Sharif Digital Repository

Gas-oil relative permeability is essential for performance predictions of reservoirs with solutions for gas drive, gas cap expansion, or gas injection. The nature of flow in reservoir is determined by the interplay of relative permeability and viscous, gravity, and capillary forces. Displacement experiments of the gas-oil system are performed on long core scale models by varying the petrophysical properties and flow conditions. Experiments are conducted in situations where capillary, gravity, and viscous forces are comparable. The effect of destabilized front velocity on relative permeability and residual saturation is investigated. The results indicate that the relative permeability varies... 

This work concerns modeling of gas-oil gravity drainage for a single block of naturally fractured reservoirs. The nonlinearity induced from saturation-dependant capillary pressure and relative permeability functions makes a gravity drainage model difficult to analytically and numerically solve. Relating the capillary pressure and relative permeability functions is a potential method to overcome this problem. However, no attempt has been made in this regard. In this study a generalized one-dimensional form of gas-oil gravity drainage model in a single matrix block, presented in the literature, is considered. In contrast with commonly used forms of capillary pressure and relative permeability... 

The vapor extraction process (or VAPEX) uses vaporized solvents injected into a horizontal well to form a vapor chamber within the reservoir. Vapor dissolves in the oil and enhances the oil production by decreasing the oil viscosity in heavy oil reservoirs. To evaluate the process we conduct a simulation study on an Iranian heavy oil reservoir called Kuh-e-Mond. In addition, a semi-analytical investigation of the VAPEX process has been performed. The idea is to perform VAPEX simulation for a laboratory model and find a methodology to compare the results of the simulator with the semi-analytical Butler's model. In particular, a semi-analytical dimensionless correlation for production rate... 

This work concerns modeling of gas-oil gravity drainage for a single block of naturally fractured reservoirs. The nonlinearity induced from saturation-dependant capillary pressure and relative permeability functions makes a gravity drainage model difficult to analytically and numerically solve. Relating the capillary pressure and relative permeability functions is a potential method to overcome this problem. However, no attempt has been made in this regard. In this study a generalized one-dimensional form of gas-oil gravity drainage model in a single matrix block, presented in the literature, is considered. In contrast with commonly used forms of capillary pressure and relative permeability... 

The vapor extraction process (or VAPEX) uses vaporized solvents injected into a horizontal well to form a vapor chamber within the reservoir. Vapor dissolves in the oil and enhances the oil production by decreasing the oil viscosity in heavy oil reservoirs. To evaluate the process we conduct a simulation study on an Iranian heavy oil reservoir called Kuh-e-Mond. In addition, a semi-analytical investigation of the VAPEX process has been performed. The idea is to perform VAPEX simulation for a laboratory model and find a methodology to compare the results of the simulator with the semi-analytical Butler's model. In particular, a semi-analytical dimensionless correlation for production rate... 

An algorithm has been developed to investigate the effect of asphaltene precipitation on calculation of minimum miscibility pressure (MMP), which is one of the key design parameters of any gas injection projects. In fact, this algorithm is the extension of procedure suggested by Jaubert et al. for prediction of MMP whatever the displacement mechanism. The vapor-liquid equilibrium calculation and then liquid-liquid equilibrium calculation are required to be taken account to estimate the amount of asphaltene precipitation. The association equation of state (AEOS) has been applied to determine the phase behavior of asphaltene. The algorithm has been used for the MMP prediction of Weyburn... 

The permeability is one of the most important reservoir parameters and its accurate prediction is necessary for reservoir management and enhancement. Although many empirical formulas are derived regarding permeability and porosity in sandstone reservoirs [1], these correlations cannot be modified accurately in carbonate reservoir for the wells which are not cored and there is no welltest data. Therefore estimation of these parameters is a challenge in reservoirs with no coring sample and welltest data. One of the most powerful tools to estimate permeability from well logs is Artificial Neural Network (ANN) whose advantages and disadvantages have been discussed by several authors [2]. In this... 

Almost all of the heavy oil reservoirs contain discontinuous permeability barriers (shales) with different structures. However, the effect of shaly layer geometrical characteristics including: spacing from wells, discontinuity, orientation, shaly layers' spacing and length, and heterogeneous distribution on oil recovery factor in the presence of gravity force are not well understood. In this work, a series of solvent injection experiments were conducted on various vertical one-quarter five-spot glass micromodels, containing barriers, which were initially saturated with a heavy oil sample. The oil recovery was measured by analysis of the pictures provided continuously during the injection... 

Screening analysis is a useful guideline that helps us with proper field selection for different enhanced oil recovery processes. In this work, reservoir simulation is combined with experimental design to estimate the effect of reservoir rock and fluid properties on performance of immiscible nitrogen injection. Reservoir dip, thickness, and horizontal permeability are found to be the most influential parameters. Possible interactions of parameters are also discussed to increase reliability and robustness of screening results. Finally, significance of both main effects and interactions are evaluated by employing a statistical inference approach (hypothesis testing) and results are compared to... 

The authors simulated a reservoir by using two-layer perceptron. Indeed a model was developed to simulate the increase in oil recovery caused by bacteria injection into an oil reservoir. This model was affected by reservoir temperature and amount of water injected into the reservoir for enhancing oil recovery. Comparing experimental and simulation results and also the erratic trend of data show that the neural networks have modeled this system properly. Considering the effects of nonlinear factors and their erratic and unknown impacts on recovered oil, the perceptron neural network can develop a proper model for oil recovery factor in various conditions. The neural networks have not been... 

