Drilling Program Research Articles

Investigation of Virtual Bimrocks to Estimate 3D Volumetric Block Proportions from 1D Boring Measurements

Serious deficiencies in ground characterization, analysis and design at engineering works can occur when working with bimrocks (block-in-matrix rocks) and bimsoils (block-in-matrix soils). Since the 1990s, serious technical problems at engineering works performed in bimrocks/bimsoils spurred practical research, which revealed that the behavior of these geomaterials is directly related to the volumetric block proportions (VBPs). However, the way that VBPs can be confidently and correctly estimated remains an ongoing critical issue that still frustrates designers, contractors and owners. Stereological techniques can be applied to overcome this challenge by inferring 3D block contents from in situ 1D and 2D measurements, but the estimates have often been demonstrated to be erroneous. This paper presents findings from a computer-aided reinvestigation, revalidation and extension of Medley’s work of 1997 and subsequent researchers to provide approachable yet statistically robust methods to limit the uncertainty associated with estimates of 3D VBPs generated from 1D boring/scanline measurements. To this aim, a specialized Matlab code was created and virtual drilling programs were performed through 3D computer-generated bimrock models. Supported by extensive statistical-based investigations, a design chart is provided that updates and extends Medley’s 1999 chart relating uncertainty in estimates of VBP as a function of total boring/scanline lengths.

Vertical distribution of excess ice in icy sediments and its statistical estimation from geotechnical data (Tuktoyaktuk Coastlands and Anderson Plain, Northwest Territories)

Excess ice, found as massive ice and within icy sediments, is an important variable to quantify as it is a dominant control on the terrain and geotechnical response to permafrost thaw. A large amount of permafrost borehole data are available from the Tuktoyaktuk Coastlands; however, field geotechnical assessments typically only involve the estimation of visible ice. To add significant value to these data sets, a cryostratigraphic data set collected along the Inuvik–Tuktoyaktuk Highway (566 boreholes) is used to develop a beta regression model which predicts the excess ice content of icy sediments based on interval depth, visible ice content, material type, and Quaternary deposits. The resulting predictions are compared to recorded massive ice intervals and show that ground ice within icy sediments can contribute up to 65% of the excess ice and potential thaw strain within the first 10 m from the surface in this area. This study shows the general applicability of this approach and indicates that comparable, quantitative data on ground ice conditions should be collected with drilling programs to derive geotechnical variables and reduce modelling uncertainties so that ground ice data are available for quantitative analysis.

The first appearance of Glacial North Atlantic Intermediate Water (GNAIW) during the Mid-Pleistocene transition

The Mid-Pleistocene Transition (MPT) is arguably the most prominent shift in the Earth's climate system during the entire Pleistocene. It is characterized by a shift from a ∼ 40 kyr to a ∼ 100 kyr glacial cyclicity, going in hand with considerable growth of glacial continental ice-sheets. In search for potential drivers of these changes in the cryosphere, a slow-down of deep ocean circulation has been proposed as an important factor that might have reduced the atmospheric pCO2 level and thus created boundary conditions favourable for pertaining large ice-sheets. Additionally, as argued for the Last Glacial Maximum, enhanced production of intermediate waters might enhance intermediate to deep oceanic stratification and thus suppress CO2 release from the deep ocean and thereby reduce atmospheric greenhouse gas concentrations. To investigate potential changes in the North Atlantic intermediate water-mass configuration across the MPT we utilize δ18O and δ13C records obtained on the deep thermocline-dwelling foraminifera Globorotalia crassaformis from mid-latitude International Ocean Discovery Program (IODP) Site U1313. In conjunction with benthic and planktic δ18O and δ13C data from reference sites for Labrador Sea Water (IODP Site U1305) and intermediate water formation in the north-eastern North Atlantic (Ocean Drilling Program Site 982) our data show that major changes in the production and dispersal of intermediate water masses took place across the MPT. In particular, we note a shoaling of glacial intermediate waters commencing with Marine Isotope Stage (MIS) 22, which we interpret as the first occurrence of Glacial North Atlantic Intermediate Water, a prominent constituent of Late Pleistocene glacial water masses in the Atlantic Ocean. We further infer that the amount and vertical position of the warm and saline Mediterranean Outflow Water (MOW) had a major impact on the spatial configuration of North Atlantic intermediate water masses during the MPT, due to its capacity to modulate subsurface heat transport and isopycnal configuration. Our new findings thus provide evidence for a so far underestimated role of intermediate water circulation in shaping oceanic and potentially atmospheric changes during the MPT.

