Fawad Chuhan - Academia.edu (original) (raw)
Papers by Fawad Chuhan
Elsevier eBooks, 2004
Abstract The reduction in porosity due to mechanical compaction and chemical processes are princi... more Abstract The reduction in porosity due to mechanical compaction and chemical processes are principally different processes and must be modelled separately even if they overlap in time. Experimental compaction of loose sand show that stresses exceeding 20-30 MPa ...
Proceedings, Nov 17, 2015
This work presents the longest, consistent records of dissolved organic carbon in rivers ever pub... more This work presents the longest, consistent records of dissolved organic carbon in rivers ever published. Long-term records of carbon flux (as water colour) were constructed for 3 catchments in Northern England for as far back as 1962. Observations show that there have been large increases in DOC concentrations over the period of study with in one case a doubling of
area has been studied using mineralogical and geochemical data from 21 wells, ranging in burial d... more area has been studied using mineralogical and geochemical data from 21 wells, ranging in burial depths from 2.0 to 4.1 km relative to seafloor (RSF). K-feldspar and plagioclase contents show variations on a re-gional scale both laterally and as a function of burial depth. The con-tent of pore–filling authigenic illite increases sharply, and the content of K-feldspar and kaolinite decreases in Garn sandstones presently at depths greater than 3.6–3.7 km RSF (120–1308C). The depletion in K-feldspar below 3.7 km RSF is not accompanied by lower potassium values in the bulk chemical composition (wt % K2O). This suggests that the potassium released during K-feldspar dissolution is retained in the sandstones and is precipitated as illite. The variations in bulk contents of potassium and sodium are therefore considered to be re-lated principally to primary variations in sandstone mineralogy. The shallower sandstones (, 3.7 km RSF) with average wt % K2O greater than 0.95 (K/Al molar ratio. 1/...
Aapg Bulletin - AAPG BULL, 1998
An extensive mineralogical and geochemical database has been compiled to evaluate the relationshi... more An extensive mineralogical and geochemical database has been compiled to evaluate the relationship between diagenesis and provenance of the Lower/Middle Jurassic sandstones from the Haltenbanken (Mid-Norway) and north Viking Graben. The data from the Haltenbanken area, from burial depths between 2.1 and 4.5 km relative to sea¯oor (RSF), show a reduction in Kfeldspar and kaolin, and a sharp increase in illite content in sandstones which are presently located at depths greater than 3.7 km RSF (120±1408C). However, there is little change in the bulk K/Al molar ratio with depth, which suggests that potassium has been conserved during the precipitation of illite and dissolution of K-feldspar. The K/Al molar ratios in most of the deeply buried Haltenbanken sandstones are greater than 1/4, which corresponds to the molar ratio in illite. This indicates that excess K-feldspar is present, which is con®rmed by petrographic observations. By contrast, deeply buried sandstones from the north Viking Graben are mostly characterised by the absence of K-feldspar, a K/Al molar ratio lower than illite and varying amounts of kaolin. This suggests that the amount of K-feldspar present at the onset of illitization (of kaolin) was lower in the north Viking Graben sandstones than in the Haltenbanken area. The degree of illitization of kaolin is higher in the Haltenbanken reservoirs as compared to the north Viking Graben, and this may be directly related to the higher K-feldspar content in the Haltenbanken sandstones. The survival of kaolin below 3.7 km RSF depth, in most of the plagioclase rich and K-feldspar poor sandstones from the north Viking Graben, therefore indicates that illitization of kaolin requires a local presence of K-feldspar in the sandstones.
Marine and Petroleum Geology, 2000
An extensive mineralogical and geochemical database has been compiled to evaluate the relationshi... more An extensive mineralogical and geochemical database has been compiled to evaluate the relationship between diagenesis and provenance of the Lower/Middle Jurassic sandstones from the Haltenbanken (Mid-Norway) and north Viking Graben. The data from the Haltenbanken area, from burial depths between 2.1 and 4.5 km relative to sea¯oor (RSF), show a reduction in Kfeldspar and kaolin, and a sharp increase in illite content in sandstones which are presently located at depths greater than 3.7 km RSF (120±1408C). However, there is little change in the bulk K/Al molar ratio with depth, which suggests that potassium has been conserved during the precipitation of illite and dissolution of K-feldspar. The K/Al molar ratios in most of the deeply buried Haltenbanken sandstones are greater than 1/4, which corresponds to the molar ratio in illite. This indicates that excess K-feldspar is present, which is con®rmed by petrographic observations. By contrast, deeply buried sandstones from the north Viking Graben are mostly characterised by the absence of K-feldspar, a K/Al molar ratio lower than illite and varying amounts of kaolin. This suggests that the amount of K-feldspar present at the onset of illitization (of kaolin) was lower in the north Viking Graben sandstones than in the Haltenbanken area. The degree of illitization of kaolin is higher in the Haltenbanken reservoirs as compared to the north Viking Graben, and this may be directly related to the higher K-feldspar content in the Haltenbanken sandstones. The survival of kaolin below 3.7 km RSF depth, in most of the plagioclase rich and K-feldspar poor sandstones from the north Viking Graben, therefore indicates that illitization of kaolin requires a local presence of K-feldspar in the sandstones.
