Effects Of Mechanical Compaction Research Articles

The effect of mechanical compaction on the soil water retention curve: Insights from a rapid image analysis of micro-CT scanning

Soil hydrological and agricultural properties are highly affected by the soil water retention characteristics, which are closely related to the void size distribution and structure of the soil. Agricultural lands are often faced with the challenge of soil compaction, which alters the size, shape, connectivity, and morphology of soil voids. To determine the water retention curve and other hydrological and agricultural functions of un-compacted and compacted sandy soils, we used micro-CT techniques and image analysis procedures in both two and three dimensions. We found that these techniques were reliable, as they were validated against physical measurements and empirical physically-based models, and provided a relatively simple and fast way to characterize the key features of soil hydrological and agricultural properties. The findings highlight the impact of compaction on the soil void size distribution, resulting in increased water holding capacity, greater water availability for root uptake, and reduced hydraulic conductivity. We also discussed the differences between the two and three-dimensional analyses, highlighting the better ability to characterize soil hydrological and agricultural functions and soil water retention curve using the three-dimensional image analysis approach.

Evolution of Fractal Pore Structure in Sedimentary Rocks

AbstractGeological processes alter pore spaces over time, and their analysis can shed light on the dynamic fractal structure and fluid flow of rocks over time. This study presents experimental evidence to illustrate that the pore fractal structure evolves with sedimentation, carbonate cementation, clay growth, and dissolution. It examines, describes and characterizes a suite of core samples from the Gaotaizi oil layer of the second and third members of the Qingshankou Formation, Songliao Basin, China. The effects of mechanical compaction and other diagenesis effects on fractal pore structure on sedimentary rocks are discussed. A schematic diagram is proposed that describes the impacts of these diagenetic processes on fractal pore structure at the microscopic scale in sedimentary rocks. This work links the state of diagenetic alteration and fractal pore structure, which can guide practical applications such as predicting the permeability of sedimentary rocks.

Hydrocarbon Source and Reservoir Rock Potential of the Paleocene Hangu Formation in the Himalayan Foreland Basin, North West Pakistan: Insight from Geochemical and Diagenetic Study

The detail study of the Paleocene Hangu Formation consisting of sandstone, carbonaceous shale, coal, and laterite has been carried out for its source and reservoir rock potential in the Salt Range, Surghar Range, and Attock-Cherat Ranges. The TOC values of the shales range from 0.33-11.19 (2.97 wt. %) and are characterized as good to very good quality source rock except the samples from Attock-Cherat Ranges. Similarly, the free (S1) and cracked hydrocarbons (S2) amount are very small suggesting Hangu Formation as a poor source rock for free and cracked hydrocarbons except the samples from the Lumshiwal Nala. The generative potential, type of kerogen and thermal maturity calculated on the basis of TOC, S1, S2, HI, PI and Tmax all characterized Hangu Formation as fair to excellent gas or oil source, type III and mixed type III/II kerogen and immature source rock. The Hangu Formation sandstone is brownish to yellowish brown, fine to coarse grained, medium to thick bedded and massive in places. The major diagenetic changes observed in a sandstone of the Hangu Formation are; compaction, cementation, replacement and grain fracturing. The effect of mechanical compaction is more evident than that of chemical compaction. Grain contact ranges from pointed to long through sutured. The type of cement present includes silica-cement, calcite-cement, dolomite-cement, and iron-oxide cement. Silica-cement is present as both overgrowth and pore-filling cement. Clay rim is present around few grains. The process of early calcite cementation, mechanical compaction, silica, and iron oxide cementation destroys the reservoir properties of the Hangu Formation sandstone. There is no visible porosity observed except the dissolution of few grains at their margins. However, during the process of uplifting such porosity usually filled by the iron- oxide cementation. Hence, Hangu Formation is an immature source rock with a poor reservoir potential.

Synergistically reinforcement of a self-setting calcium phosphate cement with bioactive glass fibers

Calcium phosphate cements (CPCs) are highly promising for clinical uses due to their in situ-setting ability, excellent osteoconductivity and bone-replacement capability. However, the low strength limits their uses to non-load-bearing applications. In the present research, first, bioactive glass fibers (BGFs) in the ternary SiO2–CaO–P2O5 system were prepared, and then the fiber composites with compositions based on CPC and BGFs were prepared and characterized. Then, the effect of structure and amount of BGF incorporation into the CPC system, and the effect of mechanical compaction on the fiber-modified system were investigated. The results showed that the compressive strength of the set cements without any BGFs was 0.635MPa which was optimally increased to 3.69MPa by applying 15% BGF and then decreased by further addition of it. In addition, both the work-of-fracture and elastic modulus of the cement were considerably increased after applying the fibers in the cement composition. Also, the setting time slightly decreased by applying the fibers. In summary, processing parameters were tailored to achieve optimum mechanical properties and strength. The prepared composite may be useful in surgical sites that are not freely accessible by open surgery or when using minimally invasive techniques.