New evidences of subaerial volcanism as a trigger for the Kilian event (Aptian-Albian transition) and major climatic changes from offshore Morocco (DSDP Site 545)

The Aptian-Albian transition is characterized by the presence of four organic-rich intervals all linked with major disturbances of the carbon cycle. Among these, the second subevent of the oceanic anoxic event (OAE) 1b, also called Kilian event, has an Aptian-Albian transition age and is characterized by a negative carbon isotope excursion. On the contrary of the Paquier OAE1b subevent, the Kilian event was not extensively studied and its triggering mechanisms and its consequences on regional climates remain uncertain. Here we present a geochemical (Rock-Eval, Mercury) and mineralogical (clay minerals) study on late Aptian-early Albian sediment cores from the Deep-Sea Drilling Program (DSDP) Site 545 (offshore Morocco, Eastern North Atlantic) where a Kilian level equivalent is present. Mercury (Hg) content results show two main peaks in the late Aptian, immediately below and above the Kilian level equivalent. The absence of correlations between Hg and total organic carbon and Hg and CaCO 3 indicates that the mercury content is mainly related to subaerial volcanic activity, probably issued from the emplacement of the Kerguelen large igneous province in the Indian Ocean. Mineralogical analyses show that the clay content, in our studied interval, mainly reflect the weathering and climatic conditions in Northwest Africa. The evolution in clay mineral assemblages depicts three distinctive climatic intervals: (i) a seasonally contrasted semi-arid climate below the first Hg anomaly; (ii) a moister and warmer climate during the Kilian level equivalent deposition; and (iii) a rapid transition toward more arid climate post Kilian level equivalent deposition that is linked with the second Hg anomaly (large increases in illite and palygorskite). Therefore, our study confirms that the Kerguelen volcanic activity was probably the trigger of the Kilian event and shows that the resulting changes in the carbon cycle caused two major climate changes before and after the Kilian event and a long term aridification of Northwest Africa. • Hg anomalies occurs immediately below and above the Kilian level. • Kerguelen volcanic activity was likely the trigger of the Kilian event • Three distinct climatic periods can be recognized along the late Aptian. • late Aptian represents a turning point for the Cretaceous climate changes.

Coccolithophore paleoproductivity since the Last Glacial Maximum in the Atlantic Ocean: Relationship with calcification and preservation variability

Paleoproductivity, calcification and preservation patterns are presented from calcareous nannoplankton paleo-assemblages records covering the last ∼25 kyr retrieved from Integrated Ocean Drilling Program Sites U1385 (37°34.285′N; 10°7.562′W) and U1313 (41°0.0′N; 32°57.4′W), located respectively along the Western Iberian Margin and in the North Atlantic Ocean. The main aim of the study is to provide paleoceanographic and paleoclimatic analyses together with an investigation of changes in coccolithophore calcification processes occurring in response to climate variability from the Last Glacial Maximum up to the Holocene. Coccolithophore calcification was investigated by comparing variations in coccolith thickness and total coccolith calcite; at the same time dissolution/preservation indices were used to better understand the response of coccolithophores to changes in environmental parameters.In general, the increasing CO2 recorded during the last 25 kyr has a negative effect on calcification, resulting in a reduction of the different species size-normalized thicknesses at both sites. However, differences between the responses at the two latitudes studied are identified, in particular during the Heinrich Stadials; in contrast, during both Younger Dryas and Holocene intervals, the different size-normalized species thicknesses show consistent patterns at the two sites. During the Last Glacial Maximum the influence of subtropical waters due to Azores Current recirculation leads to a moderate productivity, initially at Site U1385 and later at Site U1313. At the same time, temperature influences the calcification at both sites. At Site U1385, the temperature is the main parameter affecting the paleoproductivity during Heinrich Stadial events; in addition, during Heinrich Stadial 1 alone, it also affects the calcification. At Site U1313 the calcification processes during Heinrich Stadial events are apparently hampered by an increasing water turbidity, caused by icebergs acting as ice rafted debris transporters, which affects light filtration in the water column. Light availability is an important calcification-influencing factor. At Site U1313 during Heinrich Stadial 1 and at the Last Glacial Maximum inception, dissolution, a consequence of increased CO2 solubility in the colder ice-age ocean, has a negative influence on calcification. Furthermore, at Site U1313, in contrast to Site U1385, the continually increasing CO2 concentration recorded during the Bølling-Allerød hampers both calcification and preservation.

