hasan ghasemzadeh

Geomechanics is one of the sciences that plays a fundamental role in the production of energy from the earth. Today, this science is widely used in the design and drilling of wells, as well as in reservoir engineering. Safe drilling is an essential parameter in the oil and gas industry. Modern drilling methods, such as multilateral(ML) wells, increase production efficiency. However, drilling such wells is associated with mechanical instability. Those issues depend on the formation strength parameters, in-situ stress, well-direction, pore-pressure, and fluid parameters. The study of stability requires a failure criterion. Hereof, some failure criteria do not consider the role of intermediate principal stress(σ2), which is proven to have a considerable effect on mechanical failure. Our study uses the three-dimensional(3D) finite element method(FEM) to investigate the stability and solid deformation of an ML well that follows the Mohr-Coulomb(MC) and Mogi-Coulomb(Mogi-C) failure criterion to studying of mechanical failure. The results were shown in different graphs such as changes in surface pressure, flow lines around the well and fracture for different borehole pressures using Mogi-C and MC fracture criteria. Our results revealed that the weakest range in these wells is at the junction of branches. Due to the principal stress effects, using the Mogi-C criterion is more safe and closer to reality. The results demonstrate an approximate 30% reduction in predicted failure points under pressures exceeding 30 MPa when employing the Mogi-C criterion, with predicted failures decreasing from approximately 15% to 5% at 35 MPa.

The infiltration of crude oil and its derivatives into the soil leads to changes in the mechanical behavior of the soil in addition to detrimental and environmental problems. This study aims to evaluate the bearing capacity of geocell-reinforced strip footings laid on oil-contaminated sand under eccentric load via numerical modeling using PLAXIS 2D. The behavior of the footing is assessed regarding various oil contents of 0, 3, 6, 9, and 12% under loading with different eccentricities of e/B=0, 1/12, 1/6, and 1/3. Numerical results revealed that soil pollution has a negative effect on the performance of strip footings, so that an increase in oil content led to a reduction in the magnitude of the load capacity. It was observed that reinforcement with geocell increases the bearing capacity of footing located on the oil-contaminated medium under different eccentricities. The effect of reinforcing with geocell was higher for contaminated soil compared to clean one. Further, the load capacity improvement factor (IF) increased by increasing oil content and settlement value. The results revealed that the reinforcing effect increased with an increase in load eccentricity for both clean and contaminated soils. In addition, the use of geocells is most effective when the loading is outside the core of the foundation, i.e., e/B>1/6. The footing tilting around the centerline axis of the footing due to load eccentricity as well as soil reinforcement with geocell led to a reduction in the stress-affected zone and as a result the displacement depth of the soil beneath the foundation.

Sand production by eroding downhole and surface equipment, production loss, and some other impacts can greatly increase hydrocarbon recovery and operational costs. Prediction of sand production in oil wells is generally conducted by using linear Darcy’s law as the constitutive equation for oil flow. This simple law does not include the contribution of fluid inertial in pressure drop and therefore is valid when the flow velocity is low. In petroleum engineering, deviation from Darcian trend is ordinarily considered important for gas wells, however in a perforated oil well considerable flow convergence occurs near the perforation tunnels, which makes it susceptible to inertia effects. In this paper, impacts of flow inertia on sand production from vertical cased-and-perforated oil wells are numerically analyzed. In this regard, 3D coupled, poro-elastoplastic finite element methods with arbitrary Lagrangian-Eulerian adaptive mesh approach are employed. Forchheimer’s law is utilized to account for high velocity flow effects in the analysis. A pressure gradient-based erosion law is adapted for use as the sanding criterion. The helical symmetry of the perforations, generally the case in practice, is utilized to achieve a more realistic but efficient simulation. Sanding response modifications due to inertia effects are presented for the considered range of parameters. The results indicate that high velocity flow leads to an increase in hydrodynamic forces around the perforation tunnels, which in turn can lead to more sand production. It is shown that ignoring the effects of inertia in perforated oil wells can lead to significantly lower predictions of both amount and rate of sand production.

