The Occurrence of Bedding-Parallel Fibrous Calcite Veins in Permian Siliciclastic and Carbonate Rocks in Central Thailand

Bedding-parallel fibrous calcite veins crop out at two Permian carbonate localities in the Phetchabun area, central Thailand, within the Nam Duk and Khao Khwang Formations. Samples are studied to determine their petrographic, geochemical and isotopic character, depositional and diagenetic associations and controls on the formation of fibrous calcite across the region. Biomarker and non-biomarker parameters are used to interpret organic matter sources in the vein-hosting units, the depositional environment and levels of source rock maturation in order to evaluate source rock potential in the two Formations. Carbon and oxygen isotope values of the veins and the host are determined to discuss the source of carbonates and diagenetic conditions. The petroleum assessment from the Khao Khwang and Nam Duk Formations suggests that both Formations are a petroleum potential source rock with type II/III kerogen deposited in an estuarine environment or a shallow marine environment and a slope-to-basin marine environment or an open marine environment, respectively. The bedding-parallel fibrous calcite veins from the Khao Khwang and Nam Duk Formations are divided into two types: 1) beef and, 2) cone-in-cone veins. The carbon and oxygen isotope compositions from the fibrous calcite veins suggest that the calcite veins could be precipitated from a carbon source generated in the microbial methanogenic zone. The results in this study provide a better understanding of the interrelationship between the bedding-parallel fibrous calcite veins and petroleum source rock potential.

LA-ICP-MS U-Pb dating and geochemical characterization of oil inclusion-bearing calcite cements: Constraints on primary oil migration in lacustrine mudstone source rocks

To date, few isotope age constraints on primary oil migration have been reported. Here we present U-Pb dating and characterization of two fracture-filling, oil inclusion-bearing calcite veins hosted in the Paleocene siliciclastic mudstone source rocks in Subei Basin, China. Deposition age of the mudstone formation was estimated to be ca. 60.2−58.0 Ma. The first vein consists of two major phases: a microcrystalline-granular (MG) calcite phase, and a blocky calcite phase, each showing distinctive petrographic features, rare earth element patterns, and carbon and oxygen isotope compositions. The early MG phase resulted from local mobilization of host carbonates, likely associated with disequilibrium compaction over-pressuring or tectonic extension, whereas the late-filling blocky calcite phase was derived from overpressured oil-bearing fluids with enhanced fluid-rock interactions. Vein texture and fluorescence characteristics reveal at least two oil expulsion events, the former represented by multiple bitumen veinlets postdating the MG calcite generation, and the latter marked by blue-fluorescing primary oil inclusions synchronous with the blocky calcite cementation. The MG calcite yields a laser ablation−inductively coupled plasma−mass spectrometry U-Pb age of 55.6 ± 1.4 Ma, constraining the earliest timing of the early oil migration event. The blocky calcite gives a younger U-Pb age of 47.8 ± 2.3 Ma, analytically indistinguishable from the U-Pb age of 46.5 ± 1.7 Ma yielded by the second calcite vein. These two ages define the time of the late oil migration event, agreeing well with the age estimate of 49.7−45.2 Ma inferred from fluid-inclusion homogenization temperature and published burial models. Thermodynamic modeling shows that the oil inclusions were trapped at ∼27.0−40.9 MPa, exceeding corresponding hydrostatic pressures (23.1−26.7 MPa), confirming mild-moderate overpressure created by oil generation-expulsion. This integrated study combining carbonate U-Pb dating and fluid-inclusion characterization provides a new approach for reconstructing pressure-temperature-composition-time points in petroleum systems.

