Won Mo Sung

Analysis of CO2 Endpoint Relative Permeability and Injectivity by Change in Pressure, Temperature, and Phase in Saline Aquifer

Abstract Carbon dioxide capture and geological storage are considered to be imperative practical means for reducing greenhouse gas emissions into the atmosphere. Among geological formations for carbon dioxide capture and geological storage, deep saline aquifer is tracked as a key site due to its huge potential and common occurrence when compared to oil and gas reservoirs. But, the two-phase behavior of CO2 accompanied with water formation under conditions equivalent to geological storage are mostly unknown. In this study, relative permeability experiments have been conducted to measure the end-point relative permeability of CO2 and investigations have been carried out to calculate injectivity using the relative permeability. In CO2 and water system, the injectivity is the function of the CO2 endpoint relative permeability. An experimental apparatus for CO2-water relative permeability was designed and experiments were carried out under six different temperatures varying from 70°F to 120°F, while the cell pressure was varied from 500 to 1,300 psi for every respective temperature. From the results, it was evident that, in general, the endpoint relative permeability of carbon dioxide increases with decrease in viscosity ratio, while the endpoint relative permeability in the transition region between gas and supercritical decreases even with decreasing viscosity ratio. Also, based on the sensitivity studies carried out by varying pressure and temperature, it was experimentally confirmed that porous and permeable aquifers at a minimum depth of more than 800 m are the most appropriate storage sites.

Development of a FEM Reservoir Model Equipped with an Effective Permeability Tensor and its Application to Naturally Fractured Reservoirs

The numerical simulation of naturally fractured reservoirs is commonly based on the continuum dual-porosity concept. However, the model needs to assume that the fractures form very regular patterns, different from field observations. In order to overcome this problem, we proposed a method that can consider the characteristics of the real fracture system and developed a two-phase transient finite element method (FEM) (TENFEM) model able to implement an effective permeability tensor. The permeability tensors were estimated by using a single-phase, steady-state FEM (EPC) model also coded in this work, where Darcys law in matrix and cubic law in fracture were adopted for considering the flow characteristics in the discrete fracture network (DFN) approach. The developed models were applied to the paludal sand reservoir of a multiwell experiment (MWX) site to demonstrate validity and applicability of the models. The estimated average permeability in the MWX is almost identical compared to the results of the well test analysis. Then the numerical simulation with the TENFEM model was performed by using the transient pressure recorded from a gas well test on the MWX #1. From the results of bottom hole pressure and pressure distribution within the system, it was noted that the model with effective permeabilities generated almost identical results against the DFN model in the aspects of the behavior and the direction of fluid propagation with pressure decline, and therefore the proposed model is considered to be more efficient in terms of the computation time as well as the required storage capacity. Also from the upscaling study, it was shown that even with fewer numbers of grid blocks the developed model could effectively describe the directional flow caused by the fracture characteristics such as orientation and density of the fracture.

The oil production performance analysis using discrete fracture network model with simulated annealing inverse method

Naturally fractured reservoirs generally show high production in early stage, however, the oil might decrease suddenly within a few months. Because the connectivity of fracture network directly affects the oil production, the characterization of its network is extremely important, especially in fracture basement reservoirs. In order to characterize the fracture network, we have developed integrated system of fracture generation and discrete fracture network flow model coupling with simulated annealing inversion method. With the utilization of the model, parameters (fracture density, Fisher’s constant) of fracture network were analyzed. As a result, even though the same values of parameters were applied, different network systems were observed. Therefore, further study is essential to obtain unique fracture network system.

