Ryan Ramsook - Academia.edu (original) (raw)
Papers by Ryan Ramsook
Sedimentology, Nov 26, 2023
Pure and Applied Geophysics, Nov 22, 2023
West Indian journal of engineering, 2024
Durability, compactness, and natural strength of sandstones are pivotal properties for its subseq... more Durability, compactness, and natural strength of sandstones are pivotal properties for its subsequent application as a building material. If a sandstone is tight and contains petroleum, then hydraulic fracturing is necessary to achieve commercial production. The Casa Cruz Sandstone Member, southern Trinidad, is currently being explored as a potential petroleum target and building material. This study investigates the petrographic, petrophysical, and mechanical characteristics of the Casa Cruz sandstone to understand the factors that control the quality of the sandstone and to determine the sandstone's suitability as a natural resource. A thin-section analysis was performed to investigate the mineralogy, texture, and diagenesis of the sandstone. Permeability, porosity, density, P-and S-wave velocities, unconfined compressive strength (UCS) and confined compressive strength were measured. The elastic properties (Young's modulus, shear modulus, bulk modulus, and Poisson's ratio) were estimated from inversion of the P-and Swave velocities. The results show that the Casa Cruz sandstone is one of the tightest sandstone types reported in the literature with porosity of 0.7% and permeability of 4.7 x 10-22 m 2 (0.47 nD). Authigenic cementation and mechanical compaction are the main diagenetic processes that jointly controlled the quality of the sandstone. The sandstone was classified as a very strong (UCS of 128 MPa) quartz-arenite and is barren of petroleum and bioclasts. Brittle failure behaviour was exhibited, accompanied by axial splitting fractures and shear fractures under unconfined and confined conditions, respectively. The Casa Cruz sandstone is suggested to be an excellent building material as its petrophysical and mechanical properties are comparable to those of commercial industry grade of Westerly granite and Naparima Hill argillite.
International Journal of Coal Geology, Oct 1, 2020
The late Cretaceous Naparima Hill Formation in the South Trinidad Basin (southeast Caribbean) is ... more The late Cretaceous Naparima Hill Formation in the South Trinidad Basin (southeast Caribbean) is a prolific source rock with a potential for unconventional hydrocarbon exploration. It is exposed across the Central Range and extends to the city of San Fernando. This study characterized the Naparima Hill source rock using petrographic analysis techniques (X-ray diffraction and thin section analysis) and petrophysical techniques. These techniques were applied to outcrop samples that were collected from 11 locations. Firstly, petrographic analysis was used to determine the mineral composition and lithofacies. Secondly, plugs were taken perpendicular to bedding and the bulk density was determined in dry conditions. Thirdly, porosity and grain density were determined using a porosimeter at ambient conditions. Finally, permeability measurements were obtained at 10 MPa to 130 MPa effective pressures using the transient pulse decay technique. The results show that the source rock is dominated by silica with carbonate as secondary minerals. Four lithofacies were identified: (a) siliceous-calcareous mudstone (b) calcareous mudstones interbedded with black chert, (c) carbonate-rich mudstone with nodular chert and (d) siliceous mudstone. Ranges of 5.9 to 30.8%, 2362 to 2668 kg/m 3 and 1804 to 2350 kg/m 3 were determined for porosity, grain density and bulk density, respectively. The permeability ranges from 3.96 × 10 −20 to 5.94 × 10 −18 m 2 and shows very little dependence on the effective pressure. Permeability and porosity are moderately correlated (R 2 = 0.6). There is no relationship between permeability and mineralogical composition. The observed microfractures, diagenetic processes and grain sorting, are factors that have affected the permeability-porosity relationship to varying degrees. However, none of these factors can be considered as the main intrinsic factor controlling the permeability of the samples. Overall, it is difficult to predict the permeability of the Naparima Hill Formation with any of the proxies (density, mineralogy and porosity) determined in this study.. List of symbols k Permeability φ Porosity ρ Density σ Stress γ Pressure sensitivity factor
