共查询到20条相似文献，搜索用时 15 毫秒
1.
Palaeopressure reconstruction to explain observed natural hydraulic fractures in the Cleveland Basin
Natural fractures observed within the Lower Jurassic shales of the Cleveland Basin show evidence that pore pressure must have exceeded the lithostatic pressure in order to initiate horizontal fractures observed in cliff sections. Other field localities do not show horizontal fracturing, indicating lower pore pressures there. Deriving the burial history of the basin from outcrop, VR and heat-flow data gives values of sedimentation rates and periods of depositional hiatus which can be used to assess the porosity and pore pressure evolution within the shales. This gives us our estimate of overpressure caused by disequilibrium compaction alone, of 11 MPa, not sufficient to initiate horizontal fractures. However, as the thermal information shows us that temperatures were in excess of 95 °C, secondary overpressure mechanisms such as clay diagenesis and hydrocarbon generation occurred, contributing an extra 11 MPa of overpressure. The remaining 8.5 MPa of overpressure required to initiate horizontal fractures was caused by fluid expansion due to hydrocarbon generation and tectonic compression related to Alpine orogenic and Atlantic opening events. Where horizontal fractures are not present within the Lower Jurassic shales, overpressure was unable to build up as high due to proximity to the lateral draining of pressure within the Dogger Formation. The palaeopressure reconstruction techniques used within this study give a quick assessment of the pressure history of a basin and help to identify shales which may currently have enhanced permeability due to naturally-occurring hydraulic fractures. 相似文献
2.
Most of the methods currently used for pore pressure prediction in sedimentary basins assume one-dimensional compaction based on relationships between vertical effective stress and porosity. These methods may be inaccurate in complex tectonic regimes where stress tensors are variable. Modelling approaches for compaction adopted within the geotechnical field account for both the full three-dimensional stress tensor and the stress history. In this paper a coupled geomechanical-fluid flow model is used, along with an advanced version of the Cam-Clay constitutive model, to investigate stress, pore pressure and porosity in a Gulf of Mexico style mini-basin bounded by salt subjected to lateral deformation. The modelled structure consists of two depocentres separated by a salt diapir. 20% of horizontal shortening synchronous to basin sedimentation is imposed. An additional model accounting solely for the overpressure generated due to 1D disequilibrium compaction is also defined. The predicted deformation regime in the two depocentres of the mini-basin is one of tectonic lateral compression, in which the horizontal effective stress is higher than the vertical effective stress. In contrast, sediments above the central salt diapir show lateral extension and tectonic vertical compaction due to the rise of the diapir. Compared to the 1D model, the horizontal shortening in the mini-basin increases the predicted present-day overpressure by 50%, from 20 MPa to 30 MPa. The porosities predicted by the mini-basin models are used to perform 1D, porosity-based pore pressure predictions. The 1D method underestimated overpressure by up to 6 MPa at 3400 m depth (26% of the total overpressure) in the well located at the basin depocentre and up to 3 MPa at 1900 m depth (34% of the total overpressure) in the well located above the salt diapir. The results show how 2D/3D methods are required to accurately predict overpressure in regions in which tectonic stresses are important. 相似文献
3.
Differences in fluids origin, creation of overpressure and migration are compared for end member Neogene fold and thrust environments: the deepwater region offshore Brunei (shale detachment), and the onshore, arid Central Basin of Iran (salt detachment). Variations in overpressure mechanism arise from a) the availability of water trapped in pore-space during early burial (deepwater marine environment vs arid, continental environment), and b) the depth/temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development. Chemical reactions associated with smectite rich mud rocks in Iran occur shallow (∼1900 m, smectite to illite transformation) causing load-transfer related (moderate) overpressures, whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore Brunei. The basal detachment in deepwater Brunei generally lies below temperatures of about 150 °C, where chemical processes and metagenesis are inferred to drive overpressure development. Overall the deepwater Brunei system is very water rich, and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines. The result is a wide variety of fluid migration pathways and structures from deep to shallow levels (particularly mud dykes, sills, laccoliths, volcanoes and pipes, fluid escape pipes, crestal normal faults, thrust faults) and widespread inflationary-type overpressure. In the Central Basin the near surface environment is water limited. Mechanical and chemical compaction led to moderate overpressure development above the Upper Red Formation evaporites. Only below thick Early Miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms. Fluid leakage episodes across the evaporites have either been very few or absent in most areas. Locations where leakage can episodically occur (e.g. detaching thrusts, deep normal faults, salt welds) are sparse. However, in both Iran and Brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds. 相似文献
4.