Viscosity of crude oil is a fundamental factor in simulating reservoirs, forecasting production as well as planning thermal enhanced oil recovery methods which make its accurate determination necessary. Experimental determination of reservoir oil viscosity is costly and time consuming. Hence, searching for quick and accurate determination of reservoir oil viscosity is inevitable. The objective of this study is to present a reliable, and predictive model namely, Least-Squares Support Vector Machine (LSSVM) to predict reservoir oil viscosity. To this end, three LSSVM models have been developed for prediction of reservoir oil viscosity in the three regions including, under-saturated, saturated... 

Multiple contact miscible floods such as injection of relatively inexpensive gases into oil reservoirs are considered as well-established enhanced oil recovery (EOR) techniques for conventional reservoirs. A fundamental factor in the design of gas injection project is the minimum miscibility pressure (MMP), whereas local sweep efficiency from gas injection is very much dependent on the MMP. Slim tube displacements, and rising bubble apparatus (RBA) are two main tests that are used for experimentally determination of MMP but these tests are both costly and time consuming. Hence, searching for quick and accurate mathematical determination of gas-oil MMP is inevitable. The objective of this... 

CO2 injection is a potentially viable method of enhanced oil recovery for medium oil reservoirs. The authors compare the effect of gas injection strategy (simultaneous water-alternating gas [SWAG], water-alternating gas [WAG], and continuous gas injection [CGI]) on recovery in immiscible, near-miscible, and miscible modes of injection. It has been proved that CGI is not the most efficient injection scenario in oil-wet reservoirs. Miscible and near-miscible core flood tests demonstrated high oil recoveries in all injection strategies due to high capillary numbers achieved as a result of miscibility. The fluid mechanics of floods were discussed using pressure drop data, different mechanics was... 

Many bitumen reservoirs contain shale layers of varying thickness, lateral extent, and frequency. These shale layers, depending on their size, vertical and horizontal locations, and continuity throughout the reservoir, may act as a flow barrier and severely reduce vertical permeability of the pay zone and slow down the steam-assisted gravity drainage steam chamber development. Therefore, to improve productivity in these reservoirs, understanding of the effects of reservoir heterogeneities has become necessary. This work presents numerical investigation of the effects of shale barriers on steam-assisted gravity drainage performance when applied to produce mobile heavy oil. The most concern of... 

Asphaltene deposition in a reservoir severely reduces the effective permeability and results in a reduction in oil production. The main term in asphaltene deposition modeling in the porous media is pore surface deposition. Previous models do not describe the effects of different parameters (i.e., concentration, velocity, and temperature) on the pore surface deposition term. We report the results of a series of experiments carried out to study the effects of the above parameters on the surface deposition term using an accurate thermal method. Based on these data, a new expression for the surface deposition term has been developed and implemented in asphaltene deposition modeling. The... 

Interfacial tension (IFT) is known as the critical parameter affecting the efficiency of CO2 flooding during the enhanced oil recovery (EOR) process. Besides, the asphaltene precipitation phenomenon is reported as the most significant problem during CO2 injection into asphaltenic oil reservoirs. Accordingly, it is important to examine the effect of asphaltene precipitation on the IFT behavior of the oil-CO2 system at reservoir conditions. The main objective of this research work is to study of the effect of asphaltene and its type on the IFT behavior of the oil-CO2 system. The IFT between pure CO2 and a model oil both with and without asphaltene was measured using an axisymmetric drop shape... 

Interfacial tension (IFT) is known as the critical parameter affecting the efficiency of CO2 flooding during the enhanced oil recovery (EOR) process. Besides, the asphaltene precipitation phenomenon is reported as the most significant problem during CO2 injection into asphaltenic oil reservoirs. Accordingly, it is important to examine the effect of asphaltene precipitation on the IFT behavior of the oil-CO2 system at reservoir conditions. The main objective of this research work is to study of the effect of asphaltene and its type on the IFT behavior of the oil-CO2 system. The IFT between pure CO2 and a model oil both with and without asphaltene was measured using an axisymmetric drop shape... 

Gravity drainage is known to be one of the most effective methods for oil recovery in fractured reservoirs. In this study, both free fall and controlled gravity drainage processes were studied using a transparent fractured experimental model, followed by modelling using commercial CFD software. The governing equations were employed based on the Darcy and mass conservation laws and partial pressure formulation. Comprehensive examination was done on variables such as fluid saturation, velocity, and pressure distribution in the matrix and fracture, as well as fluid front level and production rate. Additionally, effects of the model parameters on the gravity drainage performance were... 

CO2 gas injection is known as one of the most popular enhanced oil recovery techniques for light and medium oil reservoirs, therefore providing an acceptable mass transfer mechanism for CO2–oil systems seems necessary. In this study, interfacial mass transfer coefficient has been evaluated for CO2–normal heptane and CO2–normal hexadecane systems using equilibrium and dynamic interfacial tension data, which have been measured using the pendant drop method. Interface mass transfer coefficient has been calculated as a function of temperature and pressure in the range of 313–393 K and 1.7–8.6 MPa, respectively. The results showed that the interfacial resistance is a parameter that can control... 

In order to investigate the feasibility and effects of core permeability on capillary imbibition recoverable oil from carbonate cores, some laboratory tests were carried out at the EOR research laboratories of Sharif University, Iran. Outcrop rocks with different permeabilities were taken away from a recognized outcrop and used in these experiments. Special core analysis tests were run on two core samples to find out relative permeability and end point saturations. Wellhead separator oil and gas samples were collected and recombined to a reservoir gas - oil ratio. A core flooding system with a capability of free and forced imbibition testing was designed and installed. A number of free and...