Reservoir Monitoring Activities for Co2 Wag Pilots

Two CO2 WAG Pilots are in progress in an Abu Dhabi Oil Reservoir. Each pilot has one horizontal producer and two horizontal injectors along with 2 vertical pilot observers to monitor the movement of flood front away from the injectors. The pilots are being monitored based on a detailed reservoir-monitoring plan. The paper discusses in detail various activities and the results related to the pilot monitoring. Methods, Procedures, Process The wells are being tested for oil rate, water cut, GOR on a daily basis using MPFM. For calibration purposes portable test separators are used every quarter to validate the rate, water cut and GOR measurements. Separator PVT samples from pilot wells are collected every quarter for PVT analysis. In addition PVT samples are also collected from the pilot wells and nearby wells every month from the sampling point near MPFM to monitor the CO2 content in the produced gas. Online CO2 analyzer is fitted on the surface flow line connecting pilot wells to the RDS to provide continuous measurement of CO2 in the produced fluid. Produced water is also sampled for detailed compositional analysis. Different gas and water tracers have been injected through the pilot injectors to trace the movement and breakthrough of injected fluids into the pilot producers. Sampling and analysis for tracer is carried out on a regular basis. Carbon and oxygen Isotope analysis for produced and injected CO2 gas is also carried out in order to monitor the breakthrough of injected CO2 into the pilot producers. There is a good difference in the carbon and oxygen isotopes of injected CO2 and the CO2 present in the reservoir. To monitor the changes in water and gas saturation with time across different layers a set of Pulsed neutron (RAS) logs are run in the observers on regular basis. PLT logs are run in the injectors and producers to check the distribution and conformance of the produced and injected fluids along the horizontal wellbore. Walk away VSP surveys are being carried out on regular intervals for one pilot to monitor the injected fluids distribution in the pilot area. The paper describes all these reservoir monitoring activities in detail. Results, Observations, Conclusions Analysis of Carbon oxygen RST logs are helpful for tracking fluid saturation changes and CO2 movement across the logged intervals. The RST logs in the observers demonstrate good sweep across different layers of the reservoir. Analysis of CO2 in produced gas has resulted into correctly pointing out the timing of CO2 breakthrough in the producers. It is well supported by the CO2 isotopes analysis for the injected and produced CO2 through pilot producer and nearly producers. The tracer analysis results show clearly the injector from where the injected CO2 has reached the producers. The PLT logs demonstrate good conformance for CO2 and water injection across the horizontal section in the injectors. All these monitoring activities provide a good source of data for further analysis and improved understanding of the pilots. Novel/Additive Information The paper discusses the usefulness of different reservoir monitoring tools for improved understanding of the pilots, which will be used as a basis for implementing CO2 WAG for the full area development.

Depositional Processes of the Cenomanian-Turonian Reworked Carbonates in the Eastern Abu Dhabi, UAE

There are a limited number of studies and exploration cases for a "reworked carbonate" in Abu Dhabi, although these sediments are composed from some large oil and gas fields around the world (e.g. Poza Rica oil field in Mexico and Ruby gas field in Indonesia). In this study, we focused on Cenomanian-Turonian carbonates and considered the depositional processes of a "reworked carbonate" in the eastern part of Abu Dhabi. To understand the stacking pattern and/or depositional process of the Cenomanian-Turonian carbonate, we conducted a well-well correlation for total 16 wells, based on the core observations, wireline logs correlation (GR, Neutron, Density, Resistivity and Sonic), carbon and oxygen isotope analysis and trace elements analysis. Sampling was conducted for 8 wells and samples were taken approximately every 5 ft. In addition, to predict the spatiotemporal expansion of the reworked deposit, a 3D seismic interpretation was conducted. The result of the well-well correlation reveals that the depositional process and the stacking pattern of the Cenomanian-Turonian shoals around eastern Abu Dhabi are well consistent with the depositional model that proposed by Razin et al., 2010, and the reworked deposits are developed around the distal environment. 3D seismic interpretation represents that these reworked sediments were input from the north-west side and spread to the south-east like as a submarine-fan. Considering the core observation result, cohesive debris flow deposits are dominated at the depositional up-dip side and dilute flow deposits are dominated in the depositional down-dip side. In addition, an obvious erosional surface can be recognized in seismic sections and it truncates the top shoal sediments. The result of both, a combination of localized up-rift and global eustatic sea level fall in the early-middle Turonian triggered the regional erosion which is recognized as the middle Turonian unconformity. The result of this study suggests that the shoal sediments were eroded and reworked to a more distal environment at the early-middle Turonian.