Research Square (Research Square), Jan 3, 2023
The compressive and tensile strengths are essential parameters used for determining the safe mud ... more The compressive and tensile strengths are essential parameters used for determining the safe mud weight window (SMWW) during borehole drilling, especially in friable rocks where the SMWW tends to be narrow and therefore, the margin for wellbore instability issues is high. However, these parameters are seldomly reported for friable rocks due to the di culties and challenges faced while recovering and preparing friable cores and outcrop samples for strength testing. This study evaluates the compressive and tensile strengths of friable rocks under dry and saturated conditions, and investigates how strength anisotropy affect the SMWW. Uncon ned compressive strength, con ned compressive strength (up to 130 MPa effective pressure), and Brazilian (tensile strength) measurements were made perpendicular and parallel to the outcrop bedding of the friable sandstone and thinbed shale lithofacies of the Erin Formation, Southern Trinidad. In spite of this Formation being one of the main petroleum reservoirs, there are no published data on the rock strength. The results show that strength anisotropy exist, which is larger under saturated conditions. Under con nement, the friable rocks accumulated large strain (an average of 20% strain) and experienced signi cant strain hardening causing the strength to be high. The ratio of the yield strength to failure strength is less than 0.2, under dry conditions. Thin section analysis of tested specimens shows intragranular fracturing across quartz grains, which led to grain crushing and pore collapse. Catalastic ow within the specimens and no stress drop after the peak stress suggest the friable rocks failed in a ductile manner. The effect of the strength anisotropy on the SMWW for the sandstone and thin-bed shale was determined for wells that are orientated in the principal stress directions (S v , S hnmi and S Hmax), of a normal faulting stress regime, at depths of 3400 to 6900 ft. The upper mud weight limit of the SMWW is not in uenced by the tensile strength anisotropy. However, the lower mud weight of the SMWW was in uenced by the compressive strength anisotropy, predominantly for S v and S hnmi aligned wells that are penetrating through the saturated friable sandstone. Since the rocks are friable, drilling outside of the SMWW by 5% to 8%, if forecasted using the strongest compressive strength, can result in wellbore instability.
International Journal of Rock Mechanics and Mining Sciences, 2022
Second International Meeting for Applied Geoscience & Energy
In the Holocene compound clinoforms are well recognized, but there are very few examples in the r... more In the Holocene compound clinoforms are well recognized, but there are very few examples in the rock record. Utilizing 191 m of measured section of exposed highstand Orinoco delta deposits along the southwest coast of Trinidad, three main facies associations (FAs) were identified: FA1: up to 35 m of coarsening upward (CU) successions with a net to gross (N:G) < 60%; FA2: 2-4 m of a muddy subaqueous platform with a N:G < 10% and ; FA3: the shoreline clinothem consisting of sandy CU units up to 15 m with a high N:G, > 85%. This study illustrates how both grain size distribution and facies can be used to successfully distinguish compound clinoforms in the rock record
Journal of Applied Geophysics
Abstract Mud volcanoes are often associated with violent eruptions which are hazardous and pose s... more Abstract Mud volcanoes are often associated with violent eruptions which are hazardous and pose significant risks to lives and livelihoods. A pseudo-3D electrical resistivity tomography (ERT) method that is integrated with digital elevation model (DEM) is used to map and monitor the near-surface structures and morphology of a mud volcano in Piparo, Trinidad. The mudflow within the vent is characterized by very low resistivity of less than 2.5 Ωm. Most of the mudflow within the near-surface is located north of the main crater. A magnitude 6.9 earthquake, located near the northern coast of Venezuela, caused the vent to enlarge, the mud volcano to be displaced towards the north, the crater region to sink by 0.2 m, and the flanks to rise by 0.7 m. This study demonstrates that the integrated pseudo-3D ERT and DEM provide means to monitor the dynamic geological interplay between the surface and subsurface geometry and structures.
