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1.
Igneous sills and laccoliths emplaced in sedimentary basins may significantly impact petroleum systems, both positively and negatively. Igneous intrusions provide heat to maturate regionally immature organic-rich host rocks, act as fractured reservoirs hosting commercial accumulations of hydrocarbons, and form structures affecting fluid flow and trapping at different scales. Nevertheless, the petrophysical implications of igneous intrusions on their host rock are poorly known. In this study, we analyse 200 wells in the Río Grande Valley oil field, Neuquén basin, Argentina, where the main reservoirs are in fractured igneous sills. This dataset represents a globally unique possibility to characterize the igneous–host rock interaction using both wireline logs and core material. We identify a systematic Contact Low Resistivity Zone (CLRsZ) at both the upper and lower contacts of the sills emplaced in the organic-rich Vaca Muerta and Agrio Formations. We characterize the nature of these CLRsZ and their petrophysical properties by integrating resistivity and gamma ray well logs, petrographic analyses, petrophysical tests and geochemical analyses. The low resistivity signal of the CLRsZ is dominantly carried by massive-sulphide deposits, mainly pyrite, observed both in the host rock and the chilled margin of the sills. Well log images and porosity-permeability analysis on core plugs show that both the sills and their associated CLRsZ can act as carrier for fluid flow and reservoir for hydrocarbons storage. The thickness of the upper and lower CLRsZ correlates linearly with the thickness of the sill, and the volume of both the upper and lower CLRsZ represents ca. 40% with respect to the volume of their associated sill. The thickness of the CLRsZ represents ca. 13% of the thickness of contact aureole induced by the sills. In the CLRsZ, a great proportion of kerogen was transformed to hydrocarbon, so that CLRsZ were restricted to the innermost contact aureole of the sills. Our results show that the CLRsZ can have major implications on fluid flow and should be considered in reservoir models in volcanic basins hosting sills emplaced in organic-rich formations. 相似文献
2.
The distribution of fractures and its dependence on lithology and petrophysical properties of rock in the Asmari Formation were examined using three wells data of one of the largest oil fields of southwestern Iran. Fractures were measured on cut cores. Mineral content and petrophysical data were obtained through thin section study and core plug measurement respectively. Influence of mineral composition and petrophysical property of rocks on fracture density was explored statistically. Increasing quartz (sand) and anhydrite content of rocks decrease and dolomite increases the threshold of fracture densities, however no significant relation was observed between calcite content of rock and fracture density. Increasing porosity and permeability of rock decrease the threshold of fracture density in some of the defined lithology groups. There are significant differences between the lithology groups in terms of fracture density, although the results in the three wells are not the same. In whole data, the highest fracture density can be observed in dolostone. Limestone and impure carbonates hold broader spaced fractures and sandstones display the least fracture density. The average fracture densities in the wells are strictly different. These differences are the result of the structural position of the wells and also the trend of the well and fractures. The distribution of fractures in most lithology groups can be explained by the function: , where F is relative frequency, D is fracture density and a, b, and c are constants. 相似文献
3.
Offset-dependent characteristics of seismic scattering are useful for characterizing fractured reservoirs. We use two models that have different background medium properties and different azimuthal AVO responses to study elastic wave propagation and scattering in gas-saturated, heterogeneously fractured reservoirs. Heterogeneous fracture density distributions are built through stochastic modelling. Synthetic seismograms are generated by 3-D finite difference modelling, and waveforms along crack-normal and strike directions are considered in this paper. The multiple signal classification (MUSIC) frequency estimator is used in waveform estimation to provide frequency-domain attributes related to seismic wave scattering by fracture heterogeneity. Our results indicate that the strength of the scattering field is a function of the background medium. The strength also increases with increasing fracture scatterer density and with decreasing correlation length of spatial variations of fracture density. The scattering field is weak at the top of the fractured reservoir. The first-order results are dominated by velocity anisotropy of the mean fracture density field. However, the base of the fractured reservoir corresponds to a strong scattering field on which fracture heterogeneity has a larger effect and is characterized by the loss of coherence. 相似文献
4.