The Use of Seismic Attributes and Well Logs in Delineating Kick Horizon; A Case Study of Nova Well, Niger Delta Basin, Nigeria

Predrill pore pressure prediction of the NOVA well suggested that the drilling program was in agreement with available seismic surveys. However, a kick was encountered while during the well. The study was carried out to ascertain the cause of the kick horizon in the NOVA Well, using seismic attributes and well log. Eight stratigraphic horizons were characterized to describe the amplitude variations. The top and base of the kick horizon were picked and sculptured to create sub-volume maps.The results revealed that the kick horizon was a shaly unit. The kick horizon was far off bright amplitudes that could have delivered high pressure which could trigger a kick. Faulting, shallow water and gas flows have been suggested as possible causes of the kick. A kill weight mud should be factored into the drilling operations to produce hydrostatic pressure where the kick is entering the NOVA well in order to prevent a blow out.

Sampling across large-scale geological gradients to study geosphere-biosphere interactions.

Despite being one of the largest microbial ecosystems on Earth, many basic open questions remain about how life exists and thrives in the deep subsurface biosphere. Much of this ambiguity is due to the fact that it is exceedingly difficult and often prohibitively expensive to directly sample the deep subsurface, requiring elaborate drilling programs or access to deep mines. We propose a sampling approach which involves collection of a large suite of geological, geochemical, and biological data from numerous deeply-sourced seeps-including lower temperature sites-over large spatial scales. This enables research into interactions between the geosphere and the biosphere, expanding the classical local approach to regional or even planetary scales. Understanding the interplay between geology, geochemistry and biology on such scales is essential for building subsurface ecosystem models and extrapolating the ecological and biogeochemical roles of subsurface microbes beyond single site interpretations. This approach has been used successfully across the Central and South American Convergent Margins, and can be applied more broadly to other types of geological regions (i.e., rifting, intraplate volcanic, and hydrothermal settings). Working across geological spatial scales inherently encompasses broad temporal scales (e.g., millions of years of volatile cycling across a convergent margin), providing access to a framework for interpreting evolution and ecosystem functions through deep time and space. We propose that tectonic interactions are fundamental to maintaining planetary habitability through feedbacks that stabilize the ecosphere, and deep biosphere studies are fundamental to understanding geo-bio feedbacks on these processes on a global scale.

A channel sampling strategy for measurement of mineral modal and chemical composition of drill cores: application to lower oceanic crustal rocks from IODP Expedition 345 to the Hess Deep rift

Abstract. We report a new sampling strategy for collecting representative samples of drill core. By splitting the core with a diamond saw into working and archive halves, the saw cuttings constitute a “channel” sample, the best subsample from which to obtain an average mineralogical and geochemical composition of a core. We apply this procedure to sampling core of the lower oceanic crust in the Hess Deep obtained during Expedition 345 of the Integrated Ocean Drilling Program (now International Ocean Discovery Program). Our results show that particles produced by sawing range from sand to clay sizes. Sand- and silt-sized cuttings can be sampled with a spatula, whereas clay-sized particles remained in suspension after 12 h and could be collected only by settling, aided by centrifuge. X-ray diffraction (XRD) analysis and Rietveld refinement show that phyllosilicates were fractionated into the clay-sized fraction. Thus, collection of both the sedimented fraction and the clay-sized suspended fraction (commonly > 15 wt % of the total) is necessary to capture the whole sample. The strong positive correlation between the recovered sample mass (in grams) and length of core cut demonstrates that this sampling protocol was uniform and systematic, with almost 1.4 g sediment produced per centimeter of core cut. We show that major-element concentrations of our channel samples compare favorably with the compositions of billet-sized samples analyzed aboard the JOIDES Resolution, but the results show that individual billet analyses are rarely representative of the whole core recovered. A final test of the validity of our methods comes from the strong positive correlation between the loss on ignition (LOI) values of our channel samples and the H2O contents calculated from the modal mineralogy obtained by X-ray diffraction and Rietveld refinement. This sampling procedure shows that grain-sized fractionation modifies both mineralogical and chemical compositions; nevertheless, this channel sampling method is a reliable method of obtaining representative samples of bulk cores. With the ever-increasing precision offered by modern analytical instrumentation, this sampling protocol allows the accuracy of the analytical results to keep pace.