Memoir 123: South America—Caribbean—Central Atlantic Plate Boundary: Tectonic Evolution, Basin Architecture, and Petroleum Systems
SEPM (Society for Sedimentary Geology) eBooks, 2007
Journal of Applied Geophysics, 2022
Sedimentology and Geological Evolution of the Late Cretaceous-Paleocene succession, Rio Grande Va... more Sedimentology and Geological Evolution of the Late Cretaceous-Paleocene succession, Rio Grande Valley, Blue Mountain Inlier, Northeast Jamaica
Electrical resistivity tomography method was used to monitor near-surface structures of a mud vol... more Electrical resistivity tomography method was used to monitor near-surface structures of a mud volcano in Piparo, Trinidad. This method utilizes the Wenner array electrode configuration, electrode spacing of 3 m, and 14 parallel lines spaced at 12 m apart. We acquired data at two different times. The first dataset were acquired in July 2018. On the 21st of August 2018, a magnitude 6.9 earthquake occurred near the northern coast of Venezuela, and greatly affected the study area, as well as the majority of Trinidad. The second dataset were acquired in January 2019. The data (electrical resistivity data.rar) contain:<br> July 2018 2D and pseudo-3D data sets<br> January 2019 2D and pseudo-3D data sets
Rock Mechanics and Rock Engineering, 2021
Argillites are indurated mudstones and have relatively high strength and low permeability. These ... more Argillites are indurated mudstones and have relatively high strength and low permeability. These rocks are: often used for aggregates in the construction industry, used as armour rock for sea walls, good sites for the waste repository (e.g. Cuisinier et al. 2009; Jia et al. 2009; Zhang et al. 2014), and unconventional petroleum reservoirs provided that the organic content is high (e.g. Rodnikova et al. 1968). In the mining of most rocks including argillites, several engineering issues are encountered, such as rock fracturing around mining pits and the support and control of the fractured rock masses, during drilling, blasting, and tunnelling (e.g. Aladejare 2020). The Uniaxial compressive strength (UCS) and tensile strength are important prerequisite parameters in the engineering design to minimize these issues (e.g. Ng et al. 2015). The lack of these data will result in poor engineering design that can lead to the collapse of the mining and tunnelling sites. Therefore them is imperative to quantify the UCS and tensile strength by direct measurement or estimating it from other available data such as velocity, and elastic properties. The UCS measurement can be time-consuming, expensive and impossible, especially for rocks that has well developed foliation and those that are highly fractured. The challenging aspect of determining the UCS is in the sample preparation, as the measurement requires sample with a length-to-diameter ratio (L/D) of 2.5–3 and their ends has to be parallel within ± 0.02 mm in accordance to ISRM (1983) standards. The Brazilian test, which is the most common indirect method used to measure the tensile strength, requires a circular disk with a thickness-to-diameter ratio (t/D) between 0.2 and 0.75 (ASTM D3967 2008). The preparation of circular disks is much easier to achieve compared to the sample dimensions required for UCS. In view of the fact that highly fractured rocks are unsuitable and high-quality rock core sample required for the UCS test are unavailable (Karaman et al. 2015; Ribeiro et al. 2016), empirical equations with a strong correlation will be more practical and efficient to estimate the UCS (Nazir et al. 2013). There are various studies in the literature proposing relationships between UCS and tensile strength, UCS and velocities, and UCS and elastic properties on different rock types but no such relationships exist for argillites to the authors’ knowledge (e.g. Arslan et al. 2008; Çobanoğlu and Çelik * O. O. Blake oshaine.blake@sta.uwi.edu
Journal of Petroleum Science and Engineering, 2021