Stratigraphic rule-based reservoir models approximate sedimentary dynamics to generate numerical models of reservoir architecture with realistic spatial distributions of petrophysical properties for reservoir forecasting and to support development decision making. A few intuitive rules for the sequential placement of surfaces bounding reservoir units render realistic reservoir heterogeneity, continuity, and spatial organization of petrophysical property distributions that are difficult to obtain using conventional geostatistical pixel- and object-based subsurface methods. While these methods are emerging in applications specifically for deepwater and fluvial clastic reservoirs, there are some remaining obstacles to broad application, such as selection of rule parameters and addressing emergent non-stationarities over the sequence of the placed surfaces. Firstly, there is a need to tune rule parameters to ensure the models honor natural heterogeneities. We demonstrate this for the compensational rule. Secondly, invariants over model sequence (from the base to the top of the model) may occur with respect to shape, volume, undulation, and gradients of surfaces. For example, for a stack of compensational lobes, the volume of individual lobes may decrease due to the onlapping of previous bathymetry and also increasing undulation over model sequence may occur. In addition, for stacking of compensational lobes, the interfacial width and average gradient of the composite surface may initially increase, but then saturate and stabilize. Such non-stationarities represent numerical artifacts that may bias the results from these rule-based models. It is essential that these features are quantified and mitigated as a prerequisite for robust application of rule-based aggradational lobe methods for reservoir modeling. 相似文献
5.
This paper evaluates the application of geothermal energy by numerically modeling the heat extraction that would result from the injection of cold water into an artificially fractured hot dry rock (HDR). The HDR that would be utilized in Alberta is expected to be granite with a network of pre-existing natural fractures. However, to ensure a continued flow of injected water from the reservoir to the production wells, creation of additional fractures is required. Thus, the properties of these fractures are of prime importance to the efficiency of geothermal energy production. The fracture networks for the simulations were created using a numerical code and were converted into a grid format to be used in a commercial thermal simulator. A new approach to embed a complex fracture system into the numerical model was applied. Various properties of the fractures such as aperture, length, and spacing were changed and their absolute and relative effects on energy production were quantified and the results are presented in this paper. This modeling technique was also verified by comparison with the conventional dual porosity model and by performing a history match with real field data obtained from literature. The applicability of this approach to provide heat for oil sands extraction was investigated using the volumes of water currently needed in northern Alberta. Based on these constraints, numerical simulations were run to evaluate the optimum well spacing that would be required using a three-well configuration. In this simulation, the fracture parameters (density and aperture) were kept fixed assuming that they are not affected by cold water injection. The results of this study suggest that geothermal energy has a potential to be a sustainable form of thermal energy for oil sands extraction in northern Alberta. 相似文献
6.
The Athabasca oil sands deposit, Alberta, Canada, is one of the largest known hydrocarbon accumulations. The efficient exploitation of this deposit, as well as other oil sand accumulations throughout the world, is based on in situ recovery and surface mining methods. Quantitative modeling of deposit heterogeneity provides a valuable engineering tool. In the present study, conditional simulation was used to model oil-saturated zones in part of the Athabasca deposit. This technique generates equiprobable models of the in situ variability of essential deposit attributes that honor the available data and their spatial statistics. The application of the technique is based on the delineation of geologically homogeneous zones within the host McMurray Formation, their statistical validity, and the integration of geological interpretations. The geological framework is developed, and subsequently, high resolution conditionally simulated models of three identified hydrocarbon-bearing zones are generated, in terms of the zone boundaries and the percent weight of oil saturation. These models serve as “what-if” tools for risk assessment and future planning. 相似文献
7.