Influence of Mechanical Compaction and Clay Mineral Diagenesis on the Microfabric and Pore-Scale Properties of Deep-Water Gulf of Mexico Mudstones

AbstractWe report on how the effects of mechanical compaction and clay mineral diagenesis have affected the alignment of phyllosilicates in a suite of Miocene-Pliocene mudstones buried to sub-seabed depths of between 1.8 and 5.8 km in the deep-water Gulf of Mexico. Mechanical compaction has reduced the porosity of the samples to 15% at 5 km, with modal pore sizes between 10 and 20 nm. High-resolution X-ray texture goniometry data show that the intense mechanical compaction has not resulted in a strongly aligned phyllosilicate fabric. The muds were apparently deposited with a weak or isotropic phyllosilicate fabric which was not substantially realigned by mechanical compaction. Unusually, X-ray diffraction of <0.2 µm separates shows that: (1) there is no illitization trend between 90 and 120°C; and (2) discrete smectite persists to ∼120°C, coexisting with R1 I-S or R0 I-S with 30–40% expandable layers. Between 120 and 130°C, discrete smectite disappears and the expandability of I-S decreases to ∼25–30%. We propose a two-stage diagenetic process involving (1) the alteration of volcanic glass to smectite and (2) the illitization of smectite and I-S; the alteration of glass results in smectite without a preferred orientation and retards the illitization reaction. We suggest that the lack of a strongly aligned phyllosilicate fabric reflects the apparently limited extent of illitization, and thus recrystallization, to which these mudstones have been subjected.

Effects of fibre reinforcement on the mechanical properties of brushite cement

In this study the effect of structure and amount of polyglactin fibre incorporation into a brushite forming calcium phosphate cement system and the effect of mechanical compaction on the fibre modified system were investigated. In comparison the effect of resorbable polycaprolactone surface coating of cement specimens was investigated. The results showed that, apart from the mechanical properties of the reinforcing material, the structure of the incorporated fibres, regular or random, is crucial for the resulting flexural strength and modulus of elasticity. Fibre reinforcement could also be combined with mechanical compaction of the cement/fibre composite paste leading to a possible 7-fold increase in flexural strength or an almost 5-fold increase in modulus of elasticity. Reinforcement of the tensile surface of cement grafts may ultimately improve strength where required, especially in conjunction with bone fixation devices.

Proposition d'un modele de silicification superficielle des gres neogenes de Montjuic, Barcelone (Espagne); parageneses minerales, environments geochimiques et circulation des fluides