Abstract The upper Cretaceous Naparima Hill Formation, a primary source rock for conventional oil... more Abstract The upper Cretaceous Naparima Hill Formation, a primary source rock for conventional oil and gas reservoirs in Southern and Columbus basins, Trinidad is now considered an unconventional reservoir. Effective fracability evaluation is critical to the entire process of unconventional reservoir exploitation. At present, there exists no information on the fracability of the Naparima Hill Formation. A recent study have shown that the Formation consist of four lithofacies (siliceous-calcareous mudstone, calcareous mudstones, carbonate-rich mudstone and siliceous mudstone) that are highly brittle, implying that they are easily fractured. This is debatable because brittle rocks can have a higher fracture toughness, making them more difficult to fracture. In this study, an existing fracability evaluation model that incorporates brittleness, fracture toughness, and minimum horizontal insitu stress was used to evaluate the fracability of the four lithofacies within the Naparima Hill Formation. Through a series of laboratory testing (measurements of P- and S-wave velocities, uniaxial compression tests and Brazilian tests) of the dry outcrop samples, elastic properties (Young's modulus and Poisson's ratio), uniaxial compressive strength and tensile strength were determined. X-ray diffraction analysis (XRD) was also performed on the outcrop samples to determine their mineral compositions. Brittleness indices based on the rock elastic properties, rock strength and mineral compositions were used to evaluate the rock brittleness, and the fracture toughness was estimated from the tensile strength. The study results indicate that all lithofacies are highly brittle, which is consistent with the previous study. The fracability evaluation results showed that the siliceous calcareous mudstones and siliceous mudstones are more fracable than the calcareous and carbonate-rich mudstones. The key factors that control the fracability of the Formation were found to be the amount of quartz, and the rock strength that is influenced by calcite cementation.
Pure and Applied Geophysics, 2021
Bulk modulus is one of the mechanical properties used in any rock engineering related project. Th... more Bulk modulus is one of the mechanical properties used in any rock engineering related project. This property can be measured statically, where it is derived from stress–strain data, and dynamically, where it is derived from P- and S-wave velocities. The static bulk modulus is generally different from the corresponding dynamic bulk modulus. As the static bulk modulus is required in computation or modelling of the deformation of the rock when it is stressed hydrostatically, empirical relationships between the static and dynamic bulk moduli are needed to convert the dynamic bulk modulus to static values. In this study, the static and dynamic bulk moduli were measured simultaneously, at effective pressures up to 130 MPa, for dry and fluid-saturated argillites. The samples were collected from four different lithofacies within the upper Naparima Hill Formation, Trinidad. The results show that the dynamic bulk modulus is greater than the static bulk modulus, except for hard lithofacies under dry conditions where the static and dynamic moduli are approximately equal. Under saturated conditions, the porosity plays a key role in increasing the difference between the static and dynamic bulk moduli. A linear relationship with high correlation (R2 greater than 0.85) was established between the static and dynamic bulk moduli, which is dependent on the effective pressure and saturation state.
Journal of Sedimentary Research, 2020
Icehouse continental-shelf-margin accretion is typically driven by high-sediment-supply deltas an... more Icehouse continental-shelf-margin accretion is typically driven by high-sediment-supply deltas and repeated glacio-eustatic, climate-driven sea-level changes on a ca. 100 ky time scale. The paleo–Orinoco margin is no exception to this, as the paleo–Orinoco River Delta with its high sediment load prograded across Venezuela, then into the Southern and Columbus basins of Trinidad since the late Miocene, depositing a continental-margin sedimentary prism that is > 12 km thick, 200 km wide, and 500 km along dip. The Cruse Formation (> 800 m thick; 3 My duration) records the first arrival of the paleo–Orinoco Delta into the Trinidad area. It then accreted eastwards, outwards onto the Atlantic margin, by shallow to deepwater clinoform increments since the late Miocene and is capped by a major, thick flooding interval (the Lower Forest Clay). Previous research has provided an understanding of the paleo–Orinoco Delta depositional system at seismic and outcrop scales, but a clinoform fra...
