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1.
The onshore Georgina Basin in northern Australia is prospective for unconventional hydrocarbons; however, like many frontier basins, it is underexplored. A well-connected hydraulic fracture network has been shown to be essential for the extraction of resources from the tight reservoirs that categorise unconventional plays, as they allow for economic flows of fluid from the reservoir to the well. One of the fundamental scientific questions regarding hydraulic stimulation within the sub-surface of sedimentary basins is the degree to which local and regional tectonic stresses act as a primary control on fracture propagation. As such, an understanding of present-day stresses has become increasingly important to modern petroleum exploration and production, particularly when considering unconventional hydrocarbon reservoirs. This study characterises the regional stress regime in the Georgina Basin using existing well data. Wellbore geophysical logs, including electrical resistivity image logs, and well tests from 31 petroleum and stratigraphic wells have been used to derive stress magnitudes and constrain horizontal stress orientations. Borehole failure features interpreted from wellbore image and caliper logs yield a maximum horizontal stress orientation of 044°N. Integration of density log data results in a vertical stress gradient of 24.6 MPa km–1. Leak-off and mini-fracture tests suggest that this is the minimum principal stress, as leak-off values are generally shown to be at or above the magnitude of vertical stress. The maximum horizontal stress gradient is calculated to be in the range of 31.3–53.9 MPa km–1. As such, a compressional stress regime favouring reverse/reverse–strike-slip faulting is interpreted for the Georgina Basin.  相似文献   

2.
The Tornquist Fan, a fan-shaped region in Denmark and Western Baltic, is situated in the transition zone between the Western and Northern European Stress Provinces. Breakout data from 20 wells (0.3–3.6 km) were analysed. The fan can be divided into three stress provinces: (i) The area south of the Rømø Fracture Zone is part of the Western European Stress Province and has NNW-SSE orientation of the maximum horizontal stress, (ii) The sediment cover in the Nonvegian-Danish Basin is dominated by ENE-WSW orientated maximum horizontal stress, (iii) The maximum horizontal stress is sub-parallel to the strike of the Sorgenfrei-Tornquist Zone. Deviations from the regional stress field were observed in wells close to faults and salt diapirs. In wells south of the Sorgenfrei-Tornquist Zone, breakout occurrence decreases with increasing age of the stratigraphic units. The downhole breakout distribution seems to correlate with lithology and thickness of the sediment layer.  相似文献   

3.
An analysis of Bouguer gravity anomaly data and geothermal gradient data obtained from bottom hole and drill stem tests temperature is used to determine the crustal structure of the Sahel Basin in eastern Tunisia and its role in the maturation and location of the large number of oil and gas fields in the region. The regional Bouguer gravity anomaly field is dominated by gradual increase in values from the northwest to southeast and is may be caused by crustal thinning as revealed by regional seismic studies. In addition, higher geothermal gradients in the same region as the Bouguer gravity anomaly maximum add an additional constraint for the existence of crustal thinning in the region. A detailed analysis of the Bouguer gravity anomaly data was performed by both upward continuation and horizontal gradients. These two techniques were combined to show that the study area consists of two structural regions: (1) the North–South Axis (NOSA)–Zeramedine region which is characterized by northwest-dipping, northeast-striking faults, thicker crust (30–31 km) and low geothermal gradients, and (2) the Mahres–Kerkennah region which is characterized by vertical, northwest-striking faults, thinner crust (28–29 km) and higher geothermal gradients. The correlation of a variety of features includes mapped and geophysically defined faults, volcanic rocks, a thinned crust and high geothermal gradients within the same location as known oil and gas fields indicate that the faults are a major factor in the location of these petroleum accumulations.  相似文献   