Progress in understanding middle Eocene nassellarian (Radiolaria, Polycystinea) diversity; new insights from the western equatorial Atlantic Ocean

AbstractMiddle Eocene deep-sea sediment sequences cored at Ocean Drilling Program Site 1260 (Leg 207; equatorial Atlantic Ocean) yielded diverse and abundant radiolarian faunas that are conducive to biostratigraphic and palaeoceanographic research, as well as to the study of radiolarian diversity dynamics during this epoch of significant climate changes. However, many species present in these sediments still have not been formally described and are therefore neglected in most biodiversity surveys. In an effort to improve the taxonomic resolution of middle Eocene radiolarians, 15 new species of nassellarians are described and illustrated. The species are: Cymaetron? dilatatus n. sp., Eucyrtidium levisaltatrix n. sp. (Eucyrtidiidae), Siphocampe pollen n. sp., Spirocyrtis? renaudiei n. sp. (Artostrobiidae), Pterocyrtidium eep n. sp. (Rhopalosyringiidae), Petalospyris cometa n. sp., Petalospyris castanea n. sp. (Cephalospyrididae), Velicucullus armatus n. sp. (Theophormididae), Lychnocanium nimrodi n. sp. (Lithochytrididae), Aphetocyrtis zamenhofi n. sp., Aphetocyrtis? columboi n. sp., Aphetocyrtis? spheniscus n. sp. (Lophocyrtiidae), Albatrossidium regis n. sp., Albatrossidium annikasanfilippoae n. sp., and Phormocyrtis lazari n. sp. (Pterocorythidae). Stratigraphic range data are provided for each new species, as well as the orbitally tuned ages for their first and last occurrences. In addition to these new species, we also illustrate and document the stratigraphic distribution of four species described in early radiolarian studies and rarely reported since.UUID: http://zoobank.org/b5993e6b-659b-4220-80c2-c6ddccc13793

Structural - tectonic update of the central Vietnam margin based on analysis of the merged gravity - magnetic and regional seismic data

The central Vietnam margin is part of the western continental margin of the Vietnamese East Sea - the transition zone from the Indochina continental block to the true oceanic crust. In this paper, the authors present new results from merging and interpreting gravity and magnetic data from different sources in combination with 2D seismic and Ocean Drilling Program well data for the central Vietnam margin.The results illustrate the reliability of the merged gravity - magnetic data in regional structural analysis and tectonic division. Five structural layers are vertically identified and characterised by density and thickness. Spatially, six tectonic zones are defined with different Bourguer and magnetic anomaly background values: the boundaries between these zones are clearly delineated by sudden changes of these values. In addition, development signs and extent of the Tuy Hoa Shear Zone on basement rocks are also better resolved compared to the earlier seismic data.

Application of Volume Uncertainty for Resource Classification: A Case Study on the Rondon Do Pará Bauxite Deposit, Brazil

This study illustrates the application of conditional simulations to calculate the uncertainty associated with the thickness of bauxite ores. The bauxite deposit of Rondon do Pará in northern Pará State, Brazil, is characterized by a well-defined lateritic profile, with the ore being composed of two sequential horizons: massive bauxite and ferruginous bauxite. This study used ore thickness data from 1.005 drillholes with different grid spacing. Drillhole intervals of both types of bauxite ore were accumulated, converting the database from 3D to 2D. Sequential Gaussian simulation produced probability maps calculated from certain confidence intervals, which permits obtaining the uncertainty associated with estimates in thickness. Results show that in portions with the same regular drillhole spacing there are different ranges of uncertainty and variability, which could be useful to support resource classification, associating different confidence intervals to resource classes. This analysis could also guide the drilling program for resource conversion in order to optimize costs, indicating areas where there is greater uncertainty and would need to be densified. The incorporation of this information into the resource model could be very helpful for supporting subsequent studies of economic evaluation and risk analyses with respect to this type of deposit or similarly in mineral exploration.

