Introduction: Hydraulic fracturing is used in the oil industry in order to increase the index of production and processing in wells whose efficiency has been dropped due to long-term harvest or the rocks around the well are low permeable. Since the hydraulic fracturing operation is costly, it is of special importance to determine the pressure required for hydraulic fracturing and the suitable pump for this operation to the project managers. The hydraulic fracturing technique refers to the process of initiation and extension of fractures in rocks caused by the hydraulic pressure applied by a fluid. This technique was developed by Clark (19). Haimson and Fairhorst (20) continued the research on the initiation and extension of fracture. Hubbert and Willis conducted comprehensive studies on the mechanics of hydraulic fracturing to determine the direction and condition of principal stresses using the hydraulic fracturing process. Since then, numerous studies and modellings have been conducted to investigate the factors effecting the hydraulic fracturing. The present research is important because experimental and numerical modeling were used to calculate the hydraulic fracturing pressure for different conditions and to select the suitable pump for the operation.

Nowadays, quantitative methods for seismic data interpretation are mostly used instead of qualitative evaluations for the description of reservoir from exploration to production phase and, over time, it will be more important in upstream oil industry. One of the most prosperous methods is AVO analysis that considers the variation of reflection coefficients versus offset between the source and the receiver. This method uses prestack data to identify hydrocarbon in reservoir and can be used as a direct hydrocarbon indicator in clastic rocks. In this paper, AVO analysis method has been described to detect hydrocarbon reservoir and AVO analysis was applied to the Ghar Sandstone reservoir in Hendijan oil field. This study is carried out using 3D prestack data and well logging data. At first, forward modeling has been performed using well logging data from wells. Class 1 AVO anomaly has been recognized for this reservoir. After the forward modeling step, fluid replacement modeling (FRM) in reservoir zone has been applied and the best attributes, which had a great sensitivity to fluid, were distinguished. But FRM shows that the attributes are not sensitive to changes in fluid type. AVO anomaly on upper boundary of Ghar Sandstone is affected by changes in lithology. Also, intercept-gradient cross-plot was produced by attributes. Reservoir area and zones has been discriminated with intercept-gradient cross-plots. For seismic data, various AVO attributes and cross-plots have been extracted by different methods and have delineated. Unfortunately, attributes and cross-plots were not able to detect fluids boundaries and fluid boundaries, because of the poor quality of seismic data. The results not only help to select new drilling locations more accurately, but the reservoir parameters can also be modeled with less uncertainty.

High pressure and temperature in the earth's crust lead to fracture and microcracks in rocks. Direct access to earth crust rocks at great depths is very costly and, in most cases, impossible. The study of the condition of rocks at great depths is often done using indirect methods such as seismic waves. The results of these studies are compared with the results of laboratory studies of wave velocities in different rocks and the conditions of the rocks are simulated. At high depths, hydrostatic stress is applied to the rocks of the earth's crust, and tectonic, earthquake and other stresses cause it to be anisotropic. The primary purpose of this study is to investigate the change in compressive wave velocity due to the change in compressive stress in rocks. At first, a cylindrical core of different stones with a length to diameter ratio of 2 to 2. 5 is prepared according to the standard test method (ASTM D4543) and their dimensions and weight are determined. after measuring the unconfined compressive strength of cores according to the standard test method (ASTM D2938), the hydrostatic pressure of 50% to 95% of it is applied to the rock samples prepared from the earth. This pressure is applied to the cores by using the Hoek cell (for lateral pressure) and the axial load machine and using an ultrasonic device, determine the compressive wave velocity (ultrasonic pulse) is determined according to the standard test method (ASTM D2845) in the axial direction of the sample. Then, the wave velocity was measured by decreasing the lateral pressure (increasing deviatoric stress) in a stepwise manner and the wave velocity was measured at each step. In the following, comparative diagrams of compressive wave velocity (Vp) with density (ρ, d), uniaxial compressive strength (UCS) and the effect of hydrostatic stress (σ, hyd) and deviatoric stress (σ, dev) on P-wave velocity in each sample are drawn. The results show linear relationships between compressive wave velocity and the physical properties of rock samples. Also, the Pwave velocity at hydrostatic pressure is the highest and as the lateral pressure decreases (increasing the deviatoric stress), the velocity also decreases.

