Sharif Digital Repository

Reservoir permeability is an important parameter that its reliable prediction is necessary for reservoir performance assessment and management. Although many empirical formulas are derived regarding permeability and porosity in sandstone reservoirs, these correlations cannot be accurately depicted in carbonate reservoir for the wells that are not cored and for which there are no welltest data. Therefore, having a framework for estimation of these parameters in reservoirs with neither coring samples nor welltest data is crucial. Rock properties are characterized by using different well logs. However, there is no specific petrophysical log for estimating rock permeability; thus, new methods... 

Reservoir permeability is an important parameter that its reliable prediction is necessary for reservoir performance assessment and management. Although many empirical formulas are derived regarding permeability and porosity in sandstone reservoirs, these correlations cannot be accurately depicted in carbonate reservoir for the wells that are not cored and for which there are no welltest data. Therefore, having a framework for estimation of these parameters in reservoirs with neither coring samples nor welltest data is crucial. Rock properties are characterized by using different well logs. However, there is no specific petrophysical log for estimating rock permeability; thus, new methods... 

Oil production from asphaltenic oil reservoirs has always encountered difficulties, such as plugging and unpredictable fluid properties. To physically recognize the aspects of asphaltene deposition, several dynamic and static asphaltene deposition tests were designed and performed on one of the giant south Iranian oil reservoirs using dead and live crude oil and real core samples. Moreover, the effects of fluid velocity on the extent of damage were investigated. It was found that surface deposition of asphaltene particles is the main source of formation damages in the porous media and the resulting permeability impairment obeys an exponential behavior. All of the experiments confirm that... 

Reservoir heterogeneity has a major effect on the characterization of reservoir properties and consequently reservoir forecast. In reality, heterogeneity is observed in a wide range of scales from microns to kilometers. A reasonable approach to study this multi-scale variations is through fractals. Fractal statistics provide a simple way of relating variations on larger scales to those on smaller scales and vice versa. Simple statistical fractal models (fBm and fGn) can be useful to understand the model construction and help the reservoir structure characterization. In this paper, the fractal methods (fGn and fBm) have been applied to characterize and to estimate of reservoir properties.... 

Gravity drainage is known as the controlling mechanism of oil recovery in naturally fractured reservoirs. The efficiency of this mechanism is controlled by block-to-block interactions through capillary continuity and/or reinfiltration processes. In this study, at first, several free-fall gravity drainage experiments were conducted on a well-designed three-block apparatus and the role of tilt angle, spacers’ permeability, wettability and effective contact area (representing a different status of the block-to-block interactions between matrix blocks) on the recovery efficiency were investigated. Then, an experimental-based numerical model of free-fall gravity drainage process was developed,... 

Tortuosity and cementation factor are two critical parameters that significantly affect estimates of reservoir properties. Tortuosity factor can be used to estimate permeability using the Carman-Kozeny equation and is an important parameter for formation resistivity factor calculation using a modified version of Archie's formula. It is also used to predict water saturation of reservoir rocks. Tortuosity as an input parameter in Biot's equation can be used to estimate velocity dispersion. In this work, based on the Generalized Archie Equation Curve Fitting (GAECF), tortuosity and cementation factor are determined for selected intervals in a carbonate reservoir. Formation resistivity factor... 

Coarse grid generation from finely gridded geological model is a main step in reservoir simulation. Coarse grid generation algorithms aim at optimizing size, number and location of the grid blocks by identifying the important geological and flow features which control flow in porous media. By optimizing coarse grid structure we can improve accuracy of the coarse scale simulation results to reproduce fine grid behavior. A number of techniques have been proposed in the literature. We present a novel coarse grid generation procedure based on vorticity preservation between fine and coarse grids. In the procedure, the coarse grid mesh tries to capture variations in both permeability and fluid... 

Gravity drainage is known as the controlling mechanism of oil recovery in naturally fractured reservoirs. The efficiency of this mechanism is controlled by block-to-block interactions through capillary continuity and/or reinfiltration processes. In this study, at first, several free-fall gravity drainage experiments were conducted on a well-designed three-block apparatus and the role of tilt angle, spacers’ permeability, wettability and effective contact area (representing a different status of the block-to-block interactions between matrix blocks) on the recovery efficiency were investigated. Then, an experimental-based numerical model of free-fall gravity drainage process was developed,... 