4.
R. T. van Balen  T. Skar 《Tectonophysics》2000,320(3-4):331-345
The Halten Terrace is a structural element of the Meso-Cenozoic mid-Norwegian margin. The pore fluid pressure distribution in the faulted Jurassic formations on the Halten Terrace is characterized by significant lateral variations. In general, the fluid overpressure increases stepwise across faults from east to west, from zero (hydrostatic fluid pressure) to about 30 MPa. Fault-bounded pressure cells can therefore best explain the fluid pressure distribution. The results of analyses of log-derived porosities indicate that the high overpressure in the westernmost pressure cell was built up recently. However, despite the high sedimentation rates during Plio-Pleistocene, the high overpressure cannot be explained by local mechanical compaction. Alternative explanations for the high overpressure proposed by other authors are based on pore fluid volume increase (e.g. hydrocarbon generation). We propose that the high overpressure is caused by fluid flow from the deep Rås Basin to the western part of the Halten Terrace, through fractures in the Mesozoic, deep seated Klakk Fault Complex. Opening of fractures in this fault zone by seismic and static mechanisms is possible in the present-day intraplate stress field, which is characterized by a NW–SE oriented maximum horizontal stress direction. During Miocene, the maximum horizontal stress was E–W oriented, which implies a stress rotation during Pliocene. The E–W orientation of the maximum horizontal stress has impeded the initiation and opening of fractures in the N–S striking Klakk Fault Complex during Miocene. Fluid flow from the Rås Basin through faults of the Klakk Fault Complex can therefore have occured since Pliocene. Thus, the rotation of the intraplate stress directions can explain why the build-up of overpressure on the western part of the Halten Terrace occured recently, as indicated by the results of porosity analyses. Understanding the overpressure evolution of the Halten Terrace is important for exploration in that area, as hydrocarbons have been found in the hydrostatic pressure cells, whereas they are absent in the high overpressure cells.  相似文献   

5.
Exploration of Perth's geothermal potential has been performed by the Western Australian Geothermal Centre of Excellence (WAGCoE). Detailed vertical temperature and gamma ray logging of 17 Western Australia Department of Water's (DoW) Artesian Monitoring (AM) wells was completed throughout the Perth Metropolitan Area (PMA). In addition, temperature logs from 53 DoW AM wells measured in the 1980s were digitised into LAS format. The logged data are available in the WAGCoE Data Catalogue.

Analysis of the gamma ray logs yielded the first estimates of radiogenic heat production in Perth Basin formations. Values by formation ranged between 0.24 and 1.065 μW m?3. The temperature logs provide a picture of true formation temperatures within shallow sediments in the Perth Basin. A three-dimensional model of the temperature distribution was used to produce maps of temperature at depth and on the top of the Yarragadee aquifer.

The temperature data were interpreted with a one-dimensional conductive heat model. Significant differences between the model and the observations was indicative of heat moving via non-conductive mechanisms, such as advection or convection. Evidence of non-conductive or advective heat flow is demonstrated in most formations in the region, with significant effects in the aquifers. Average conductive geothermal gradients range from 13°C km?1 to 39°C km?1, with sandstone formations exhibiting average gradients of approximately 25°C km?1, while insulating silt/shale formations show higher average gradients of over 30°C km?1.

To produce preliminary heat flow estimates, temperature gradients were combined with thermal conductivities measured elsewhere. The geometric mean heat flow estimates range between 64 mW m?2 to 91 mW m?2, with the standard deviation of the arithmetic mean heat flow ranging between 15 and 23 mW m?2.

The study characterises the shallow temperature regime in the Perth Metropolitan Area, which is of direct relevance towards developing commercial geothermal projects.  相似文献   

6.
The Australian continent displays the most complex pattern of present-day tectonic stress observed in any major continental area. Although plate boundary forces provide a well-established control on the large-scale (>500 km) orientation of maximum horizontal stress (SHmax), smaller-scale variations, caused by local forces, are poorly understood in Australia. Prior to this study, the World Stress Map database contained 101 SHmax orientation measurements for New South Wales (NSW), Australia, with the bulk of the data coming from shallow engineering tests in the Sydney Basin. In this study we interpret present-day stress indicators analysed from 58.6 km of borehole image logs in 135 coal-seam gas and petroleum wells in different sedimentary basins of NSW, including the Gunnedah, Clarence-Moreton, Sydney, Gloucester, Darling and Bowen–Surat basins. This study provides a refined stress map of NSW, with a total of 340 (A–E quality) SHmax orientations consisting of 186 stress indicators from borehole breakouts, 69 stress measurements from shallow engineering methods, 48 stress indicators from drilling-induced fractures, and 37 stress indicators from earthquake focal mechanism solutions. We define seven stress provinces throughout NSW and determine the mean orientation of the SHmax for each stress province. The results show that the SHmax is variable across the state, but broadly ranges from NE–SW to ESE–WNW. The SHmax is approximately E–W to ESE–WNW in the Darling Basin and Southeastern Seismogenic Zone that covers the west and south of NSW, respectively. However, the present-day SHmax rotates across the northeastern part of NSW, from approximately NE–SW in the South Sydney and Gloucester basins to ENE–WSW in the North Sydney, Clarence-Moreton and Gunnedah basins. Comparisons between the observed SHmax orientations and Australian stress models in the available literature reveal that previous numerical models were unable to satisfactorily predict the state of stress in NSW. Although clear regional present-day stress trends exist in NSW, there are also large perturbations observed locally within most stress provinces that demonstrate the significant control on local intraplate sources of stress. Local SHmax perturbations are interpreted to be due to basement topography, basin geometry, lithological contrasts, igneous intrusions, faults and fractures. Understanding and predicting local stress perturbations has major implications for determining the most productive fractures in petroleum systems, and for modelling the propagation direction and vertical height growth of induced hydraulic fractures in simulation of unconventional reservoirs.  相似文献   

