young sediments measured through scientific drilling

AbstractThe intrusion of igneous sills into organic-rich sediments accompanies the emplacement of igneous provinces, continental rifting, and sedimented seafloor spreading. Heat from intruding sills in these settings alters sedimentary organic carbon, releasing methane and other gasses. Recent studies hypothesize that carbon released by this mechanism impacts global climate, particularly during large igneous province emplacements. However, the direct impacts of sill intrusion, including carbon release, remain insufficiently quantified. Here, we present results from International Ocean Discovery Program (IODP) Expedition 385 comparing drill-core and wireline measurements from correlative sedimentary strata at adjacent sites cored in Guaymas Basin, Gulf of California, one altered by a recently intruded sill and one unaffected. We estimate 3.30 Mt of carbon were released due to this sill intrusion, representing an order of magnitude less carbon than inferences from outcrops and modeling would predict. This attenuated carbon release can be attributed to shallow intrusion and the high heat capacity of young, high-porosity sediments. Shallow intrusion also impacts sub-seafloor carbon cycling by disrupting advective fluxes, and it compacts underlying sediments, increasing potential carbon release in response to subsequent intrusions.

Melting of fault gouge at shallow depth during the 2008 MW 7.9 Wenchuan earthquake, China

AbstractTypical rocks at shallow depths of seismogenic faults are fluid-rich gouges. During earthquakes, on-fault frictional heating may trigger thermal pressurization and dynamic fault weakening. We show that frictional melting, rather than thermal pressurization, occurred at shallow depths during the 2008 MW 7.9 Wenchuan earthquake, China. One year after the Wenchuan earthquake, we found an ~2-mm-thick, glass-bearing pseudotachylyte (solidified frictional melt) in the fault gouges retrieved at 732.6 m depth from the first borehole of the Wenchuan Earthquake Fault Scientific Drilling Project. The matrix of pseudotachylyte is enriched in barium and cut by barite-bearing veins, which provide evidence of co- and postseismic fluid percolation. Because pseudotachylyte can be rapidly altered in the presence of percolating fluids, its preservation suggests that gouge melting occurred in a recent large earthquake, possibly the Wenchuan earthquake. Rock friction experiments on fluid-rich fault gouges deformed at conditions expected for seismic slip at borehole depths showed the generation of pseudotachylytes. This result, along with the presence of a second slip zone attributed to the Wenchuan earthquake at 589.2 m depth, implies that during large earthquakes, frictional melting can occur at shallow depths and that seismic slip can be accommodated by multiple faults. This conclusion is consistent with the evidence from surface faulting that multiple ruptures propagated during the Wenchuan earthquake.

Shallow structure of the Northern Chilean marine forearc between 19°S - 21°S using multichannel seismic reflection and refraction data

Seismic investigations and scientific ocean drilling projects have documented a remarkable degree of geologic heterogeneity in marine forearc basins in convergent margins worldwide. The mechanisms for offshore basin formation and evolution are, however, often not completely understood, especially for erosive margins. This study integrates high-resolution bathymetry, seismic reflection lines, and refraction-based P-wave velocities to better understand the shallow structure of the northern Chilean erosive convergent margin between 19° and 21°S. The data resolve a regionally developed forearc basin, which contains the previously recognized upper slope-shelf Iquique Basin, and which reaches a maximum depth along the middle slope, containing up to 2 km of accumulated sediments. The basin geometry appears to be tectonically controlled by major north-south oriented crustal faults, which (to first order) govern the morphology and shallow structure of the marine forearc. We propose subsidence due to enhanced subduction erosion by high relief/seamount subduction as a mechanism for basin formation. Spatial correlation between the forearc basin and the highest slip area for the Iquique earthquake highlight the relevance of future studies to understand the relationship between the shallow structure of the marine forearc and the processes occurring on the subduction interface.

Evaluating geophysical logs as proxies for cyclostratigraphy in lacustrine deposits using power ratio accumulation

Using a single insensitive proxy in cyclostratigraphy may lead to misleading conclusions regarding timescale, paleoenvironment, paleoclimate and orbital behavior. How to obtain the most reliable one from multiple solutions of geophysical log proxies without time constraints is still an outstanding problem. Here, we develop a new method (power ratio accumulation, or PRA) combining power decomposition and null hypothesis of no astronomical forcing with the Monte Carlo simulation. This method obtains both optimal sedimentation rate and optimal proxy from multiple untuned proxy datasets. The sensitivity of multiple geophysical log proxies in lacustrine deposits is first revealed from member 1 of Nenjiang Fm of Cretaceous Continental Scientific Drilling in the Songliao Basin using this method. The results show that the optimal proxy is thorium content, followed by potassium content, uranium content and natural gamma-ray intensity, while total organic carbon content, resistivity, interval transit time and density are the worst. Evidence of phase reversal of proxies caused by the joint influence of astronomically forced weathering, water level and burial of biogenic materials is found. This supports a new mechanism that explains the sensitivity of geophysical log proxies from the perspective of phase stability. Our research not only provides a powerful tool (PRA method) for astrochronologic testing and sensitivity evaluation of multiple untuned proxy datasets, but also builds a bridge (new mechanism) between geophysical parameters and astronomically forced cycles. This will promote the application of geophysical data in the field of cyclostratigraphy.

