Exploratory Drilling Program Research Articles

Geostatistical Mapping of Folded Itabiritic Rocks of the Bonito Mine, Northeastern Brazil

Geological modeling is the primary task of any exploratory geological investigation, and it is performed even during the mine development. In the study area, the Serra dos Quintos Formation hosts banded iron formations represented by assorted itabirites. The database used in this work was exploited from a geological databank which was structured to gather data and information depicted from an exhaustive exploratory drilling program. A survey was performed throughout the entire databank to collect the available thickness data values (measured in meters) from drill core logs that intersected the itabirite. Since structural heterogeneities can occur within these rocks, this study aims to identify such features. Geostatistical estimation and simulation methods were employed to map folded itabiritic beds based on thickness data accurately. Kriging estimators are often used for practical reasons; however, sometimes, the estimates can be smoothed and do not represent the entire original data range. Simulation algorithms can yield several stochastic images, but local accuracy cannot always be guaranteed. Simulated annealing was performed by adjusting the global statistics and preserving the local accuracy. We demonstrated that the banded iron formations’ thicker areas might correspond to the antiform fold as the dominant tectonic feature in the study area. Finally, we show that the simulated thickness map discloses the thicker mineralized spots. Meanwhile, the thinner ones may unveil intrinsic structural heterogeneities mainly observed at the limbs of the Bonito fold, where intensive deformation within the itabiritic layer was higher than expected. Concerning the mining issues, information obtained from the simulated thickness map could provide ancillary data to improve mining planning in the study area.

Interpretation of Subsurface Fault Through Multi-Level Second Vertical Derivative Gravitational Data in Bittuang Geothermal Working Area, South Sulawesi, Indonesia

The research was conducted in Bittuang, Tana Toraja Regency, South Sulawesi Province, as one of the geothermal prospect areas and targets for the initial stage of the Government exploration drilling program for the 2020-2024 period. One aspect of geothermal is the manifestation control structure as a fluid migration path from below the surface. Therefore, identification of existing structures in the Bittuang geothermal area was carried out and confirmed the surface geological structure contained in the Bittuang geothermal geological map. In determining the presence of a fault and knowing its characteristics such as the type of fault, the direction of the dip, and the magnitude of the dip of the fault, the gravity data is processed using the multi-level second vertical derivative (ML-SVD) method. To strengthen the interpretation, the results from the ML-SVD were matched with the data from the horizontal gradient (HG) method and the geological data of the structure of the study area. From this process, there are 27 faults in the Bittuang geothermal area, two of which are indicated as controlling faults for the manifestation of the Balla group and the Cepeng group. This research is expected to describe faults in the Bittuang geothermal area, which can support detailed exploration activities.

Application of bulk fluid volatile chemistry to exploration for metasedimentary rock-hosted orogenic gold deposits: An example from the Meguma terrane, Nova Scotia, Canada