Differences in fluids origin, creation of overpressure and migration are compared for end member Neogene fold and thrust environments: the deepwater region offshore Brunei (shale detachment), and the onshore, arid Central Basin of Iran (salt detachment). Variations in overpressure mechanism arise from a) the availability of water trapped in pore-space during early burial (deepwater marine environment vs arid, continental environment), and b) the depth/temperature at which mechanical compaction becomes a secondary effect and chemical processes start to dominate overpressure development. Chemical reactions associated with smectite rich mud rocks in Iran occur shallow (∼1900 m, smectite to illite transformation) causing load-transfer related (moderate) overpressures, whereas mechanical compaction and inflationary overpressures dominate smectite poor mud rocks offshore Brunei. The basal detachment in deepwater Brunei generally lies below temperatures of about 150 °C, where chemical processes and metagenesis are inferred to drive overpressure development. Overall the deepwater Brunei system is very water rich, and multiple opportunities for overpressure generation and fluid leakage have occurred throughout the growth of the anticlines. The result is a wide variety of fluid migration pathways and structures from deep to shallow levels (particularly mud dykes, sills, laccoliths, volcanoes and pipes, fluid escape pipes, crestal normal faults, thrust faults) and widespread inflationary-type overpressure. In the Central Basin the near surface environment is water limited. Mechanical and chemical compaction led to moderate overpressure development above the Upper Red Formation evaporites. Only below thick Early Miocene evaporites have near lithostatic overpressures developed in carbonates and marls affected by a wide range of overpressure mechanisms. Fluid leakage episodes across the evaporites have either been very few or absent in most areas. Locations where leakage can episodically occur (e.g. detaching thrusts, deep normal faults, salt welds) are sparse. However, in both Iran and Brunei crestal normal faults play an important role in the transmission of fluids in the upper regions of folds. 相似文献
5.
《Marine and Petroleum Geology》2012,32(1):110-124
The transport properties of Permian to Miocene oil shales (Torbanite, Posidonia, Messel, Himmetoglu, and Condor) were studied using petrophysical and geochemical techniques. The aims of this study were to assess permeability of oil shales, evaluate the evolution of porosity, specific surface area and intergranular permeability during high temperature compaction tests and to verify the suitability of intergranular permeability for petroleum expulsion. Measured permeability coefficients for two samples were 0.72 × 10−21 m² for the Eocene Messel shale and 2.63 × 10−21 m² for the Lower Jurassic Posidonia shale from S. Germany, respectively. BET specific surface areas of the original samples ranged from 0.7 to 10.6 m²/g and decreased after compaction to values from 0.3 to 3.7 m²/g. Initial porosity values ranged from 7.6 to 20.1 % for pre-deformation and from 9.99 to 20.7 % for post-deformation samples. Porosity increased during the high-temperature compaction experiments due to petroleum generation and expulsion. Permeability coefficients estimated using the Kozeny–Carman equation varied from 6.97 × 10−24 m² to 5.22 × 10−21 m² for pre-deformation and from 0.2 × 10−21 m² to 4.8 × 10−21 m² for post-deformation samples reflecting the evolution of their porosity and BET specific surface areas. Measured and calculated permeability were similar for the Messel shale whereas calculated permeability was two orders of magnitude lower for the Posidonia shale from S. Germany. Petroleum expulsion efficiencies under the experimental conditions ranged from 38.6% for the Torbanite to 96.2% for the Posidonia shale from S. Germany. They showed strong positive correlation with the petroleum generation index (R² = 0.91) and poor correlations with porosity (R² = 0.46), average pore throat diameters (R² = 0.22), and compaction (R² = 0.02). Estimated minimum pore-system saturations for petroleum expulsion during the experiments were 12% for the Torbanite and 30% for the Posidonia shale from N. Germany. Pore-system saturation determines whether expulsion occurs mainly through matrix or fracture permeability. For samples with saturation levels above 20%, fracture permeability dominated during the experiments. Evidence based on the measured permeability coefficients, expulsion flow rates, consideration of capillary displacement during generation-related pore invasion and the existence of transport porosity suggests that fracture permeability is the principal avenue of petroleum expulsion from source rocks. This conclusion is supported by microscopic observations. 相似文献
6.