Development and Application of Inverse Model Using Genetic Algorithm for Reservoir Characterization

This article presents the development of the inverse model and its application for the characterization of heterogeneous reservoir. Until now, in a area of reservoir characterization, researches that reduce their uncertainty have been performed by integrating static data of cores, logs, seismic, experiment, etc., and dynamic data of production and 4D seismic data. In order to integrate dynamic data into reservoir characterization models, an optimization algorithm must be used in order to minimize the difference between observed and calculated data. In this study, we developed the inverse model using a genetic algorithm, and the optimization method for the inverse calculation was the real-coded genetic algorithm, which is not sensitive for initial value and is possible to search the global optimum. By utilizing the developed model, we performed the characterization to estimate the distributions of porosity and permeability. Firstly, in order to determine the optimal constraint for this system, the inverse calculations were carried out by increasing the maximum values of initial constraints estimated by Kriging method. To obtain results, we determined the case for 2.5 times the maximum permeability as the optimal constraint. From the results of inverse calculations to determine the optimal parameters, such as population size, operator and operation probability for this system, it was found that the selection operator was more sensitive than the crossover, and the roulette wheel operator was more suitable than the tournament as the selection operator. Also, the optimal population size and crossover probability were determined to be 450 and 0.85, respectively. Finally, as the result of characterization for this reservoir system, it is proved that the developed model have been generated the favorable porosity and permeability distributions.

The interpretation of DST data for donghae-1 gas field, block VI-1, Korea

Donghae-1 gas field is located in Ulleung basin at offshore Ulsan, Korea, and its recoverable reserve is expected to be 170 to 200 BCF (Billion cubic feet). The field was confirmed to have potential gas and condensate reserves from an exploration well in 1998 and two appraisal wells in 1999. This field consists of five zones, with an average reservoir depth of about 7,000 to 8,000 ft. In this study, we have performed an analysis of Gorae V DST (Drillstem test) #2 for testing B4 zone which has the biggest reserves and Gorae V-1 DST #2 for testing B3 and B4 zones simultaneously among DST data achieved in a total of 11 zones at three wells. The pressure and flow rate recorded from two tested zones were used to obtain the reservoir characteristics and the well productivity. For pressure transient test data, we carried out the analysis of reservoir permeability, skin factor, wellbore storage effect and barrier effect by using the Homer plot and type curve matching methods. Also, with the deliverability test data, we estimated the absolute open flow which is the maximum flow rate of the gas well, and extracted the correlations representing production rate with reservoir pressure. According to the analysis, Gorae V DST #2 of B4 zone has a permeability and skin factor of 37 md (Millidarcy), 4.54, and Gorae V-1 DST #2 of B3 and B4 zones has 23 md and 21.0, respectively. It was also found that the wellbore storage effect was not significant for the two wells tested. From the deliverability test analysis, the AOF (Absolute open flow) of the Gorae V DST #2 is 152.8 MMSCFD (Million standard cubic feet per day), and that of the Gorae V-1 DST #2 is calculated to be 68.2 MMSCFD.

An Analysis of Gas Tightness Around Unlined Storage Cavern Using a Discrete Fracture Flow FEM Model

ABSTRACT Water curtain method has been utilized to prevent the escape of gas from storage caverns excavated in the rock. The water curtain method appears to be increasingly used in various forms of storage caverns. Fluid flow in crystalline fractured rock where most of water curtains are constructed is basically controlled by the geometry of fracture network and the properties of the individual fracture. The concept of discrete fracture flow is more appropriate approach for analyzing the stability of water curtain system. In order to analyze the groundwater flow in fracture network, we have developed an unsteady state discrete fracture flowing FEM simulator and have applied it to underground LPG storage facilities at Ulsan, Korea. In this site the hydraulic head of observation well Y was monitored as −7.5 m. With the continuum model concept for the fractured rock the hydraulic head of well Y was calculated as −18.62 m, whereas −4 m was estimated with discrete fracture flow model. The result showed that th...

Microbial Activation of Bacillus subtilis-Immobilized Microgel Particles for Enhanced Oil Recovery.