7.
The magnitude of the in situ stresses in the Cooper–Eromanga Basins have been determined using an extensive petroleum exploration database from over 40 years of drilling. The magnitude of the vertical stress (Sv) was calculated based on density and velocity checkshot data in 24 wells. Upper and lower bound values of the vertical stress magnitude are approximated by Sv = (14.39 × Z)1.12 and Sv = (11.67 × Z)1.15 functions respectively (where Z is depth in km and Sv is in MPa). Leak-off test data from the two basins constrain the lower bound estimate for the minimum horizontal stress (Shmin) magnitude to 15.5 MPa/km. Closure pressures from a large number of minifrac tests indicate considerable scatter in the minimum horizontal stress magnitude, with values approaching the magnitude of the vertical stress in some areas. The magnitude of the maximum horizontal stress (SHmax) was constrained by the frictional limits to stress beyond which faulting occurs and by the presence of drilling-induced tensile fractures in some wells. The maximum horizontal stress magnitude can only be loosely constrained regionally using frictional limits, due to the variability of both the minimum horizontal stress and vertical stress estimates. However, the maximum horizontal stress and thus the full stress tensor can be better constrained at individual well locations, as demonstrated in Bulyeroo-1 and Dullingari North-8, where the necessary data (i.e. image logs, minifrac tests and density logs) are available. The stress magnitudes determined indicate a predominantly strike-slip fault stress regime (SHmax > Sv > Shmin) at a depth of between 1 and 3 km in the Cooper–Eromanga Basins. However, some areas of the basin are transitional between strike-slip and reverse fault stress regimes (SHmax > Sv ≈ Shmin). Large differential stresses in the Cooper–Eromanga Basins indicate a high upper crustal strength for the region, consistent with other intraplate regions. We propose that the in situ stress field in the Cooper–Eromanga Basins is a direct result of the complex interaction of tectonic stresses from the convergent plate boundaries surrounding the Indo-Australian plate that are transmitted into the center of the plate through a high-strength upper crust.  相似文献   

8.
We conducted hydraulic fracturing (HF) in situ stress measurements in Seokmo Island, South Korea, to understand the stress state necessary to characterize a potential geothermal reservoir. The minimum horizontal principal stress was determined from shut-in pressures. In order to calculate the maximum horizontal principal stress (S Hmax) using the classical Hubbert–Willis equation, we carried out hollow cylinder tensile strength tests and Brazilian tests in recovered cores at depths of HF tests. Both tests show a strong pressure rate dependency in tensile strengths, from which we derived a general empirical equation that can be used to convert laboratory determined tensile strength to that suitable for in situ. The determined stress regime (reverse-faulting) and S Hmax direction (ENE–WSW) at depths below ~300 m agrees with the first order tectonic stress. However the stress direction above ~300 m (NE–SW) appears to be interfered by topography effect due to a nearby ridge. The state of stress in Seokmo Island is in frictional equilibrium constrained by optimally oriented natural fractures and faults. However, a severe fluctuation in determined S Hmax values suggests that natural fractures with different frictional coefficients seem to control stress condition quite locally, such that S Hmax is relatively low at depths where natural fractures with low frictional coefficients are abundant, while S Hmax is relatively high at depths where natural fractures with low frictional coefficients are scarce.  相似文献   