The Kuqa Foreland Basin (KFB) immediately south of the South Tianshan Mountains is a major hydrocarbon producing basin in west China. The Kelasu Thrust Belt in the basin is the most favorable zone for hydrocarbon accumulations. Widespread overpressures are present in both the Cretaceous and Paleogene reservoirs with pressure coefficients up to 2.1. The tectonic compression process in KFB resulted from the South Tianshan Mountains uplift is examined from the viewpoint of the overpressure generation and evolution in the Kelasu Thrust Belt. The overpressure evolution in the reservoir sandstones were reconstructed through fluid inclusion analysis combined with PVT and basin modeling. Overpressures at present day in the mudstone units in the Kelasu Thrust Belt and reservoir sandstones of the Dabei Gas Field and the Keshen zone are believed to have been generated by horizontal tectonic compression. Both disequilibrium compaction and horizontal tectonic compression are thought to contribute to the overpressure development at present day in the reservoir of the Kela-2 Gas Field with the reservoir sandstones showing anomalously high primary porosities and low densities from wireline log and core data. The overpressure evolution for the Cretaceous reservoir sandstone in the Kelasu Thrust Belt evolved through four stages: a normal hydrostatic pressure (>12–5 Ma), a rapidly increasing overpressure (∼5–3 Ma), an overpressure release (∼3–1.64 Ma) and overpressure preservation (∼1.64–0 Ma). Overpressure developed in the second stage (∼5–3 Ma) was generated by disequilibrium compaction as tectonic compression due to the uplift of the Tianshan Mountains acted at the northern monocline of KFB from 5 Ma to 3 Ma, which provided abundant sediments for the KFB and caused the anomalously high sedimentation rate during the N2k deposition. From 3 Ma to 1.64 Ma, the action of tectonic compression extended from the northern monocline to the Kelasu Thrust Belt and returned to the northern monocline of KFB from 1.64 Ma to present day. Therefore, the horizontal tectonic compression was the dominant overpressure mechanism for the overpressure generation in the third stage (∼3–1.64 Ma) and overpressure caused by disequilibrium compaction from 5 Ma to 3 Ma was only preserved in the Kela-2 Gas Field until present day. 相似文献
7.
A new, inexpensive and easy-to-handle box corer (47 × 47 × 114 cm3) is described. It is found to be extremely handy when operated from ships equipped with piston coring devices. The box corer uses the same piston core-head (～1000 kg) and the same trigger mechanism as used in piston coring. The whole operation is similar to that of piston coring. At three sites in the nodule-rich abyssal-hill province in the northwest Atlantic, the vertical distributions of the manganese nodules were obtained from the box cores. More than 75% of the nodules by weight is present in the top 10 cm of the sediment; 16–24% is present in the 10–20 cm interval and about 1% in the 20–30 cm interval. Very few nodules are found below 30 cm. 相似文献
8.