Waterflooding is one of the most common secondary recovery methods in the oil and gas industry. Globally, this process sometimes suffers a technical failure and inefficiency. Therefore, a better understanding of geology, reservoir characteristics, rock typing and discrimination, hydraulic flow units, and production data is essential to analyze reasons and mechanisms of water injection failure in the injection wells. Water injection failure was reported in the Middle Miocene Hammam Faraun reservoir at El Morgan oil field in the Gulf of Suez, where two wells have been selected as injector’s wells. In the first well (A1), the efficiency of injection was not good, whereas in the other analog A2 well good efficiency was assigned. Therefore, it is required to assess the injection loss in the low efficiency well, where all aspects of the geological, reservoir and production data of the studied wells were integrated to get a complete vision for the reasons of injection failure. The available data include core analysis data (vertical and horizontal permeabilities, helium porosity, bulk density, and water and oil saturations), petrographical studies injection and reservoir water chemistry, reservoir geology, production, and injection history. The quality of the data was examined and a set of reliable X–Y plots between the available data were introduced and the reservoir quality in both wells was estimated using reservoir quality index, normalized porosity index, and flow zone indicator. Integration and processing of the core and reservoir engineering data indicate that heterogeneity of the studied sequence was the main reason for the waterflooding inefficiency at the El Morgan A1 well. The best reservoir quality was assigned to the topmost part of the reservoir, which caused disturbance of the flow regime of reservoir fluids. Therefore, it is clearly indicated that rock typing and inadequate injection perforation strategy that has not been aligned with accurate hydraulic flow units are the key control parameters in the waterflooding efficiency. 相似文献
8.
This paper identifies the drivers of the phenomenal growth in productivity in hydraulically fractured horizontal oil wells producing from the middle member of the Bakken Formation in North Dakota. The data show a strong underlying spatial component and somewhat weaker temporal component. Drivers of the spatial component are favorable reservoir conditions. The temporal component of well productivity growth is driven by increasing the number of fracture treatments and by increasing the volume of proppant and injection fluids used on a per fracture treatment basis. Random Forest, a nonparametric modeling procedure often applied in the context of machine learning, is used to identify the relative importance of geologic and well completion factors that have driven the growth in Bakken well productivity. The findings of this study suggest that a significant part of the well productivity increases during the period from 2010 to 2015 has been the result of improved well site selection. For the more recent period, that is, from 2015 through 2017, part of the improved well productivity has resulted from substantial increases in the proppant and injection fluids used per stage and per well. 相似文献
9.
Knowledge of the permeability structure of fault‐bearing reservoir rocks is fundamental for developing robust hydrocarbon exploration and fluid monitoring strategies. Studies often describe the permeability structure of low porosity host rocks that have experienced simple tectonic histories, while investigations of the influence of faults with multiple‐slip histories on the permeability structure of porous clastic rocks are limited. We present results from an integrated petrophysical, microstructural, and mineralogical investigation of the Eumeralla Formation (a tight volcanogenic sandstone) within the hanging wall of the Castle Cove Fault which strikes 30 km NE–SW in the Otway Basin, southeast Australia. This late Jurassic to Cenozoic‐age basin has experienced multiple phases of extension and compression. Core plugs and thin sections oriented relative to the fault plane were sampled from the hanging wall at distances of up to 225 m from the Castle Cove Fault plane. As the fault plane is approached, connected porosities increase by ca. 10% (17% at 225 m to 24% at 0.5 m) and permeabilities increase by two orders of magnitude (from 0.04 mD at 225 m to 1.26 mD at 0.5 m). Backscattered Scanning Electron Microscope analysis shows that microstructural changes due to faulting have enhanced the micrometre‐scale permeability structure of the Eumeralla Formation. These microstructural changes have been attributed to the formation of microfractures and destruction of original pore‐lining chlorite morphology as a result of fault deformation. Complex deformation, that is, formation of macrofractures, variably oriented microfractures, and a hanging wall anticline, associated with normal faulting and subsequent reverse faulting, has significantly influenced the off‐fault fluid flow properties of the protolith. However, despite enhancement of the host rock permeability structure, the Eumeralla Formation at Castle Cove is still considered a tight sandstone. Our study shows that high‐resolution integrated analyses of the host rock are critical for describing the micrometre‐scale permeability structure of reservoir rocks with high porosities, low permeabilities, and abundant clays that have experienced complex deformation. 相似文献
10.
