Miscible Displacement Research Articles

A non-aqueous foam concept for improving hydrocarbon miscible flooding in low permeability oil formations

Enhanced oil recovery (EOR) from carbonate formations has been challenging due to reservoir heterogeneity, unfavorable wettability, and low permeability. Thus, the application of traditional water-based EOR methods such as micellar-polymer flood in these reservoirs has been limited. With the increasing availability of natural gas, we introduce a new foam EOR concept utilizing the raw mixture of natural gas liquids (MNGLs). This process involves the injection of a non-condensable gas (i.e., nitrogen or methane) and MNGLs with dissolved non-aqueous foam stabilizing additive to maximize oil recovery based on crude oil-MNGLs miscibility and sweep efficiency due to foam improved mobility control.The objective of this study is to evaluate the performance of this unconventional foam process to improve miscible displacement in low permeability rocks. Coreflood experiments were conducted using heterogeneous carbonate cores with sub-10-mD permeability. It was found that non-aqueous foam-assisted miscible displacement can achieve promising ultimate recovery factors while significantly reducing the amount of injected MNGLs. The overall recovery could be increased up to 18% with a foaming additive dissolved in the MNGLs slug. The measured pressure drops along the core indicate that in-situ generation of foam significantly delayed the injectant breakthrough and recovered the unswept oil much further away from the injection point.

Chemical-assisted minimum miscibility pressure reduction between oil and methane

Miscible gas injection is an important enhanced oil recovery technique due to favourable displacement efficiency by eliminating interfacial tension (IFT) between the injected gas and oil phases. Miscible displacement often results in far higher recovery compared to immiscible displacement. However, miscibility can be difficult to achieve in high temperature reservoirs due to high minimum miscibility pressure (MMP) with increasing reservoir temperature and in shallow reservoirs where MMP would be higher than fracture pressure. Limited studies have been performed to explore the potential of reducing MMP in CO2-oil system using chemical additives. These additives work by collecting at the boundary between the two phases thereby reducing the interfacial tension. Specifically, none have investigated potential chemical additives to reduce the MMP in methane-oil systems, which limits the potential of methane injection. We thus investigated the effect of promising chemicals (surfactant based & alcohol based) for reducing the MMP in the methane-oil system at different temperatures (333 & 373 K) for an oil with a high acidity (4.0 mg KOH/g). Results using the vanishing interfacial tension (VIT) technique show that the tested surfactant-based chemicals reduce the MMP (methane-crude oil) by up to 9% at 373 K, whereas the tested alcohol-based chemicals have little effect on the MMP. Moreover, the results show that increasing temperature improves chemical performance and yields a higher MMP reduction, suggesting that these additives are more effective in high temperature reservoirs. The outlined research likely expands the application envelop of miscible natural gas injection in shallow and high-temperature reservoirs, in addition to the environmental benefits of reducing the associated gas flaring.

Primary cementing of horizontal wells. Displacement flows in eccentric horizontal annuli. Part 1. Experiments

Abstract

Estimation of Minimum Miscibility Pressure for Hydrocarbon Gas Injection Based on EOS

The important parameter used for determining the probable application of miscible displacement is the MMP (minimum miscibility pressure). In enhanced oil recovery, the injection of hydrocarbon gases can be a highly efficient method to improve the productivity of the well especially if miscibility developed through the displacement process. There are a lot of experiments for measuring the value of the miscibility pressure, but they are expensive and take a lot of time, so it's better to use the mathematical equations because of it inexpensive and fast. This study focused on calculating MMP required to inject hydrocarbon gases into two reservoirs namely Sadi and Tanomaa/ East Baghdad field. Modified Peng Robenson Equation of State was used to estimate MMP values for the two samples. The parameters of this equation have been tuned by splitting the plus component and regression process to obtain the best match for PVT properties between the calculated and that measured in the laboratory. Then the MMPs value compared with the results most reliable correlation. Ternary diagram for these samples has been constructed to illustrate the occurrence of miscibility.