9.
利用四川盆地磨溪地区12口井岩心、8口井成像测井资料、14口井的测井评价等资料,系统分析磨溪地区龙王庙组储层特征,划分了储层类型,探讨了储层形成主控因素,预测了优质储层展布。结果表明：1）川中磨溪地区龙王庙组储层主要岩石类型为中粗晶砂屑白云岩,储层中小洞发育,见到大量的构造缝和水平缝,整体表现为中低孔、中-高渗特征;2）龙王庙组储层类型可划分为溶蚀孔洞型、溶蚀孔隙型和基质孔隙型3种类型,其中高角度构造缝、水平缝、网状成岩缝和缝合线4种裂缝与3种储集类型形成整体连通的缝洞体系;3）优质储层主要在中细晶砂屑白云岩颗粒滩相中发育,颗粒滩后期经历3期岩溶作用,特别是表生期“顺层”溶蚀使溶蚀孔、洞型储层横向叠置连片,大面积分布,延伸5～20 km,井间连通性好,形成了孔洞发育的优质储层。  相似文献   

10.
Evaluation of fractures and their parameters, such as aperture and density, is necessary in the optimization of oil production and field development. The purpose of this study is the calculation of fracture parameters in the Asmari reservoir using two electrical image logs (FMI, EMI), and the determination of fracture parameters’ effect on the porosity and permeability using thin sections and velocity deviation log (VDL). The results indicate that production in the Asmari reservoir is a combination of fractures and rock matrix. Fracture aperture (VAH) and fracture porosity (VPA) are only measurable with core and image logs directly. However, regarding core limitations, the image log has been recognized as the best method for fracture parameter determination due to their high resolution (2.5 mm). In this study, VDL log and thin sections have been used as auxiliary methods which may be available in all wells. The VDL log provides a tool to obtain downhole information about the predominant pore type in carbonates. Results indicate that between fracture parameters, VAH is considered as the most important parameter for determining permeability. For well No. 3, VAH ranges from minimum 51 × 10?5 mm to maximum 0. 047 mm and VPA changes from min 10?5% to maximum 0.02056%. For well No. 6, VAH varies from 5 × 10?4 to 0.0695 mm and VPA varies from 10?5 to 0.015%. Therefore, due to high fracture density and fracture aperture, it seems that most of effective porosity originates from fractures especially in well No. 3. However, VDL for well No. 6 indicates that intercrystalline and vuggy porosity are the dominant porosity. This result may be an indication for fracture set diversity in the two studied wells. While in well No. 3, they related to the folding and active faults, in well No. 6 they are only of folding type. Furthermore, results indicate the high capability for both of EMI and FMI image logs for calculation of fracture and vug parameters in the carbonate reservoirs.  相似文献   

11.
The Australian Cooper Basin is a structurally complex intra-cratonic basin with large unconventional hydrocarbon potential. Fracture stimulation treatments are used extensively in this basin to improve the economic feasibility; however, such treatments may induce fault activity and risk the integrity of hydrocarbon accumulations. Fault reactivation may not only encourage tertiary fluid migration but also decrease porosity through cataclasis and potentially compartmentalise the reservoir. Relatively new depth-converted three-dimensional seismic surveys covering the Dullingari and Swan Lake 3D seismic surveys were structurally interpreted and geomechanically modelled to constrain the slip tendency, dilation tendency and fracture stability of faults under the present-day stress. A field-scale pore pressure study found a maximum pressure gradient of 11.31 kPa/m within the Dullingari 3D seismic survey, and 11.14 kPa/m within the Swan Lake 3D seismic survey. The present-day stress tensor was taken from previously published work, and combined with local pore pressure gradients and depth-converted field-scale fault geometries, to conclude that SE–NW-striking strike-slip faults are optimally oriented to reactivate and dilate. High-angle faults striking approximately E–W appear most likely to dilate, and act as fluid conduits irrespective of being modelled under a strike-slip or compressional stress regime. Near-vertical SE–NW and NE–SW-striking faults were modelled to be preferentially oriented to slip and reactivate under a strike-slip stress regime. Considering that SE–NW-striking strike-slip faults have only recently been interpreted in the literature, it is possible that many reservoir simulations and development plans have overlooked or underestimated the effect that fault reactivation may have on reservoir properties. Future work investigating the likelihood that fracture stimulation treatments may be interacting, and reactivating, pre-existing faults and fractures would benefit field development programs utilising high-pressure hydraulic fracture stimulation treatments.  相似文献   