Disseminated gold (Au) deposits hosted in metasedimentary rocks present unique exploration challenges because the Au is generally very fine-grained or refractory, and not vein-hosted. Exploration programs in such settings rely on extensive lithogeochemical surveys, lesser structural analysis, and little emphasis on ore-fluid geochemistry. The Moose River anticline (MRA) in the Lower Paleozoic Meguma terrane (Nova Scotia, Canada) hosts several high-tonnage (~10–20 Mt), low-grade (≤1–4 g/t Au) Au deposits comprised of disseminated ± quartz vein-hosted mineralization in metamudstones. Here, the Touquoy deposit hosted in the MRA is used to evaluate a new approach to geochemical exploration by examining if the volatile chemistry of host rocks preserves a signature related to Au mineralization, using a gas chromatographic (GC) technique that analyzes bulk volatiles released from crushed rock. Since GC is a bulk analytical technique, (i.e., multiple generations of fluid inclusion volatiles yielding a mixed analytical volume), the volatile composition of fluid inclusions were also investigated in-situ using laser Raman microspectroscopy to reconcile bulk analyses with the composition and abundance of different inclusion types. Inclusions in quartz pressure shadows associated with porphyroblasts host N2 ± CH4-dominant vapor phases and represent wall rock-equilibrated fluids. In comparison, fluid inclusion vapor phases in quartz veinlets crosscutting the metamudstones are more complex in composition and show a continuum between CO2-dominant and N2 ± CH4-dominant compositions; the former is interpreted as the fluid responsible for Au mineralization in the Meguma terrane (e.g., H2O-CO2 ± CH4 ± N2 fluids). GC shows statistically significant differences in the compostion of the bulk volatiles released from crushed metamudstones from the Touquoy deposit (n = 21) and barren (n = 24) settings. Whereas the former commonly contain detectable CO2 (50% of samples; LoQ(CO2) ~ 10−10 mol/g), only ~4% of metamudstones from barren settings along the MRA contain CO2, yielding a t-test p-value of 0.0103 between the two sample populations. Whereas the more frequent detection of CO2 in mineralized samples is related to increasing carbonate alteration proximal to Au mineralization, no correlation is observed between bulk CO2 abundance and Au grade. Additionally, anomalous differences in abundances of released C3 (t-test p-value = 0.043) and C4 (t-test p-value = 0.03) hydrocarbons (HC) are recognized between the two populations (LoQ(HC) ca. 10−13 to 10−12 mol/g), with Touquoy metamudstones having higher Σ(C3)/CH4 and Σ(C4)/CH4 ratios compared to barren equivalents. The compositional differences suggest that more aqueous-carbonic fluids infiltrated metamudstone units where locally favorable physical and/or chemical conditions were present, resulting in increased Au endowment. The relative increase in fluid flux, and thus Au grade, resulted in more trapped CO2 (i.e., resulting from more trapped inclusions and/or greater CO2 fluid component) and modification to hydrocarbon signatures through homologation and/or degradation reactions. Rigorous sample preparation ensures these compositional differences are related to paleofluids and not contamination.Tentatively, the results suggest that the bulk analysis of volatiles released from fluid inclusions in metamudstones may be a useful vectoring tool for disseminated Au mineralization in Meguma-type gold systems and similar environments (e.g., Carlin-type). This technique may be appropriately scaled to complement exploration drilling programs and may be more sensitive in determining ore proximity than often ambiguous pathfinder elements.

Gold Exploration in Two and Three Dimensions: Improved and Correlative Insights from Microscopy and X-Ray Computed Tomography

In this contribution, we highlight a correlative approach in which three-dimensional structural/positional data are combined with two dimensional chemical and mineralogical data to understand a complex orogenic gold mineralization system; we use the Kirk Range (southern Malawi) as a case study. Three dimensional structures and semi-quantitative mineral distributions were evaluated using X-ray Computed Tomography (XCT) and this was augmented with textural, mineralogical and chemical imaging using Scanning Electron Microscopy (SEM) and optical microscopy as well as fire assay. Our results detail the utility of the correlative approach both for quantifying gold concentrations in core samples (which is often nuggety and may thus be misrepresented by quarter- or half-core assays), and for understanding the spatial distribution of gold and associated structures and microstructures in 3D space. This approach overlays complementary datasets from 2D and 3D analytical protocols, thereby allowing a better and more comprehensive understanding on the distribution and structures controlling gold mineralization. Combining 3D XCT analyses with conventional 2D microscopies derive the full value out of a given exploration drilling program and it provides an excellent tool for understanding gold mineralization. Understanding the spatial distribution of gold and associated structures and microstructures in 3D space holds vast potential for exploration practitioners, especially if the correlative approach can be automated and if the resultant spatially-constrained microstructural information can be fed directly into commercially available geological modelling software. The extra layers of information provided by using correlative 2D and 3D microscopies offer an exciting new tool to enhance and optimize mineral exploration workflows, given that modern exploration efforts are targeting increasingly complex and low-grade ore deposits.

Integrated interpretation of seismic and magnetotelluric data on Shurab diapirs in Qom basin, Central Iran

In recent decades, diapirs are frequently used for CO2 and natural gas storage due to their extremely impermeable and non-reactive characteristics. Among various approaches, we use an integrated interpretation approach to resolve the diapir no. 4 belonging to the Shurab diapirs (SD). The SD is a group of diapirs that have pierced to the surface of the Qom basin of Central Iran, which is a candidate for natural gas storages. The complex geology of the SD is the main cause that previous 2D seismic surveys across the diapir could not provide required information to propose any location for any exploration borehole. Consequentially, 28 magnetotelluric (MT) and 1 audio-magnetotelluric station were measured along a SW-NE profile. Dimensionality and strike analysis for all stations is done by the use of phase tensor analysis. We used the nonlinear conjugate gradient algorithm to invert the TE- and TM-modes data simultaneously in 2D. The resistivity model was compared with the interpreted results of the post-stack depth migration model using seismic attributes. In order to extract the determinative geological information from the low-quality seismic section, envelope, variance, sweetness and instantaneous frequencies attributes were used. The integrated interpretation of the seismic and MT data resolves a precise geometry of the salt body, location of the dense part of the diapir as well as the tectonics around the diapir. The integrated interpretation of seismic and MT data of diapir no. 4 resulted in an exploration drilling program.

