首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 171 毫秒
1.
Bioturbated sediments recording distal expressions of paralic depositional environments are increasingly being exploited for hydrocarbons in the super-giant Pembina Field (Cardium Formation), Alberta, Canada. These strata were previously considered unproductive due to limited vertical and horizontal connectivity between permeable beds. In these “tight oil” plays (0.1–10 mD), pressure decay profile permeametry (micropermeability) data indicate that sand-filled burrows provide vertical permeable pathways between bioturbated and parallel-laminated sandstone beds in the central, northeast and northwest parts of the field. This relationship enables the economic exploitation of hydrocarbons via horizontal drilling and multi-stage hydraulic fracturing. As the exploitation of bioturbated strata progresses in the Pembina Field, additional primary targets are being sought out, and horizontal waterflooding is being considered in areas where horizontal wells exist. Proximal to historical produced conventional targets, reservoir analyses indicate that areas where the bioturbated facies average permeability lies between 0.35 mD and 0.85 mD and sandstone isopach thicknesses are between 0.25 m and 2.5 m should be targeted in east-central Pembina.Micropermeability values enable correlation of bulk permeability from plugs and full-diameter samples to the heterogeneous permeability distributions in intensely bioturbated strata. Bulk and micropermeability data are graphically compared, and permeability distributions are mapped across the field. Using isopach thickness of bioturbated facies, production data, and permeability data, “sweet spots” are identified for placement of effective waterfloods.Production information for recently drilled horizontal wells in the Pembina Field demonstrate that bioturbated muddy sandstones and sandy mudstones in paralic environments can be economically exploited when sand-filled burrows provide connectivity between sand beds. However, well performance within these poorly understood unconventional tight oil plays can better be predicted with an in-depth characterization of their facies and complex permeability heterogeneities. Based on our results, it is clear that micropermeability analysis can be effectively employed to differentiate between economic and sub-economic plays, identify areas with high effective permeability, and high-grade areas for enhanced oil recovery schemes.  相似文献   

2.
Sediments from Baffin Island fiords are graded, massive, laminated, or bioturbated. Plasticity indices vary with sediment type (lowest = laminated or graded; intermediate = massive; and highest = bioturbated). Graded and massive silty/sandy muds are most common on prodelta or proglacial slopes. Bioturbated graded and laminated muds, and rare massive pebbly muds occur more distally down-fiord from the deltas or glaciers. Clays are mostly mica, with only minor to moderate amounts of chlorite, kaolinite, and swelling clays. On the Casagrande plasticity chart, the sediments plot in fields for clay-size material of medium to high plasticity.  相似文献   

3.
A detailed laboratory study of 53 sandstone samples from 23 outcrops and 156 conventional core samples from the Maastrichtian-Paleocene Scollard-age fluvial strata in the Western Canada foredeep was undertaken to investigate the reservoir characteristics and to determine the effect of diagenesis on reservoir quality. The sandstones are predominantly litharenites and sublitharenites, which accumulated in a variety of fluvial environments. The porosity of the sandstones is both syn-depositional and diagenetic in origin. Laboratory analyses indicate that porosity in sandstones from outcrop samples with less than 5% calcite cement averages 14%, with a mean permeability of 16 mD. In contrast, sandstones with greater than 5% calcite cement average 7.9% porosity, with a mean permeability of 6.17 mD. The core porosity averages 17% with 41 mD permeability. Cementation coupled with compaction had an important effect in the destruction of porosity after sedimentation and burial. The reservoir quality of sandstones is also severely reduced where the pore-lining clays are abundant (>15%). The potential of a sandstone to serve as a reservoir for producible hydrocarbons is strongly related to the sandstone’s diagenetic history. Three diagenetic stages are identified: eodiagenesis before effective burial, mesodiagenesis during burial, and telodiagenesis during exposure after burial. Eodiagenesis resulted in mechanical compaction, calcite cementation, kaolinite and smectite formation, and dissolution of chemically unstable grains. Mesodiagenesis resulted in chemical compaction, precipitation of calcite cement, quartz overgrowths, and the formation of authigenic clays such as chlorite, dickite, and illite. Finally, telodiagenesis seems to have had less effect on reservoir properties, even though it resulted in the precipitation of some kaolinite and the partial dissolution of feldspar.  相似文献   

