Sandstone Grain Size Research Articles

Geological characteristics and exploration potential of the coal measure gas from Shan 2 of the Shanxi formation in the eastern Ordos Basin

“Coal measure gas,” excluding tight (low-permeability) sandstone gas, refers in this study to the self-sourcing unconventional natural gas stored in coal, shale, and fine siltstone. It is characterized by various types of occurrences and reservoirs, a distinct cyclic succession of coal measure strata, widely distributed mosaic hydrocarbon accumulations, three types of coal measure gas accumulations, and configurations of vertically multiple-stacked gas-bearing reservoirs. Coal measure gas from Shan 2 can be divided—according to the grain size of sandstone, configurations of sandstone–coal–mudstone association, thickness, and layers—into four types: thick massive sandstone–coal–mudstone (type I), fine siltstone–coal–mudstone (type II), thin sandstone–mudstone–sandstone (type III), and coal–mudstone (type IV). Comprehensive evaluation suggests that the coal measure gas in the Suide-Mizhi area of the southern Ordos Basin presents an important and favorable accumulation option, characterized by coalbed methane, shale gas, and tight gas stored in sandstone–mudstone–coal strata. Therefore, it is essential to conduct full future assessments for the coal beds, shale, and tight gas controlling exploration for the “vertical gas-bearing zone” by three-dimensional exploration.

Process of porosity loss and predicted porosity loss in high effective stress sandstones with grain crushing and packing texture transformation

Grain crushing is common, and porosity loss due to mechanical compaction dominates in cool, young, rapidly subsiding and deep basins where cementation do not have enough time to significantly reduce porosity. However, the application of existing porosity predicted model during compaction in deep buried sandstone may be doubt when the grain crushing is intense. Based on compaction experiments, the grain crushing, grain size distribution and packing texture were analyzed, and a quantitative evaluation method for predicting compaction porosity loss (COPL) were proposed, which consider grain breakage and packing texture evolution stages. The results of compaction experiments confirmed that grain crushing, grain size, grain packing texture and effective stress in sandstone all influence porosity reduction during compaction in cool, young, rapidly subsiding basins. The sandstones experienced grain sliding, grain crushing, and grain rearrangement after crushing during compaction. The grain packing texture transforms from one-component packing to binary packing texture due to intense grain crushing in well-sorted coarse sandstone. Parameter ‘S’, which is named as grain-crushing factor is significantly linear with effective stress. Analysis of our results leads to a dynamic equilibrium that describes the grain crushing in sandstone during compaction. The relationship between σ*(MZ)2 and COPL reflects the dynamic equilibrium during the compaction of sandstone with grain crushing. When mean grain size of sandstone under different stress can be obtained from experiment, the function between parameter σ*(Mz)2 and COPL are well applied in porosity prediction. The partial derivative (∂COPL/∂σ*) calculated by existing logarithmic porosity predicted model agree with the measured data better than that of values calculated by existing exponential porosity predicted model in sandstone with intense grain crushing. For underground sandstone which mean grain size under different stress cannot be obtained, the logarithmic porosity predicted model can be applied in sandstone which grain crushing is intense, the constant parameter in logarithmic porosity predicted model can be predicted by mean grain size. The exponential porosity predicted model were well applied in sandstone without grain crushing. The selection of porosity predicted model of sandstone during compaction should be based on the intense of grain crushing and the stage of compaction.

Analysis and modeling of fluvial-reservoir petrophysical heterogeneity based on sealed coring wells and their test data, Guantao Formation, Shengli oilfield