Orbital phasing of the Paleocene-Eocene Thermal Maximum

Paleocene-Eocene sedimentary archives record a series of global warming events called hyperthermals. These events occurred across a long-term increasing temperature trend and were associated with light carbon injections that produced carbon isotope excursions (CIEs). Early Eocene hyperthermals occurred close to both long (∼405 kyr) and short (∼100 kyr) eccentricity maxima. It has been proposed that under long-term global warming, orbital forcing of climate crossed a thermodynamic threshold that destabilized carbon reservoirs and produced Early Eocene hyperthermals. However, orbital control on triggering of the largest hyperthermal, the Paleocene-Eocene Thermal Maximum (PETM), remains unclear. Identification of the precise orbital phasing of the PETM has been hindered by extensive calcium carbonate (CaCO3) dissolution, which introduces uncertainty into PETM age models. Here, we report orbital signatures in marine sediments from Contessa Road (Italy), a western Tethyan section with reduced PETM CaCO3 dissolution compared to other deep ocean sites. Orbitally controlled lysocline depth adjustments and orbital phasing of the PETM CIE onset close to both long and short eccentricity maxima are documented here. Precession-based age models from the well-resolved PETM section of Ocean Drilling Program (ODP) Site 1262 (South Atlantic) confirm these results and reveal that the PETM CIE onset was partially triggered by an orbitally controlled mechanism. Climate processes associated with orbital forcing of both long and short eccentricity maxima played an important role in triggering the carbon cycle perturbations of all Paleocene-Eocene CIE events.

E&P Notes (October 2022)

E&P Notes (October 2022)

Plio-Pleistocene Planktic Foraminiferal Biochronology of ODP Site 762B, Exmouth Plateau, Southeast Indian Ocean

ABSTRACTThe Indonesian Throughflow region connects the tropical Pacific Ocean with the eastern Indian Ocean, and variability of the Throughflow during the Plio-Pleistocene has been related to major climate shifts at the global level. Planktic foraminiferal biostratigraphy integrated with magnetochronology provides a robust time framework for assigning age control to major paleoceanographic events. Understanding of the coupled histories of the El Niño Southern Oscillation, Western Pacific Warm Pool, Indonesian Throughflow, and the eastern Indian Ocean has greatly benefitted from the chronological framework provided by planktic foraminiferal biostratigraphies from these regions. Ocean Drilling Program (ODP) Hole 762 lies under the influence of the Leeuwin Current, originating from the Indonesian Throughflow. Multiproxy data have been collected from Hole 762B and other nearby sites for paleoceanographic interpretation. However, a detailed planktic foraminiferal biostratigraphy integrated with magnetochronology is not available from this site. We provide here the sequential order of planktic foraminiferal First Occurrence (FO) and Last Occurrence (LO) events, which allowed us to divide the examined section into seven biostratigraphic zones. The biostratigraphy was integrated with magnetostratigraphy using revised ages of magnetochrons, which yielded biochronological age estimates for planktic foraminiferal events. A major planktonic faunal turnover between 3.4 and 2.7 Ma is probably related to the onset of the Northern Hemisphere glaciation and related changes in the Indonesian Throughflow. We have compared our numerical age estimates with published ages from other parts of the world. The diachronism observed probably is related to the local oceanographic setting of ODP Hole 762B, which has been alternatively influenced by changing strengths of the warm Leeuwin Current and the cold west Australian Current. The biochronology established here will be useful for correlating paleoceanographic events in the region.