4.
Diagenesis is of decisive significance for the reservoir heterogeneity of most clastic reservoirs. Linking the distribution of diagenetic processes to the depositional facies and sequence stratigraphy has in recent years been discipline for predicting the distribution of diagenetic alterations and reservoir heterogeneity of clastic reservoirs. This study constructs a model of distribution of diagenetic alterations and reservoir heterogeneity within the depositional facies by linking diagenesis to lithofacies, sandstone architecture and porewater chemistry during burial. This would help to promote better understanding of the distribution of reservoir quality evolution and the intense heterogeneity of reservoirs. Based on an analogue of deltaic distributary channel belt sandstone in Upper Triassic Yanchang Formation, 83 sandstone plug samples were taken from 13 wells located along this channel belt. An integration of scanning electron microscopy, thin sections, electron microprobe analyses, rate-controlled porosimetry (RCP), gas-flow measurements of porosity and permeability, and nuclear magnetic resonance (NMR) experiments, together with published data, were analysed for the distribution, mineralogical and geochemical characteristics of detrital and diagenetic components and the distribution of reservoir quality within the distributary channel belt.Distribution of diagenetic alterations and reservoir heterogeneity within the distributary channel belt sandstones include (i) formation of high quality chlorite rims in the middle part of thick sandstones with coarser grain sizes and a lower content of ductile components resulted from the greater compaction resistance of these sandstones (providing larger pore spaces for chlorite growth), leading to formation of the intergranular pore – wide sheet-like throat and intergranular pore - intragranular pore – wide sheet-like throat (Φ>15%, k>1mD) in the middle part of thick sandstones; (ii) formation of thinner chlorite rims in the middle part of thinner sandstones is associated with the intergranular pore - intragranular pore – narrow sheet-like throat (9%<Φ<14%, 0.2mD<k<0.8mD); (iii) strong cementation by kaolinite in the more proximal sandstones of distributary channel owing to the strong feldspar dissolution by meteoric water, resulting in the intragranular pore - group of interstitial cement pores – narrow sheet-like throat/extremely narrow sheet-like throat (8%<Φ<11%, 0.1mD<k<0.3mD) due to the pore-filling kaolinite occluding porosity; (iv) formation of dense ferrocalcite zones (δ18OVPDB = −23.4‰ to −16.6‰; δ13 CVPDB = −4.0‰ to −2.3‰) favoured in the top and bottom of the channel sandstone which near the sandstone-mudstone bouding-surface, destroying pore space (Φ<8%, k<0.1mD); (v) strong compaction in sandstone of distributary channel edge laterally as a result of fine grain size and high content of ductile components in those sandstones, forming the group of interstitial cement pores – extremely narrow sheet-like throat with porosity values less than 8%.  相似文献   

5.
Microporosity may account for a significant part of the total porosity of Cretaceous limestone reservoirs of the Middle East. In these microporous facies porosity is moderate to excellent (up to 35%) while permeability is poor to moderate (up to 190 mD). Micritic limestones also may form dense layers with very low porosity and permeability values.Micritic samples were collected from three fields of the Habshan and Mishrif Formations, to examine the spatial relationship with their porosity, permeability and pore throat radius distributions. Two key parameters of the micritic particles are studied using scanning electron microscopy: their morphology (shape and inter-crystal contacts), and their crystallometry.Results reveal that micrite matrixes can be subdivided into three petrophysical classes. Class C (strictly microporous limestones with coarse punctic-to-partially coalescent micrites) is made up of coarse (>2 μm) polyhedral to rounded micritic crystals, it has good to excellent porosity (8-28%), poor to moderate permeability (0.2-190 mD) and a mean pore threshold radius of more than 0.5 μm. The class C is usually observed in rudist shoal facies where relatively high hydrodynamic energy disfavoured deposition of the finer micritic crystals. It also developed within meteoric leaching intervals below exposure surfaces. Class F (strictly microporous limestones with fine punctic-to-partially coalescent micrites) is composed of fine (<2 μm) polyhedral to rounded micrites with poor to excellent porosity (3-35%), but permeability values of less than 10 mD and a mean pore threshold radius of less than 0.5 μm. It is mostly observed in sediments deposited in a low energy muddy inner platform setting. Class D (strictly microporous mud-dominated facies with compact anhedral to fused dense micrites) comprises subhedral to anhedral crystals with sutured contacts forming a dense matrix. It has very low porosity and permeability. Class D is only found in low energy muddy inner platform facies and forms inter-reservoir or caps rock layers in close association with stylolites and clay contents that usually exceed 10%.  相似文献   