Microbially enhanced oil recovery involves the use of microorganisms to extract oil remaining in reservoirs. Here, we report fabrication of microgel particles with immobilized Bacillus subtilis for application to microbially enhanced oil recovery. Using B. subtilis isolated from oil-contaminated soils in Myanmar, we evaluated the ability of this microbe to reduce the interfacial tension at the oil-water interface via production of biosurfactant molecules, eventually yielding excellent emulsification across a broad range of the medium pH and ionic strength. To safely deliver B. subtilis into a permeable porous medium, in this study, these bacteria were physically immobilized in a hydrogel mesh of microgel particles. In a core flooding experiment, in which the microgel particles were injected into a column packed with silica beads, we found that these particles significantly increased oil recovery in a concentration-dependent manner. This result shows that a mesh of microgel particles encapsulating biosurfactant-producing microorganisms holds promise for recovery of oil from porous media.

Characterization of Reservoir Heterogeneity Using Inverse Model Equipped with Parallel Genetic Algorithm

Abstract This study presents the development of reservoir characterization inverse model equipped with ANN type of ISGA and MSGA parallel processing algorithms. In order to run the developed model efficiently, homogeneous PC-cluster was constructed by four connecting PCs that have the same features. The model adapted ANN to automatically determine optimum GA parameters of operator, number of individuals and the operation rate that is appropriate for the reservoir heterogeneity. By utilizing the developed model in this study, inverse calculation was conducted for the synthetic reservoir system with the aid of an ISGA-PP. As a result, it was found that convergence is stably progressed. In the result of permeability distribution, it shows that low permeable zone in the central area for the system studied appeared to be little different compared to the result obtained by Kriging method, which is used only as static data. In the matching result of pressure, maximum relative error of 1.54% was presented at OP-4, and hence, the calculated permeability distribution is thought to be quite reliable. When MSGA-PP was applied to the same reservoir system as ISGA-PP, it converged stably similar to ISGA-PP. The difference between ISGA-PP and MSGA-PP appeared only at convergence rate and the resulting permeability distribution is very similar to each other. In the evaluation of computing efficiency of ISGA-PP and MSGA-PP against GA-SP, the result shows that the efficiency of parallel processing system is greater as the number of individual increases. Also, regardless of the number of individuals, the calculating time in parallel processing system was greatly reduced by 3.6 times compared to serial processing system of GA-SP. Finally, inverse calculation was carried out with MSGA-PP-ANN. As a result, it converged much faster than MSGA-PP, which does not have an artificial neural network system. This is the reason why the superior individuals are selected by the optimum operators, which are determined by ANN in the early time of the inverse calculation.

The Kinetics on Hydrate Formation in Pipelines

This study presents the experimental apparatus of flow loop type to investigate the hydrate plugging phenomena. The experiments for formation and dissociation of methane hydrate were conducted using the experimental apparatus setup in this study. Through the experiments, (gas + water + hydrate) three-phase equilibrium conditions were measured and enthalpy change in the dissociation process was analyzed based on the equilibrium results. The equilibrium conditions and the enthalpy of dissociation have been found to be consistent with previously published reference data. To examine the effect of hydrate formation under the flowing condition, experiments were carried out at varying flow velocities under a constant pressure. As a result, hydrate forming temperature tends to increase linearly with increasing flow velocity. Therefore, it was verified experimentally that flow velocity can be considered as one of the significant factors triggering the increase in the formation temperature.

The Development of a Generalized 3D DFN Simulator Implementing 2D Rectangular Fracture Flow

Abstract According to the Nelsons classification scheme, naturally fractured basement reservoirs are Type 1 systems in which the fractures provide porosity and permeability. Hydrocarbon production from basement reservoirs only occurs through the connected fracture network. Thus, characterization and prediction of flow behavior in basement reservoirs is extremely difficult due to the heterogeneity of the fractures. In this study, a generalized multiphase discrete fracture network simulator was developed. The model implements 2D flow within a rectangular fracture, which is important in thick fractured reservoirs like basement rocks. The discrete fracture network model developed in this study was validated for two synthetic fracture systems using a commercial model, ECLIPSE. Comparison showed excellent agreement between the results for both models. To examine the changing production behavior in fractured basement reservoirs, an attempt was made to analyze the effect of a bottom-water aquifer on production behavior. It was confirmed that the discrete fracture network model is a useful tool in predicting water breakthrough and remaining oil phenomena.