Sand production has been a major problem in the oil industry worldwide for years. Operating costs multiply when sand production wears out equipment and forces expensive workovers. Production of sand seems to be rate sensitive. That is, below some producing rate, no sand is produced. This rate quite often is vanishingly small. The producer has no choice but to produce at a higher rate and to learn to live with the sand. The bridging methods for sand control are either screens or gravel packs. Sand control by any bridging method requires knowledge of the formation size distribution. This is most commonly found with a sieve analysis.In this study, sieve analyses have been performed on samples from an Iranian field, which has sand production problems. The data obtained could be used for gravel pack design. The other problem in these kinds of wells is the lack of petrophysical information due to unconsolidated nature of core samples therefore; the data from sieve analyses were also utilized to estimate the original petrophysical properties of the unconsolidated intervals.

A sequence of the Upper Devonian age (Frasnian-Lower Famennian) on the western side of Zard Mountain is located near the Zefreh village. W of central Iran Basin (ca. 65 km NE of Esfahan). It is composed of five lithostratigraphic units, including two lowermost Sandstone and three uppermost carbonate unites. Sandstones are mainly quartz arenite in composition. Low percentage of feldspar. Unstable minerals and presence of heavy minerals (Zircon and Turmaline) suggests high weathering rate in source region, the high weathering rate in samples. Revealed by petrographic studies and, CIW index as well, suggests a warm humid climate. The geochemical and modal data analysis of Sandstones samples, plotted on the discriminate function diagrams determined the quartzose recycled provenance and reveals that the source material was deposited on a passive margin tectonic setting, after transport and recycling.

The tensile strength (σ t) of a rock plays an important role in the reliable construction of several civil structures such as dam foundations and types of tunnels and excavations. Determination of σ t in the laboratory can be expensive, difficult, and time-consuming for certain projects. Due to the difficulties associated with the experimental procedure, it is usually preferred that the σ t is evaluated in an indirect way. For these reasons, in this work, the adaptive network-based fuzzy inference system (ANFIS) is used to build a prediction model for the indirect prediction of σ t of Sandstone rock samples from their physical properties. Two ANFIS models are implemented, i. e. ANFIS-subtractive clustering method (SCM) and ANFIS-fuzzy c-means clustering method (FCM). The ANFIS models are applied to the data available in the open source literature. In these models, the porosity, specific gravity, dry unit weight, and saturated unit weight are utilized as the input parameters, while the measured σ t is the output parameter. The performance of the proposed predictive models is examined according to two performance indices, i. e. mean square error (MSE) and coefficient of determination (R2). The results obtained from this work indicate that ANFIS-SCM is a reliable method to predict σ t with a high degree of accuracy.

Hydraulic fracturing is used in the oil industry in order to increase the index of production and processing in wells whose efficiencies have been dropped due to long-term harvest or the rocks around the well are low permeable. Since the hydraulic fracturing operation is costly, it is of special importance to determine the pressure required for hydraulic fracturing and the suitable pump for this operation to the project managers. In this research, Sandstone specimens of Lushan area were used and investigated the effect of thermal stress on hydraulic fracturing pressure of Sandstone. The Hoek triaxial cell was adapted for a laboratory modelling of hydraulic fracturing. The specimens under study are in the shape of thick-walled hollow cylinders with an external diameter of 54. 7 mm, an internal diameter of 12 mm, and a height of 108 mm. To study the effect of thermal stress, the tests were conducted on the specimens that heated up to 100 ° C in the furnace at heating process and then cooled in water 5, 10 and 15 ° C. Results indicated that hydraulic fracturing pressure reduced with decreasing Cooling temperature of samples. In hydraulic fracturing operations, this decreasing fracture pressure causes the pump to be purchased at a lower pressure production capacity, resulting in lower operating costs. Hydraulic fracturing pressure changes in the effect of thermal stress were consistent with the variations of velocity of longitudinal waves, dry unit weight, uniaxial compressive strength and permeability. CT scan images were used to examine micro cracks changes in the effect of thermal stress and the CT value calculated by the images confirms hydraulic fracturing pressure variations.