The Wufeng-Longmaxi organic-rich shales host the largest shale gas fields of China. This study examines sealed fractures within core samples of the Wufeng-Longmaxi shales in the Jiaoshiba shale gas field in order to understand the development of overpressures (in terms of magnitude, timing and burial) in Wufeng-Longmaxi shales and thus the causes of present-day overpressure in these Paleozoic shale formations as well as in all gas shales. Quartz and calcite fracture cements from the Wufeng-Longmaxi shale intervals in four wells at depth intervals between 2253.89 m and 3046.60 m were investigated, and the fluid composition, temperature, and pressure during natural fracture cementation determined using an integrated approach consisting of petrography, Raman spectroscopy and microthermometry. Many crystals in fracture cements were found to contain methane inclusions only, and aqueous two-phase inclusions were consistently observed alongside methane inclusions in all cement samples, indicating that fluid inclusions trapped during fracture cementation are saturated with a methane hydrocarbon fluid. Homogenization temperatures of methane-saturated aqueous inclusions provide trends in trapping temperatures that Th values concentrate in the range of 198.5 °C–229.9 °C, 196.2 °C-221.7 °C for quartz and calcite, respectively. Pore-fluid pressures of 91.8–139.4 MPa for methane inclusions, calculated using the Raman shift of C-H symmetric stretching (v1) band of methane and equations of state for supercritical methane, indicate fluid inclusions trapped at near-lithostatic pressures. High trapping temperature and overpressure conditions in fluid inclusions represent a state of temperature and overpressure of Wufeng-Longmaxi shales at maximum burial and the early stage of the Yanshanian uplift, which can provide a key evidence for understanding the formation and evolution of overpressure. Our results demonstrate that the main cause of present-day overpressure in shale gas deposits is actually the preservation of moderate-high overpressure developed as a result of gas generation at maximum burial depths. 相似文献
9.
The complex fluvial sandstones of the Triassic Skagerrak Formation are the host reservoir for a number of high-pressure, high-temperature (HPHT) fields in the Central Graben, North Sea. All the reservoir sandstones in this study comprise of fine-grained to medium-grained sub-arkosic to arkosic sandstones that have experienced broadly similar burial and diagenetic histories to their present-day maximum burial depths. Despite similar diagenetic histories, the fluvial reservoirs show major variations in reservoir quality and preserved porosity. Reservoir quality varies from excellent with anomalously high porosities of up to 35% at burial depth of >3500 m below seafloor to non-economic with porosities <10% at burial depth of 4300 m below seafloor.This study has combined detailed petrographic analyses, core analysis and pressure history modelling to assess the impact of differing vertical effective stresses (VES) and high pore fluid pressures (up to 80 MPa) on reservoir quality. It has been recognised that fluvial channel sandstones of the Skagerrak Formation in the UK sector have experienced significantly less mechanical compaction than their equivalents in the Norwegian sector. This difference in mechanical compaction has had a significant impact upon reservoir quality, even though the presence of chlorite grain coatings inhibited macroquartz cement overgrowths across all Skagerrak Formation reservoirs. The onset of overpressure started once the overlying Chalk seal was buried deeply enough to form a permeability barrier to fluid escape. It is the cumulative effect of varying amounts of overpressure and its effect on the VES history that is key to determining the reservoir quality of these channelised sandstone units. The results are consistent with a model where vertical effective stress affects both the compaction state and subsequent quartz cementation of the reservoirs. 相似文献
10.