6.
  相似文献   

7.
The siliciclastic Gadvan Formation from Abadan Plain, southwestern Iran, is highly bioturbated and allows relationships between changes in ichnocoenoses within a depositional system to be documented and placed in a high-resolution sequence stratigraphic framework. Relying on the sedimentary and ichnological characteristics, the siliciclastic succession is divided into two facies associations: a wave-dominated offshore-shoreface complex and a tide-river influenced delta. The first includes facies that have been deposited in shelf-offshore, upper offshore, lower shoreface and upper/middle shoreface environments, the latter includes facies that have been deposited in prodelta and delta front. Integrated ichnologic and sedimentologic studies of the Gadvan Formation, allow distinction between prodelta and delta front and open marine deposits. With the identification of maximum flooding and ravinement surfaces as bounding surfaces of the stratal units, detailed analysis on systematic changes in the stacking pattern (cycle thickness, cycle type, and facies proportion) are made. Eight ichnocoenoses could be differentiated in the studied sections. The positions of the ichnocoenoses within genetically related stratal units (genetically related ichnocoenoses), indicate three large-scale cycles (DS1 to DS3, from oldest to youngest). The cyclical nature of the Gadvan Formation is attributed to low-amplitude eustasy in greenhouse conditions formed under interaction of eustatic high-frequency cycles and longer term tectonically driven sea-level variations during the long-term transgressive sea-level trend of the early Cretaceous. Stratigraphic architectural style of sequences DS1 to DS3 (which includes scarce evidence of lowstand deposits, partial or total truncation of the HST, and predominance of thick transgressive deposits), is remarkably similar to long-term transgressive sea-level trend of the Early Cretaceous across the Arabian Plate. This study suggests a more relatively seaward position of the siliciclastic successions of the Gadvan Formation of Abadan Plain than the Mesopotamian Basin (upper Zubair Formation equivalent in western Iraq and Kuwait), which would be concordant with the prevailing view of an easterly prograding coastline across the Arabian Plate.This study reveals important sedimentological and ichnological features and permits the development of predictive models for the paleoenvironmental and sequence stratigraphical significance of trace fossil assemblages that can be readily compared or translated to analogous depositional systems worldwide. The ichnological analysis is based on cores and can be especially applied to evaluate the applicability of current ichnological models to the study of Cretaceous reservoirs of western Iraq, Kuwait and western Saudi Arabia.  相似文献   

8.
This study aims at unravelling the diagenetic history and its effect on the pore system evolution of the Triassic redbeds exposed in SE Spain (TIBEM1), an outcrop analogue of the TAGI (Trias Argilo-Gréseux Inférieur) reservoir (Berkine-Ghadames Basin, Algeria). Similar climatic, base level and tectonic conditions of aforementioned alluvial formations developed analogue fluvial facies stacking patterns. Furthermore, interplay of similar detrital composition and depositional facies in both formations resulted in analogue early diagenetic features. Petrographic observations indicate lithic subarkosic (floodplain facies) and subarkosic (braidplain facies) compositions which are considered suitable frameworks for potential reservoir rocks. Primary porosity is mainly reduced during early diagenesis through moderate mechanical compaction and formation of K-feldspar overgrowth, gypsum, dolomite and phyllosilicate cements. Early mesodiagenesis is testified by low chemical compaction and quartz cementation. Telodiagenetic calcite filling fractures and K-feldspar dissolution determined the final configuration of analysed sandstones. Mercury injection-capillary pressure technique reveals overbank deposits in the floodplain as the least suitable potential reservoirs because of their lowest open porosity (OP < 16%), permeability (k < 5 mD) and small dimensions. On the other hand, braidplain deposits show the highest values of such properties (OP up to 31.6% and k > 95 mD) and greater thickness and lateral continuity, so being considered the best potential reservoir. The accurate estimation of TIBEM microscale attributes can provide important input for appraisal and enhanced oil recovery performance in TAGI and in others reservoirs consisting on similar fluvial sandy facies.  相似文献   