The Pilgangoora Lithium-Tantalum Deposit - Geological Overview and Evolution of Discovery

The Pilgangoora Lithium-tantalum pegmatite deposit with a total resource of 156.3 Mt grading 1.25% Li2O and 128ppm Ta2O5, is a globally significant hard-rock lithium-tantalum deposit. The deposit is located in the East Pilbara Terrane of the northwest Pilbara Craton in Western Australia. The Northwest Pilbara Craton is one of the world’s major lithium-tanatlum provinces with large scale lithium-caesium-tantlum bearing pegmatites located at Mt Francisco, Wodgina, Pilgangoora and Strelley. Pegmatites bearing columbite-tantalite at Mt. York were first described in government geological surveys in 1906. Subsequent interest in the pegmatites focussed on their tin and tantalum mineral potential, with small scale hardrock, eluvial and alluvial mining, chiefly in the period 1947-1978. Larger scale alluvial and eluvial mining of tin-tantalum was carried out over 1978-1982 and 1992-1996 by a number of junior companies. In May 2014, Pilbara Minerals acquired the Pilgangoora Project for its lithium potential and has since drilled over 1450 holes for approximately 120,000 metres. The Pilgangoora pegmatite intrusions crop out in a well exposed greenstone belt, with little weathering at surface. Exploration drilling programs along with detailed geological mapping of the Pilgangoora tenement group has provided a better understanding of the geological setting of the fractionated pegmatite intrusions within the East Strelley greenstone belt. This work has led to the recognition of some valuable exploration criteria that may be applied locally to locate additional resources and, longer term, may be used more strategically to review other pegmatite fields across the Pilbara region.

Spatio-temporal modelling of underwater noise related to an arctic exploration drilling program

One concern related to oil and gas industry activities in the arctic is the potential impact of anthropogenic noise on marine mammals. To gain understanding of the temporal evolution of the acoustic noise footprint from such activities, and to quantify the geographic extent at which sound levels remain within regulatory thresholds for marine mammal injury and behavioral disturbance, this work presents a comprehensive monitoring and modeling study of anthropogenic noise resulting from an exploration drilling project in the northeastern Chukchi Sea, conducted from July to October, 2015. Measured acoustic source levels of multiple vessels and drilling equipment were used to generate time-dependent wide-area noise fields. Model validation was carried out by comparing simulated results with high-resolution acoustic data acquired at multiple stations in the area. The study shows that noise radiating from up to 19 supporting vessels is usually dominant, but noise from certain drilling-related activities occasionally rises above vessel noise within a radius of 8 km from drillsites. Modeled scenarios also show that by constraining vessel positions to within a few kilometers of the drilling location, simultaneous construction of two oil well top holes results in minor increment of the aggregate acoustic footprint’s extent relative to single-well drilling.

VARIABILITY OF ORE MINERALIZATION IN THE NORTH-WEST-TRENDING EXTENSIONOF THE LUBIN–SIEROSZOWICE DEPOSIT

The Polish Geological Institute – NRI has conducted investigations of the Kupferschiefer series since 1957, when the giant sediment-hosted stratiform Cu-Ag ore deposit was discovered in the central part of the Fore-Sudetic Monocline. Until 1991, a number of drilling programs were completed by PGI-NRI and later research has been focusing mainly on cooperation with oil and gas industry and their core material. Over the last few years, thanks to systematic examination of the drill holes located in the north-western extension, many prospective areas have been recognized and delineated. These prospects are located between Lubin-Sieroszowice deposit and the eastern part of the Zielona Góra oxidized field. In the Kożuchów area, the lower part of Zechstein copper-bearing series contain only relict sulphide mineralization accompanied by iron oxides while reduced rocks with metal sulphides occur in the uppermost part of Zechstein Limestone or at the base of Lower Anhydrite. Grochowice area, where reduced facies prevail in copper-bearing series, is characterized by the predomination of rich Cu-Ag mineralization proximaly to oxidized area. The western part of studied area is dominated by Cu-S type sulphides (chalcocite, digenite, covellite) whereas the eastern part is represented by Cu-Fe-S type minerals (bornite, chalcopyrite) with high galena and sphalerite concentrations. The spatial variability of sulphide mineralization with respect to the oxidized rocks indicates that Bytom Odrzański deposit extends in the north-west direction, continuing in the form of a copper belt along the eastern border of the oxidized area. An extensive deep exploration drilling program is implemented to verify the resource potential within predicted copper belt.