The Paraná Basin, southern Brazil, has an atypical thermal and fluid history due to the occurrence of an episodic continental flood volcanism during the Early Cretaceous. So far, there are few data about the influence of this volcanic event on the paleotemperatures and paleofluids of the Paraná Basin sedimentary rocks. The Teresina Formation in the northern flank of the Ponta Grossa dyke swarm hosts high concentration of subsurface igneous rock bodies (sills and dykes), besides its covering by a hundreds meter thick volcanic rock cap. In this study, we used fluid inclusion analysis performed in horizontal and vertical calcite veins from the Teresina Formation and from a Late Cretaceous basic dyke to estimate paleotemperatures and to characterize the composition of diagenetic paleofluids. Homogenization temperatures of requilibrated fluid inclusions show that the Teresina Formation reached temperatures above 200 °C. Horizontal parallel bedding calcite veins from the Teresina Formation record low to high salinity (2–26 wt.% NaCl eq.) aqueous paleofluids. The prevalence of high salinity fluid inclusions associated with light hydrocarbon fluid inclusions indicates deep buried fluids. Fluid inclusions in vertical calcite vein from basic dyke comprise only low salinity aqueous fluids (0–3 wt.% eq.NaCl) interpreted as dominated by meteoric water. The recorded paleotemperatures are attributed to the heating by the Paraná volcanic event during the Early Cretaceous, with the thermal effect of the volcanic rock cap surpassing the effect of nearby sills and dykes. Estimated paleotemperatures higher than 200 °C would allow the generation of light liquid and gaseous hydrocarbons. Overpressured compartments in the Teresina Formation allowed the expulsion of buried pore fluids (high salinity aqueous fluids and hydrocarbons) to fracture systems, where they mixed with meteoric water. The input of meteoric water through fracture systems connected with the surface favored hydrocarbons degradation in the early stages of source rock maturation during the Early Cretaceous. 相似文献
11.
In recent years, new oil reservoirs have been discovered in the Eocene tight sandstone of the Huilu area, northern part of the Pearl River Mouth basin, South China Sea, indicating good prospects for tight oil exploration in the area. Exploration has shown that the Huilu area contains two main sets of source rocks: the Eocene Wenchang (E2w) and Enping (E2e) formations. To satisfy the requirements for further exploration in the Huilu area, particularly for tight oil in Eocene sand reservoirs, it is necessary to re-examine and analyze the hydrocarbon generation and expulsion characteristics. Based on mass balance, this study investigated the hydrocarbon generation and expulsion characteristics as well as the tight oil resource potential using geological and geochemical data and a modified conceptual model for generation and expulsion. The results show that the threshold and peak expulsion of the E2w source rocks are at 0.6% vitrinite reflectance and 0.9% vitrinite reflectance, respectively. There were five hydrocarbon expulsion centers, located in the western, eastern, and northern Huizhou Sag and the southern and northern Lufeng Sag. The hydrocarbon yields attributed to E2w source rocks are 2.4 × 1011 tons and 1.6 × 1011 tons, respectively, with an expulsion efficiency of 65%. The E2e source rock threshold and peak expulsion are at 0.65% vitrinite reflectance and 0.93% vitrinite reflectance, respectively, with hydrocarbon expulsion centers located in the centers of the Huizhou and Lufeng sags. The yields attributed to E2e source rocks are 1.1 × 1011 tons and 0.2 × 1011 tons, respectively, with an expulsion efficiency of 20%. Using an accumulation coefficient of 7%–13%, the Eocene tight reservoirs could contain approximately 1.3 × 1010 tons to 2.3 × 1010 tons, with an average of 1.8 × 1010 tons, of in-place tight oil resources (highest recoverable coefficient can reach 17–18%), indicating that there is significant tight oil potential in the Eocene strata of the Huilu area. 相似文献
12.
The Mississippian Barnett Shale (Texas, USA), consisting of organic-rich shales and limestones, hosts the largest gas fields of North America. This study examines sealed fractures from core and outcrop samples of the Barnett Shale of the Fort Worth Basin and aims to: 1) characterize the phases occurring in the fractures from samples having experienced different burial histories; 2) establish a paragenetic sequence to relate the timing of fracture origin and sealing with the burial history of the basin; and 3) contribute to the understanding of the mechanisms of fracture formation in shales, including overpressure origin.Four fracture generations were distinguished in the most deeply buried core samples by characterizing the sealing minerals petrographically and geochemically. The generations were inserted into the framework of a reconstructed burial history for the Fort Worth Basin, which allowed a time sequence for fracture development to be established. This in turn allowed inference of conditions of fracture development, and consideration of fracture mechanisms as well as the origin of the parent fluids of sealing minerals.Type 1 fractures formed during early mechanical compaction (at a few 10 s to 100 m of depth) of still not fully cemented sediments. Type 2 fractures formed during moderate burial (∼2 km), from slightly modified seawater. Their timing is consistent with overpressure generated during rapid deposition and differential compaction of Pennsylvanian lithologies during the onset of the Ouachita compressional event. Type 3 fractures formed during deep burial (>3 km) from silica-rich basinal brines possibly derived from clay diagenesis. Type 4 fractures formed at very deep burial (>4 km), from hot and 18O-rich fluids, carrying light oil (20-30 API) and record the opening of the fluid system after hydrocarbon migration.Differences are highlighted between the timing and thermal regimes under which fractures formed in Barnett lithologies from different areas of the basin, this suggesting that extrapolation of outcrop observations to subsurface must be used with due care. 相似文献
13.
