Effects of magmatic intrusions on temperature history and diagenesis in sedimentary basins – and the impact on petroleum systems

For many volcanic basins, the thermal effect of igneous intrusions is decisive for their petroleum potential because such thermal impact may lead to maturation of organic material in areas that otherwise would remain immature. Many factors contribute to the outcome of such intrusions, and in this thesis the influence of a number of parameters, including sill thickness, timing of emplacement, structural changes of sedimentary basins, lithologies and diagenesis, have been modeled to improve the ability to predict the development of the whole petroleum system as a function of its thermal history. By quantifying the effect of several of these factors, the aim of this project has been to estimate the thermal impact of magmatic intrusions on maturation and diagenesis, from the very first temperature increase in the host rock to the long term influence, in terms of permeability and migration. Sill thickness and timing of emplacement is central in the first Paper where the thermal effect of 0 m, 50 m and 100 m thick sills are compared. The results show large differences on the thermal effect of the tested thicknesses, particularly for 0 m versus 100 m, but also 50 m versus 100 m thick sills. Whereas immature areas in the vicinity of sills that are 50 m thick will remain immature, they become fully matured when the sills are twice as thick. Timing of sill emplacement can be essential, particularly if the source rocks are between two or more sills intruded with a time lapse. Transient thermal effects of normal faulting in basins with magmatic intrusions are in focus in the second Paper. As fault movements occur, the basin momentarily experiences thermal instability in the proximity of the fault zone. How long this thermal instability lasts, depends on several factors, such as the physical properties of the rocks and the time lapse of fault movement. The results show that the largest differences between steady state and transient thermal calculations are found in the hanging wall. If sills intrude shortly after fault movement, the rocks in the hanging wall are colder than the rocks at the same depth in the foot wall. As the thermal effect of magmatic intrusions is dependent on the pre-intrusion host-rock temperatures, the thermal effect of the sills is smaller in the hanging wall than the foot wall due to the lower host rock temperatures. However, if the sills intrude with a time lapse in relation to the fault slip, the sedimentary rocks have become warmer and the effect of the intruding sills is larger. Other factors that influence the thermal effects of sill intrusions in sedimentary basins are fault displacement, time span of faulting and deposition, fault angle, the thermal conductivity of the rocks, specific heat capacity and basal heat flow. How the faults are restored in the modeling process also influences the thermal development in the basin after fault slip. Diagenesis/chemical compaction is the focus of the third Paper. The study quantifies the thermal effect of magmatic intrusions on three different diagenetic processes: the transition of opal A to opal CT to quartz; the smectite to illite transition; and the dissolution and re-precipitation of quartz. All these processes are temperature dependent and may induce deterioration of the reservoir quality by reducing the porosity. Diagenetic alterations can contribute to changes in the physical properties of the rocks. These changes can cause rocks to respond differently to stress conditions in the subsurface. Emplacement of magmatic intrusions influences all the studied diagenetic processes and result in porosity loss of rocks in their proximity. Results show that stresses build up in the stiffer rocks, like the sills and diagenetic altered areas. Such stress accumulations may potentially lead to fault slip or opening of fractures and thus increase the permeability and the potential of fluid migration. Overall, this study shows the need for good representation of the subsurface sill thicknesses and structural development, particularly prior to emplacement of magmatic intrusions. Through magmatic intrusion and their impact on the maturation of organic material, diagenetic processes, location of stress concentrations, and the potential effect on permeability and migration pathways, this study highlights how these factors may have long-term effect on the petroleum system. Other crucial variables are sill thickness and clustering of the sills at multiple levels. The thermal conductivity of host rocks is the factor influencing the transient thermal effects the most, after fault slip and the increased temperatures enhance maturation and diagenesis in their vicinity

Effects of magmatic intrusions on temperature history and diagenesis in sedimentary basins – and the impact on petroleum systems