High resolution benthic foraminiferal δ18O and δ13C records at ODP site 807 over the past 5 Ma, Ontong Java Plateau: Evolution of North Pacific ventilation, Pliocene to Holocene

The western equatorial Pacific is pivotal to precisely understand the global climate change and its evolution over geological time. However, continuous paleoceanographic records with high time resolution and accurate age model over the last 5 Myr are few in this important ocean region. Here, we present a high time resolution (2–3 kyr) benthic foraminiferal δ 18 O and δ 13 C record from Ocean Drilling Program Site 807 on Ontong Java Plateau in the western equatorial Pacific and establish an accurate age model for the past 5.025 Myr. Comparison of the benthic δ 13 C records from the west and east equatorial Pacific, and the North and South Pacific indicates that water aging effects have dominated since the Pliocene. From 4.0 Ma to 2.7 Ma, a rapid decrease in benthic δ 13 C gradients (Δδ 13 C W-E ) between the west (Hole 807A) and east (ODP Site 849 and IODP Site U1338) equatorial Pacific potentially resulted from strong ventilation in the North Pacific during the warm Pliocene. The subsequent gentle decrease in benthic δ 13 C gradients might indicate stratification in the North Pacific and reduction of biogenic flux with the intensification of the Northern Hemisphere Glaciation (NHG) at 2.7 Ma. Both the Δδ 18 O W-E and Δδ 13 C W-E are strongly paced by 405 ka long eccentricity cycles and 41 kyr obliquity cycle, revealing the complex interplay of both high and low latitude climatic processes on deep Pacific circulation changes. • Continuous 5 Myr long high time resolution benthic foraminiferal δ 18 O and δ 13 C records in the western equatorial Pacific. • West-east equatorial Pacific δ 13 C gradient indicates the evolution of the Pacific deep ocean circulation over the past 5 Myr. • 405-kyr eccentricity cycle modulates the Pacific deep ocean circulation changes.

Middle-Late Pleistocene Eastern Mediterranean nutricline depth and coccolith preservation linked to Monsoon activity and Atlantic Meridional Overturning Circulation

The eastern Mediterranean Sea lies under the influence of high- and low-latitude climatic systems. The northern part of the basin is affected by Atlantic depressions and continental and polar air masses that promote intermediate and deep-water formation. The southern part is influenced by subtropical conditions and monsoon activity. Monsoon intensification results in enhanced freshwater discharge from the Nile River and other (now dry) systems along the North African margin. This freshwater influx into the Mediterranean Sea reduces surface water buoyancy loss. Disentangling the influences of these diverse climatic forcings is hindered by inherent proxy data limitations and by interactions between the climatic forcings. Here we use a wealth of published and new paleoclimate records across Termination II to understand the impacts of the higher latitude and subtropical/monsoon climate influences on coccolithophore ecology and holococcolith preservation in Aegean Sea sediment core LC21. We then use these findings to interpret coccolith assemblage variations at Ocean Drilling Program Site 967 (located nearby LC21, at the Eratosthenes Seamount) during multiple glacial-interglacial cycles across the Middle Pleistocene (marine isotopic stages 14–9). The LC21 analysis suggests that holococcolith preservation was enhanced during Heinrich Stadial 11 (∼133 ka) and cold spell C26 (∼119 ka). These two events have been previously linked to cold conditions in the North Atlantic and Atlantic Meridional Overturning Circulation weakening. We propose that associated atmospheric perturbations over the Mediterranean Sea promoted deep-water formation, and thus holococcolith preservation. Similarly, in the Middle Pleistocene (MIS 14-9) of Site 967, we observe temporal coincidence between ten episodes of enhanced holococcolith preservation and episodes of Atlantic Meridional Overturning Circulation slowdown. In Site 967, we also identified repeated fluctuations in placoliths and in Florisphaera profunda, which indicate nutricline depth variations. The development of a deep chlorophyll maximum is associated with the North Africa and wet phases, as recently observed using elemental proxy records at Site 967, during the deposition of sapropel layers. A further deep chlorophyll maximum development is identified during MISs 12 and 10, as a result of pycnocline and nutricline shoaling within the lower part of the photic zone due to glacial sea-level lowering and water mass transport reduction at both the Gibraltar and Sicily Straits. Finally, enhanced holococcolith preservation during cold/dry events is clearly correlated to weakened monsoon activity in both Africa and Asia.