Journal of Petroleum Science and Engineering, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Sedimentology, Nov 26, 2023
Pure and Applied Geophysics, Nov 22, 2023
West Indian journal of engineering, 2024
Durability, compactness, and natural strength of sandstones are pivotal properties for its subseq... more Durability, compactness, and natural strength of sandstones are pivotal properties for its subsequent application as a building material. If a sandstone is tight and contains petroleum, then hydraulic fracturing is necessary to achieve commercial production. The Casa Cruz Sandstone Member, southern Trinidad, is currently being explored as a potential petroleum target and building material. This study investigates the petrographic, petrophysical, and mechanical characteristics of the Casa Cruz sandstone to understand the factors that control the quality of the sandstone and to determine the sandstone's suitability as a natural resource. A thin-section analysis was performed to investigate the mineralogy, texture, and diagenesis of the sandstone. Permeability, porosity, density, P-and S-wave velocities, unconfined compressive strength (UCS) and confined compressive strength were measured. The elastic properties (Young's modulus, shear modulus, bulk modulus, and Poisson's ratio) were estimated from inversion of the P-and Swave velocities. The results show that the Casa Cruz sandstone is one of the tightest sandstone types reported in the literature with porosity of 0.7% and permeability of 4.7 x 10-22 m 2 (0.47 nD). Authigenic cementation and mechanical compaction are the main diagenetic processes that jointly controlled the quality of the sandstone. The sandstone was classified as a very strong (UCS of 128 MPa) quartz-arenite and is barren of petroleum and bioclasts. Brittle failure behaviour was exhibited, accompanied by axial splitting fractures and shear fractures under unconfined and confined conditions, respectively. The Casa Cruz sandstone is suggested to be an excellent building material as its petrophysical and mechanical properties are comparable to those of commercial industry grade of Westerly granite and Naparima Hill argillite.
International Journal of Coal Geology, Oct 1, 2020
The late Cretaceous Naparima Hill Formation in the South Trinidad Basin (southeast Caribbean) is ... more The late Cretaceous Naparima Hill Formation in the South Trinidad Basin (southeast Caribbean) is a prolific source rock with a potential for unconventional hydrocarbon exploration. It is exposed across the Central Range and extends to the city of San Fernando. This study characterized the Naparima Hill source rock using petrographic analysis techniques (X-ray diffraction and thin section analysis) and petrophysical techniques. These techniques were applied to outcrop samples that were collected from 11 locations. Firstly, petrographic analysis was used to determine the mineral composition and lithofacies. Secondly, plugs were taken perpendicular to bedding and the bulk density was determined in dry conditions. Thirdly, porosity and grain density were determined using a porosimeter at ambient conditions. Finally, permeability measurements were obtained at 10 MPa to 130 MPa effective pressures using the transient pulse decay technique. The results show that the source rock is dominated by silica with carbonate as secondary minerals. Four lithofacies were identified: (a) siliceous-calcareous mudstone (b) calcareous mudstones interbedded with black chert, (c) carbonate-rich mudstone with nodular chert and (d) siliceous mudstone. Ranges of 5.9 to 30.8%, 2362 to 2668 kg/m 3 and 1804 to 2350 kg/m 3 were determined for porosity, grain density and bulk density, respectively. The permeability ranges from 3.96 × 10 −20 to 5.94 × 10 −18 m 2 and shows very little dependence on the effective pressure. Permeability and porosity are moderately correlated (R 2 = 0.6). There is no relationship between permeability and mineralogical composition. The observed microfractures, diagenetic processes and grain sorting, are factors that have affected the permeability-porosity relationship to varying degrees. However, none of these factors can be considered as the main intrinsic factor controlling the permeability of the samples. Overall, it is difficult to predict the permeability of the Naparima Hill Formation with any of the proxies (density, mineralogy and porosity) determined in this study.. List of symbols k Permeability φ Porosity ρ Density σ Stress γ Pressure sensitivity factor