Determination of the Minimum Miscible Pressure of the Supercritical Carbon Dioxide and the Formation Oil System by the Pendant Drop Method

Carbon dioxide miscible displacement plays an important role in the field of miscible displacement for enhanced oil recovery. However, there is a very important relationship between the formation of miscible displacement and the minimum miscible pressure. The pendant drop method in the interfacial tension method was firstly used to predict the minimum miscible pressure of the supercritical carbon dioxide and the formation oil of the test area oilfield. Under the condition of the simulated reservoir temperature 111.5 °C, the interfacial tension of the supercritical carbon dioxide and the formation oil system was tested experimentally by using formation oil samples of the test area oilfield. The range of test pressure was from 10.06 MPa to 28.57 MPa. Beside, the relation curve of the test pressure and the interfacial tension was drawn. The results show that under the reservoir temperature, the interfacial tension between the supercritical carbon dioxide and the formation oil shows approximately linear downward trend with increasing the test pressure. The mathematical expression was obtained by the linear regression analysis. According to the extrapolation, the vanishing point of the interfacial tension was obtained. Then the minimum miscible pressure of the supercritical carbon dioxide and the formation oil system was determined. The actual test was carried out to verify the result by the pendant drop method. Finally, the minimum miscible pressure of the supercritical carbon dioxide and the formation oil system of the test area oilfield was determined to be 29.4 MPa.

Two‐grid method for miscible displacement problem with dispersion by finite element method of characteristics

AbstractA combined method consisting of the mixed finite element method for the pressure equation and finite element method with characteristics for the concentration equation is proposed to solve the coupled system of incompressible two‐phase flow in porous media. Two‐grid algorithm based on the Newton iteration method is developed and analyzed for the nonlinear coupled system. It is shown, both theoretically and numerically, that our schemes are efficient and achieve asymptotically optimal accuracy as long as the mesh sizes satisfy .

English

We demonstrate some a priori estimates of a scheme using stabilization and hybrid interfaces applying to partial differential equations describing miscible displacement in porous media. This system is made of two coupled equations: an anisotropic diffusion equation on the pressure and a convection-diffusion-dispersion equation on the concentration of invading fluid. The anisotropic diffusion operators in both equations require special care while discretizing by a finite volume method SUSHI. Later, we present some numerical experiments.

Fate and transport of bromide and mononuclear aromatic hydrocarbons in aqueous solutions through Berea Sandstone

A series of miscible displacement tests were performed on a 51 mm wide by 76 mm long well-laminated core of Berea Sandstone to determine the transport parameters of the anion bromide and a homologous series of seventeen mononuclear aromatic hydrocarbons (MAHs). In each test, a continuous input pulse of a single tracer was passed through the cylindrical core housed in a hydrostatic core holder at a confining pressure of 200 bar. The effluent concentration, as measured by in-line UV absorbance, versus time resulted in smooth high-resolution sinusoidal breakthrough curves (BTCs). In comparison to the near Gaussian BTCs of bromide, the transport of the MAHs was differentially retarded with minimal levels of delayed transport along the more rapid flow lines, but with progressively more along the slower flow paths. These results show that despite a lack of significant hydraulic heterogeneity, there is a high degree of heterogeneity among the sorption sites. The BTCs were aptly modeled with a one-dimensional flow model consisting of a mixture of instantaneous equilibrium and rate-limited reversible sorption sites. The relative fraction of instantaneous sites increased proportionately with the rate the subject MAH passed through the core. Potential quantitative structure-retention relationships (QSRR) between common chemical parameters of the MAHs and their overall retardation factors, sorption coefficients and the fraction of instantaneous equilibrium were evaluated. Among the compounds examined, relatively strong correlations were found with molecular weight, aqueous solubility, and octanol-water partitioning coefficient with which relative MAH transport retardation, the linear phase distribution coefficient, and the dimensionless partitioning coefficient between sorption sites.

