Experimental and Modelling Study of Gravity Drainage in a Three-Block System (original) (raw)
Analytical modeling of oil production from a matrix block by free fall gravity drainage mechanism
Energy, Exploration & Exploitation, 2013
Free fall gravity drainage is the most effective mechanism in gas invaded zone of fractured reservoirs. Although several analytical models have been proposed to characterize this mechanism, most of them suffer from inadequate reality, such as neglecting capillary pressure. In this study, a new analytical model was proposed to predict the oil recovery versus time for a homogeneous matrix block under a free fall gravity drainage mechanism. Considering the effect of viscous, gravity as well as capillary forces, the model was developed. This model is applicable to different conditions of gravity and capillary force, as well as when both forces are active. Along with core scale experimental data available in the literature, a series of micro model experiments was also conducted and used to check the model's validity. In addition, a synthetic computer model was constructed and used for further model validation. Results showed that the suggested model predicts the physics of the gravity drainage mechanism very well. The results of this work can be helpful to develop a new transfer function for gravity drainage process modeling in fractured reservoir.
Gas-oil gravity drainage in fractured porous media
Discovery Publication
"Gas-oil gravity drainage is considered to be one of the most dependable recovery mechanisms in naturally fractured reservoirs. The Production mechanism is as a result of the density difference between the phases and capillary contrast between the matrixes and the fractures. This mechanism is contingent upon certain factors such as capillary threshold height and capillary discontinuity, among others. To assess the efficiency and contributions of these factors, a simulation study was carried out on a modeled fractured porous system using ECLIPSE-100 simulator. The results obtained show that oil recovery from a single matrix block (RUN1) was higher than matrix blocks with two, three and five stacks with capillary continuity (RUNS 2, 3 and 4 respectively). Additionally, with capillary discontinuity (RUNS 5, 6 and 7), the results depicted an increase in oil recovery compared to the cases of capillary continuity. However, varying the degree of capillary discontinuity with the respective matrix block stacks in the fractured model yielded no significant increase in oil recovery. Thus, the results show that while both capillary threshold height and capillary discontinuity remain significant factors in gas-oil gravity drainage, capillary continuity and varying the degree of discontinuity between the matrixes degree has little or no effect on this recovery mechanism in fractured porous media. Keywords: Gas-oil gravity drainage, Oil recovery, Capillary threshold height, Capillary discontinuity, Fractured porous media."
Experimental Investigation of Tertiary Oil Gravity Drainage in Fractured Porous Media
Special Topics & Reviews in Porous Media - An International Journal, 2010
The amount of residual oil trapped in the matrix of a fractured reservoir after water drive, either natural water drive or water injection, depends on the wettability of the matrix rocks. Gas oil gravity drainage (GOGD) has been proposed as the tertiary oil recovery process for this type of oil reservoir. The current work focuses on experimental investigation of tertiary GOGD in fractured porous media under different types of matrix wettability. Results of a set of experiments performed in artificial porous media composed of sand packs and glass beads of different wettability have been used to check the GOGD rate and the ultimate oil recovery for previously waterflooded models. A novel experimental setup to study flow behavior in fractured artificial porous media was designed to perform the GOGD process. Results show that tertiary gravity drainage increases oil recovery efficiency from a fractured matrix block, which also depends on the post-waterflood residual oil saturation and the wettability of the medium. Observation of the gas front location and oil recovery profile with time during the tertiary recovery stage reveals that the oil recovery of post-waterflood residual oil in a fractured matrix block starts before stabilization of the gas-liquid front. Oil recovery mechanisms similar to those presented in tertiary GOGD recovery in a conventional reservoir are proposed to explain the gradual drainage of matrix blocks in a naturally fractured stratum.
Experimental Study of the Fracture and Matrix Effects on Free-Fall Gravity Drainage With Micromodels
SPE Journal, 2015
Summary Free-fall gravity drainage (FFGD) is the main production mechanism in the gas-invaded zone of fractured reservoirs. The gravity and capillary forces are two major forces that control the production performance of a fractured system under an FFGD mechanism. Gravity force acts as a driving force to remove oil from the matrix block whereas the resistive capillary force tends to keep oil inside the matrix. In this study, a series of experiments was performed to study the effects of the geometrical characteristics of the fracture and matrix on the oil-production rate under an FFGD mechanism by use of a glass micromodel. The oil-recovery factor (RF) was also obtained for a single matrix block by use of different patterns. Results from the experiments show that different flow regimes occur during the production life of a single matrix block under a FFGD mechanism. The fluid flow is controlled by the capillary-dominated regime at the early stage and late time of production life, whe...
Journal of Canadian Petroleum Technology, 2010
Corefloods and field investigations confirm that a large amount of incremental tertiary oil can be recovered from dipping waterdrive reservoirs using gravity-assisted tertiary gas-injection processes. These processes include the double-displacement process (DDP) and the second-contact water-displacement (SCWD) process. The DDP consists of injecting gas into waterflooded oil zones. The SCWD process consists of submitting these gasflooded zones to a new water-displacement process.