The Penglai 9-1 (PL9-1) oil field, which contains China's third largest offshore oil accumulation (in-place reserves greater than 2.28 × 108 ton or 1.49 × 109 bbl), was found in shallow reservoirs (700–1700 m, 2297–5577 ft) within the most active fault zone in east China. The PL9-1 field contains two oil-bearing series, the granite intrusions in Mesozoic (Mz) and both the sandstone reservoirs in Neogene Guantao (Ng) and Neogene Minghuazhen (Nm) Formation. The origins of the PL9-1 field, both in terms of source rock intervals and generative kitchens, were determined by analyzing biomarker distributions for 61 source rock samples and 33 oil samples. The Mesozoic granite intrusions, which hold more than 80% of the oil reserves in the field, were charged in the west by oil generated from the third member (Es3) of the Shahejie Formation in the Bodong depression. The Neogene reservoirs of the PL9-1 field were charged in the west by oil generated from the third member (Es3) of the Shahejie Formation in the Bodong depression and in the south by oil generated from the first member (Es1) of the Shahejie Formation in the Miaoxibei depression. Interactive contact between the large fan delta and the mature source rocks residing in the Es3 Formation of the Bodong depression resulted in a high expulsion efficiency from the source rocks and rapid oil accumulation in the PL9-1 field, which probably explains how can this large oil field accumulate and preserve within the largest and most active fault zone in east China. 相似文献
14.
Deniz Cukur Senay Horozal Dae C. Kim Gwang H. Lee Hyun C. Han Moo H. Kang 《Marine Geophysical Researches》2010,31(4):299-313
This paper presents results of two-dimensional seismic mapping of the northern East China Sea Shelf Basin. Various igneous
features such as sills, volcanic edifices and stocks were identified by the geophysical exploration. The sills are most common,
and are observed at more than 90 locations. Most mapped sills in the study area are characterized by high-amplitude continuous
reflections with distinct terminations. Saucer- and cup-shaped sills are observed locally. The stocks are discordant (nearly
vertical) igneous bodies and they are characterized by seismic transparency, with upturned host rocks and uplifted overburden.
The volcanic edifices and/or necks consist of irregular mounds and peaks and are characterized by strong positive top reflections
with chaotic internal facies. The oldest igneous activity in the northern East China Sea Shelf Basin is Early Cretaceous (123.3 ± 3.7).
This igneous activity coincides with those observed in eastern China which has been related mainly to the subduction of the
Pacific Plate beneath Eurasia Plate. The Miocene igneous activity is well constrained based on seismic stratigraphic relationships
within the folded stratigraphy, age dating, and the occurrence of igneous sills. The timing of this intrusion is coincident
with the intensive igneous activity as previously suggested for the eastern China. Igneous rocks can produce hydrocarbon traps,
reservoirs and they can act as a seal, and therefore are of great importance in petroleum study. 相似文献
15.
Marginal seas provide a globally important interface between land and interior ocean where organic carbon is metabolized, buried or exported. The trophic status of these seas varies seasonally, depending on river flow, primary production, the proportion of dissolved to particulate organic carbon and other factors. In the Strait of Georgia, about 80% of the organic carbon in the water column is dissolved. Organic carbon enters at the surface, with river discharge and primary production, particularly during spring and summer. The amount of organic carbon passing through the Strait (∼16 × 108 kg C yr−1) is almost twice the standing inventory (∼9.4 × 108 kg C). The organic carbon that is oxidized within the Strait (∼5.6 × 108 kg yr−1) presumably supports microbial food webs or participates in chemical or photochemical reactions, while that which is exported (7.2 × 108 kg yr−1) represents a local source of organic carbon to the open ocean. 相似文献
16.