Some Aspects of Sedimentology of the Wanganui Basin, North Island, New Zealand

<p>The thesis comprises studies of the marine Pleistocene sediments of the Wanganui Basin, North Island, New Zealand. Part I deals with the chronology of the sediments and correlation of horizons within and outside the basin, by dating glass shards from tephra horizons using the fission-track method. Correlation to similar tephras from Hawke's Bay, to deep-sea cores taken 1000km east of New Zealand and to the central North Island volcanic district is attempted. These fission-track ages fill a dating gap that previously existed in the New Zealand marine Quaternary sequence. Thirteen tephras were examined in the Wanganui Basin and were found to range in age from 1.50 [plus or minus] 0.21m.y.B.P. (Ohingaiti Ash) to 0.28 [plus or minus] 0.05m.y.B.P. (uppermost Finnis Road Ash). These tephras record major rhyolitic eruptive phases in the central volcanic region. The most significant eruptive phase began 1.06 [plus or minus]0.16m.y.B.P. with the deposition of the Makirikiri Tuff sediments, continued to 0.88 [plus or minus]0.13m.y.B.P. and is tentatively associated with the older ignimbrites of the King Country, west of Lake Taupe. A volcanically quiet period followed when no volcanic glass was deposited in the sediments, until 0.74 [plus or minus] 0.09m.y.B.P. Several large eruptions then occurred between 0.74 and 0.28m.y.B.P. The age of the Plio-Pleistocene boundary, at the base of the Hautawan Stage in the Wanganui Basin is 1.87m.y.B.P. The age of the base of the Nukumaruan is 1.55m.y.B.P., the Okehuan, 1.06m.y.B.P., the Castleclifflan 0.45m.y.B.P., and the Hawera Series is less than 0.38m.y.B.P. Palaeomagnetic stratigraphy was determined for the upper Nukumaruan and lower Okehan sequence in the Rangitikei River. Viscous components of magnetism were removed from the samples by thermal demagnetising, extreme care being needed to obtain consistent results. Independent dates from the palaeomagnetic stratigraphy substantially confirm the fission-track dates. The Bruhnes-Matuyama boundary is clearly defined between the Rewa and Potaka Pumice Members (aged 0.74 and 0.61m.y.B.P. respectively) of the Kaimatira Pumice Send Formation. The Jaramillo event was not recognised and is probably represented in part of the sequence where sediments are too coarse and friable to yield palaeomagnetic cores. Part II deals with the detailed sedimentology of the lower Okehuan Stage sequence which is composed of two volcaniclastic formations, the Makirikiri Tuff and Kaimatira Pubmice Sand, separated by a non-volcaniclastic siltstone formation, the Okehu Siltstone. Interpretations of the Sedimentary structures in the Makirikiri Tuff and the Kaimatira Pumice Sand Formation confirm previous conclusions of shallow water deposition based on palaeontological evidence. Some structures also indicate the high rate of sediment accumulation during deposition of the volcancic sediments. Size analysis statistics show influence of source material and processes acting on the sediment during transport and deposition. Rapid sediment accumulation is emphasised by poor sorting, and processed inferred from the sedimentary structures are confirmed by the grain size analyses of the same structures. Analysis of the attitude of large and small scale cross-stratification reveals a complex polymodal palaeocurrent pattern, as might be expected of shallow water to intertidal sequences. Although often bipolar-bimodal, the dominant sediment transport appears to have been from west to east, similar to the direction of current movement along the Wanganui coast today. Size and petrography of clasts from the conglomeratic horizons indicated sediment sources both from the central volcanic region of North Island and from the Mesozoic "greywackes" of the axial mountain ranges which were emergent and probably significantly elevated at the time when the sediments were accumulating. No volcanic debris was deposited with the Okehu Siltstone. The mineralogy of the sands points to the same sediment sources but also indicates that some metamorphic material was being introduced most likely from South Island. Part III of the thesis represents a pilot study undertaken to determine whether isotopic differences in fossil shell composition could be used to distinguish shells that grew in fully marine water from those that grew in less saline conditions. Carbon and oxygen isotope ratios were determined on shells from three formations whose environments had been adequately studied by paleontologists. The horisons chosen were the Waipuru Shellbed, the Tewkesbury Formation and the Tainui Shellbed. Agreement with the palaeontological evidence and thus distinction between the fully marine and the fresh water contaminated marine environments was possible with the technique.</p>