Marine and Petroleum Geology, 2002
ABSTRACT The compaction of loose sands has been tested up to high effective stresses (50 MPa). Mo... more ABSTRACT The compaction of loose sands has been tested up to high effective stresses (50 MPa). More than 50 test runs were made on five different types of sands, which were of well-sorted fine- to coarse-grained, mono-quartz and lithic compositions. The compaction curves are related directly to observations made from thin sections prepared at different stress levels. The image analyses of the thin sections show that the degree of grain fracturing increases continuously as a function of stress level. Fracturing is more intense in coarse- than in fine-grained sands and a lithic sand, fractures more readily than a mono-quartz sand in a given grain size category. Petrographic observations and grain size analyses show that, although the average grain size reduces with increasing stress level, grain fracturing is most effective in producing grains between 50 and 200 μm, which also reduces the sorting of the sands. Grain size reduction and porosity losses are higher in coarse-grained and lithic sands than in fine-grained and mono-crystalline quartz dominated sands. Fractures similar to those experimentally produced are also seen in the deeply buried Jurassic reservoir sandstones from Haltenbanken area. The experimental compaction data may provide a basis to predict reservoir quality prior to extensive quartz cementation.
Journal of Sedimentary Research, 2001
The Middle Jurassic Garn Formation of the Haltenbanken area has been studied using mineralogical ... more The Middle Jurassic Garn Formation of the Haltenbanken area has been studied using mineralogical and geochemical data from 21 wells, ranging in burial depths from 2.0 to 4.1 km relative to seafloor (RSF). K-feldspar and plagioclase contents show variations on a regional scale both laterally and as a function of burial depth. The content of pore-filling authigenic illite increases sharply, and the content of K-feldspar and kaolinite decreases in Garn sandstones presently at depths greater than 3.6-3.7 km RSF (120-130؇C). The depletion in Kfeldspar below 3.7 km RSF is not accompanied by lower potassium values in the bulk chemical composition (wt % K 2 O). This suggests that the potassium released during K-feldspar dissolution is retained in the sandstones and is precipitated as illite. The variations in bulk contents of potassium and sodium are therefore considered to be related principally to primary variations in sandstone mineralogy. The shallower sandstones (Ͻ 3.7 km RSF) with average wt % K 2 O greater than 0.95 (K/Al molar ratio Ͼ 1/3) have a K-feldspar:kaolinite ratio greater than one. The deeply buried (Ͼ 3.7 km RSF) sandstones with similar potassium contents contain excess K-feldspar and most of the kaolinite is illitized. However, deeply buried sandstones containing an average of 0.38 wt % K 2 O (K/Al molar ratio Ͻ 1/4) contain a significant amount of kaolinite but negligible K-feldspar. This suggests that the K-feldspar:kaolinite ratio before the onset of illitization was less than one, and hence that the kaolinite-illite reaction has been restricted by an insufficient supply of potassium (absence of K-feldspar). This illustrates how illitization of kaolinite depends upon K-feldspar as a local source of potassium. Prediction of illitization in sandstones, therefore, must be based on integration of models for provenance, facies, and early diagenesis in addition to burial and thermal history. The formation of pore-filling authigenic illite in these sandstones is an important influence on the total reservoir quality.
Canadian Geotechnical Journal, 2003
This study examines the one-dimensional stressstrain behaviour of sand at effective stresses as ... more This study examines the one-dimensional stressstrain behaviour of sand at effective stresses as high as 50 MPa. Experiments were performed on 22 sands (approx. 150 tests) with different grain size, uniformity coefficient, angularity, density, grain mineralogy, and clay content. The results show that minor grain corner crushing starts at stresses of 28 MPa. The point of maximum curvature (yield point) in the porosity (n) versus logarithm of vertical effective stress (σ'v) curve defines the initiation of marked particle crushing. The stress at the yield point varies between 3 and 31 MPa depending on sand characteristics. A low yield stress is indicative of high porosity loss in the interval of intermediate stress (525 MPa). The yield stress is low when the grain size is large, grains are angular, grain strength is low, and uniformity coefficient is low. The lowest yield stress value occurs in the coarser carbonate sand, and the highest in the chert-rich sands. The sands rich in...