Extracting geologic information directly from high-resolution full-waveform inversion velocity models — A case study from offshore Trinidad

The East Coast Marine Area (ECMA) of Trinidad and Tobago contains producing gas fields where the imaging of seismic data is known to be challenging. This difficulty has been attributed to the combination of the Dolphin Main Fault, with more than 1 km of throw and large velocity contrasts of up to 30% in magnitude across it, and shallow gas and gas clouds causing very high attenuation. These factors lead to difficulties producing reliable and consistent velocity models. Previous velocity models — generated using traveltime tomography — contained inaccuracies that led to poor imaging and structural positioning, resulting in uncertainty when planning exploration and development drilling programs. In an attempt to reduce these uncertainties, a full-waveform inversion (FWI) feasibility study was performed over the most problematic area, with an initial velocity model built from a combination of legacy prestack time and depth migration velocity models and additional first-break refraction tomography. The geologic complexity near the main fault and the associated poor seismic data quality meant this model gave a poor fit between the synthetic and observed data (from a cycle-skipping point of view) at the lowest usable frequency. This led to the idea of applying a diving-wave-driven, offset-stripping workflow across each frequency band in the FWI, going from 3.5 Hz to 7.5 Hz. After successful application on the test area, the workflow was applied to ∼1400 km2 of 3D seismic over the ECMA. The final velocity model is structurally consistent and highly resolved, containing detailed shallow geologic features such as mud volcanoes, well-defined faults, and potential gas anomalies that were not visible on the legacy tomographic model. A blind test of well-pressure data correlates strongly with velocity drops in the FWI model, showing that FWI models can potentially provide very good input to regional pore-pressure-prediction studies.

Exploration trenches for uranium resource evaluation

The Jordanian Uranium Mining Company (JUMCO) needed to determine the most appropriate method for sampling and assaying the surficial uranium deposits of central Jordan. This type of mineralisation presents a number of challenges including; i. occurrence of best mineralisation within 5 m of surface, ii. observed secular isotopic disequilibrium, iii. erratic distribution of uranium mineralisation, iv. problems with drill sample recovery close to surface, v. difficulty in reliably logging geology in percussion drill chip samples. Previous exploration drilling programs that relied on gamma logging were shown to be unreliable because of secular disequilibrium close to surface. The percussion chip samples used for chemical assaying were shown to be unreliable because of poor sample recoveries and the possible loss of fine-grained uranium mineralisation. In an effort to maximise sample recovery, avoid disequilibrium problems and assess the short-scale continuity of mineralisation, trenching was chosen as the preferred exploration method to evaluate the upper part of the surficial uranium deposits of central Jordan.

Application of modern 2-D and 3-D seismic-reflection techniques for uranium exploration in the Athabasca BasinThis article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent.

Seismic-reflection techniques have been applied in several studies over the last 20 years as a uranium-exploration tool within the Athabasca Basin and have been utilized to provide the larger structural context for known uranium deposits within the basin. At the crustal scale, deposits within the eastern Athabasca Basin are shown to be associated with deep-seated shear zones that originated during Trans-Hudson orogeny and have subsequently been reactivated during and subsequent to deposition of the basin-fill sandstones. Seismic properties of the Athabasca sandstones and underlying basement have been determined through in situ borehole measurements. Reflectivity within the sandstones is generally weak. Seismically recognizable signatures are primarily associated with variations in fracture density, porosity, and degree of silicification. The basement unconformity and regolith, a prime target of exploration, is widely imaged as it is characterized by variable but generally distinct reflectivity. Results from the McArthur River mine site suggest that the spatial coincidence of seismically imaged high-velocity zones and deep-seated faults that offset the unconformity may be a more broadly applicable exploration targeting tool. Three-dimensional (3-D) seismic imaging near existing ore zones can define the local structural controls on the mineralization and point the way to new targets, thus leading to more efficient exploration drilling programs. Furthermore, seismically generated structural maps of the unconformity and rock competence properties may play a significant role at the outset of mine planning.