Pore Connectivity of Deep Lacustrine Shale and Its Effect on Gas‐bearing Characteristics in the Songliao Basin: Implications from Continental Scientific Drilling

AbstractThe lacustrine shale of deep Shahezi formation in the Songliao basin has great gas potential, but its pore evolution, heterogeneity, and connectivity characteristics remain unclear. In this work, total organic carbon analysis, rock pyrolysis, X‐ray diffraction, field emission scanning electron microscopy, the particle and crack analysis system software, low‐temperature nitrogen adsorption experiment, fractal theory, high‐pressure mercury injection experiment and nuclear magnetic resonance experiment were used to study the Shahezi shale from Well SK‐2. The result indicated that the organic pores in Shahezi shale are not developed, and the intergranular and intragranular pores are mainly formed by illite‐dominated clay. As the burial depth increases, the pore size and slit‐shaped pores formed by clay decrease, and dissolved pores in the feldspar and carbonate minerals and dissolved fractures in the quartz increase. The pore evolution is affected by clay, compaction, and high‐temperature corrosion. Based on the pore structure characteristics reflected by the pore size distribution and pore structure parameters obtained by multiple experimental methods, the pore development and evolution are divided into three stages. During stage I and II, the pore heterogeneity of the shale reservoirs increases with the depth, the physical properties and pore connectivity deteriorate, but the gas‐bearing property is good. In stage III, the pore heterogeneity is the highest, its gas generation and storage capacity are low, but the increase of micro‐fractures makes pore connectivity and gas‐bearing better.

CAGE22-5 Cruise Report: High-resolution 2D and 3D seismic investigations on the Vøring Margin

The overall goal of this expedition was the acquisition of geophysical data on the Vøring Plateau and the southernmost part of the Lofoten Basin to improve the understanding of the subsurface structures and geological processes at four sites (U1571-U1574) where scientific drilling was recently successfully completed as a part of the the International Ocean Discovery Program (IODP) Expedition 396
 The cruise may be known as: CAGE22_5

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.

Mediterranean–Black Sea gateway exchange: scientific drilling workshop on the BlackGate project

Abstract. The MagellanPlus workshop “BlackGate” addressed fundamental questions concerning the dynamic evolution of the Mediterranean–Black Sea (MBS) gateway and its palaeoenvironmental consequences. This gateway drives the Miocene–Quaternary circulation patterns in the Black Sea and governs its present status as the world's largest example of marine anoxia. The exchange history of the MBS gateway is poorly constrained because continuous Pliocene–Quaternary deposits are not exposed on land adjacent to the Black Sea or northern Aegean. Gateway exchange is controlled by climatic (glacio-eustatic-driven sea-level fluctuations) and tectonic processes in the catchment as well as tectonic propagation of the North Anatolian Fault Zone (NAFZ) in the gateway area itself. Changes in connectivity trigger dramatic palaeoenvironmental and biotic turnovers in both the Black Sea and Mediterranean domains. Drilling a Messinian to Holocene transect across the MBS gateway will recover high-amplitude records of continent-scale hydrological changes during glacial–interglacial cycles and allow us to reconstruct marine and freshwater fluxes, biological turnover events, deep biospheric processes, subsurface gradients in primary sedimentary properties, patterns and processes controlling anoxia, chemical perturbations and carbon cycling, growth and propagation of the NAFZ, the timing of land bridges for Africa and/or Asia–Europe mammal migration, and the presence or absence of water exchange during the Messinian salinity crisis. During thorough discussions at the workshop, three key sites were selected for potential drilling using a mission-specific platform (MSP): one on the Turkish margin of the Black Sea (Arkhangelsky Ridge, 400 m b.s.f., metres below the seafloor), one on the southern margin of the Sea of Marmara (North İmrali Basin, 750 m b.s.f.), and one in the Aegean (North Aegean Trough, 650 m b.s.f.). All sites target Quaternary oxic–anoxic marl–sapropel cycles. Plans include recovery of Pliocene lacustrine sediments and mixed marine–brackish Miocene sediments from the Black Sea and the Aegean. MSP drilling is required because the JOIDES Resolution cannot pass under the Bosporus bridges. The wider goals are in line with the aims and scope of the International Ocean Discovery Program (IODP) “2050 Science Framework: Exploring Earth by Scientific Ocean Drilling” and relate specifically to the strategic objectives “Earth's climate system”, “Tipping points in Earth's history”, and “Natural hazards impacting society”.