《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(10):2205-2220
Under present-day conditions, rivers are the main source of fine sediments dispersed to the Bay of Biscay. They deliver about 2.5×106 t yr−1 of continental fine sediments, 60% of which is derived from the Gironde estuary. Of this flux, 65% is believed stored on the shelf. Two kinds of mud fields can be found in the Bay of Biscay: coastal mud and shelf mud belts. The total mass of fine sediments stored during the past 2000 years is 3.2×109 t. Consequently, about 0.9×106 t yr−1 could reach the shelf edge and eventually the open sea. From this amount of displaced material and the deposition surface areas, an evaluation of sediment fluxes across the margin during the late Holocene period is discussed. This evaluation is compared with results obtained from ECOsystéme du canyon du cap-FERret (ECOFER) data from sediment traps and surficial box cores. 相似文献
17.
Jeffrey R. Allwardt G. Eric MichaelChuck R. Shearer Philip D. HeppardHongxing Ge 《Marine and Petroleum Geology》2009
This study demonstrates the utilization of 2D basin models to address overpressure development due to compaction disequilibrium in supra-allochthonous salt mini-basins with very high sedimentation rates in the Gulf of Mexico. By properly selecting 2D line sections with moderate stratigraphic resolution, it is possible to predict timing of overpressure development and approximate present-day overpressure distributions in the mini-basin. This study shows that even low resolution models with approximate information on the net-to-gross (sand:shale ratio) can average ±0.4 ppg with a maximum error of 1.0 ppg relative to pressure measurements in sandstones. The models based on age, depth, approximate lithology and an interpretation of complicated salt movement are adequate to evaluate pressure to address issues around trap containment and may be used for preliminary well planning. This study tested the results of overpressure prediction utilizing different stratigraphic resolutions and shows the sensitivity of overpressure modeling to 2D line selection. Also, three models were built to investigate how the permeability of salt welds affects overpressure development in an adjacent salt mini-basin. These results indicate that even a salt weld permeability reduction of 1.5 log mD results in a pressure difference between neighboring mini-basins. Additionally, these models qualitatively reproduced the seismic velocity volume which is supporting evidence that the salt welds in this mini-basin are at least partially sealing. 相似文献
18.
We describe (1) bedding-parallel veins of fibrous calcite (beef) and (2) thrust detachments, which we believe provide good evidence for fluid overpressure in source rocks for petroleum. Our examples are from the surface or subsurface of the Magallanes-Austral Basin, which lies at the southern tip of South America. There, the best source rocks for petroleum are of Early Cretaceous age. In the central parts of the basin these source rocks have become overmature, but at the eastern edge, onshore and offshore, they are today either immature or in the oil window.In Tierra del Fuego, the foothills of the Andes consist mainly of sedimentary rocks, which have undergone thin-skinned thrusting. In the Vicuña area (Chile), Early Cretaceous source rocks have reached the surface above thrust detachments, which are visible on seismic data and well data. At the surface, we have found calcite beef, containing hydrocarbons (solid and/or fluid), in the Rio Jackson and Vicuña formations, which have reached the wet gas window. In the Rio Gallegos area (Argentina), the source rocks have not reached the surface, but seismic and well data provide good evidence for thin-skinned thrusting above flat-lying detachments in Early Cretaceous source rock, where it is in the early oil window. In contrast, there is little or no deformation where the source rock is still immature. Thus the deformation front coincides with the maturity front. Next to the central parts of the basin, where the source rocks have reached the surface within the Andes proper, they have undergone low-grade metamorphism. Within these source rocks, we have found beef veins, but of quartz, not calcite. To the east, within the foreland basin, seismic and well data provide evidence for a few compressional structures, including thin-skinned detachments in the deeply buried source rock. Finally, in the northern part of the basin (Santa Cruz province, Argentina), where it is shallower, the source rocks have reached the surface in the foothills, above a series of back-thrusts. At Lago San Martín, the source rocks have reached the oil window and they again contain calcite beef.In conclusion, where we have examined Early Cretaceous source rocks at the surface, they contain either calcite beef (if they have reached the late oil window or wet gas window) or quartz beef (if they are overmature). Independent evidence for overpressure, in the form of source-rock detachments, comes from subsurface data, especially at the southern end of the basin, where the source rocks are not overmature and deformation is relatively intense. Thus we argue that hydrocarbon generation has led to overpressure, as a result of chemical compaction and load transfer, or volume changes, or both. 相似文献
19.