A pore-scale experimental study of non-aqueous foam for improving hydrocarbon miscible flooding

Mobility control in hydrocarbon miscible flooding is crucial for commercial vitality where severe reservoir heterogeneity causes poor sweep efficiency. This study introduced a new concept of non-aqueous foam-assisted hydrocarbon miscible flooding in water-sensitive oil formations. This process involves the injection of a non-condensable gas (i.e., nitrogen or methane) and a raw mixture of NGLs (MNGLs) with a foaming additive to improve displacement and sweep efficiency. Foaming a light hydrocarbon liquid and the impact of non-aqueous foam on miscible displacement are the main focuses of this study. n-Pentane was used as a MNGLs (solvent) model for foam stability tests. Transient foam propagation and rheology were directly visualized and characterized based on the apparent gas (nitrogen) viscosity associated with foam texture and fluid saturations. Oil recovery factors were directly related to different degrees of in-situ foaming. For the injection of a solvent slug followed by a gas drive, the displacement of oil became unstable as nitrogen fingered through the solvent-oil mixing zone, resulting in a high residual liquid saturation. However, gas fingering was significantly hindered as the solvent was injected with a foaming agent. Dynamic fluid distribution indicate that the improved oil recovery could be attributed to the propagation of foam in the swept zone, which provided essential flow resistance for better displacement stability. To investigate the effect of initial gas saturation in the reservoir on flow behavior, a slug of gas was injected before solvent injection. Delayed solvent breakthrough and better sweep efficiency were observed in the presence of foam due to the reduced liquid phase mobility in preferential flow paths and the diversion of solvent into small pores by the trapped gas at the displacing front. Furthermore, it was possible to obtain stable foam flow with an apparent viscosity of 20 times greater than the solvent viscosity.

Miscible Fluid Displacement in Rock Cores Evaluated with NMRT2Relaxation Time Measurements

NMR T2 relaxation times for fluids in a porous medium are, in principle, proportional to the relevant occupied pore size. Here, we exploit this relationship to monitor the pore size distribution oc...

A new discontinuous Galerkin mixed finite element method for compressible miscible displacement problem

A new combined discontinuous Galerkin method is proposed for compressible miscible displacement problem in porous media. Here, a splitting positive definite mixed finite element method is used for the pressure and Darcy velocity, while an interior penalty discontinuous Galerkin (IPDG) method is used for the transport equation. The stability and convergence of this algorithm are considered, and the optimal a priori error estimate in l∞(L2) for velocity, pressure and concentration are given. Finally we provide some numerical results to confirm our theoretical analysis, and simulate compressible fluid flows through homogeneous and isotropic porous media.

Viscoplastic displacements in axially rotating pipes

We investigate experimentally the effects of a pipe axial rotation on buoyant miscible displacement flows in an inclined pipe. The displacing Newtonian fluid (salt-water solution) is heavier than the displaced viscoplastic one (Carbopol solution). Via image processing techniques and ultrasound Doppler velocity measurements, we analyze the key flow features such as the flow patterns, the velocity and concentration fields, and the leading front velocity (Vˆf) as well as the trailing front velocity (Vˆt) of the displacement flow. The main flow parameters in our experiments are the pipe inclination angle, the small density difference between the two fluids, the yield stress of the displaced fluid, the imposed mean flow velocity (Vˆ0), and most importantly the pipe rotation speed. We find that increasing the pipe rotation speed enhances the transverse mixing between the two fluids and, above a critical transition, leads to a complete removal of the displaced viscoplastic fluid. We classify the flow regimes into efficient and inefficient displacement flows, using appropriate dimensionless groups, i.e. the Rossby number (Rb) and the Froude number (Fr). We find that the critical transition between the two flow regimes can be roughly described by a critical Rossby number (Rbc), as a function of Fr, independent of the other flow dimensionless numbers. For Rb≤Rbc, we find that Vˆf≈1.6Vˆ0 and Vˆt≈Vˆ0, while for Rb>Rbc we propose an empirical relation for the leading front velocity versus the Rossby number. These findings can offer new insight to control viscoplastic displacement flows using rotational motion.