Evaluation of Hydrocarbon Generation Potential of Laiyang Formation Source Rocks in Ri-Qing-Wei Basin, Eastern Shandong

The Ri-Qing-Wei Basin is a newly discovered Late Mesozoic rift basin on the eastern Shandong coast in recent years. Thick, continuous deposited source rocks are found in the Lingshan Island scientific drilling project. Therefore, it is necessary to evaluate the distribution and hydrocarbon generation potential of source rocks in this area. Organic geochemical experiments were carried out on samples from the core of LK-1 and outcrops in the Lingshan Island, the Laoshan area, and the Jimo Zhougezhuang area to evaluate the maturity, abundance, and type of organic matter in source rocks. The results show that the cumulative thickness of the source rocks in the study area is more than 500 m, and the TOC content is generally greater than 1.0%. The organic matter type is good (mainly type II1 and type II2 kerogen) and the Ro value is more than 2.0. The thermal evolution degree of the organic matter is high with natural gas predominantly generated. We carried out Rock-Eval, PY-GC and gold tube experiments on low-maturity samples of Laikong 2 and established a chemical kinetic model to quantitatively evaluate the study area in combination with sedimentary burial history and thermal history data. The results show that the total resources of the five sags in the study area are about 476 billion cubic meters, and the average resource intensity is about 82.2 million cubic meters/km2. Among them, the resource intensities of the Lingshan Island Sag and Laoshan Sag are 112.6 million cubic meters/km2 and 98.8 million cubic meters/km2, respectively. Studied sites are “small and fertile” and may be used as favorable exploration prospect areas.

Accumulation mechanism of natural gas hydrate in the Qilian Mountain permafrost, Qinghai, China

Qilian Mountain is the only permafrost area in China where natural gas hydrates have been obtained through scientific drilling. Many studies have been performed on natural gas hydrates in permafrost regions from the perspectives of sedimentology and petroleum geochemistry, especially on reservoir forming conditions and exploration methods. However, there are still more divergences in its evolutionary process, time, and accumulation mechanism. In this study, a total of 500 core samples were collected in the gas hydrate drilling wells DK-8, DK13-11, and DK12-13 in the Qilian Mountain permafrost. Gas components, carbon isotopes of methane, total organic carbon (TOC), chloroform bitumen “A,” concentrations of kerogen element, and vitrinite reflectance (Ro) are analyzed. The results show that the hydrocarbon source rocks in the Middle Jurassic Muli formation and the Upper Triassic Galedesi formation are good source rocks, with good total organic carbon content and chloroform bitumen “A.” The rocks of Muli formation are at the mature stage of organic matters, and the organic matter types are mainly Ⅱ1 and Ⅱ2 and the peak of generating crude oil with immense petroleum-associated gas. Also, the rocks of the Galedesi formation are in a highly mature stage, producing more gas and offering efficient gas for the natural gas hydrate, and the organic matter types are mainly Ⅲ and Ⅱ1. Laboratory experiments and numerical analysis indicate that the formation of natural gas hydrates in the Qilian Mountain has experienced three phases: gas migration and aggregation in the Late Jurassic to Early Cretaceous, overall uplift in the Middle and Late Miocene to Pliocene, and free gas to natural gas hydrate deposits in the Quaternary. The experimental results show that gas sources, permafrost thickness, and structural conditions played a key role in controlling the occurrence and distribution of gas hydrates.

Fault associated with the 1967 M 6.3 Koyna earthquake, India: A review of recent studies and perspectives for further probing