The aim of this study is to analyze relationships between lithological heterogeneity and petrophysical properties in fluvial features of the Guantao Formation (Miocene) in view of reservoir water flooding in the Shengli oilfield (Shandong Province, RPC). Black oil simulation models of intermediate scale elements such as point bars and their lateral accretion beds. Using analysis assay data from sealed coring wells demonstrates permeability, rather than porosity, as the determining constraining parameter.The Guantao formation consists of fluvial deposits of braided and meandering river. In the Shengli Oil Field, the target layer of Ng52+3 is mainly composed of well-sorted fine-grain sandstone, and it mainly develops in-channel point bars which are characterized by lateral accretion with graded sand-shale beds showing notable variations in porosity and permeability.Dense well spacing sections were used to identify geometric architectural parameters of the subsurface sandstone interpreted as fluvial point bars. These parameters were used to build the model of the point-bar stratigraphic framework, accurately reflecting the Guantao Formation channel-fill architecture. An exponential function was used to reconstruct the permeability model of intermediate-scale elements and lateral-accretion beds in contrast with models constrained by porosity and shale drapes.Analysis assay data of sealed coring wells indicate that porosity does not display obvious changes in the main body part of point-bar sandstone, and porosity has less obvious correlations with permeability and grain size. The grain size of sandstone exhibits regular variation in intermediate-scale depositional elements and lateral-accretion beds. Vertically, the change of permeability presents exponential functions in the same intermediate-scale element and lateral-accretion bed.Two- and three-dimensional (2-D and 3-D) models and black-oil simulations compare scenarios based on different lithologies, shale drapes, observed grain-size trends, petrophysical properties, and modeling methods. Affected by the shape features of lateral-accretion interfaces, the enrichment areas of remaining oil obviously exhibit morphological characteristics of the echelon. There is little difference in breakthrough time between the “shale drapes” model using porosity as constraint and that using the permeability-distribution function as constraint, but the recovery percentage of the latter model is obviously lower than that of the former. The model in which lateral-accretion beds and units were modeled with the permeability-distribution function as the constraint is about 6% lower than the “shale drapes” model constrained by porosity in recovery percent after 10 years. From the development effect, the injection-production method in which the water-flooding direction is along the dip direction of lateral-accretion surfaces is a little better than that in which the water-flooding direction is opposite to the dip direction of intersurfaces.

Lithostratigraphy of the Siwalik Group, Khutia Khola section, Far Western Nepal Himalaya

The Neogene fluival sediments (Siwalik Group) forming the southernmost hills in the Himalaya is well exposed along the Khutia Khola in the Far Western Nepal. The newly established lithostratigraphy is subdivided into the Jagati Formation (2110 m, equivalent to the Lower Siwalik) and the Kala Formation (2050 m, equivalent to the Middle Siwalik) in ascending order. Each formation is further divided into three members; the lower, middle and upper, based on the ratio of mudstone vs. sandstone beds as well as color and grain size of sandstone. The Jagati Formation is characterized by reddish-brown mudstones interbedded with very fine- to coarse-grained sandstones. Paleosols characterized with burrows, rhizoliths, desiccation cracks, concretions and nodules are present in higher proportion than thinly laminated or massive mudstone beds. The Kala Formation comprises thin- to thick-bedded, very fine- to very coarse-grained sandstones and pebbly sandstones interbedded with reddishbrown, greenish-grey to dark-grey mudstones. Sandstone beds exhibit "salt and pepper" appearance. In the lower part of the upper member sub-rounded to rounded pebbles are scattered along with trough and planar cross-laminations in sandstone beds, whereas the gravel size tends to be larger and few cobble size gravels also appear in the upper part. Thinly laminated or massive mudstones are common and paleosols are less frequent. The age of the boundary between the Jagati and Kala Formations (Lower-Middle Siwaliks) is around 11.05 Ma. The boundaries age between the middle and upper members of the Jagati Formation is around 12.7 Ma and between the lower and middle members of the Kala Formation is around 9.0 Ma. The dominance of finer sediments and thinner sandstone units than that of neighboring Siwalik successions indicate the fluvial fancies of the Khutia Khola section is deposited by a small river system and may represent the inter fluve setting of major river systems.

Mesoproterozoic delta systems of the Açuruá Formation, Chapada Diamantina, Brazil

Facies analysis, distinct depositional paleoflow directions and grain size ranges suggest that different fluvial systems fed coeval distinct, independent river-dominated and tide-dominated braid delta systems in the Mesoproterozoic Açuruá Formation. The river-dominated delta system is characterized by: (a) vertical stacking of parasequences up to 30m which are characterized by coarsening- and thickening-upward trends; (b) gradationally based vertical succession of prodelta, delta front, distributary channels, and floodplain; (c) grain size of sandstone from delta front and distributary channels varies respectively from very fine to medium and medium to coarse; (d) lacking of wave or tide reworking suggests delta development in a relatively low energy marine basin; (e) paleocurrent readings indicate delta front sandstone bodies shifting laterally towards NE to SE directions. The tide-dominated delta system is characterized by: (a) vertical stacking of parasequences up to 25m which are characterized by coarsening- and thickening-upward trends; (b) gradationally based vertical succession of prodelta, delta front and tide-influenced distributary channels; (c) grain size of sandstone from delta front and tide-influenced distributary channels varies respectively from very fine to coarse and fine to granular; (d) abundance of tide-influenced sedimentary structures suggest tidal dominated delta development; (e) consistent bidirectional paleocurrents with northwards ebb-tide direction and no lobe shifting. The studied braid delta systems belong to a highstand system tract and as such, they exhibit classic parasequence sets with progradational stacking pattern. The facies association variability and overall characteristics of these Mesoproteozoic delta systems are compatible with delta systems of all ages. However, contrary to typically Phanerozoic deltas – which are characterized by progradational clinoforms – the coalescence of the studied braid delta facies associations promoted fairly sheet-like geometry limited by marine flooding surface that more likely resulted from the response of deposition on shallow and wide epeiric sea.