Non-coaxiality plays a key role in modelling of problems with significant stress rotation in soil mechanics. This will be more crucial in types of soils or granular materials with anisotropy. Many of the constituent rocks of oil and gas reservoirs are of the anisotropic type, so considering anisotropy in the study of oil reservoirs will have special significance. Neglecting to account for stress and strain non-coaxiality would result in errors and overestimating soil capacity. A mathematical solution is developed and applied within the framework of multi-laminate model, to deal with this issue. Selecting multi-laminate frame as the base of the model facilitates consideration of anisotropy with less mathematical effort. In addition, tracing fabric evolution may be much easier in this framework. Concept of stress and strain vector fields are introduced for shear components of planes, and in contrast to ancestor multi-laminate models, shear stress is calculated through this concept for each plane in the proposed model. Using this method, non-coaxiality may be considered on planes, and consequently the integrated result of plane stresses will be non-coaxial as well. Finally, to apply the model for greater problems, a code is developed to introduce the new model to FE program, Opensees. The program is implemented for analyzing an experimental plane-strain loading test of an anisotropic dense specimen of Toyoura sand. The results show a good agreement between theory and experiment.

An accurate estimation of methane absolute adsorption in nanopores of shale gas is crucial for a good estimation of gas in place (GIP). However, experimental studies would only provide us with the excess adsorption isotherm directly. In this regard, knowing the adsorbed density is necessary to calculate the absolute adsorption. For this purpose, most researchers calculate the absolute adsorption isotherm via the Langmuir adsorption model with a constant value for the adsorbed density. In the present study, using hybrid grand canonical Monte Carlo/molecular dynamics simulations, we explained how to improve the calculation of the adsorbed density in calcite. For this purpose, methane inside calcite mineral with a pore size of 4 nm at temperatures of 30 and 90 °C and pressures up to 50 MPa is simulated, and the effects of temperature and pressure on the amount of adsorption and adsorbed density are investigated. This study showed that adsorbed density increases and decreases with increasing pressure and temperature, respectively. The results verify that the Langmuir adsorption model with constant adsorbed density will underestimate the absolute adsorption capacity, which is exacerbated with pressure. Finally, the adsorbed density obtained from molecular simulations to convert excess adsorption to absolute values can provide acceptable results that can be improved the GIP assessments.

 In this study, we present an analytical model developed to describe broadband inhomogeneous wave propagation in an unsaturated visco-poroelastic layered medium which can applied in geomechanics issues as hydrocarbon reservoirs. By taking into account the effect of the tortuosity parameter on the movement of pore fluids, the proposed formulation is capable of describing the wave behavior at high as well as mid and low frequencies. The boundary conditions proposed in this study, account for the connection between the surface pores, along with the slip that occurs between the two media at their interface. This enables us to model the layered medium in a more realistic way, where, the pore fluids are able to pass through the layers and the layers are able to move relative to each other. Finally, a sensitivity analysis is carried out and the effect of the various parameters on wave propagation inside the layered medium is observed.

Estimation of absolute adsorption in shale gas reservoirs is one of the key parameters. Experimental studies can only measure the excess adsorption isothermal directly. Also, in most experimental studies, excess adsorption up to a pressure of 15 MPa is measured. As a result, Langmuir and supercritical Dubinin–Radushkevich (SDR) adsorption models are used to convert the excess to absolute adsorption at measured pressures and above. Using hybrid grand canonical Monte Carlo/molecular dynamics (GCMC/MD) simulations, we simulate methane fluid in kerogen with 4 nm pore size at three temperatures of 303.15, 333.15, and 363.15 K up to a pressure of 50 MPa. Then the accuracy of adsorption models to estimate the absolute adsorption is investigated. The molecular simulation results show that the adsorbed density is a function of pressure and temperature and is always less than the liquid methane density. The Langmuir and SDR adsorption models show low accuracy of both models in estimating the absolute adsorption at all temperatures. Finally, using the adsorbed volume obtained from molecular simulation to estimate the absolute adsorption at all temperatures and pressures has an error of less than 10%, and the use of this method is recommended.