Urbanization is an important issue concerning diverse scientific and policy communities. Computational models quantifying locations and quantities of urban growth offer numerous environmental and socioeconomic benefits. Traditional urban growth models are based on a single-algorithm fitting procedure and thus restricted on their ability to capture spatial heterogeneity. Accordingly, a GIS-based modeling framework titled multi-network urbanization (MuNU) model is developed that integrates multiple neural networks. The MuNU model enables a filtering approach where input data patterns are automatically reallocated into appropriate neural networks with targeted accuracies. We hypothesize that observations classified by individual neural networks share greater homogeneity, and thus modeling accuracy will increase with the integration of multiple targeted algorithms. Land use and land cover data sets of two time snapshots (1977 and 1997) covering the Denver Metropolitan Area are used for model training and validation. Compared to a single-step algorithm – either a stepwise logistic regression or a single neural network – several improvements are evident in the visual output of the MuNU model. Statistical validations further quantify the superiority of the MuNU model and support our hypothesis of effective incorporation of spatial heterogeneity. 相似文献
11.
The Albian to Santonian Colorado Group in the heavy oil area of Cold Lake, east-central Alberta represents a relatively condensed
section of shale-dominated sedimentation within the Western Interior Sea. These shales form the cap rock to the underlying
Clearwater and Grand Rapids formations that are exploited for bitumen extraction. Two cores covering the entire Colorado Group
provide a unique opportunity for establishment of a stratigraphic reference in an area that has received attention only for
its heavy oil-bearing Mannville Group. Based on sedimentology, geochemistry, micropaleontology, nannofossils, and wireline
log data, the Colorado Group was subdivided into the Joli Fou, Viking, Westgate, Fish Scales, Belle Fourche, Second White
Specks, and Niobrara formations. The Niobrara Formation was subdivided further into the Verger Member, informal Cold Lake
member, and First White Specks Member. Because of this region’s small accommodation space and distance to sources of coarse
clastic sediment, disconformities are indicated lithologically by bioclastic layers and missing biozones. Foraminiferal subzones
revealed two erosional boundaries associated with the Viking Formation. Faunal and floral evidence coupled with wireline log
correlations suggest that the Middle to Upper Turonian Carlile Formation, as described from southeastern Alberta, is missing.
That extends the Middle Turonian to Coniacian unconformity, as recognized in central Saskatchewan, westwards into Alberta. 相似文献
12.
1 Introduction On the basis of flowing direction and characteristics of karst processes, four basic vertical karst zones were divided long ago, namely, vertical cycle zone, seasonal alternative cycle zone, horizontal cycle zone and deep cycle zone (Yang e… 相似文献
13.
Vertical cycle karst zone has been studied for more than 100 years, however karst subzones in the zone have never been divided and affected depth of CO2 from rainwater in the zone has never been studied. On the basis of field observation, survey and chemical analysis, the difference of karst processes indicated by CaCO3and pH values in fine and loose sedimentary strata as well as limestone strata, and the vertical cycle zone ascertained by predecessors can be divided into three subzones, that is, the upper first subzone, characterized by unsaturated water solution and strong dissolution processes, the middle second subzone, characterized by supersaturated water solution and precipitation, and the lower third subzone, characterized by unstable water solution and weak dissolution or weak precipitation. The three subzones can indicate the vertical co2 cycle. In fine and loose sediment strata, the bottom of the first subzone is the lower boundary strongly influenced by co2 from rainwater, soil and air; all co2 from rainwater, soil and air is almost exhausted in the second subzone. In the early developmental period of karst process in limestone strata, karst funnels and vertical caves do not form, vertical seeping of rainwater and soil water is very slow, and co2 from soil, rainwater and air almost can reach the third subzone, but in the middle and late developmental periods, karst funnels and vertical caves occur, co2 from soil, rainwater and air can reach deep seasonal change zone and horizontal cycle zone and quicken development of karst morphology. Deep karst morphology near groundwater level under vertical cycle zone develops better in the middle and late periods of karst process. 相似文献
14.