12.
Formation of fractured zones in overburden due to longwall mining   总被引：6，自引：0，他引：6  
The fractured zones caused by mining were studied in the overburden of the Torezko-Snezhnyanskaya area, Ukraine, through the change in natural gas emission from these zones during longwall coal excavation. Zones of interconnected fractures and separate horizontal fractures were studied with vertical wells drilled from the ground surface down to active underground workings. The maximum heights of the zone of interconnected fractures and separate horizontal fractures may reach 19–41 and 53–92 times the thickness of the coal seam respectively. It was found that the ratio between the maximum height of the zone of interconnected fractures and the thickness of the extracted coal seam increases with the increasing number of rock layer interfaces and decreases with the increasing stiffness of immediate roof. It is shown that the growth of the zone of interconnected fractures occurred during 17–39 days at an average rate of 0.94–1.97 m day?1 and it was accompanied by increasing methane emission from overburden. Observation shows that the formation of separate horizontal fractures began only 11–49.5 days after the height of the zone of interconnected fractures reached its maximum value. Formation of separate horizontal fractures in overburden over the longwall excavation occurred as a stepped process from lower to upper sandstone–sandy shale layer interfaces in the direction of the ground surface.  相似文献   

13.
裂缝是川西北地区九龙山构造上三叠统须家河组二段致密砂岩天然气藏分布的重要控制因素。利用野外露头、岩心、成像测井和薄片等资料,并结合实验分析,对该区裂缝的成因类型、发育特征、形成期次及其形成机理进行了分析。研究区须二段致密砂岩储层发育有构造裂缝和成岩裂缝两种类型,其中以构造裂缝为主,主要有北东东-南西西向、北北东-南南西向和北西-南东向3组。按照裂缝的倾角,构造裂缝又可分为高角度构造裂缝和低角度构造裂缝。其中,高角度构造剪切裂缝主要是在印支晚期、燕山晚期和喜马拉雅期3期构造作用下形成,形成构造裂缝的力源来自于龙门山以及米仓山-大巴山的水平构造挤压作用、深埋藏造成的异常高压流体压力以及抬升剥蚀造成的应力作用。低角度构造裂缝主要与构造挤压作用下断层的逆冲作用或层间滑动造成的近水平剪切作用有关。  相似文献   

14.
The Deccan trap basalt, laid down by multiple lava flows during upper Cretaceous to Paleocene times forms the basement of current study in Cambay basin. As such, there is great interest and value in fracture detection and evaluation of fractured basement reservoirs in the Cambay basin. The procedure for identification and evaluation of natural as well as induced fractures in basaltic basement of the Cambay basin is presented in this work. In this study formation micro-imager (FMI) and extended range micro-imager (XRMI) log data for fracture identification is used. The Deccan trap basaltic basement of the study area, comprising five wells in the Tarapur-Cambay block, has potential for holding commercial hydrocarbon due to the presence of fractures and weathered basement. Both image logs (FMI, XRMI) identify three types of fracture including open (conductive), partially open and closed (resistive) fractures, of which open and partially open fractures are important for hydrocarbon accumulation. Fracture dip ranges from 10° to 80°. Image logs have also identified washout, breakout and drilling-induced fracture zones. The strike direction of the open natural fractures for four wells varies from N60°E to N30°E whereas the strike direction of most natural fracture in the fifth well is oriented towards N20°W. The orientations of drilling-induced fractures and breakouts may be interpreted for the in-situ stress direction over the logged interval. Drilling-induced tensile fractures, identified over the depth interval of 1969–1972 m, and borehole breakouts over the interval of 1953–1955 m in one well, suggest an orientation of maximum in-situ horizontal compressive stress (SH) lies in the north-south direction. The azimuths of open natural fractures in the same well vary from north-south to N30°E. It is expected that the direction of fluid flow will be controlled by open natural fractures and therefore would be in a direction parallel to the SH direction, which is orthogonal to the minimum horizontal stress (Sh) direction. The orientations observed are consistent with the present day SH direction in the study area of Cambay basin.  相似文献   