9.
The large-scale stratigraphic architecture of forced regressive deposits has been documented in many previous studies. Bed-scale facies architectural analyses of these deposits, however, are still very limited. The Cretaceous Ferron “Notom Delta” in southern Utah, U.S.A. contains a 20 km dip-oriented exposure of a stepped, forced regressive systems tract. The main focus of this paper is to reconstruct the paleogeography and depositional history of the systems tract based on detailed stratigraphic and facies architectural analysis using 23 geological sections, photomosaics, and walking out of beds.Internally, the systems tract consists of 6 parasequences, 11f to 11a from the oldest to the youngest. During the progradation of parasequences 11f to 11b the paleoshorelines were wave-dominated, as indicated by the abundance of HCS and/or SCS beds, wave-ripple cross-laminated beds, and the occurrence of diverse and robust ichnological suites attributable to the Skolithos and Cruziana Ichnofacies. Progradation of the wave-dominated shorelines resulted in more homogeneous and laterally continuous sand bodies. From 11b to 11a, however, there is a distinct change in paleoshoreline regime from wave-dominated to tide-influenced as indicated by the common occurrence of tidal facies in 11a, including: (1) lenticular, wavy, and flaser bedding and bidirectional dipping cross strata; (2) reactivation surfaces, double-mud drapes, and ripple cross lamination with opposing dips at the toe of large dune-scale cross sets; (3) inclined heterolithic strata (IHS) and sigmoidal bedding with tidal rhythmites; and (4) cyclic vertical variation in facies and bed thickness and the common occurrence of sand-mud couplets. These tide-influenced facies show overall lower bioturbation intensity (BI 0-3). Progradation of the tide-influenced shoreline results in more heterolithic delta-front facies. Tidal and/or tidal-fluvial channels further dissect delta-front sandstones, forming more isolated sand bodies.Data from this study, as well as previous work, show that width and thickness of the forced regressive parasequences are small, typically less than 5 km and 20 m respectively. In subsurface studies, identifying and correlating such small-scale parasequences using sparse data involve significant uncertainties. A combination of the diagnostic features indicating forced regression and different data sets is essential to better constrain the geometry and architecture these small-scale bodies.  相似文献   

10.
A series of two-dimensional numerical flow simulations were carried out to investigate the production characteristics of a sheet sandstone bed with a linked-debrite interval. A deterministic geological model was used based on a two-dimensional representation of a bed from the Marnoso Arenacea Formation. The model was 60 km long and 1 m thick and contained three zones, arranged in a vertical facies arrangement typical of many linked-debrite beds: i) a lower, coarse-to-medium grained, clean turbidite sandstone interval; ii) a middle, muddy sandstone, debrite interval; iii) an upper, fine-grained, clean, laminated sandstone interval. Simulation involved only a 3-km long sector of the model, with one injector well and one production well, placed 1-km apart in the middle of the sector model. The simulated sector was moved progressively down the length of the bed, in 1-km steps, sampling different parts of the bed with different facies proportions. The petrophysical properties of the debrite interval were varied to produce different porosity–permeability cases. All other modelling parameters, including the upper and lower interval petrophysics, were kept constant. Results indicate that, in most cases, key production parameters such as cumulative oil production with time and water cut are proportional to the volume of movable oil between the wells. This relationship does not hold, however, for cases with relatively low values of debrite porosity (≤0.15) and permeability (kh ≤ 100 mD) where the debrite interval accounts for more than 20% of the interwell volume. In these models, production efficiency declines systematically with reducing reservoir quality and increasing debrite percentage, resulting in relatively low oil production and early water breakthrough.  相似文献   