Elsevier eBooks, 2004
Abstract The reduction in porosity due to mechanical compaction and chemical processes are princi... more Abstract The reduction in porosity due to mechanical compaction and chemical processes are principally different processes and must be modelled separately even if they overlap in time. Experimental compaction of loose sand show that stresses exceeding 20-30 MPa ...
Proceedings, Nov 17, 2015
This work presents the longest, consistent records of dissolved organic carbon in rivers ever pub... more This work presents the longest, consistent records of dissolved organic carbon in rivers ever published. Long-term records of carbon flux (as water colour) were constructed for 3 catchments in Northern England for as far back as 1962. Observations show that there have been large increases in DOC concentrations over the period of study with in one case a doubling of
area has been studied using mineralogical and geochemical data from 21 wells, ranging in burial d... more area has been studied using mineralogical and geochemical data from 21 wells, ranging in burial depths from 2.0 to 4.1 km relative to seafloor (RSF). K-feldspar and plagioclase contents show variations on a re-gional scale both laterally and as a function of burial depth. The con-tent of pore–filling authigenic illite increases sharply, and the content of K-feldspar and kaolinite decreases in Garn sandstones presently at depths greater than 3.6–3.7 km RSF (120–1308C). The depletion in K-feldspar below 3.7 km RSF is not accompanied by lower potassium values in the bulk chemical composition (wt % K2O). This suggests that the potassium released during K-feldspar dissolution is retained in the sandstones and is precipitated as illite. The variations in bulk contents of potassium and sodium are therefore considered to be re-lated principally to primary variations in sandstone mineralogy. The shallower sandstones (, 3.7 km RSF) with average wt % K2O greater than 0.95 (K/Al molar ratio. 1/...
Aapg Bulletin - AAPG BULL, 1998
An extensive mineralogical and geochemical database has been compiled to evaluate the relationshi... more An extensive mineralogical and geochemical database has been compiled to evaluate the relationship between diagenesis and provenance of the Lower/Middle Jurassic sandstones from the Haltenbanken (Mid-Norway) and north Viking Graben. The data from the Haltenbanken area, from burial depths between 2.1 and 4.5 km relative to sea¯oor (RSF), show a reduction in Kfeldspar and kaolin, and a sharp increase in illite content in sandstones which are presently located at depths greater than 3.7 km RSF (120±1408C). However, there is little change in the bulk K/Al molar ratio with depth, which suggests that potassium has been conserved during the precipitation of illite and dissolution of K-feldspar. The K/Al molar ratios in most of the deeply buried Haltenbanken sandstones are greater than 1/4, which corresponds to the molar ratio in illite. This indicates that excess K-feldspar is present, which is con®rmed by petrographic observations. By contrast, deeply buried sandstones from the north Viking Graben are mostly characterised by the absence of K-feldspar, a K/Al molar ratio lower than illite and varying amounts of kaolin. This suggests that the amount of K-feldspar present at the onset of illitization (of kaolin) was lower in the north Viking Graben sandstones than in the Haltenbanken area. The degree of illitization of kaolin is higher in the Haltenbanken reservoirs as compared to the north Viking Graben, and this may be directly related to the higher K-feldspar content in the Haltenbanken sandstones. The survival of kaolin below 3.7 km RSF depth, in most of the plagioclase rich and K-feldspar poor sandstones from the north Viking Graben, therefore indicates that illitization of kaolin requires a local presence of K-feldspar in the sandstones.
Marine and Petroleum Geology, 2000
An extensive mineralogical and geochemical database has been compiled to evaluate the relationshi... more An extensive mineralogical and geochemical database has been compiled to evaluate the relationship between diagenesis and provenance of the Lower/Middle Jurassic sandstones from the Haltenbanken (Mid-Norway) and north Viking Graben. The data from the Haltenbanken area, from burial depths between 2.1 and 4.5 km relative to sea¯oor (RSF), show a reduction in Kfeldspar and kaolin, and a sharp increase in illite content in sandstones which are presently located at depths greater than 3.7 km RSF (120±1408C). However, there is little change in the bulk K/Al molar ratio with depth, which suggests that potassium has been conserved during the precipitation of illite and dissolution of K-feldspar. The K/Al molar ratios in most of the deeply buried Haltenbanken sandstones are greater than 1/4, which corresponds to the molar ratio in illite. This indicates that excess K-feldspar is present, which is con®rmed by petrographic observations. By contrast, deeply buried sandstones from the north Viking Graben are mostly characterised by the absence of K-feldspar, a K/Al molar ratio lower than illite and varying amounts of kaolin. This suggests that the amount of K-feldspar present at the onset of illitization (of kaolin) was lower in the north Viking Graben sandstones than in the Haltenbanken area. The degree of illitization of kaolin is higher in the Haltenbanken reservoirs as compared to the north Viking Graben, and this may be directly related to the higher K-feldspar content in the Haltenbanken sandstones. The survival of kaolin below 3.7 km RSF depth, in most of the plagioclase rich and K-feldspar poor sandstones from the north Viking Graben, therefore indicates that illitization of kaolin requires a local presence of K-feldspar in the sandstones.