Rocks are usually exposed to freeze-thaw and/or heating-cooling conditions in many environments. In this research, Sandstone specimens of Lushan area were used and investigated the impact of number of freeze-thaw cycles and the effect of temperature in the heating-cooling process on Sandstone permeability. The freezing temperature of-16° C was considered to study the effect of number of cycles. In this state, the tests were carried out on the specimens withstood 1, 5, 10, and 20 freeze-thaw cycles. To study the effect of heating-cooling, the tests were conducted on the specimens that withstood one heating-cooling cycle. The specimens withstood temperatures of 60, 100, 200, 400, 600, 800, and 1000 ° C at the heating process and then cooled in the laboratory environment. Results indicated that permeability rate reduced after one cycle of freeze-thaw cycles the reduction continued to 5 cycles. Permeability increased slightly in 10 cycles and the increase was significant in 20 cycles. Sandstone permeability reduced up to 100 ° C and then increased with the temperature increasing at the heating-cooling process. Permeability changes in the heating-cooling process were consistent with the variations of velocity of longitudinal waves, dry unit weight, and effective porosity.

Deposits of the Warchha Sandstone in the Salt Range, Pakistan are characterised by a range of fluvial facies and architectural elements that together preserve a record of both the proximal and distal parts of a meandering river system that drained the northern margin of Gondwanaland. Several fining-upward cycles are recognised and completely preserved cycles can be divided in to three parts; a lower part composed of an erosive base with gravel- and coarse sand-grade trough cross-bedded facies, a middle part composed of planar cross-bedded, ripple cross-laminated and horizontally laminated Sandstone facies, and an upper part composed predominantly of horizontally laminated and massive mudstone facies. Nine architectural elements are recognised within these cycles and these record the presence of channels, downstream and laterally accreting barforms, laminated sand sheets, crevasse splays, levees, over-bank floodplain units and shallow lakes. A broad range of sedimentary structures is recognised, including different forms of bedding, cross bedding, ripple marks and stratification, channels, flute casts, load casts, desiccation cracks, rain prints, conein-cone structures, a variety of concretions and bioturbation.The occurrence and abundance of these structures varies in a systematic manner throughout the vertical thickness of the succession. Cross bedding is the most prominent and consistent sedimentary structure, including various trough and planar varieties. The clasts are mainly of plutonic and low-grade metamorphic origin, with an additional minor sedimentary component. Textural properties of the Sandstone are fine- to coarse-grained, poorly to moderately sorted, sub-angular to sub-rounded and with generally loose packing. Based on modal analyses, the Sandstone is dominantly a sub-arkose to arkose. Detrital constituents of this formation are mainly composed of monocrystalline quartz, feldspars (more K-feldspar than plagioclase) and various types of lithic clasts. XRD and SEM studies indicate that kaolinite is the dominant clay mineral. Detailed palaeocurrent analysis reveals a broad unimodal palaeocurrent pattern within each cycle but significant changes in local migration direction between each vertically stacked cycle, supporting the notion of a high-sinuosity system with an overall dominant flow direction to the north-northwest. Petrographic analysis indicates the provenance of the Warchha Sandstone to have been the Aravalli Range to the southeast and the Malani Range to the south of the Salt Range, suggesting northward transport across a broad alluvial plain towards the margin of the Tethys Ocean in the north.

: Design, selection and performance prediction of excavators are very delicate for project planning and cost estimation in mechanical mining and mechanized tunneling. Rock cuttability assessment in mechanized excavation includes investigation of rock mechanical behavior and rock-cutting tool interaction. Use of laboratory scale rock cutting tests is the most reliable method for accurate assessment of rock-tool interactive behavior in a situation close to its actual field condition. In this study, small scale linear cutting test was used for evaluating the rock cuttability and its relationship with rock mechanical parameters. To perform this action, rock samples of Upper-red Sandstone were prepared for rock physical and mechanical characterization tests. The results obtained from cutting tests revealed that the cutting depth has a direct linear and a non-linear relationship with the cutting force, and the specific energy, respectively. Also, the cutting velocity showed no significant relationship with cutting force and specific energy. Moreover, the cutting forces obtained from the experiments showed a good agreement with those obtained from the theoretical model developed by Evans. However, these results are preliminary and need to be further verified with much larger cutting tests on various rock specimens.