Oil-contaminated soil should be remediated or can be used as filling materials .The evaluation of bearing capacity of geocell-reinforced soil abutment wall is the purpose of present study under conditions of the backfill contaminated soil through numerical modeling based on PLAXIS 2D. The behavior of the wall is studied based on changes in the amount of oil, the distance between the strip footing and the wall facing (D), the height (hg) the length (L) and the number of geocell layers as well as the wall slope. The numerical results showed that the maximum length geocell layer required is 2.16 times the footing width and the optimum geocell length is equal to 1.0 times the wall height (H). The increase in the geocell height and number of geocell layers leads to increase in the soil stiffness, leading to increase in the bearing capacity of footing and decrease in the horizontal displacement of wall. The results showed that reducing the slope of the wall is very effective in reducing the horizontal displacement of the wall. In general, the soil contamination due to the oil has a negative effect on wall performance. In other words, an increase in the amount of oil reduces the percentage improvement in the wall behavior due to an increase in the height, length and the number of geocell layers. For example at hg/B = 0.6 and settlement equal to 10% of the footing width, the bearing capacity of footing for soil contamination with 9% oil reduces by 35%.

In this paper, a theoretical approach is established to determine the active wedge angle of unsaturated soils, based on the limit equilibrium method, while matric suction varies linearly with respect to depth. In the previous researches, constant suction distribution profile within the soil has been pointed out, however, generally linear and nonlinear suction profiles develop above the ground water table. The range of suction value covers transition zone and residual zone of unsaturation. Sensitivity of the proposed model, with respect to different parameters, shows that the value of active wedge angle is more dependent on the internal friction angle, in comparison to other properties. Therefore, instead of a complex relation, simple equation can be used. The results show that the active wedge angle for unsaturated soils is equal to π6+78ϕ. Comparisons between the presented model and experimental data show that, for some values of internal friction angle, the active wedge angle in unsaturated state is close to saturated state.

Porous media of hydro-carbon reservoirs is influenced from several scales. Effective scales of fluid phases and solid phase are different. To reduce calculations in simulating porous hydro-carbon reservoirs, each physical phenomenon should be assisted in the range of its effective scale. The simulating with fine scale in a multiple physics hydro-carbon media exceeds the current computational capabilities. So, the Improved Multiscale Multiphysic Mixed Geomechanical Model (IM3GM), has been recently developed. An elaso-plastic model which consider the hydraulic and mechanical behaviors of media is used to simulate the solid phase deformation in IM3GM. Also, the multiscale and adaptive mesh refinement (AMR) method is used to reduce the computational time. In this study, IM3GM is introduced by simulating the effects of surrounding area of reservoirs. Finally, a reservoir sample is simulated by IM3GM and reasonable agreements are obtained. It seems that the effect of surrounding area is undeniable and should be taken into consideration.

the porous media of oil reservoirs have different layers with wide range scales which are different from effective scale of fluid flow in reservoirs. To reduce the calculating time of porous reservoirs modeling, each physical effect should be treated separately on its scale and area of influence. In this paper, the capillary pressures parameters between fluid phases were added on a multiscale deformable model to increase the accuracy of modeling. So, the governing equation was revised and a homogeneous oil reservoir was analyzed considering capillary influences. Comparing the results of analyzing the homogeneous oil reservoir with or without capillary effect shows that the water pressure was increased around the injection point and was decreased around the production point after considering capillary. It seems that the effects of capillary pressures on fluid pressures was significant and should be considered especially in modeling of inhomogeneous reservoirs due to increasing the irregularity flowing.

Reservoir formations exhibit a wide range of heterogeneity from micro to macro scales. A simulation that involves all of these data is highly time consuming or almost impossible; hence, a new method is needed to meet the computational cost. Moreover, the deformations of the reservoir are important not only to protect the uppermost equipment but also to simulate fluid pattern and petroleum production strategy. In this regard, multiscale multiphysic mixed geomechanical model (M3GM) is recently developed. However, applications of petroleum reservoirs through gas or water injection in the depleted reservoir are in concern. In the present paper, a multiscale finite volume framework and a finite element method are employed to simulate fluid flow and rock deformation respectively. The interactions of solid and fluid phases are instated through the M3GM framework. Then, its application in the petroleum reservoir through injection process is validated. The numerical results are compared with the fine scale simulations and reasonable agreement with high computational efficiency is obtained.