Marine and Petroleum Geology, 2002
ABSTRACT The compaction of loose sands has been tested up to high effective stresses (50 MPa). Mo... more ABSTRACT The compaction of loose sands has been tested up to high effective stresses (50 MPa). More than 50 test runs were made on five different types of sands, which were of well-sorted fine- to coarse-grained, mono-quartz and lithic compositions. The compaction curves are related directly to observations made from thin sections prepared at different stress levels. The image analyses of the thin sections show that the degree of grain fracturing increases continuously as a function of stress level. Fracturing is more intense in coarse- than in fine-grained sands and a lithic sand, fractures more readily than a mono-quartz sand in a given grain size category. Petrographic observations and grain size analyses show that, although the average grain size reduces with increasing stress level, grain fracturing is most effective in producing grains between 50 and 200 μm, which also reduces the sorting of the sands. Grain size reduction and porosity losses are higher in coarse-grained and lithic sands than in fine-grained and mono-crystalline quartz dominated sands. Fractures similar to those experimentally produced are also seen in the deeply buried Jurassic reservoir sandstones from Haltenbanken area. The experimental compaction data may provide a basis to predict reservoir quality prior to extensive quartz cementation.
Journal of Sedimentary Research, 2001
The Middle Jurassic Garn Formation of the Haltenbanken area has been studied using mineralogical ... more The Middle Jurassic Garn Formation of the Haltenbanken area has been studied using mineralogical and geochemical data from 21 wells, ranging in burial depths from 2.0 to 4.1 km relative to seafloor (RSF). K-feldspar and plagioclase contents show variations on a regional scale both laterally and as a function of burial depth. The content of pore-filling authigenic illite increases sharply, and the content of K-feldspar and kaolinite decreases in Garn sandstones presently at depths greater than 3.6-3.7 km RSF (120-130؇C). The depletion in Kfeldspar below 3.7 km RSF is not accompanied by lower potassium values in the bulk chemical composition (wt % K 2 O). This suggests that the potassium released during K-feldspar dissolution is retained in the sandstones and is precipitated as illite. The variations in bulk contents of potassium and sodium are therefore considered to be related principally to primary variations in sandstone mineralogy. The shallower sandstones (Ͻ 3.7 km RSF) with average wt % K 2 O greater than 0.95 (K/Al molar ratio Ͼ 1/3) have a K-feldspar:kaolinite ratio greater than one. The deeply buried (Ͼ 3.7 km RSF) sandstones with similar potassium contents contain excess K-feldspar and most of the kaolinite is illitized. However, deeply buried sandstones containing an average of 0.38 wt % K 2 O (K/Al molar ratio Ͻ 1/4) contain a significant amount of kaolinite but negligible K-feldspar. This suggests that the K-feldspar:kaolinite ratio before the onset of illitization was less than one, and hence that the kaolinite-illite reaction has been restricted by an insufficient supply of potassium (absence of K-feldspar). This illustrates how illitization of kaolinite depends upon K-feldspar as a local source of potassium. Prediction of illitization in sandstones, therefore, must be based on integration of models for provenance, facies, and early diagenesis in addition to burial and thermal history. The formation of pore-filling authigenic illite in these sandstones is an important influence on the total reservoir quality.
Canadian Geotechnical Journal, 2003
This study examines the one-dimensional stressstrain behaviour of sand at effective stresses as ... more This study examines the one-dimensional stressstrain behaviour of sand at effective stresses as high as 50 MPa. Experiments were performed on 22 sands (approx. 150 tests) with different grain size, uniformity coefficient, angularity, density, grain mineralogy, and clay content. The results show that minor grain corner crushing starts at stresses of 28 MPa. The point of maximum curvature (yield point) in the porosity (n) versus logarithm of vertical effective stress (σ'v) curve defines the initiation of marked particle crushing. The stress at the yield point varies between 3 and 31 MPa depending on sand characteristics. A low yield stress is indicative of high porosity loss in the interval of intermediate stress (525 MPa). The yield stress is low when the grain size is large, grains are angular, grain strength is low, and uniformity coefficient is low. The lowest yield stress value occurs in the coarser carbonate sand, and the highest in the chert-rich sands. The sands rich in...