Pervasive fracture networks are common in many reservoir‐scale carbonate bodies even in the absence of large deformation and exert a major impact on their mechanical and flow behaviour. The Upper Cretaceous Jandaíra Formation is a few hundred meters thick succession of shallow water carbonates deposited during the early post‐rift stage of the Potiguar rift (NE Brazil). The Jandaíra Formation in the present onshore domain experienced <1.5 km thermal subsidence and, following Tertiary exhumation, forms outcrops over an area of >1000 km 2. The carbonates have a gentle, <5?, dip to the NE and are affected by few regional, low displacement faults or folds. Despite their simple tectonic history, carbonates display ubiquitous open fractures, sub‐vertical veins, and sub‐vertical as well as sub‐horizontal stylolites. Combining structural analysis, drone imaging, isotope studies and mathematical modelling, we reconstruct the fracturing history of the Jandaíra Formation during and following subsidence and analyse the impact fractures had on coeval fluid flow. We find that Jandaíra carbonates, fully cemented after early diagenesis, experienced negligible deformation during the first few hundreds of meters of subsidence but were pervasively fractured when they reached depths >400–500 m. Deformation was accommodated by a dense network of sub‐vertical mode I and hybrid fractures associated with sub‐vertical stylolites developed in a stress field characterised by a sub‐horizontal σ 1 and sub‐vertical σ 2. The development of a network of hybrid fractures, rarely reported in the literature, activated the circulation of waters charged in the mountainous region, flowing along the porous Açu sandstone underlying the Jandaíra carbonates and rising to the surface through the fractured carbonates. With persisting subsidence, carbonates reached depths of 800–900 m entering a depth interval characterised by a sub‐vertical σ 1. At this stage, sub‐horizontal stylolites developed liberating calcite which sealed the sub‐vertical open fractures transforming them in veins and preventing further flow. During Tertiary exhumation, several of the pre‐existing veins and stylolites opened and became longer, and new fractures were created typically with the same directions of the older features. The simplicity of our model suggests that most rocks in passive margin settings might have followed a similar evolution and thus display similar structures. 相似文献
15.
Conditioning stochastic simulations are very important in many geostatistical applications that call for the introduction of nonlinear and multiple-point data in reservoir modeling. Here, a new methodology is proposed for the incorporation of different data types into multiple-point statistics (MPS) simulation frameworks. Unlike the previous techniques that call for an approximate forward model (filter) for integration of secondary data into geologically constructed models, the proposed approach develops an intermediate space where all the primary and secondary data are easily mapped onto. Definition of the intermediate space, as may be achieved via application of artificial intelligence tools like neural networks and fuzzy inference systems, eliminates the need for using filters as in previous techniques. The applicability of the proposed approach in conditioning MPS simulations to static and geologic data is verified by modeling a real example of discrete fracture networks using conventional well-log data. The training patterns are well reproduced in the realizations, while the model is also consistent with the map of secondary data. 相似文献
16.
Fractured tight sandstone reservoirs are dual-pore systems including matrix pores and natural fractures, which both contribute to the system permeability. However, most previous studies either calculated the matrix permeability or obtained the fracture permeability to represent the system permeability in the logging evaluation of fractured tight sandstones because existing logging methods cannot distinguish the two types. In this study, a novel method is proposed to estimate the system permeability in fractured tight sandstones using geophysical logs. First, the fracture characteristics in the Upper Triassic Chang 8 member of the Yanchang Formation, southwest Ordos Basin, China, were analyzed. Based on the hydraulic flow unit approach, the formation classification criteria and the corresponding permeability–porosity models were established; then, the pure matrix permeability in the dual-pore system was calculated using geophysical logs. Based on the fracture characteristics, the relative pure fracture permeability was obtained using the Sibbit and Faivre method. By applying the Parsons’ model in boreholes, the system permeability was then calculated by coupling the relationship between the two permeabilities. Finally, two field applications in the study area demonstrate the feasibility of the proposed method, and the logging responses, application effects and applicable conditions of this method are discussed in detail. These applications indicate that the proposed method is suitable for tight reservoirs with fracture widths less than 200 μm, and considered to be dual-pore systems. 相似文献
18.