11.
Compared to conventional reservoirs, pore structure and diagenetic alterations of unconventional tight sand oil reservoirs are highly heterogeneous. The Upper Triassic Yanchang Formation is a major tight-oil-bearing formation in the Ordos Basin, providing an opportunity to study the factors that control reservoir heterogeneity and the heterogeneity of oil accumulation in tight oil sandstones.The Chang 8 tight oil sandstone in the study area is comprised of fine-to medium-grained, moderately to well-sorted lithic arkose and feldspathic litharenite. The reservoir quality is extremely heterogeneous due to large heterogeneities in the depositional facies, pore structures and diagenetic alterations. Small throat size is believed to be responsible for the ultra-low permeability in tight oil reservoirs. Most reservoirs with good reservoir quality, larger pore-throat size, lower pore-throat radius ratio and well pore connectivity were deposited in high-energy environments, such as distributary channels and mouth bars. For a given depositional facies, reservoir quality varies with the bedding structures. Massive- or parallel-bedded sandstones are more favorable for the development of porosity and permeability sweet zones for oil charging and accumulation than cross-bedded sandstones.Authigenic chlorite rim cementation and dissolution of unstable detrital grains are two major diagenetic processes that preserve porosity and permeability sweet zones in oil-bearing intervals. Nevertheless, chlorite rims cannot effectively preserve porosity-permeability when the chlorite content is greater than a threshold value of 7%, and compaction played a minor role in porosity destruction in the situation. Intensive cementation of pore-lining chlorites significantly reduces reservoir permeability by obstructing the pore-throats and reducing their connectivity. Stratigraphically, sandstones within 1 m from adjacent sandstone-mudstone contacts are usually tightly cemented (carbonate cement > 10%) with low porosity and permeability (lower than 10% and 0.1 mD, respectively). The carbonate cement most likely originates from external sources, probably derived from the surrounding mudstone. Most late carbonate cements filled the previously dissolved intra-feldspar pores and the residual intergranular pores, and finally formed the tight reservoirs.The petrophysical properties significantly control the fluid flow capability and the oil charging/accumulation capability of the Chang 8 tight sandstones. Oil layers usually have oil saturation greater than 40%. A pore-throat radius of less than 0.4 μm is not effective for producible oil to flow, and the cut off of porosity and permeability for the net pay are 7% and 0.1 mD, respectively.  相似文献   

12.
Facies and diagenetic heterogeneities in carbonate reservoir rocks affect both, fracture distribution and fracture permeability. Many studies focussed on fracture patterns in limestone–marl alternations, as e.g. fluid flow models, are based on laterally continuous beds. Here we examine 4010 fractures in multiple layers of limestone–marl alternations using a modified scan-line method. The studied successions belong to the Blue Lias Formation (Hettangian–Sinemurian), exposed on the coast of the Bristol Channel, United Kingdom. We combine methods of sedimentology and structural geology with rock physics to gain a better understanding of the role of facies, diagenesis and petrophysical properties (tensile and compressive strength, hardness, porosity) on the distribution of fractures (fracture orientation, density, spacing and height). Fracture distribution varies significantly despite similar bed thicknesses, indicating that planar bedding planes (i.e. well-bedded limestones, WBL) and beds with bedding plane irregularities (i.e. semi-nodular limestones, SNL) must be distinguished. SNL show higher percentages of non-stratabound fractures (67%) while they are more stratabound in WBL (57%). Additionally, beds with variable bed thicknesses (in scale of 15 m long beds) exhibit a wide range of fracture spacing, whereas fractures in beds with more continuous bed thicknesses are more regularly spaced. Considering all lithologies, the percentage of non-stratabound fractures increases proportionally with CaCO3 content. Three subsections studied in detail reveal different main sedimentological and diagenetic features (from early lithified over differentially compacted to physically compacted). All of them are characterised by dissimilar percentages of stratabound and non-stratabound fractures in limestone beds and marl interbeds. Our findings demonstrate that the distribution of fractures in individual well-bedded limestones is not necessarily representative for successions of limestone–marl alternations; multiple layers should therefore be studied in outcrop analogues as basis for fluid flow models of reservoirs composed of such lithologies.  相似文献   

13.
Sediments of the continental slope are commonly bioturbated by endo- and epibenthic organisms, particularly in and around submarine canyons and channels. This study reviews the architecture and depositional environments associated with canyons and channels on the continental slope, and assesses the key physical and chemical conditions encountered in and around these conduits. Hydrodynamic energy, concentration and quality of organic carbon, dissolved oxygen concentration and sedimentation rate are identified as key controls on the composition of benthic ecosystems in slope environments. Submarine canyons and channels focus a variety of turbid and clear-water currents, all of which serve to increase the concentration of oxygen, labile organic carbon and other nutrients, which tend to elevate the abundance and biodiversity in the seafloor sediments, compared with those of the surrounding slope. Ancient slope channel and canyon systems reflect some of the variation in ichnological assemblages that is seen in modern analogues, although processes of erosion and trace fossil preservation mean that the benthic environment is often incompletely preserved in the ancient record. By integrating current understanding of sedimentology, oceanography, biology and ichnology of slope environments it is possible to provide a first order summary of the inter-relationships between ichnology and depositional environments on the continental slope. The combination of these data has the potential to improve our understanding of changes in deep marine benthic ecosystems through geological time, and to further the use of ichnology in assessing hydrocarbon reservoir presence, quality and performance from bioturbated slope, canyon and channel-levee hydrocarbon reservoirs.  相似文献   