This paper documents and describes through the use of 3D seismic data a prolific mud volcano province within the Eastern Mediterranean. As many as 386 mud volcanoes were mapped within the post-salt succession of the western slope of the Nile Cone, offshore Egypt, using high resolution 3D seismic data. The mud volcanoes within this field display significant geometrical variability in diameter (c. 550 m to c. 5660 m), height (c. 25 m to c. 510 m) and volume (c. 0.1 km3 to c. 3.3 km3) and lie at depths ranging from c. > 6000 m subsea to c. 3100 m at the seafloor. A close spatial relationship between mud volcanoes and base-salt depressions and regions of anomalous thinning within the immediate pre-salt succession, combined with documented core samples taken from mud volcanoes within this region present a powerful argument for a pre-salt source of mud. 3D seismic interpretation and volumetric analysis of these mud volcanoes and their source region permit the definition and quantification of their depletion zones. A conceptual model for a dynamic liquefaction and sediment withdrawal process is proposed whereby mud is fed into a central conduit as the depletion zone propagates radially and episodically outwards resulting in a the formation of a concentric depletion zones. Prolonged mud volcanism within this region over the last ∼5.3 Ma implies the potential for long lived pre-salt overpressure and continued mud volcanism following the catastrophic hydrodynamic impact of the Messinian Salinity Crisis. It is suggested that the scale of mud volcanism means that this region should be considered as among the largest mud volcano provinces in the world. 相似文献
20.
《Estuarine, Coastal and Shelf Science》2003,56(3-4):845-860
Recent efforts to construct global ocean budgets for carbon have recognized the importance of continental margins. In this study, we constructed budgets for the Strait of Georgia, a temperate, North American west coast basin that receives the inflow of one of the world's major rivers. Drawing from published and unpublished data, we have estimated the magnitude of the various sources and sinks of fresh water, sediment and organic carbon.The Fraser River is the dominant source of fresh water and particles to the strait, contributing approximately 73% of the 158×109 m3 year−1 of water and 64% of the 30×109 kg year−1 of particles. Other rivers supply most of the remainder, while rain, groundwater and anthropogenic sources of water and particles are negligible in comparison. Fresh water escapes the Strait of Georgia through Juan de Fuca Strait, but particulate inputs are approximately balanced by sedimentation within the greater Strait of Georgia, implying almost complete trapping of particles.Dissolved and particulate organic carbon are derived mainly from in situ primary production (855×106 kg year−1) and from the Fraser River (550×106 kg year−1). Other rivers contribute 200×106 kg year−1 of organic carbon, and anthropogenic sources (ocean dumping, sewage, pulp mills and aquaculture) a further 119×106 kg year−1. Particulate organic carbon is predominantly buried (428×106 kg year−1) or oxidized (90×106 kg year−1) in the sediments of the strait. About 70% of the organic carbon that enters or is produced in the strait is dissolved. Most of the dissolved organic carbon is oxidized within the strait (784×106 kg year−1), but the remainder (400×106 kg year−1) is exported to the Pacific Ocean. Although the particulate organic carbon budget by itself implies net autotrophy, dissolved organic carbon oxidation may make the Strait of Georgia slightly net heterotrophic. 相似文献