Journal of Petroleum Science and Engineering, 2017
Capillary and gravity forces are the controlling mechanisms in fractured reservoirs recovery. Most of the fractured reservoirs are carbonate formations with mixed wet and oil wet rocks. One of the techniques to improve the oil recovery from these reservoirs is surfactant treatment in the water invaded zone of carbonate fractured formation known as surfactant-aided gravity drainage. A number of experimental and modeling studies are available in this research area however, a modeling approach validated with the experimental data to consider different conditions in the reservoir, including rock physics, fluid properties, water salinity and surfactant functionalities is still a necessary element before the pilot tests for this recovery technique. In this work, a modeling approach is proposed to provide insight into the engineering aspects of this process. It defines a reservoir rock matrix (core scale) surrounded by the surfactant-brine solution in the fracture that acts as a boundary for the matrix in an imbibition test scenario. The reservoir rock is oil wet, therefore at first, the diffusive forces drive the solution into the matrix leading to wettability alteration. Afterward the counter-current imbibition takes place in the early through the middle time of the experiment. Finally, the gravity drainage controls the recovery process. The parametric analysis investigates the effects of various parameters. Different modifications to the base case (validated with the experimental data) are performed for each parameter and then the resultant recovery curves are compared with the base case recovery. The parametric study
Empirical Modeling of Gravity Drainage in Fractured Porous Media
Energy & Fuels, 2011
Gravity drainage is considered to be the main mechanism in primary oil production from naturally fractured reservoirs, but mathematical models to adequately predict the oil recovery and flux rate between the matrix and fracture network under gravity drainage are rarely described in the literature. To address this lacuna, gas-oil contact movement and oil recovery rates in a thin glass-bead-packed simulator were measured, allowing for the capture of information about the matrix-fracture fluidtransfer process. A two-dimensional mathematical model was developed to numerically simulate the process under the same conditions as the experiments, and then empirical models were proposed for oil production in such fractured systems because the final liquid recovery was found to be correlated to dimensionless groups, such as the Bond number. The empirical model approach was then extended to predict the matrix-fracture liquid-transfer rate during the free-fall gravity drainage process. On the basis of experimental data and empirical correlations, the matrix-fracture liquid flux rate appears to be proportional to the liquid level difference in the matrix and fracture. These correlations were tested against numerical simulation results and actual field data of oil production by free-fall gravity drainage. The empirical models have been judged to perform acceptably in the prediction of the oil production and fluid-transfer rate in the oil-gas gravity drainage cases studied.
Gravity Drainage Mechanism in Naturally Fractured Carbonate Reservoirs; Review and Application
Energies, 2019
Gravity drainage is one of the essential recovery mechanisms in naturally fractured reservoirs. Several mathematical formulas have been proposed to simulate the drainage process using the dual-porosity model. Nevertheless, they were varied in their abilities to capture the real saturation profiles and recovery speed in the reservoir. Therefore, understanding each mathematical model can help in deciding the best gravity model that suits each reservoir case. Real field data from a naturally fractured carbonate reservoir from the Middle East have used to examine the performance of various gravity equations. The reservoir represents a gas–oil system and has four decades of production history, which provided the required mean to evaluate the performance of each gravity model. The simulation outcomes demonstrated remarkable differences in the oil and gas saturation profile and in the oil recovery speed from the matrix blocks, which attributed to a different definition of the flow potentia...
Pore-Level Observation of Free Gravity Drainage of Oil in Fractured Porous Media
Transport in Porous Media, 2011
This work presents results from two sets of experiments conducted to study, in pore level, the role of fracture aperture and tilt angle on the stability of liquid bridges and the shape of a front during free gravity drainage process. Glass micromodels of two different aperture sizes were used to monitor the mechanism of gravity drainage of air-crude oil system, rotating around a bottom corner to create different tilting angles. Oil content within the matrix blocks was determined as a function of time using a series of images obtained during the experiments, from which net drainage rate from the upper and lower matrix blocks is calculated. Liquid bridges are more frequent but less stable at early time of drainage. The liquid bridges, which have widths as thin as 50 µm, can resist instability to maintain continuity. Liquid bridges formed in stacks with higher tilt angles are more stable, enhancing oil drainage from the upper matrix block and causing higher recoveries. Quantitative analysis of the results shows that a wider fracture aperture increases the oil production rate, but reduces the ultimate recovery. Furthermore, stacks with higher tilt angles present larger ultimate recoveries and smaller production rates. The front geometry in the lower block deviates from linearity due to formation of liquid bridges in the middle fracture. The results of this work can be helpful to better understand the interaction between fractures and matrix blocks.
Journal of Canadian Petroleum Technology, 2010
Summary Miscible injection of carbon dioxide has seen a significant increase in interest for the purpose of enhanced oil recovery (EOR) in conventional oil reservoirs. However, naturally fractured reservoirs, which are among the largest oil reserves in the world, are considered poor candidates for this process because of presumed low-performance efficiency. This paper presents the results of an experimental study that explains the effect of connate water saturation, matrix permeability and oil viscosity on the performance of gravity drainage from the matrix (into fracture) when it is surrounded by a CO2-filled fracture. Experiments were performed in an experimental model under different operating pressures to cover both immiscible and miscible conditions. Experiments were conducted using synthetic oil (nC10) and light crude oil in two Berea cores having large differences in permeability. In addition, the effect of connate water saturation was studied by performing experiments in an ...