Detrital quartz sources in the Scotian Basin, eastern Canada, using hot-cathode cathodoluminescence: Availability of coarse-grained sand for reservoirs

Quartz is the principal framework mineral in clastic sediment reservoirs. In a frontier basin with sparse wells, the source of quartz in sandstones may be a predictor of the availability of medium- to coarse-grained quartz sand from plutonic sources, likely to provide good reservoirs. The Scotian Basin, offshore eastern Canada, was used to test this hypothesis because of its well-understood provenance history and geographic variability in known medium- to coarse-grained reservoir sandstones. The sources of detrital quartz in fine-grained sandstones were determined using hot-cathode cathodoluminescence (CL), supplemented by other petrographic techniques. The CL color shift for different quartz types was calibrated against the CL properties of representative source rocks in the hinterland, because generalizations in the literature do not precisely match our basin-specific observations. Grain size of sandstone exerts a strong control over quartz type, with plutonic-hypabyssal quartz and high-grade metamorphic quartz more abundant in coarse-grained sandstones and low-grade metamorphic quartz more abundant in fine-grained sandstones. Nevertheless, the analysis of fine-grained sandstones shows that plutonic-hypabyssal quartz is more abundant in fine-grained sandstones of the Sable subbasin than in those of the Abenaki subbasin. The abundance of plutonic-hypabyssal quartz correlates with the abundance of medium- to coarse-grained sandstone reservoirs in the Sable subbasin. This study suggests that, in frontier basins, the abundance of plutonic-hypabyssal quartz in fine-grained sandstones can be used as an indicator of available medium- to coarse-grained sandstone reservoir.

Prediction of the Distribution Range of Deep Basin Gas Accumulations and Application in the Turpan-Hami Basin

Deep Basin Gas is short for deep basin gas accumulation. It is an abnormal gas accumulation whose formation conditions, trapping mechanism and distribution are different from those of normal gas accumulations. Deep basin gas accumulation is characterized by gentle dip angles, subnormal pressure, gaswater inversion and co-occurrence of reservoir and source rock. The fundamental conditions favourable to the formation of deep basin gas accumulation include a plentiful gas source, tight reservoir and tight seal under the reservoir. Two balances are the prerequisite for formation and preservation of deep basin gas accumulation. One is the force balance that occurs between the upward forces, including gas volume expansion pressure and buoyancy, and the downward forces including hydrostatic pressure and capillary pressure. The other is material balance that occurs between the supply amount of gas and the escaping gas. If the amount of gas charging the reservoir is more than that of escaping gas, the distribution...

Lithostratigraphy and late Cenozoic fluvial styles of Siwalik Group along Kankai River section, East Nepal Himalaya

This paper describes on lithostratigraphy as well as evolution of the fluvial styles in late Cenozoic Siwalik Group along the Kankai River section of east Nepal Himalaya. The Siwalik Group lies on the southern flank of the Himalaya, is composed of molasse sediments, which were derived from the rising Himalaya in the north. The group along the Kankai River section is lithologically divided into the Lower, Middle and Upper Siwaliks, in ascending order based on increasing grain size and lithology. The Lower Siwaliks is subdivided into the lower and upper members, whereas the Middle Siwaliks is subdivided into the lower, middle and upper members on the basis of the relative thickness of the sandstone and mudstone beds, frequency of occurrence of these beds, and grain size of sandstone. The Upper Siwaliks is subdivided into the lower and upper members based on the clast size in conglomerate and constituent of the Siwalik sandstone boulders in conglomerate. Based on the lithology, assemblages of sedimentary structure and sediment body architectures, seven facies associations (FA1 to FA7) are recognised. These facies associations are closely related to each lithostratigraphic units of the area. The sediments of the lower and upper members of the Lower Siwaliks are products of the fine-grained meandering and flood flow-dominated meandering systems, respectively. The lower, middle and upper members of the Middle Siwaliks are interpreted as the deposits by sandy meandering, deep sandy braided and shallow braided systems, respectively whereas the lower and upper members of the Upper Siwaliks are the products of gravelly braided to debris flow-dominated braided systems, respectively. doi: 10.3126/bdg.v12i0.2251 Bulletin of the Department of Geology, Vol. 12, 2009, pp. 63-74