Abstract The Montjuic hill is part of the Neogene horst and graben system of the Catalan Coastal Ranges at the northwestern edge of the Valencia Trough. It is located to the SE of Barcelona City and consists of a 200 m thick strongly silicified detrital succession (mainly conglomerate and sandstone units alternating with lutitic units) of Miocene age. The geological constraints of this area (young age, shallow depositional environment and no evidence of burial processes) ensure that authigenic minerals formed during silicification have not been modified by further diagenetic processes and allow to constrain the age and nature of the silicification. Silicification has strongly increased the hardness of the original sediment. Textural effects of mechanical compaction are rare, testifying that burial processes had no effect on diagenesis and pointing towards an early and/or shallow cementation. Two main diagenetic facies with characteristic associations of authigenic minerals can be identified, namely: (1) non silicified facies are present in ochre-coloured, fine-grained sandstones with high clay and carbonate content. In these facies, cementation is scarce and generally forms minor feldspar overgrowths around detrital K-feldspar as well as layers or nodules of calcite spar cement mainly filling interparticle porosity; (2) silicified facies are red, purple-coloured and characterized by the presence of opal, microquartz and quartz overgrowths as well as other minor authigenic minerals such as Ti and Fe oxides and alunite. Particularly, alunite and opal appear often at the boundary of the silicified/non silicified facies, coming with the development of bleached facies and are replaced by silica. In this paper, a detailed sampling of the silicification fronts has been made, in order to establish the main silicification pathways. In the sampled zone the non silicified sandstones are mainly made up of quartz, K-feldspar, muscovite, phyllite fragments and bioclasts and cemented by thin K-feldspar overgrowths and decimetric concretions of intergranular calcite spar with spherical and tabular shapes. Sandstones contain some pyrite pseudomorphs and 20 to 30% of clay minerals, essentially illite-mica. Samples collected perpendicular to the silicification fronts reveal significant textural, compositional and petrographical transformations, namely: (1) The color of the sample varies strongly from ochre in the non silicified facies to white and red in the bleached weakly silicified front and finally to red, purple and grey in the massively silicified facies; (2) The siliciclastic framework of Montjuic sandstones remains stable during the silicification, only detrital feldspars are partially altered into illite, and biotites are completely altered. The detrital carbonate components disappear quickly towards silicified facies; (3) Within the silicification front, either bleached or not, authigenic minerals show quite important variability. Calcite disappears progressively. The first silicification stage is built by incipient quartz overgrowths, then microquartz develops towards the massively silicified facies. Alunite and opal are usually present in samples collected in this silicification boundary; (4) In the massively silicified facies quartz overgrowths and microquartz take up almost all the intergranular volume of sandstones. Clay content is strongly reduced to 5-10% (mainly illite), so the primary clay-carbonate matrix has been replaced and/or transformed to microquartz. Iron oxides appear around feldspar and phyllite fragments. Because of the geological constraints Montjuic sandstones silicification was a surface/sub-surface phenomenon. Therefore, silicification occurred at relatively low temperature and pressure conditions. Partly, silica may have an internal origin (supplied by clay and feldspar hydrolysis). Supposing that diagenetic transformations inside sandstones are made at steady state conditions it is necessary to consider a strong external supply of silica. The presence of alunite points to acidic fluids with pH between 1,5 and 4. In these conditions, quartz solubility is unaffected, but the aluminium becomes mobile, thus aluminosilicate minerals (like feldspars) are hydrolyzed and clay minerals are transformed into opal CT. A feasible process which may have contributed to the acidification is the oxidation of the pyrite and organic matter present in the original sediments, testified by numerous pyrite ghosts in the non silicified and silicified sandstones. Silicification occurred in an oxidizing environment where sulfides were oxidized and iron oxides precipitated, explaining the colour of these materials. At the basin scale, different models can be considered: (a) a topographic driven flow that moved groundwater from the horst towards the basin; (b) a thermoconvective driven flow that moved phreatic and formation waters along the main faults of the graben or (c) a compaction driven flow that also moved formation waters. Only shallow systems driven by topographic flows can explain the oxidizing nature of the silicification solutions of Montjuic. Conclusions. The Montjuic sandstone silicification is remarkable in several aspects. (1) The lack of compaction and the oxidizing nature of the silicification indicate that this diagenesis was induced by subsurface groundwater, in shallow environments. (2) Silicification is pervasive in medium and coarse-grained sandstones and conglomerates. On the contrary, silicification is restricted to fracture zones in fine-grained sandstones.

Cementing Materials in Sandstones and Their Probable Influence on Migration and Accumulation of Oil and Gas

Detailed petrographic studies of sandstone cores from productive and non-productive structures in the Rocky Mountain region were made to determine not only the physical characteristics of the sandstones but also the nature and distribution of the cementing materials. The sandstones have been divided into two general groups on the basis of the cementing or binding materials: first, those in which the grains are bound together by argillaceous materials; and second, those in which crystalline minerals form the cement or bond. In the first group, effects of mechanical compaction were noted. In the second group, sequence of deposition of cementing minerals was observed. The deposition of quartz, dolomite, and anhydrite, in the order given, is common in some sandstones. In othe s, quartz and calcite are the only cementing minerals, and of these, calcite is the last mineral deposited. Other combinations of these four minerals were observed. Furthermore, sequence of deposition of the same minerals has been established tentatively for the geologic section from the Bell sandstone which is the basal member of the Minnelusa formation (Pennsylvanian) upward through the Mesaverde (Upper Cretaceous) sandstone. Also presented are some probable effects of crystalline cementing minerals upon pressures existing in oil and gas fields, the probable control exercised by these mineral precipitates upon the movement of fluids in reservoir rocks between areas of cementation and pressure relief, and the relationship of this fluid movement to the migration and accumulation of oil and gas.