For many volcanic basins, the thermal effect of igneous intrusions is decisive for their petroleum potential because such thermal impact may lead to maturation of organic material in areas that otherwise would remain immature. Many factors contribute to the outcome of such intrusions, and in this thesis the influence of a number of parameters, including sill thickness, timing of emplacement, structural changes of sedimentary basins, lithologies and diagenesis, have been modeled to improve the ability to predict the development of the whole petroleum system as a function of its thermal history. By quantifying the effect of several of these factors, the aim of this project has been to estimate the thermal impact of magmatic intrusions on maturation and diagenesis, from the very first temperature increase in the host rock to the long term influence, in terms of permeability and migration. Sill thickness and timing of emplacement is central in the first Paper where the thermal effect of 0 m, 50 m and 100 m thick sills are compared. The results show large differences on the thermal effect of the tested thicknesses, particularly for 0 m versus 100 m, but also 50 m versus 100 m thick sills. Whereas immature areas in the vicinity of sills that are 50 m thick will remain immature, they become fully matured when the sills are twice as thick. Timing of sill emplacement can be essential, particularly if the source rocks are between two or more sills intruded with a time lapse. Transient thermal effects of normal faulting in basins with magmatic intrusions are in focus in the second Paper. As fault movements occur, the basin momentarily experiences thermal instability in the proximity of the fault zone. How long this thermal instability lasts, depends on several factors, such as the physical properties of the rocks and the time lapse of fault movement. The results show that the largest differences between steady state and transient thermal calculations are found in the hanging wall. If sills intrude shortly after fault movement, the rocks in the hanging wall are colder than the rocks at the same depth in the foot wall. As the thermal effect of magmatic intrusions is dependent on the pre-intrusion host-rock temperatures, the thermal effect of the sills is smaller in the hanging wall than the foot wall due to the lower host rock temperatures. However, if the sills intrude with a time lapse in relation to the fault slip, the sedimentary rocks have become warmer and the effect of the intruding sills is larger. Other factors that influence the thermal effects of sill intrusions in sedimentary basins are fault displacement, time span of faulting and deposition, fault angle, the thermal conductivity of the rocks, specific heat capacity and basal heat flow. How the faults are restored in the modeling process also influences the thermal development in the basin after fault slip. Diagenesis/chemical compaction is the focus of the third Paper. The study quantifies the thermal effect of magmatic intrusions on three different diagenetic processes: the transition of opal A to opal CT to quartz; the smectite to illite transition; and the dissolution and re-precipitation of quartz. All these processes are temperature dependent and may induce deterioration of the reservoir quality by reducing the porosity. Diagenetic alterations can contribute to changes in the physical properties of the rocks. These changes can cause rocks to respond differently to stress conditions in the subsurface. Emplacement of magmatic intrusions influences all the studied diagenetic processes and result in porosity loss of rocks in their proximity. Results show that stresses build up in the stiffer rocks, like the sills and diagenetic altered areas. Such stress accumulations may potentially lead to fault slip or opening of fractures and thus increase the permeability and the potential of fluid migration. Overall, this study shows the need for good representation of the subsurface sill thicknesses and structural development, particularly prior to emplacement of magmatic intrusions. Through magmatic intrusion and their impact on the maturation of organic material, diagenetic processes, location of stress concentrations, and the potential effect on permeability and migration pathways, this study highlights how these factors may have long-term effect on the petroleum system. Other crucial variables are sill thickness and clustering of the sills at multiple levels. The thermal conductivity of host rocks is the factor influencing the transient thermal effects the most, after fault slip and the increased temperatures enhance maturation and diagenesis in their vicinity

The Influence of Magmatic Intrusions on Diagenetic Processes and Stress Accumulation

Diagenetic changes in sedimentary basins may alter hydrocarbon reservoir quality with respect to porosity and permeability. Basins with magmatic intrusions have specific thermal histories that at time of emplacement and in the aftermath have the ability to enhance diagenetic processes. Through diagenesis the thermal conductivity of rocks may change significantly, and the transformations are able to create hydrocarbon traps. The present numerical study quantified the effect of magmatic intrusions on the transitions of opal A to opal CT to quartz, smectite to illite and quartz diagenesis. We also studied how these chemical alterations and the sills themselves have affected the way the subsurface responds to stresses. The modeling shows that the area in the vicinity of magmatic sills has enhanced porosity loss caused by diagenesis compared to remote areas not intruded. Particularly areas located between clusters of sills are prone to increased diagenetic changes. Furthermore, areas influenced by diagenesis have, due to altered physical properties, increased stress accumulations, which might lead to opening of fractures and activation/reactivation of faults, thus influencing the permeability and possible hydrocarbon migration in the subsurface. This study emphasizes the influence magmatic intrusions may have on the reservoir quality and illustrates how magmatic intrusions and diagenetic changes and their thermal and stress consequences can be included in basin models

Tilting and Flexural Stresses in Basins Due to Glaciations—An Example from the Barents Sea