Research Square (Research Square), Jan 3, 2023
The compressive and tensile strengths are essential parameters used for determining the safe mud ... more The compressive and tensile strengths are essential parameters used for determining the safe mud weight window (SMWW) during borehole drilling, especially in friable rocks where the SMWW tends to be narrow and therefore, the margin for wellbore instability issues is high. However, these parameters are seldomly reported for friable rocks due to the di culties and challenges faced while recovering and preparing friable cores and outcrop samples for strength testing. This study evaluates the compressive and tensile strengths of friable rocks under dry and saturated conditions, and investigates how strength anisotropy affect the SMWW. Uncon ned compressive strength, con ned compressive strength (up to 130 MPa effective pressure), and Brazilian (tensile strength) measurements were made perpendicular and parallel to the outcrop bedding of the friable sandstone and thinbed shale lithofacies of the Erin Formation, Southern Trinidad. In spite of this Formation being one of the main petroleum reservoirs, there are no published data on the rock strength. The results show that strength anisotropy exist, which is larger under saturated conditions. Under con nement, the friable rocks accumulated large strain (an average of 20% strain) and experienced signi cant strain hardening causing the strength to be high. The ratio of the yield strength to failure strength is less than 0.2, under dry conditions. Thin section analysis of tested specimens shows intragranular fracturing across quartz grains, which led to grain crushing and pore collapse. Catalastic ow within the specimens and no stress drop after the peak stress suggest the friable rocks failed in a ductile manner. The effect of the strength anisotropy on the SMWW for the sandstone and thin-bed shale was determined for wells that are orientated in the principal stress directions (S v , S hnmi and S Hmax), of a normal faulting stress regime, at depths of 3400 to 6900 ft. The upper mud weight limit of the SMWW is not in uenced by the tensile strength anisotropy. However, the lower mud weight of the SMWW was in uenced by the compressive strength anisotropy, predominantly for S v and S hnmi aligned wells that are penetrating through the saturated friable sandstone. Since the rocks are friable, drilling outside of the SMWW by 5% to 8%, if forecasted using the strongest compressive strength, can result in wellbore instability.
International Journal of Rock Mechanics and Mining Sciences, 2022
Second International Meeting for Applied Geoscience & Energy
In the Holocene compound clinoforms are well recognized, but there are very few examples in the r... more In the Holocene compound clinoforms are well recognized, but there are very few examples in the rock record. Utilizing 191 m of measured section of exposed highstand Orinoco delta deposits along the southwest coast of Trinidad, three main facies associations (FAs) were identified: FA1: up to 35 m of coarsening upward (CU) successions with a net to gross (N:G) < 60%; FA2: 2-4 m of a muddy subaqueous platform with a N:G < 10% and ; FA3: the shoreline clinothem consisting of sandy CU units up to 15 m with a high N:G, > 85%. This study illustrates how both grain size distribution and facies can be used to successfully distinguish compound clinoforms in the rock record
Journal of Applied Geophysics
Abstract Mud volcanoes are often associated with violent eruptions which are hazardous and pose s... more Abstract Mud volcanoes are often associated with violent eruptions which are hazardous and pose significant risks to lives and livelihoods. A pseudo-3D electrical resistivity tomography (ERT) method that is integrated with digital elevation model (DEM) is used to map and monitor the near-surface structures and morphology of a mud volcano in Piparo, Trinidad. The mudflow within the vent is characterized by very low resistivity of less than 2.5 Ωm. Most of the mudflow within the near-surface is located north of the main crater. A magnitude 6.9 earthquake, located near the northern coast of Venezuela, caused the vent to enlarge, the mud volcano to be displaced towards the north, the crater region to sink by 0.2 m, and the flanks to rise by 0.7 m. This study demonstrates that the integrated pseudo-3D ERT and DEM provide means to monitor the dynamic geological interplay between the surface and subsurface geometry and structures.