15.
A geomechanical model can reveal the mechanical behavior of rocks and be used to manage the reservoir programs in a better mode. Fluid pressure will be reduced during hydrocarbon production from a reservoir. This reduction of pressure will increase the effective stress due to overburden sediments and will cause porous media compaction and surface subsidence. In some oil fields, the compacting reservoir can support oil and gas production. However, the phenomena can also cause the loss of wells and reduced production and also cause irreparable damage to the surface structures and affect the surrounding environment. For a detailed study of the geomechanical behavior of a hydrocarbon field, a 3D numerical model to describe the reservoir geomechanical characteristics is essential. During this study, using available data and information, a coupled fluid flow-geomechanic model of Fahlian reservoir formation in X-field in SW of Iran was constructed to estimate the amount of land subsidence. According to the prepared model, in this field, the maximum amount of the vertical stress is 110 MPa and the maximum amount of the horizontal stress is 94 MPa. At last, this model is used for the prediction of reservoir compaction and subsidence of the surface. The maximum value of estimated ground subsidence in the study equals to 29 mm. It is considered that according to the obtained values of horizontal and vertical movement in the wall of different wells, those movements are not problematic for casing and well production and also the surrounding environment.  相似文献   

16.
The Matt Wilson structure is a circular 5.5 km-diameter structure in Early Mesoproterozoic or Neoproterozoic rocks of the Victoria Basin, Northern Territory. It lies in regionally horizontal to gently dipping Wondoan Hill and Stubb Formations (Tijunna Group) and Jasper Gorge Sandstone (Auvergne Group). An outer circumferential syncline with dips of 5?–?40° in the limbs surrounds an intermediate zone with faulted sandstone displaying horizontal to low dips, and a central steeply dipping zone about 1.5 km across. Several thrust faults in the outer syncline appear to indicate outward-directed forces. The central zone, marked by steeply dipping to overturned Tijunna Group and possibly Bullita Group sandstone and mudstone, indicates uplift of at least 300 m. The rocks are intensely fractured with some brecciation, and contain numerous planar to subtly undulating surfaces displaying striae which resemble shatter cleavage. Thin-sections of sandstone from the central area show zones of intense microbrecciation and irregular and planar fractures in quartz, but no melt-rocks have been identified. The planar fractures occur in multiple intersecting parallel sets typical of relatively low-level (5?–?10 GPa) shock-pressure effects. Alternative mechanisms, i.e. igneous intrusion, carbonate collapse, diapirism and regional deformation processes, have been discounted. The circular nature, central uplift, faulting, shatter features and planar fractures are all consistent with an impact origin. The Matt Wilson structure is most likely a deeply eroded impact structure in which the more highly shocked rocks of the original crater floor have been removed by erosion. Estimates of the age of the Auvergne and Tijunna Groups range from Early Mesoproterozoic (which we favour) to Late Neoproterozoic. Early Cambrian Antrim Plateau Volcanics near the impact structure show no signs of impact effects, allowing the age of impact to be constrained between Early Mesoproterozoic and Early Cambrian. The presence of widespread soft-sediment deformation features, apparently confined to a single horizon in the Saddle Creek Formation some 700?–?1000 m stratigraphically higher in the Auvergne Group than the rocks at the impact site, and apparently increasing in thickness towards the Matt Wilson structure, lead us to speculate that this probable event horizon is related to the impact event: if correct the impact occurred during deposition of the Saddle Creek Formation.  相似文献   

17.
Fractures can provide valuable information for tectonic evolution. According to the data of outcrops, cores, thin sections and well logs, the tectonic fractures in the Qaidam Basin can be divided into four types: small faults (including small normal fault and small reverse fault), vertical open fracture, bedding plane slip fracture and horizontal open fracture. Our fracture observations provide new constraints on the Cenozoic tectonic evolution of the Qaidam Basin. Syn-sedimentary small normal faults in the Paleogene strata indicate the extension deformation during the Paleogene. Small reverse faults, vertical open fractures and bedding plane slip fractures occurred in the Paleogene and Neogene strata have genetic relationship. According to the burial history and homogenization temperature of fluid inclusions of gypsum and calcite filled in the vertical open fractures, it can be deduced that the vertical open fractures being formed mainly from the late Miocene Shangyoushashan Formation with age of 5.1?Ma to the end of Pliocene Shizigou Formation with age of 2.6?Ma, indicating small reverse faults, vertical open fractures and bedding plane slip fractures were simultaneously formed in the Neogene. These fractures were resulted from the compression deformation. The horizontal open fractures occurred in the Paleogene, Neogene and Quaternary strata with apertures and intensities decreasing with depth were formed by the large-scale quick uplift and denudation resulted from the strong compression deformation since the Quaternary.  相似文献   