Deploying Common Process Across Global Wells Teams

This article, written by Features Editor Diane Langley, contains highlights of paper SPE 95442, "Deploying Common Process Across Global Wells Teams - Integrating an Online Project Management Application With Effective Behaviors To Enable High Performance," by S. Sawaryn, SPE, BP plc; D. Dressler and K. Been, SPE, Frontline Group; and T. Bailey, SPE, BP plc, prepared for the 2005 SPE Annual Technical Conference and Exhibition, Dallas, 9-12 October. The full-length paper details the concept and integration of a Web-based project-management application to support the common processes for well delivery now in use across BP’s global wells teams. Applicable to both managers and engineers, the paper not only presents a case study of project implementation and documents goals, results, critical success factors, and challenges and lessons learned, but it also highlights behavioral effects, customization, and how the application actually becomes a part of the common process. Introduction As pointed out in a published study, 70% of the deficiencies in earlier well delivery processes lie in the lack of project definition and planning rather than poor performance. Poor planning and scheduling, conflicting goals, poor teamwork, incomplete authorization-for-expenditure costs, and an inadequate learning process top the list of causes. Predecessors of the BP “Beyond the Best” initiative and subsequent Web-based application include the Well Learning System adopted in 1995 and a three-team approach employed in 1997 on a five-well Norwegian exploration drilling program. The rigorous learning loop involved with the 1995 system captured more valuable information than was its primary objective, revealing that the functional elements of the common-process tool and the manner of implementation within an organization are very valuable aspects. Similarly, it was determined from the 1997 drilling-team efforts that there is great value in separating a well project into distinct phases, engaging in detailed planning, and adhering to key principles. These early successes offered valuable learning and laid the foundation for development of the BP proprietary Common Process Online (CPoL) system. This highly dynamic system can be customized for each project and improved upon for subsequent projects and, at the same time, preserve process integrity. Common Process Defined as the application of best practices and the building of a common language across a multidisciplinary community, common process provides a means to define what activities are core and mandatory, reducing workload and less-valuable activities to free up time for tasks that are deemed most valuable. The four elements of common process include: Drilling Value Assurance (DVA), Right Scoping, No Drilling Surprises, and Technical Limit. DVA, consisting of three “gates,” or stages, assures choice of the appropriate project and proper development, execution, and delivery. Work progression through each of these gates is controlled by a “gate-keeper” appointed by the business unit. A front-end-loading assessment is conducted by trained assessors to measure the effectiveness of a well team’s planning effort. For critical wells, scores of more than 80%are expected.

Shallow Water Flow Planning and Operations: Titan No. 1 Exploration Well, Deepwater Gulf of Mexico

Summary Shallow water flows (SWF) from overpressured aquifers have been a persistent problem in the deepwater Gulf of Mexico (GOM) and can create significant financial and operational risks for exploration and development drilling programs. For the GOM, SWF intervals typically occur between 300 and 2,500 ft below mudline (BML) and in water depths greater than 1,500 ft. If left unchecked, the disturbance from the water flow can cause loss of soil strength surrounding the wellbore, thereby compromising the structural integrity of the well. In industry, extreme cases have led to collapsed casing and/or total loss of wellbores. This paper details the up-front planning efforts implemented and the operational procedures utilized to successfully mitigate a SWF event experienced at the Titan No. 1 exploration well drilled in Garden Banks Block 785 (GOM), in 4,640 ft of water. Operations at Titan were based on the philosophy that performing a shallow hazards assessment, preparing and implementing SWF contingency plans, drilling a 9|-?. pilot hole (for dynamic kill), identifying a SWF zone quickly, controlling a water-flow zone with weighted mud (while drilling riserless), and using nitrified foam cement to seal off a water flow behind 20-in. conductor pipe, were all critical in successfully containing and drilling through a SWF occurrence.