14.
Hydrothermal travertines develop various depositional geometries, from tabular to high-relief mounds or aprons with steep slopes, under the control of local topography, location and geometry of the vents, fault activity, hydrology, water physico-chemical properties, rates of thermal water flow and carbonate precipitation rates. This study focuses on two Pleistocene, tens of metres thick, travertine slope aprons accumulated on fluvial terraces in the Tronto River Valley (Acquasanta Terme, Central Italy) to investigate their facies character, geochemical signature, porosity and evolution of the depositional geometry through time.The two travertine aprons consist of four aggradational-progradational units, vertically and laterally stacked with onlap and downlap stratal terminations, separated by erosional unconformities produced by events of non-deposition and erosion, due to temporary interruptions of vent activity, shifts of the vent location and/or deviation of the flow directions. The travertine units include various depositional environments: 1) smooth slope, 2) terraced slope with metre-scale sub-horizontal pools separated by rounded rims and vertical walls, and 3) sub-horizontal, tens of metres wide ponds. Smooth slope clinoforms are made of centimetre to decimetre thick layers of crystalline dendrite cementstone, laminated boundstone and radial coated grain grainstone, precipitated by fast-flowing water on inclined substrates. Rims and walls of terraced slopes are built by crystalline dendrites and laminated boundstone. Sub-horizontal layers of terrace pools and ponds consist of facies precipitated by slow-flowing to standing water (clotted peloidal micrite dendrite, coated bubble boundstone, raft rudstone) associated with radial coated grains and laminated boundstone. Carbonate coated reeds occur in distal ponds adjacent to toe of slopes or overlie packstone/rudstone with travertine intraclasts and substrate extraclasts, marking events of subaerial exposure and erosion. Travertine facies porosity and permeability range from 4 to 21% and 0.03 to 669 mD, respectively, showing no direct correlation. Stable isotope values (δ13C: 5.7–9.3‰; δ18O −9.6‰ to −12.2‰) are similar to other travertines precipitated by thermal water in Central Italy.This study identifies the centimetre-scale travertine facies variability linking it to the environment of deposition and to the depositional geometry of travertine units affected by the substrate topography and lateral shifts of the active springs. Despite the different scale and facies composition, the geometry of aggradational-progradational units of travertine aprons might resemble marine flat-topped high-relief carbonate platforms. Travertine units in the subsurface, if present with sizes that can be seismically resolved, might be wrongly interpreted as carbonate platforms with steep slopes without a detailed facies analysis.  相似文献   

15.
The Melut Basin is a rift basin in the interior Sudan linked to the Mesozoic-Cenozoic Central and Western African Rift System. The Paleocene Yabus Formation is the main reservoir deposited in heterogeneous fluvial/lacustrine environment. Delineation of channel sandstone from shale is a challenge in reservoir exploration and development. We demonstrate a detailed 3D quantitative seismic interpretation approach that integrates petrophysical properties derived from well logs analysis. A porosity transform of acoustic impedance inversion provided a link between elastic and rock properties. Thus, we used seismic porosity to discriminate between different facies with appropriate validation by well logs. At the basin scale, the results revealed lateral and vertical facies heterogeneity in the Melut Basin. Good reservoir quality is observed in the Paleocene Yabus Formation. The sand facies indicated high porosity (20%) corresponding to low acoustic impedance (20000–24000 g ft/(cm3.s)). However, lower quality reservoir is observed in the Cretaceous Melut Formation. The porosity of sand/shale facies is low (5%), corresponding to high acoustic impedance (29000–34000 g ft/(cm3.s)). This suggests that the Yabus Sandstone is potentially forming a better reservoir quality than Melut Formation. At the reservoir scale, we evaluated the facies quality of Yabus Formation subsequences using petrophysical analysis. The subsequences YB1 to YB3, YB4 to YB7 and YB8 to YB10 showed relatively similar linear regressions, respectively. The subsequence of YB4 to YB7 is considered the best reservoir with higher porosity (25%). However, subsequence YB1 to YB3 showed lower reservoir quality with higher shale volume (30%). This attributed to floodplain shale deposits in this subsequence. Similarly, the high porosity (20%) recognized in deeper subsequences YB6 to YB9 is due to clean sand facies. We learnt a lesson that appropriate seismic preconditioning, exhaustive petrophysical analysis and well log validation are important keys for improved reservoir quality prediction results in fluvial/lacustrine basins.  相似文献   