Exploratory variography was used to examine the spatial continuity of water–well yields in the Pinardville 7
Minute Quadrangle in southern New Hampshire and to link the variography to the characteristics of the fractured igneous and metamorphic rocks within the aquifer system. In addition to the analyses of variograms computed by using data from 939 wells, analyses were performed on subsets of the data that were stratified according to the level of yield and to five rock types. The stratification according to yield was defined by using the industry standard of a high-yield well that produces 40 gallons per minute or more. The stratification of the low-yield wells by rock type was defined by using the classification on the bedrock map for the State of New Hampshire. Although the variability is high in the low-yield wells, as indicated by the large nugget value, overall continuity ranges to 6000 feet in the fracture zones in which these wells have been drilled. This continuity is dominant in the northwesterly direction, as indicated by the directional variography. This result is consistent with the general trend in the larger tectonic configuration of the region. A lack of spatial correlation for 81 high-yield wells is consistent with the geologic interpretation that these wells occur in locally determined configurations of sheeting and steeply dipping fractures. Yield data in only three of the five rock types were sufficient for variography. Within these three, the dominant direction of the correlation structure ranged from northwesterly for the Massabesic Gneiss Complex to northeasterly for the Rangeley Formation to northerly for the Spaulding Granite, where the signature of the continuity in the low-yield wells is predominately attributed to the fracture system. 相似文献
19.
Proterozoic metasupracrustal rocks form a NNW-SSE trending basement zone along the western coast of Spitsbergen. The rocks show complex structures as a result of both Caledonian and Tertiary deformation, and most of the subordinate metaigneous rocks are not suitable for isotopic age determination. Some zircon-bearing rocks were found in the southwestern part of Spitsbergen and an attempt of U-Pb dating was performed. U-Pb dating was carried out on zircon fractions from quartz porphyry and rhyolite clasts in a metaconglomerate unit of the Pyttholmen Formation northwest of Hornsund, southwestern Spitsbergen. The Pyttholmen Formation is considered to be a lateral equivalent of the upper part of the Gulliksenfjellet quartzite and in the same time as the upper part of the Skålfjellet metavolcanites. Therefore, the obtained ages are applicable to the age of the Skålfjellet igneous activities. Some of the dated samples are strongly schistose and their magmatic origin is difficult to confirm; the interpretation of the isotopic results is not well constrained; however, some explanations are possible which refer to the known geological conditions; an igneous age of siliceous volcanic rocks of ca. 1200 Ma, inherited zircon ages of ca. 2500 Ma and a regional metamorphic age of ca. 930 Ma. The last age belongs to the Grenvillian period and is conformable with the Rb/Sr whole rock age obtained from the garnet-biotite schists of the Isbjernhamna Group underlying the Skålfjellet metavolcanites. 相似文献
20.
Summary. Three-component VSP borehole seismograms taken in the vicinity of an active normal fault in California show strong systematic shear-wave splitting that increases with proximity to the fault. Using Červený's method of characteristics for ray tracing in anisotropic heterogeneous media and Hudson's formulation of elastic constants for media-bearing aligned fractures, we have fitted a suite of P, SV and SH hanging-wall and foot-wall travel times with a simple model of aligned fractures flanking the fault zone. The dominant fracture set is best modelled as parallel to the fault plane and increasing in density with approach to the fault. The increase in fracture density is non-uniform (power law or Gaussian) with respect to distance to the fault. Although the hanging-wall and the foot-wall rock are petrologically the same unit, the fracture halo is more intense and extensive in the hanging wall than in the foot wall. Upon approach to the fault plane, the fracture density or fracture-density gradient becomes too great for the seismic response to be computed by Hudson–Červený procedures (the maximum fracture density that can be modelled is about 0.08). Within this 25 m fracture domain it appears more useful to model the fault and near field fractures as a low-velocity waveguide. We observe production of trapped waves within the confines of the intense fracture interval. 相似文献
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