Delivering World-Class Exploration Drilling-Integration of Design, Planning, and Execution

Summary Over the last 2 years, a series of organizational structures, systems, and processes produced outstanding results from a five-well exploration drilling program that involved three different rigs and teams. Risk assessment is a key thread that runs through the process, from high level risks in a conceptual design to details of day-to-day execution. It is robustly linked to the process for estimating well times and contingency costs and provides a means of communicating risks to business delivery up to management. A correct set of well objectives and design basis is the foundation of an effective detailed planning phase involving a large team of contractors. Integration of service suppliers and drilling contractor into a comprehensive planning effort is key to planning and execution success. Standard project-management techniques are combined with structuring of the organization around delivery of key elements of the well to ensure that a large project team is properly focused on achieving a world-class operational target. Detailed planning ensures flawless operation and efficient recovery from setbacks. The rig team is critical to getting the detail right. In the end, rigorous post-analysis is essential to ensure that lessons learned, not only about the technical aspects of the well, but also the process, are fed back into the planning of future operations. Introduction Development of the work described here coincided with many things happening throughout the industry during 1997-98. BP Norway was evolving into an organization that delivered its activities on a project basis, while an industry wide capital projects benchmarking study demonstrated a close correlation between the quality of preplanning (front-end loading) and efficiency of execution. Added to this, the deepwater drilling campaign in Norway was a cause for management concern. None of the wells drilled by early 1998 delivered within budget (Fig. 1). Seen in this context-as an issue of credibility for BP's Norwegian operation-continuation of the status quo was unacceptable. Consequently, in late 1997, we reviewed factors that contributed to previously successful projects and seemed to be common to these operations. From these factors and subsequent experience, we have developed a set of 10 principles.Commitment of project manager and full management support.Highly competent team members.Clear delivery-focused accountabilities.Early and effective planning.In-depth risk assessment and management.Efficient processes (cost, schedule, documentation, logistics).Alignment of the team to a world-class goal.Everyone involved and able to listen and speak openly.Performance assessed continuously vs. stretch targets.Seriousness about the principles rather than just lip service. In addition, we concluded that the conventional plan needed to be extended and made the execute/evaluate cycle into a five-stage project.Prepare to plan.Plan the operation.Prepare to drill.Drill the well.Close the loop-learn. The motivation here is that "business-as-usual" results follow from standard working practices. To do things differently, we had to spend time early in the project thinking about how to do the planning and execution rather than jumping straight into them like we normally do. Earlier work1–3 indicated that critical attributes of the project team included its ability to learn, its sense of purpose, its structure, associated work processes, target setting, and performance measurement. This paper describes how we put that thinking into action, from the original well concept, through the planning phase, to execution and post-analysis; how the risk-assessment process is an integral part of the whole and the results achieved to date on the Norwegian operations; and how our approach is evolving as our experience grows. Conceptual Well Design Clearly defined well objectives are critical to an effective and efficient operation. In many instances, compromises are made during well operations for "operational reasons," such as not running logs and not cutting cores. This is symptomatic of a defective objective-setting process. If the data from the missing logs really are required to fulfill well objectives, the drilling team must ensure that the proposed design guarantees delivery rather than leaving it to operational chance. Colocating an experienced drilling engineer with the exploration team (geologist, geophysicist, petroleum engineer, operations geologist, and petrophysicist) during prospect development seems to work.

北海道の鉱物資源

This lecture introduces histories and present conditions of development of mineral resources in Hokkaido.The history of gold digging goes back to 12th century. But systematic development of mineral resources started from Meiji era especially for coal. Lyman's geological survey in this period established a foundation of mining industry in Hokkaido.Metal, non-metal and coal minings and oil development grew rapidly during the World War I. And metal, non-metal and coal minings reached their highest production during the World War II. But the mining industries started declining from mid-1950's. Especially severe decline took place in coal mining due to its high production cost.Activities of oil and gas exploration started increasing in 1970's according to MITI's exploratory drilling program as the fourth five-year-project. And Yufutsu gas field was found in 1989.Currently three metal mines, seventeen non-metal mines, eight oil/gas fields and eleven coal mines are working in Hokkaido. Zinc and limestone mines have large shares of production in Japan. Yufutsu gas field started production from 1996 for town gas used in Sapporo.Finally this lecture introduces new surveys for mineral resources in Hokkaido, because its potential is still high. And oil and gas development in Sakhalin is expected to give a great influence on Hokkaido.