18.
Grand Mesa is an erosional remnant on the southern margin of the Piceance basin (Colorado, USA) that appears to host topographically driven groundwater flow in low permeability strata via a pervasive network of vertical extensional fractures. The vertical fractures cut more than 1 km of clay-rich lithology ranging in age from Upper Cretaceous through Eocene, and likely formed from horizontal dilation, cooling, and erosional unloading associated with 2.8 km of regional uplift and 1.5 km of incision by the Gunnison and Colorado rivers. The vertical fractures create anisotropy in which vertical permeability exceeds horizontal permeability. This enhances vertical flow and depth of penetration of groundwater, favors local flow regimes over regional flow, and results in groundwater temperatures that are elevated by up to 10°C over mean surface temperatures at the location of springs. The uplift and cooling that formed the fractures may also have produced domains of abnormally underpressured pore fluids and natural gas within blocks of low permeability bedrock bounded by the fractures. Pore pressures inside these blocks may be in disequilibrium with the groundwater flow system due to ongoing stress release, and the long time scales required for pressure equilibration in the low permeability strata.  相似文献   

19.
Cortés  & Maestro 《地学学报》1998,10(5):287-294
Palaeostresses inferred from brittle mesostructures in the eastern Duero Basin show a recent stress field characterized by an extensional regime, with local strike-slip and compressional stress states. Orientations of the maximum horizontal stress ( SHmax ) show a relative scattering with two main modes: NNE to NE–SW and NW–SE. These orientations suggest the existence of two stress sources responsible for the dominant directions of the maximum horizontal stress in northeastern Iberia. Extensional structures within a broad-scale compressional stress field can be related to both the decrease in relative stress magnitudes from active margins to intraplate regions and rifting proccesses ocurring in eastern Iberia. Stress states with NW–SE-trending SHmax are compatible with the dominant pattern established for western Europe. NE–SW orientations of SHmax suggest the occurrence of tectonic forces coming from the Pyrenean zone. Geological and geophysical data indicate the existence of both orientations from the upper Miocene to the present-day in NE Iberia.  相似文献   

20.
Carbon dioxide (CO2) sequestration in depleted sandstone hydrocarbon reservoirs could be complicated by a number of geomechanical problems associated with well drilling, completions, and CO2 injection. The initial production of hydrocarbons (gas or oil) and the resulting pressure depletion as well as associated reduction in horizontal stresses (e.g., fracture gradient) narrow the operational drilling mud weight window, which could exacerbate wellbore instabilities while infill drilling. Well completions (casing, liners, etc.) may experience solids flowback to the injector wells when injection is interrupted due to CO2 supply or during required system maintenance. CO2 injection alters the pressure and temperature in the near wellbore region, which could cause fault reactivation or thermal fracturing. In addition, the injection pressure may exceed the maximum sustainable storage pressure, and cause fracturing and fault reactivation within the reservoirs or bounding formations. A systematic approach has been developed for geomechanical assessments for CO2 storage in depleted reservoirs. The approach requires a robust field geomechanical model with its components derived from drilling and production data as well as from wireline logs of historical wells. This approach is described in detail in this paper together with a recent study on a depleted gas field in the North Sea considered for CO2 sequestration. The particular case study shows that there is a limitation on maximum allowable well inclinations, 45° if aligning with the maximum horizontal stress direction and 65° if aligning with the minimum horizontal stress direction, beyond which wellbore failure would become critical while drilling. Evaluation of sanding risks indicates no sand control installations would be needed for injector wells. Fracturing and faulting assessments confirm that the fracturing pressure of caprock is significantly higher than the planned CO2 injection and storage pressures for an ideal case, in which the total field horizontal stresses increase with the reservoir re-pressurization in a manner opposite to their reduction with the reservoir depletion. However, as the most pessimistic case of assuming the total horizontal stresses staying the same over the CO2 injection, faulting could be reactivated on a fault with the least favorable geometry once the reservoir pressure reaches approximately 7.7 MPa. In addition, the initial CO2 injection could lead to a high risk that a fault with a cohesion of less than 5.1 MPa could be activated due to the significant effect of reduced temperature on the field stresses around the injection site.  相似文献   

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