The Physical Meaning of the Koval Factor

When originally developed, the Koval theory was meant to interpret the core-scale production of oil by a miscible displacement by solvent injection. An essential parameter in the theory is the Koval factor, KV, which combines both the viscosity contrast effect (E) and the heterogeneity effect (HK) as KV = E HK. The Koval method has done an excellent job of interpreting oil recovery; however, the physical origin of this simple model is not clear. To address the physical significance of these factors, this paper explains a novel approach to derive the Koval factor using petrophysical data and vertical equilibrium theory. The study examines core data from 112 vertical production wells from fields located in the United States and Algeria. The heterogeneity factor is estimated from the flow- and storage-capacity relations, according to the Koval theory. Then, using fractional flow theory and assuming vertical equilibrium, we derive a mathematical expression that conveys the physical interpretation of the Koval factor. The results indicate that the physical explanation of the Koval factor is that of a product of the mobility ratio and the heterogeneity of the reservoir. The Koval factor simplifies computations of oil recovery by transforming the original reservoir to one with uniform layers, in vertical equilibrium, and piston-like displacement within each using only the flow and storage capacities. The physical interpretation of the Koval factor could offer new insights to examine previous results obtained from the theory itself.

A combined hybrid mixed element method for incompressible miscible displacement problem with local discontinuous Galerkin procedure

AbstractIn this article, we propose a combined hybrid discontinuous mixed finite element method for miscible displacement problem with local discontinuous Galerkin method. Here, to obtain more accurate approximation and deal with the discontinuous case, we use the hybrid mixed element method to approximate the pressure and velocity, and use the local discontinuous Galerkin finite element method for the concentration. Compared with other combined methods, this method can improve the efficiency of computation, deal with the discontinuous problem well and keep local mass balance. We study the convergence of this method and give the corresponding optimal error estimates in L∞(L2) for velocity and concentration and the super convergence in L∞(H1) for pressure. Finally, we also present some numerical examples to confirm our theoretical analysis.

Combustion in miscible displacement for high-pressure air injection

This paper describes miscible displacement upon air injection in a porous medium saturated with oil corresponding to conditions of high-pressure air injection (HPAI). We assume that injection fluids and produced fluids are fully miscible with the oil at the prevailing high pressure. We use three pseudo-components, viz., oxygen, oil, and an inert component, which includes nitrogen, carbon dioxide, etc. To model the fingering instabilities, we follow a similar procedure as proposed by Koval (SPE J. 3(02):145–154, 1963) and include the reaction between oxygen and oil in the Koval model. The equations are solved numerically, using a finite element software package (COMSOL). The results show that a combustion wave is formed. We study the performance at low and high viscosities and show that the reaction improves the speed and degree of recovery at later times.

A two-grid Eulerian–Lagrangian localized adjoint method to miscible displacement problems with dispersion term

In this paper, we propose a novel two-grid method of Eulerian–Lagrangian localized adjoint method (ELLAM)-mixed finite element method (MFEM) solutions for nonlinear and coupled miscible displacement problems, which describe complex fluid flow processes in porous media. An ELLAM is used to solve the nonlinear convection–diffusion equation for concentration, and we present a MFEM to compute the pressure equation for the pressure and Darcy velocity. A two-grid scheme is investigated to linearize and decouple the mixed-method equations. It is illustrated that the coarse space can be selected as coarse as H=O(h1∕2) and the asymptotically optimal approximation as the nonlinear schemes can be still achieved. As a result, a large class of such nonlinear and coupled problems can be solved efficiently with large time steps.