16.
This study characterizes cored and logged sedimentary strata from the February 2007 BP Exploration Alaska, Department of Energy, U.S. Geological Survey (BPXA-DOE-USGS) Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope (ANS). The physical-properties program analyzed core samples recovered from the well, and in conjunction with downhole geophysical logs, produced an extensive dataset including grain size, water content, porosity, grain density, bulk density, permeability, X-ray diffraction (XRD) mineralogy, nuclear magnetic resonance (NMR), and petrography.This study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate. Gas hydrate (GH) occurs in three unconsolidated, coarse silt to fine sand intervals within the Paleocene and Eocene beds of the Sagavanirktok Formation: Unit D-GH (614.4 m-627.9 m); unit C-GH1 (649.8 m-660.8 m); and unit C-GH2 (663.2 m-666.3 m). These intervals are overlain by fine to coarse silt intervals with greater clay content. A deeper interval (unit B) is similar lithologically to the gas-hydrate-bearing strata; however, it is water-saturated and contains no hydrate.In this system it appears that high sediment permeability (k) is critical to the formation of concentrated hydrate deposits. Intervals D-GH and C-GH1 have average “plug” intrinsic permeability to nitrogen values of 1700 mD and 675 mD, respectively. These values are in strong contrast with those of the overlying, gas-hydrate-free sediments, which have k values of 5.7 mD and 49 mD, respectively, and thus would have provided effective seals to trap free gas. The relation between permeability and porosity critically influences the occurrence of GH. For example, an average increase of 4% in porosity increases permeability by an order of magnitude, but the presence of a second fluid (e.g., methane from dissociating gas hydrate) in the reservoir reduces permeability by more than an order of magnitude.  相似文献   

17.
Accurate porosity and permeability evaluation of rock formations is critical to estimate the quality and resource potential of a reservoir. In addition to directly measure the porosity and pore size distribution, low field Nuclear Magnetic Resonance (NMR) is able to measure the effective porosity and estimate the in-situ formation permeability, though its robustness is arguable and requires calibrations on cores with specific lithologies.The Mesozoic formations of the central Perth Basin (Western Australia) host hot sedimentary aquifers and recently became key targets for geothermal heat extraction. A collection of cores was retrieved from three wells intersecting these units. The characterisation of their flow properties complements the current evaluation of the Perth Basin by adding new data on effective porosity, pore size distribution, pore geometry and calibration of predictive models for the permeability according to a comprehensive facies classification scheme.This study highlights the consistency of the NMR approach when compared to conventional helium injection method. Most favourable lithologies for well production correspond to very coarse to fine sandstones of fluvial channel fill with porosities >15% and permeabilities >>1 mD. Similarly, these facies exhibit (i) the highest effective porosities, (ii) the highest pore space to pore throat ratio, and (iii) the lowest contribution of clay bound water. These aspects confirm the importance of clay occurrence in the assessment of the flow efficiency of a formation.The Yarragadee Formation presents the best reservoir quality regarding its porosity and permeability, even though high discrepancies occur locally owing to the great variability of lithofacies encountered. The scattered values observed for the Lesueur Sandstone are likely to be due to the basin architecture and fault system which generate different mechanical compaction and secondary cementation. Given an adequate facies analysis, the NMR method represents a powerful tool to estimate the flow efficiency of a reservoir.  相似文献   