Microgravity investigations of foundation conditions

A microgravity investigation was conducted in the upstream and downstream switchyards of the Wilson Dam powerplant, Florence, Alabama. The objective of the survey was the detection in the switchyard foundations of subsurface cavities or other anomalous conditions that could threaten the stability of the switchyard structures. The survey consisted of 288 gravity stations in the downstream switchyard and 347 stations in the upstream switchyard. Significant anomalous areas in the switchyards were selected on the basis of residual gravity anomaly maps. These results were prioritized and used to guide an exploratory drilling program to investigate the cause of the anomalies. Highest‐priority boring location recommendations were in negative gravity anomaly areas, since negative anomalies could be caused by actual cavities or low‐density zones that might represent incipient cavity formation. Remaining boring locations were in positive anomaly areas for verification purposes. The results of the borings confirm the presence of cavities and soft zones indicative of cavity formation.

A Quarter Century of Coal Mining and Hydrogeologic Research in Southeastern Montana

Two valuable natural resources coexist in eastern Montana--coal and ground water. Water related issues are the major concerns during coal mine permit decisions. Due to the concerns about mining related impacts, ground water in the vicinity of coal mines has been continuously monitored since 1970. The continuity and duration of the Montana Bureau of Mines and Geology monitoring program under a variety of geologic, mining, and post-mining conditions have provided a fundamental knowledge on impacts to water levels and water quality. Coal beds are among the most dependable and utilized aquifers in eastern Montana, due to their lateral continuity and fracture-related transmissivity. In response to coal strip mining, water levels in coal-bed aquifers have dropped at distances as far as 2 miles away from mines near Colstrip, and as far as 15 miles from mines near Decker. Water levels typically return to pre-mining levels within several years after pits are backfilled. Mining-induced drawdown in stratigraphically deeper aquifers exceed those in mined aquifers in some areas, and relate to inadequately plugged boreholes from older exploration drilling programs. Dissolved-solids concentrations of water in the spoils aquifers have increased by 50 to 200% due to the dissolution of newly available salts of calcium,more » magnesium, sodium and sulfate. However, in some sites freshening of the water appears to be occurring as initial salt loads are flushed through the systems. Water-quality impacts are expected in off-site and deeper aquifers due to normal ground-water flow, and in deeper aquifers due to poorly plugged exploration drill holes. However, downgradient impacts to water quality are rarely observed. Future ground-water monitoring should document stable water levels and improving water quality as spoils aquifers reach equilibrium with local undisturbed hydrologic systems.« less

SEQUENCE BIOSTRATIGRAPHY, PETROLEUM EXPLORATION AND A. CINCTUM

Sequence biostratigraphy is a relatively new discipline that has rapidly expanded in parallel with the development of sequence stratigraphy. Sequence bios- tratigraphic concepts have resulted in significant improvements in our ability to calibrate biozones, correlate and determine ages of sedimentary units, and to estimate environments of deposition. Significant advances in the development of integrated biostratigraphic methods and knowledge during the past 20 years are now being rapidly integrated into the physical framework provided by depositional sequences. Sequence stratigraphy provides a physical framework consisting of a predictable hierarchy of correlation surfaces, ranging from sequence boundaries to parasequence boundaries, within which biostratigraphic observations may be placed. These correlation surfaces define chronostratigraphic units with varying degrees of lateral extent that can be used to assess, using time-distance grids, the relative position of biozone 'tops' or 'bases'. They also provide a physical link between the open-ocean planktonic microfossil chronozones and chronozones developed in paralic and non-marine strata. In addition, the delineation of large, apparently sudden, water depth changes across downlap surfaces, associated with condensed sections, has resulted in more accurate and precise paleobathymetric estimation in exploration wells. Recognition and biostratigraphic 'fingerprinting' of major water depth changes are essential for correlation through intensely faulted areas.The rate of return from biostratigraphic and geochemi- cal sampling is generally poor primarily because of the lack of emphasis on the importance of developing and maintaining well planned sampling strategies and programs throughout an exploration drilling program. The design of biostratigraphic and geochemical sampling strategies has been improved by sequence stratigraphic concepts. Biostratigraphic sample quality (high) is inversely proportional to sedimentation rate (low). Sequence biostratigraphy provides a consistent, predictable, method of recognising low sedimentation rate units in the subsurface using a variety of tools, ranging from seismic to well log facies analysis.Some of the basic principles of sequence biostratigraphy are illustrated using an example from the Carnarvon Basin. The Barremian A. cinctum andM. australis dinocyst Acme and Oppel zones respectively, appear to be strongly associated with distinct environments. Consequently, it is difficult to calibrate them to the AGSO timescale and to use them regionally as reliable zones to subdivide the Barremian. Abundant numbers of A. cinctum appear to be restricted to specific regions of the Carnarvon dominated by shallower marine conditions and associated with the infilling of major incised river systems. Further biostratigraphic subdivisions within the Early Cretaceous and specifically the M. australis - A. cinctum interval are warranted, especially in light of the number of plays and prospects defined and discoveries made within this interval of the Carnarvon Basin. More detailed biostratigraphic work coupled with regional sequence stratigraphy and a more focussed sampling strategy should produce a high quality age-model for this prospective interval that had not received significant attention until recently.