Memoir 123: South America—Caribbean—Central Atlantic Plate Boundary: Tectonic Evolution, Basin Architecture, and Petroleum Systems
SEPM (Society for Sedimentary Geology) eBooks, 2007
Journal of Applied Geophysics, 2022
Sedimentology and Geological Evolution of the Late Cretaceous-Paleocene succession, Rio Grande Va... more Sedimentology and Geological Evolution of the Late Cretaceous-Paleocene succession, Rio Grande Valley, Blue Mountain Inlier, Northeast Jamaica
Electrical resistivity tomography method was used to monitor near-surface structures of a mud vol... more Electrical resistivity tomography method was used to monitor near-surface structures of a mud volcano in Piparo, Trinidad. This method utilizes the Wenner array electrode configuration, electrode spacing of 3 m, and 14 parallel lines spaced at 12 m apart. We acquired data at two different times. The first dataset were acquired in July 2018. On the 21st of August 2018, a magnitude 6.9 earthquake occurred near the northern coast of Venezuela, and greatly affected the study area, as well as the majority of Trinidad. The second dataset were acquired in January 2019. The data (electrical resistivity data.rar) contain:<br> July 2018 2D and pseudo-3D data sets<br> January 2019 2D and pseudo-3D data sets
Rock Mechanics and Rock Engineering, 2021
Argillites are indurated mudstones and have relatively high strength and low permeability. These ... more Argillites are indurated mudstones and have relatively high strength and low permeability. These rocks are: often used for aggregates in the construction industry, used as armour rock for sea walls, good sites for the waste repository (e.g. Cuisinier et al. 2009; Jia et al. 2009; Zhang et al. 2014), and unconventional petroleum reservoirs provided that the organic content is high (e.g. Rodnikova et al. 1968). In the mining of most rocks including argillites, several engineering issues are encountered, such as rock fracturing around mining pits and the support and control of the fractured rock masses, during drilling, blasting, and tunnelling (e.g. Aladejare 2020). The Uniaxial compressive strength (UCS) and tensile strength are important prerequisite parameters in the engineering design to minimize these issues (e.g. Ng et al. 2015). The lack of these data will result in poor engineering design that can lead to the collapse of the mining and tunnelling sites. Therefore them is imperative to quantify the UCS and tensile strength by direct measurement or estimating it from other available data such as velocity, and elastic properties. The UCS measurement can be time-consuming, expensive and impossible, especially for rocks that has well developed foliation and those that are highly fractured. The challenging aspect of determining the UCS is in the sample preparation, as the measurement requires sample with a length-to-diameter ratio (L/D) of 2.5–3 and their ends has to be parallel within ± 0.02 mm in accordance to ISRM (1983) standards. The Brazilian test, which is the most common indirect method used to measure the tensile strength, requires a circular disk with a thickness-to-diameter ratio (t/D) between 0.2 and 0.75 (ASTM D3967 2008). The preparation of circular disks is much easier to achieve compared to the sample dimensions required for UCS. In view of the fact that highly fractured rocks are unsuitable and high-quality rock core sample required for the UCS test are unavailable (Karaman et al. 2015; Ribeiro et al. 2016), empirical equations with a strong correlation will be more practical and efficient to estimate the UCS (Nazir et al. 2013). There are various studies in the literature proposing relationships between UCS and tensile strength, UCS and velocities, and UCS and elastic properties on different rock types but no such relationships exist for argillites to the authors’ knowledge (e.g. Arslan et al. 2008; Çobanoğlu and Çelik * O. O. Blake oshaine.blake@sta.uwi.edu
Journal of Petroleum Science and Engineering, 2021