18.
In the tidally influenced Fraser River, Canada, palynological and carbon isotope (δ13Corg) signatures of channel-margin sediments are compared to environmental parameters (e.g., grain size, water salinity) to establish how the signatures vary across the tidal–fluvial transition. Palynological assemblages in the Fraser River are dominated by tree pollen, which constitutes between 85% and 95% of all assemblages. Dinocyst abundances do not exceed 2% of the total palynological assemblage, and the number and diversity of dinocysts gradually decreases landward. The calculated landward limit for dinocysts is at approximately 83 river km, which is relatively close to the upstream limit of the tidal backwater (at ∼100 km). δ13Corg values show minimal variability across the tidal–fluvial transition, and the average value is approximately −26‰. The δ13Corg signature of river sediments indicates a dominance of terrestrially sourced organic matter regardless of brackish-water and tidal influence on sediment deposition.Six palynological and geochemical trends are identified as relevant to the rock record. 1) In deltaic environments, palynological and geochemical characteristics are less useful than sedimentological and ichnological characteristics for establishing depositional conditions. 2) In marginal-marine settings, low abundances and low species diversities of dinocysts, coupled with a “terrestrial” geochemical signature (δ13Corg < −25‰) do not necessarily indicate deposition in a terrestrial environment. 3) Dinocyst abundances above 1% of the total palynomorph population can indicate a significant marine influence on sediment deposition. 4) Mud beds, preferably bioturbated, should be preferentially sampled in order to maximize palynomorph recovery. 5) Marine palynomorphs can occur, albeit in very low concentrations, to the landward limit of the tidal–backwater zone. 6) Palynological and geochemical data should be compared across the paleo-depositional environment in order to establish general trends and remove local variations caused by biases such as grain size.  相似文献   

19.
GSWA Harvey 1 was drilled as part of the South West CO2 Geosequestration Hub carbon capture and storage project (South West Hub) to evaluate storage volume, injectivity potential and carbon dioxide retention capacity in the south-western Perth Basin. Six cored intervals from the Triassic Lesueur Sandstone contain nine lithofacies consistent with fluvial depositional environments: the lower Wonnerup Member is dominated by fluvial lithofacies consisting of stacked beds of porous, permeable sandstone deposited as high-energy fill and barforms, with rare finer-grained swampy/overbank deposits. The overlying Yalgorup Member contains mainly floodplain palaeosols with low- to moderate-energy barforms. The high- to moderate-energy fluvial facies typically have a low gamma response and contain clean, medium to very coarse-grained quartz-dominated sandstones. Other clastic components include K-feldspar (8–25%) with trace muscovite, garnet and zircon, and interstitial diagenetic kaolinite (up to 15%) and Fe-rich chlorite (up to 13%). The low-energy facies contain variably interbedded mudstone and thin, moderate to well sorted fine-grained sandstone, typically with a high gamma response, and are consistent with deposition under swampy, overbank and palaeosol conditions. These facies have significantly higher proportions of mica and diagenetic clays, including smectite (up to 8%) and illite (up to 10%), and detrital plagioclase (up to 21%) and trace carbonate bioclasts. High porosity and permeability in the cored intervals of the Wonnerup Member indicate good reservoir characteristics in terms of storage capacity and injectivity at depths relevant to CO2 injection (>1500 m). High porosity and extremely variable permeability values in the Yalgorup Member were measured. The variation is due to permeable vertical sandstone features in low permeability sandy mudstone and indicate limited sealing potential, although the spatial connectivity of the vertical features cannot be resolved from the available core. A preliminary assessment of the area as a CCS site seems favourable; however, the project is only in the early stages of its characterization and far more regional and site-specific data are needed to evaluate how injected CO2 may behave in the subsurface.  相似文献   

20.
Petroleum exploration in many North African intracratonic basins targets Early Paleozoic sandstones as the primary reservoir objective. These sandstones are often characterized by highly variable reservoir quality (0.0001–1000 mD), and the ability to predict and selectively target areas of enhanced porosity and permeability is crucial to unlock the hydrocarbon potential. The objective of this study is to characterize the primary controls on reservoir quality in an Ordovician field in the Illizi Basin of Algeria through detailed core and petrographic analysis, and establish if variations in thermal history across the field have a material impact on reservoir quality. The best reservoir quality is observed in facies where primary intergranular porosity has been preserved in fine to coarse grained quartzarenites with less than 1% fibrous illite. These lithologies are most commonly found within the high-energy, tidally reworked, post-glacial facies sandstones of the uppermost Ordovician succession. Observed differences in quartz cement volume within compositionally and texturally similar samples from the southern and northern parts of the field are interpreted to reflect variations in thermal exposure due to deeper burial. This interpretation is supported by field-wide numerical modelling of sandstone diagenesis. This study indicates that subtle variations in thermal history can have a material impact on the spatial trends in reservoir permeability. Thermal history, therefore, is an important consideration in reservoir quality studies in exhumed basins where variations in present-day burial depth will be a poor guide for evaluating reservoir quality risk across a basin or play.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号