Many of the Earth’s sedimentary basins are affected by glaciations. Repeated glaciations over millions of years may have had a significant effect on the physical conditions in sedimentary basins and on basin structuring. This paper presents some of the major effects that ice sheets might have on sedimentary basins, and includes examples of quantifications of their significance. Among the most important effects are movements of the solid Earth caused by glacial loading and unloading, and the related flexural stresses. The driving factor of these movements is isostasy. Most of the production licenses on the Norwegian Continental Shelf are located inside the margin of the former Last Glacial Maximum (LGM) ice sheet. Isostatic modeling shows that sedimentary basins near the former ice margin can be tilted as much as 3 m/km which might significantly alter pathways of hydrocarbon migration. In an example from the SW Barents Sea we show that flexural stresses related to the isostatic uplift after LGM deglaciation can produce stress changes large enough to result in increased fracture-related permeability in the sedimentary basin, and lead to potential spillage of hydrocarbons out of potential reservoirs. The results demonstrate that future basin modeling should consider including the loading effect of glaciations when dealing with petroleum potential in former glaciated areas

The influence of magmatic intrusions on diagenetic processes and stress accumulation

Diagenetic changes in sedimentary basins may alter hydrocarbon reservoir quality with respect to porosity and permeability. Basins with magmatic intrusions have specific thermal histories that at time of emplacement and in the aftermath have the ability to enhance diagenetic processes. Through diagenesis the thermal conductivity of rocks may change significantly, and the transformations are able to create hydrocarbon traps. The present numerical study quantified the effect of magmatic intrusions on the transitions of opal A to opal CT to quartz, smectite to illite and quartz diagenesis. We also studied how these chemical alterations and the sills themselves have affected the way the subsurface responds to stresses. The modeling shows that the area in the vicinity of magmatic sills has enhanced porosity loss caused by diagenesis compared to remote areas not intruded. Particularly areas located between clusters of sills are prone to increased diagenetic changes. Furthermore, areas influenced by diagenesis have, due to altered physical properties, increased stress accumulations, which might lead to opening of fractures and activation/reactivation of faults, thus influencing the permeability and possible hydrocarbon migration in the subsurface. This study emphasizes the influence magmatic intrusions may have on the reservoir quality and illustrates how magmatic intrusions and diagenetic changes and their thermal and stress consequences can be included in basin models

Transient Thermal Effects in Sedimentary Basins with Normal Faults and Magmatic Sill Intrusions—A Sensitivity Study

Magmatic intrusions affect the basin temperature in their vicinity. Faulting and physical properties of the basin may influence the magnitudes of their thermal effects and the potential source rock maturation. We present results from a sensitivity study of the most important factors affecting the thermal history in structurally complex sedimentary basins with magmatic sill intrusions. These factors are related to faulting, physical properties, and restoration methods: (1) fault displacement, (2) time span of faulting and deposition, (3) fault angle, (4) thermal conductivity and specific heat capacity, (5) basal heat flow and (6) restoration method. All modeling is performed on the same constructed clastic sedimentary profile containing one normal listric fault with one faulting event. Sills are modeled to intrude into either side of the fault zone with a temperature of 1000 °C. The results show that transient thermal effects may last up to several million years after fault slip. Thermal differences up to 40 °C could occur for sills intruding at time of fault slip, to sills intruding 10 million years later. We have shown that omitting the transient thermal effects of structural development in basins with magmatic intrusions may lead to over- or underestimation of the thermal effects of magmatic intrusions and ultimately the estimated maturation

The influence of magmatic intrusions on diagenetic processes and stress accumulation

Diagenetic changes in sedimentary basins may alter hydrocarbon reservoir quality with respect to porosity and permeability. Basins with magmatic intrusions have specific thermal histories that at time of emplacement and in the aftermath have the ability to enhance diagenetic processes. Through diagenesis the thermal conductivity of rocks may change significantly, and the transformations are able to create hydrocarbon traps. The present numerical study quantified the effect of magmatic intrusions on the transitions of opal A to opal CT to quartz, smectite to illite and quartz diagenesis. We also studied how these chemical alterations and the sills themselves have affected the way the subsurface responds to stresses. The modeling shows that the area in the vicinity of magmatic sills has enhanced porosity loss caused by diagenesis compared to remote areas not intruded. Particularly areas located between clusters of sills are prone to increased diagenetic changes. Furthermore, areas influenced by diagenesis have, due to altered physical properties, increased stress accumulations, which might lead to opening of fractures and activation/reactivation of faults, thus influencing the permeability and possible hydrocarbon migration in the subsurface. This study emphasizes the influence magmatic intrusions may have on the reservoir quality and illustrates how magmatic intrusions and diagenetic changes and their thermal and stress consequences can be included in basin models