Some Aspects of Sedimentology of the Wanganui Basin, North Island, New Zealand

<p>The thesis comprises studies of the marine Pleistocene sediments of the Wanganui Basin, North Island, New Zealand. Part I deals with the chronology of the sediments and correlation of horizons within and outside the basin, by dating glass shards from tephra horizons using the fission-track method. Correlation to similar tephras from Hawke's Bay, to deep-sea cores taken 1000km east of New Zealand and to the central North Island volcanic district is attempted. These fission-track ages fill a dating gap that previously existed in the New Zealand marine Quaternary sequence. Thirteen tephras were examined in the Wanganui Basin and were found to range in age from 1.50 [plus or minus] 0.21m.y.B.P. (Ohingaiti Ash) to 0.28 [plus or minus] 0.05m.y.B.P. (uppermost Finnis Road Ash). These tephras record major rhyolitic eruptive phases in the central volcanic region. The most significant eruptive phase began 1.06 [plus or minus]0.16m.y.B.P. with the deposition of the Makirikiri Tuff sediments, continued to 0.88 [plus or minus]0.13m.y.B.P. and is tentatively associated with the older ignimbrites of the King Country, west of Lake Taupe. A volcanically quiet period followed when no volcanic glass was deposited in the sediments, until 0.74 [plus or minus] 0.09m.y.B.P. Several large eruptions then occurred between 0.74 and 0.28m.y.B.P. The age of the Plio-Pleistocene boundary, at the base of the Hautawan Stage in the Wanganui Basin is 1.87m.y.B.P. The age of the base of the Nukumaruan is 1.55m.y.B.P., the Okehuan, 1.06m.y.B.P., the Castleclifflan 0.45m.y.B.P., and the Hawera Series is less than 0.38m.y.B.P. Palaeomagnetic stratigraphy was determined for the upper Nukumaruan and lower Okehan sequence in the Rangitikei River. Viscous components of magnetism were removed from the samples by thermal demagnetising, extreme care being needed to obtain consistent results. Independent dates from the palaeomagnetic stratigraphy substantially confirm the fission-track dates. The Bruhnes-Matuyama boundary is clearly defined between the Rewa and Potaka Pumice Members (aged 0.74 and 0.61m.y.B.P. respectively) of the Kaimatira Pumice Send Formation. The Jaramillo event was not recognised and is probably represented in part of the sequence where sediments are too coarse and friable to yield palaeomagnetic cores. Part II deals with the detailed sedimentology of the lower Okehuan Stage sequence which is composed of two volcaniclastic formations, the Makirikiri Tuff and Kaimatira Pubmice Sand, separated by a non-volcaniclastic siltstone formation, the Okehu Siltstone. Interpretations of the Sedimentary structures in the Makirikiri Tuff and the Kaimatira Pumice Sand Formation confirm previous conclusions of shallow water deposition based on palaeontological evidence. Some structures also indicate the high rate of sediment accumulation during deposition of the volcancic sediments. Size analysis statistics show influence of source material and processes acting on the sediment during transport and deposition. Rapid sediment accumulation is emphasised by poor sorting, and processed inferred from the sedimentary structures are confirmed by the grain size analyses of the same structures. Analysis of the attitude of large and small scale cross-stratification reveals a complex polymodal palaeocurrent pattern, as might be expected of shallow water to intertidal sequences. Although often bipolar-bimodal, the dominant sediment transport appears to have been from west to east, similar to the direction of current movement along the Wanganui coast today. Size and petrography of clasts from the conglomeratic horizons indicated sediment sources both from the central volcanic region of North Island and from the Mesozoic "greywackes" of the axial mountain ranges which were emergent and probably significantly elevated at the time when the sediments were accumulating. No volcanic debris was deposited with the Okehu Siltstone. The mineralogy of the sands points to the same sediment sources but also indicates that some metamorphic material was being introduced most likely from South Island. Part III of the thesis represents a pilot study undertaken to determine whether isotopic differences in fossil shell composition could be used to distinguish shells that grew in fully marine water from those that grew in less saline conditions. Carbon and oxygen isotope ratios were determined on shells from three formations whose environments had been adequately studied by paleontologists. The horisons chosen were the Waipuru Shellbed, the Tewkesbury Formation and the Tainui Shellbed. Agreement with the palaeontological evidence and thus distinction between the fully marine and the fresh water contaminated marine environments was possible with the technique.</p>

Role of Hydrothermal Fluids in the Formation of the Kamioka Skarn-Type Pb–Zn Deposits, Japan

The Kamioka mine, located in Gifu Prefecture in Japan, is famous for the large water Cherenkov detector system, the Super-Kamiokande. The Kamioka skarn-type Pb–Zn deposits are formed in crystalline limestone and are replaced by skarn minerals within the Hida metamorphic rocks. The Kamioka deposits mainly consist of the Tochibora, Maruyama, and Mozumi deposits. The present study focuses on the ore-forming hydrothermal fluid activity in the Kamioka deposits and the peripheral exploration area based on the carbon and oxygen isotope ratios of calcite and rare earth element (REE) analyses. The carbon and oxygen isotope ratios of crystalline limestone (as the host rock) are not homogeneous, and depending on the degree of hydrothermal activity, they decreased to various degrees because of the reaction with the ore fluids. Thus, the carbon and oxygen isotope ratios of crystalline limestone can be used as an indicator of the influence of the hydrothermal fluids for the ore mineralization. The REE contents in the ores of igneous origin are one order of magnitude higher than the limestone origin. Further, depending on the formation temperatures, calcites precipitated during ore mineralization have a stable carbon isotope ratio and a widely varying oxygen isotope ratios. The Kamioka district fracture system is likely a major control factor on ore mineralization from hydrothermal activity. In addition, the skarnization-related ore-forming fluids are mostly meteoric in origin, confirming the conclusions from previous studies.