Impact of production wells operational changes on high-viscosity oil recovery

As light oil reserves are developed, the share of heavy high-viscosity oil (HVO) reserves, which are considered difficult to recover, increases in the total balance of oil reserves. Therefore, the future of the oil industry is inevitably linked to the development of highly viscous heavy oil deposits. Today, according to various estimates, epy reserves of high-viscosity oil and bitumen range from 790 billion tons to 1 trillion tons. This is more than 5 times more than the residual recoverable reserves of low and average viscosity oil. The world experience of developing high-viscosity oil deposits shows that the cost-effective development of most of them is limited due to low efficiency of oil wells and low oil recovery achieved through natural operation mode or flooding. If the first of these problems is successfully solved in recent times by drilling horizontal and multilateral wells, the second one requires the introduction of various technologies to influence the formation (thermal methods, miscible displacement, etc.), which are not always highly efficient. In this work we will consider the impact of changing the operation modes of production wells on the production of high-viscosity oil reserves on the example of the Northern Buzachi field (Republic of Kazakhstan).

Hp-discontinuous Galerkin Finite Element Method for Incompressible Miscible Displacement in Porous Media

We used (hp-DGFEM) for solving the coupled system of incompressible miscible displacement problem in porous media. Flow and transport equations are solved by hp-symmetric interior penalty Discontinuous Galerkin (hp-SIPG) method. We prove the error analysis in the energy norm to the coupled system of incompressible one-phase flow problem.

Modeling and simulation of partially miscible two-phase flow with kinetics mass transfer

Multiphase flow equations for two components (for instance water and hydrogen) and two phases (liquid and gas), with equilibrium phase exchange, have been used to simulate the process of miscible displacement in porous media. Laboratory and field studies have shown that this assumption fails under certain circumstances especially for accurate description of the pollution and a finite transfer velocity, called here the kinetics. We propose a numerical scheme based on a two-step convection/diffusion-relaxation strategy to simulate the non-equilibrium model. In the first step we solve the intra-phase transfer (convection/diffusion) working with liquid saturation, liquid pressure and dissolved hydrogen concentration as primary variables. In the second step, we address the interphase transfer using the solubility relation that is solved by projection on the equilibrium state. This technique also ensures the positivity for the liquid saturation and produces energy estimates. One important advantage of this approach is the fact that the simulation can be easily adapted to different linear and non-linear equilibrium laws between phases. Another advantage is that our proposed method includes the kinetics in a projection step and keeps the displacement of the components. We implemented this new model in in-house simulation code and present numerical results comparing the model with equilibrium and non-equilibrium one.

Numerical modeling of viscous fingering during miscible displacement of oil by a paraffinic solvent in the presence of asphaltene precipitation and deposition

We study the mixing dynamics of a paraffinic solvent with oil in the context of miscible displacement in porous media for enhanced oil recovery. Typically, injected solvents are less viscous compared to the resident oil, leading to the rise of interfacial instabilities known as viscous fingering. This, in turn, accelerates precipitation of initially dissolved asphaltene particles in the oil. The formed precipitates are carried with the flow and may deposit in the porous media, altering porosity and permeability fields. Although asphaltene precipitation and deposition are inevitable in most of the solvent-based recovery techniques, they have been neglected in the previous works of miscible displacement due to their added complexity. In this work, we present a rigorous formulation of the physics of the problem and conduct high-resolution nonlinear numerical simulations to investigate the effects of asphaltene precipitation and deposition and the resulting formation damage. For this purpose, the related governing equations are derived based on the velocity-vorticity formulation, and a high-order hybrid scheme is applied to solve them. This type of handling enables us to simulate viscous fingering at large viscosity ratios and Peclet numbers, beyond what has been previously reported in the literature. Furthermore, experimental measurements are conducted for viscosity and asphaltene content of the oil at various solvent concentrations and are used in the simulations. The results of our numerical simulations reveal that despite having a great impact on the permeability field, asphaltene precipitation and deposition do not influence the growth of viscous fingers, noticeably, which is due to the substantial viscosity ratio of the studied system. However, deposition of the formed precipitates leads to in-situ upgrading of the oil and thus enhances the quality of the produced liquid. Finally, regarding the effect of the choice of viscosity mixing rule, we compare two commonly used viscosity mixing rules in the previous works (exponential and quarter-power) and elaborate on their main differences in terms of the observed dynamics.