Several methods have been developed in the past for analyzing the porosity and other types of well logs for large-scale porous media, such as oil reservoirs, as well as their permeability distributions. We developed a method for analyzing the porosity logs φ(h) (where h is the depth) and similar data that are often nonstationary stochastic series. In this method one first generates a new stationary series based on the original data, and then analyzes the resulting series. It is shown that the series based on the successive increments of the log y(h)=φ(h+δh)-φ(h) is a stationary and Markov process, characterized by a Markov length scale hM. The coefficients of the Kramers-Moyal expansion for... 

Aqueous phase trapping in many oil and gas reservoirs is a noteworthy mechanism of formation damage during drilling, completion, work over, and stimulation operation. Aqueous phase trapping can limit the productivity of a well to a high extent, especially in low permeable gas reservoirs. In this article, using aqueous phase trapping laboratory tests on low permeable sandstone cores' effect of key factors on gas reservoir's potential for aqueous phase trapping was investigated. Studied factors were initial water saturation, permeability, water filtrate viscosity, and drawdown pressure. Results showed that severity of formation damage caused by aqueous phase trapping increases as each of the... 

Obtaining a reliable reservoir permeability map that is consistent with all available data is of great important for reservoir engineers. However, there is not enough core from existing wells to estimate the reservoir permeability directly but Well log data are more widely available. This study aims to model permeability within the reservoir while there is no enough data. In particular, we use artificial neural networks to estimate permeability using four input logs of sonic, gravity, porosity and neutron logs in six existing wells. In order to eliminate the correlated data, we have done Principal Component Analysis on selected input logs. Collocated cokriging is considered as a valuable... 

Acidizing is one of the most effective techniques to remove the formation damage and restore (or even increase) the permeability of the near wellbore region. Although this technique is widely used to resolve the skin problem, it could initiate new damages itself that hinder the fluid flow and decrease the well production, consequently. Acid-oil emulsion and sludge formation are known as two major induced formation damage and the main reasons for the oil well acid treatment failures. Despite its critical effects, no comprehensive study has been addressed this specific type of formation damages in details. In this study, the acid-oil emulsion and asphaltic sludge formation were evaluated... 

Constructing an accurate geological model of the reservoir is a preliminary to make any reliable prediction of a reservoir's performance. Afterward, one needs to simulate the flow to predict the reservoir's dynamic behaviour. This process usually is associated with high computational costs. Therefore, alternative methods such as the percolation approach for rapid estimation of reservoir efficiency are quite desirable. This study tries to address the Well Testing (WT) interpretation of heterogeneous reservoirs, constructed from two extreme permeabilities, 0 and K. In particular, we simulated a drawdown test on typical site percolation mediums, occupied to fraction "p"at a constant rate Q/h,... 

Oil reservoirs are very complex with geological heterogeneities that appear on all scales. Proper modeling of the spatial distribution of these heterogeneities is crucial, affecting all aspects of flow and, consequently, the reservoir performance. Reservoir connectivity and conductivity evaluation is of great importance for decision-making on various possible development scenarios including infill drilling projects. This can be addressed by using the percolation theory approach. This statistical approach considers a hypothesis that the reservoir can be split into either permeable (good sands) or impermeable flow units (poor sands) and assumes that the continuity of permeability contrasts... 

In the last years, an appreciable effort has been directed toward developing empirical models to link the relative permeability of gas condensate reservoirs to the interfacial tension and velocity as well as saturation. However, these models suffer from non-universality and uncertainties in setting the tuning parameters. In order to alleviate the aforesaid infirmities in this study, comprehensive modeling was carried out by employing numerous smart computer-aided algorithms including Support Vector Regression (SVR), Least Square Support Vector Machine (LSSVM), Extreme Learning Machine (ELM), Multilayer Perceptron (MLP), Group Method of Data Handling (GMDH), and Gene Expression Programming...