The Koyna region in western India, characterized by recurrent seismic activity over more than five decades and confined largely within a 20 km × 30 km area and ∼10 km in depth, is a classical site to study earthquake processes. The largest earthquake in the region, the M 6.3 Koyna earthquake of December 1967, formed a ∼NNE-SSW trending surface rupture, known as Donichawadi fissure zone. The fissure zone, mapped originally over a length of ∼4 km and width of ∼200 m between Nanel and Kadoli by the Geological Survey of India (GSI) in the wake of the earthquake, comprises en-echelon fractures, near-vertical fissures, oblique or diagonal tensional cracks, mole tracks, soil lumps and laterite boulders in paddy cultivated land. We review the Donichawadi fissure zone in the light of extensive seismological data acquired in the past five decades, surface mapping studies, recent geophysical studies, soil-gas helium studies over the fissure zone during 1996–1997, chemical and noble gas isotope compositions of formation gases, and subsurface fracture data from downhole image logs in a 3 km - deep scientific borehole drilled in 2017. Integration of the datasets provide clinching evidence that the Donichawadi fissure zone is the surface manifestation of a deeper crustal fault (referred as Donichawadi fault) that has been active for more than 55 years and yield critical new insights on the geometry, distribution and possible subsurface disposition of the fissures and the associated fractures in the subsurface. We conclude that the Donichawadi fault offers a potential target for further deep probing through scientific drilling, downhole measurements and long-term monitoring to gain new insights into the genesis of triggered earthquakes in the area.

Logging evaluation of deep multi-type unconventional gas reservoirs in the Songliao basin, northeast China: Implications from continental scientific drilling

Multi-type unconventional gas-bearing reservoirs with different lithologies and gas accumulation potential occur in the deep part of the Songliao basin. However, the reservoirs are non-homogeneous, the gas components differ substantially, and not all types of gas-bearing reservoirs have been identified or evaluated. The International Continental Scientific Drilling Program (ICDP) is used as an example to conduct qualitative and quantitative evaluations of deep multi-type unconventional gas-bearing reservoirs using conventional and specialized logging data. The core test data are used to determine the physical properties. The porosity and permeability are compared and analyzed using different methods and models. The results show that the reservoirs have low to ultra-low porosity and ultra-low permeability. Based on the comparison of the rock mechanical parameters and mineral composition, brittleness evaluation parameters are proposed for different types of deep reservoirs in the study region. The mineral brittleness index is highly consistent with the brittleness index based on rock mechanics. An identification method for deep multi-type gas-bearing reservoir and a classification approach for different gas properties are established based on the logging response and parameter interpretation. The methane gas reservoirs have low density (DEN) and low compensated neutron logging (CNL) values and high acoustic (AC) time difference and high resistivity (RT) values. The CO2 gas reservoirs have lower RT values and higher CNL values than the hydrocarbon gas reservoirs. The comprehensive analysis of deep gas source rock conditions and of the source-reservoir relationship provides insights for the evaluation of deep multi-type unconventional gas reservoirs. The discovery of high hydrogen content is of significant importance for developing new areas for deep natural gas exploration.

In Pursuit of Understanding, a Career in Marine Geology

AbstractMy interest in the oceans first developed when I was a teenager, but I did not actually go to sea until I was in the U.S. Navy. With that experience, I developed a love of the oceans and an interest in oceanography. My graduate training was a time when oceanography and marine geology were blossoming with new ideas and new tools to explore the ocean world. The theory of plate tectonics was becoming widely accepted and scientific ocean drilling was just starting. My thesis study area was in the tropical Pacific. Soon after receiving my PhD, I sailed on Deep Sea Drilling Project Leg 8, which drilled the first transect across the Pacific equator. The nature of the sediments there posed many scientific questions that continued to intrigue me. Some of these questions remained unanswered for a long time. Early in my career I was fortunate to work with a group of specialists from outside my field of expertise to study the global climate during the last glacial maximum (the CLIMAP Project). Subsequently, I spent 8 years working in the oil industry. This experience taught me the skills of interpreting seismic reflection records that help unravel the history of sediment deposition. When I returned to academia, these skills proved particularly useful in studies of large lakes. Late in my career, I returned to studies of the tropical Pacific, where new tools and techniques helped answer some of my unanswered questions.

Characteristics of Fault Rocks Within the Aftershock Cloud of the 2014 Orkney Earthquake (M5.5) Beneath the Moab Khotsong Gold Mine, South Africa

AbstractCores recovered during the International Continental Scientific Drilling Program project “Drilling into Seismogenic zones of M2.0 to M5.5 earthquakes in deep South African Gold Mines” include fault breccia from within the aftershock cloud of the 2014 Orkney earthquake (M5.5). The breccia and surrounding intrusive rocks, probably lamprophyres rich in talc, biotite, calcite, and amphibole, had high magnetic susceptibilities owing to the presence of magnetite. All of these characteristics can be attributed to fluid‐related alteration. Both the breccia and the lamprophyres had low friction coefficients and showed evidence of velocity strengthening, which is inconsistent with the occurrence of earthquakes. Variable amounts of talc, biotite, calcite, and amphibole within the lamprophyres might have produced complex frictional properties and spatial heterogeneity of fault stability. The altered lamprophyres may be the host rocks of the 2014 Orkney earthquake, but frictional complexity may have governed the magnitudes of the main‐ and aftershocks and their distributions.