In the oil industry, production of sand particles or detached sand clumps together with the formation fluids is called sand production. Sand production in oil wells is usually related to two fundamental mechanisms. The first mechanism is mechanical instability and degradation of the rock in the vicinity of the wellbore and the other is hydrodynamical instability due to flow induced drag force on the degraded material. In this paper, considering both the mechanisms, a new numerical model for predicting the onset of sanding as well as the amount of sanding is proposed. Implementation of the model in an explicitly coupled flow and deformation finite element program is described. The proposed model by removing the elements that have satisfied the sanding criteria as well as isolated rock chunks from reservoir can capture cavity evolution associated with sand production. The model is calibrated and validated against published results of a sanding experiment in a perforated reservoir rock. Results of the model in terms of initiation and amount of sanding are compares well with the experimental observations which suggests it can be used for sanding analysis of oil wells.

The contamination of soils and groundwater by toxic and/or hazardous organic pollutants is a widespread environmental problem. One group of these contaminants is petroleum products. Soil pollution caused by petrochemical activities, oil spills and leakage is not only an environmental issue but also a geotechnical issue. Physical and chemical reactions between soil and contaminant lead to change in soil properties and behaviour. In this paper, a set of laboratory tests including the direct shear test, uniaxial compression test, Atterberg limits and Scanning Electron Microscope (SEM) have been carried out on Kaolinite samples polluted with different percentages of gasoil. The direct shear test results demonstrate that increasing the pollutant percentage leads to an increase of cohesion and a decrease in internal friction angle of the soil. Also, increasing the amount of gasoil to a certain percentage results in a decrease in the uniaxial strength and the plasticity index of the soil.

Pavement design using mechanistic-empirical methods is often carried out based on the some assumptions for pavement layer''s properties (thickness، elastic modulus، Poisson''s ratio and ….)، loading properties (axial weight، tire coordinates، number of repetitions and …) and also the failure mechanism for different materials. Fulfillment of these assumptions for evolution of pavement performance during service life is impossible. This is because of the uncertainty in the traffic preaiction of different vehicles،problem ofprecise determination of material specifications due to high cost of some tests and also errors and limitations in the construction phase. The error Existance in the estimation of input pavement design parameters leads to the probabilistic procedure. for the pavement design This helps the designer to study the influence of uncertainty of input parameters on the pavement performance parameters and finally controlling the design reliability. Because of the complicated computations for pavement analysis and its performance prediction، classical methods based on the deviation are not applicable to the reliability analysis of pavement performance. In this paper، the effect of the error in estimating the different input parameters of pavement design (elastic modulus، thickness and tire pressure) on prediction error of the fatigue and rutting life is studied using Monte Carlo Simulation method. For this purpose، three pavement sections with different structural capacity were considered and importance of each input parameter on prediction error of fatigue and rutting lifehave been prioritized. The possibility of using Monte Carlo simulation to develop some relationships to estimating the pavement rutting and fatigue life error has been explored. These relationships can be applied for future reliability analysis without using simulation

In this study compressive strength of carbon nanotube (CNT)/cement composite is computed by analytical method. For this purpose representative elementary volume (REV) as an indicator element of composite is chosen and analyzed by elasticity relationships and Von mise's criterion applied to it. It is assumed that carbon nanotubes are distributed uniformly in the cement and there is perfect bonding in the interface of cement and nanotube. At first for simplicity of computations, carbon nanotubes (CNTs) are assumed to have unidirectional orientation in the cement matrix. In following, the relations are generalized to consider random distribution of nanotubes in cement, and a new factor suggested for random orientation of fibers in the CNT/cement composite. The results of analytical method are compared with experimental results.