Abstract The upper Cretaceous Naparima Hill Formation, a primary source rock for conventional oil... more Abstract The upper Cretaceous Naparima Hill Formation, a primary source rock for conventional oil and gas reservoirs in Southern and Columbus basins, Trinidad is now considered an unconventional reservoir. Effective fracability evaluation is critical to the entire process of unconventional reservoir exploitation. At present, there exists no information on the fracability of the Naparima Hill Formation. A recent study have shown that the Formation consist of four lithofacies (siliceous-calcareous mudstone, calcareous mudstones, carbonate-rich mudstone and siliceous mudstone) that are highly brittle, implying that they are easily fractured. This is debatable because brittle rocks can have a higher fracture toughness, making them more difficult to fracture. In this study, an existing fracability evaluation model that incorporates brittleness, fracture toughness, and minimum horizontal insitu stress was used to evaluate the fracability of the four lithofacies within the Naparima Hill Formation. Through a series of laboratory testing (measurements of P- and S-wave velocities, uniaxial compression tests and Brazilian tests) of the dry outcrop samples, elastic properties (Young's modulus and Poisson's ratio), uniaxial compressive strength and tensile strength were determined. X-ray diffraction analysis (XRD) was also performed on the outcrop samples to determine their mineral compositions. Brittleness indices based on the rock elastic properties, rock strength and mineral compositions were used to evaluate the rock brittleness, and the fracture toughness was estimated from the tensile strength. The study results indicate that all lithofacies are highly brittle, which is consistent with the previous study. The fracability evaluation results showed that the siliceous calcareous mudstones and siliceous mudstones are more fracable than the calcareous and carbonate-rich mudstones. The key factors that control the fracability of the Formation were found to be the amount of quartz, and the rock strength that is influenced by calcite cementation.
Pure and Applied Geophysics, 2021
Bulk modulus is one of the mechanical properties used in any rock engineering related project. Th... more Bulk modulus is one of the mechanical properties used in any rock engineering related project. This property can be measured statically, where it is derived from stress–strain data, and dynamically, where it is derived from P- and S-wave velocities. The static bulk modulus is generally different from the corresponding dynamic bulk modulus. As the static bulk modulus is required in computation or modelling of the deformation of the rock when it is stressed hydrostatically, empirical relationships between the static and dynamic bulk moduli are needed to convert the dynamic bulk modulus to static values. In this study, the static and dynamic bulk moduli were measured simultaneously, at effective pressures up to 130 MPa, for dry and fluid-saturated argillites. The samples were collected from four different lithofacies within the upper Naparima Hill Formation, Trinidad. The results show that the dynamic bulk modulus is greater than the static bulk modulus, except for hard lithofacies under dry conditions where the static and dynamic moduli are approximately equal. Under saturated conditions, the porosity plays a key role in increasing the difference between the static and dynamic bulk moduli. A linear relationship with high correlation (R2 greater than 0.85) was established between the static and dynamic bulk moduli, which is dependent on the effective pressure and saturation state.
Journal of Sedimentary Research, 2020
Icehouse continental-shelf-margin accretion is typically driven by high-sediment-supply deltas an... more Icehouse continental-shelf-margin accretion is typically driven by high-sediment-supply deltas and repeated glacio-eustatic, climate-driven sea-level changes on a ca. 100 ky time scale. The paleo–Orinoco margin is no exception to this, as the paleo–Orinoco River Delta with its high sediment load prograded across Venezuela, then into the Southern and Columbus basins of Trinidad since the late Miocene, depositing a continental-margin sedimentary prism that is > 12 km thick, 200 km wide, and 500 km along dip. The Cruse Formation (> 800 m thick; 3 My duration) records the first arrival of the paleo–Orinoco Delta into the Trinidad area. It then accreted eastwards, outwards onto the Atlantic margin, by shallow to deepwater clinoform increments since the late Miocene and is capped by a major, thick flooding interval (the Lower Forest Clay). Previous research has provided an understanding of the paleo–Orinoco Delta depositional system at seismic and outcrop scales, but a clinoform fra...
Journal of Petroleum Science and Engineering, 2021
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.