Northward Shift of the Northern Hemisphere Westerlies in the Early to Late Miocene and Its Links to Tibetan Uplift

AbstractDespite the importance of the westerlies to the global climate system, we still know little about their long‐term evolution and possible orographic controls during the late Cenozoic because of the lack of sedimentary records with precise chronological control. Eolian deposition in the North Pacific preserved past information about the westerlies, the major wind system delivering Asian dust to the Pacific. A continuous, high‐resolution eolian flux record since 23 Ma was reconstructed from sediments at Deep Sea Drilling Project Site 296 in the North Pacific. Combined with dust flux at Ocean Drilling Program Site 1208, variations in their difference indicated a northwards shift of the westerlies during 23‒9 Ma and a relatively stable state since then. We suggest that Tibetan uplift since the early Miocene began to drive the poleward shift of the westerlies until 9 Ma, after which the westerlies remained relatively stable over Asia on million‐year timescales.

Non-Productive Time Reduction during Oil Wells Drilling Operations

Often there is no well drilling without problems. The solution lies in managing and evaluating these problems and developing strategies to manage and scale them. Non-productive time (NPT) is one of the main causes of delayed drilling operations. Many events or possibilities can lead to a halt in drilling operations or a marginal decrease in the advancement of drilling, this is called (NPT). Reducing NPT has an important impact on the total expenditure, time and cost are considered one of the most important success factors in the oil industry. In other words, steps must be taken to investigate and eliminate loss of time, that is, unproductive time in the drilling rig in order to save time and cost and reduce wasted time. The data of six oil wells were approved for the purpose of the study, where it was noted that there are many factors affecting the NPT, which differ from one well to another. Its impact was limited to drilling rig, mud pump and equipment failure. There is also a difference between the planned program and what is actually happening on the ground, due to several reasons, including human errors during the implementation of the drilling program and others due to technical errors, Misuse of equipment, in addition to human errors related to the failure to implement the drilling program.

Fracture pressure, leak-off tests and Poisson's ratio

Fracture pressure models are used to create pre-drill fracture pressure–depth plots that are essential to the design of drilling and casing programmes in oil and gas wells, and for the future development of carbon capture and underground storage. Some of these models include an empirical term (stress ratio) that relates effective horizontal stress to effective vertical stress. Based on the literature, the stress ratio is assumed to vary with compaction and can be calculated from Poisson's ratio ( ν ). An alternative to models that utilize the stress ratio term is a model that relates fracture pressure to a constant fraction of the vertical stress. This paper demonstrates that a constant fraction of vertical stress is equivalent to a stress ratio that increases slightly with depth. Estimation of how the ν changes with compaction is complicated by the multiple methods that are commonly employed to measure ν . The available static and dynamic ν data suggest a substantial decrease in ν with porosity reduction. Evaluation of in situ ν data from leak-off tests (LOTs) and associated fluid pressure data in Tertiary basins indicates that in situ ν does not decline as rapidly as indicated by the other methods of ν determination. In situ ν data indicate that calibration of the stress ratio from traditional ν methods is not appropriate and may substantially underestimate the fracture pressure (FP). Fracture pressure models that utilize a constant fraction of vertical stress or estimate the stress ratio empirically from LOT data should be employed for pre-drill estimation of fracture pressure. Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/cc/geopressure

Early accretion and prolonged carbonation of the Pacific Ocean's oldest crust

Abstract Newly formed oceanic crust is altered by seawater and carbonated at low temperatures over poorly defined periods of time. We applied in situ U-Pb dating to investigate 28 carbonate veins from Ocean Drilling Program Hole 801C, which is situated in the oldest Jurassic-age oceanic crust preserved in the western Pacific Ocean. Our results indicate that Pacific Ocean crust began accreting at 192 ± 6 Ma, which is ~25 m.y. earlier than previously recognized. Carbonation peaked at 171 ± 5 Ma and continued at a low rate for more than ~65 m.y. after accretion. Jurassic carbonation rates varied over ~10 m.y. timescales but encompassed a range similar to that observed today. These data suggest that carbonation rates are relatively insensitive to changes in atmospheric CO2, but confirm the longevity of seafloor alteration as a critical control in global volatile cycling.