メキシコ合衆国ティサパ鉱山の開発

The Tizapa Mine is located approximately 130 line kilometers west of Mexico City, the United States of Mexico.The deposit is classified into strata-bound massive sulfide deposit similar to the Kuroko type deposit in Japan, in which Dowa Mining Co., Ltd. has accumulated much experience and technology for its exploration and development. In fact, the Tizapa Mine is the first example in Mexico developed by+using this technology.Following the discovery of the deposit by Consejo Recurso de Mineral (CRM) in 1977, exploration was carried out as an Official Development Assistance project between the Mexican and Japanese governments through CRM and Japan International Cooperation Agency/Metal Mining Agency of Japan in 1987. After an international tender offered by Mexican government, the result of the project was succeeded as the development of the Tizapa Mine by Minera Tizapa, S. A. de C. V., a private joint venture company, among Dowa Mining Co., Ltd., Sumitomo Corporation and Industrias Penoles, S. A. de C. V., which is the leading Mexican mining company and the largest silver producer in the world.The development of the Tizapa Mine has been very successful by mutual cooperation among the parties and now the production is reached at 25, 000 tonnes per month, crude ore. Following the successful result of a surface exploration drilling program around the deposit, an expansion plan aiming at 40, 000 tone per month production is now underway.

Lower and lower Middle Pennsylvanian coal palynofloras, southwestern Virginia

Lower and lower Middle Pennsylvanian coals, recovered from an exploratory drilling program in southwestern Virginia, were analyzed for their palynomorph content. Results show them to be dominated by spores produced by arboreous lycopsids. Lycospora pellucida and Lycospora pusilla generally are the most common species, with others, namely Lycospora granulata, L. micropapillata and Lycospora orbicula being locally abundant. Densosporites, Cristatisporites, Radiizonates and Cingulizonates, representing small lycopsids, and Granulatisporites, produced by small ferns, and perhaps some pteridosperms typically are sub-dominant taxa. The recovered palynofloras are similar in overall composition making individual coal bed identification and correlation very difficult, if not impossible. However, the introduction and extinction of a few forms do assist the correlation of packages of strata, on both an intra- and interbasinal scale. Dictyotriletes bireticulatus is first observed in basal Lee Formation strata, at about the level of the Cove Creek coal bed. Radiizonates aligerans and R. striatus also appear more abundantly at this level, although some forms have been observed in older, Pocahontas Formation coals. This level essentially coincides with the Namurian C/Westphalian A boundary, based on plant megafossil evidence. Laevigatosporites minor, L. vulgaris, Endosporites globiformis, E. zonalis and Granasporites medius are first seen consistently just above the Sewell coal bed. Radiizonates aligerans, R. striatus and Densosporites irregularis are last seen in the early Middle Pennsylvanian, at about the level of the Splash Dam coal bed. Schulzospora rara occurs throughout Early and early Middle Pennsylvanian strata, and is last seen in the Manchester coal. The Manchester is directly overlain by the Betsie Shale, a widespread marine unit; the base of the Betsie marks the Westphalian A/B contact. When compared with palynomorph assemblage zonations published for the Western Interior, and Eastern Interior Basins, Early and early Middle Pennsylvanian palynofloras from the Central Appalachian Basin compare most favorably with early Morrowan strata. Analysis of bench samples indicates that Lycospora typically dominates basal and middle portions of Early and early Middle Pennsylvanian coals. More terminal layers often contain higher percentages of Granulatisporites (and related trilete, sphaerotriangular genera, e.g. Lophotriletes, Acanthotriletes, Deltoidspora) and Densosporites (and related trilete, crassicingulate genera, e.g. Cristatisporites, Cingulizonates, Radiizonates). This temporal change is consistently observed and may primarily reflect a water table change within the paleomires from consistently high (covered with water or at least water-logged most of the time) to intermittently low (occasional substrate exposure).