Experimental studying of pore morphology and wettability effects on microscopic and macroscopic displacement efficiency of polymer flooding

Pore morphology and wettability of a porous medium have dominating effects on microscopic displacement efficiency, and consequently on the ultimate oil recovery. To provide a better understanding of the effects of these parameters on microscopic displacement mechanisms and macroscopic performance of a polymer flood process, a comprehensive experimental study was conducted using five two-dimensional glass micromodels. A combination of three wettability conditions and five different pore structures was used in this study. The selected scenarios include four homogeneous synthetic pore networks at water-, mixed- and oil-wet conditions. A random network that represents the pore space in Berea sandstone was also used for further investigation.Image processing technique was applied to analyze and compare displacement mechanisms and displacement process efficiency in each experiment. Microscopic mechanisms, such as oil and polymer solution trapping, configuration of wetting and non-wetting phases, flow of continuous and discontinuous strings of polymer solution, polymer solution snap-off, distorted flow of polymer solution, emulsion formation, and microscopic pore-to-pore sweep of oil phase were observed and monitored in conducted experiments. Experimental results showed that water- and mixed-wet media generally have comparable and higher recoveries in contrast with oil-wet media. Moreover, the results confirmed a significant dependency on the pore structure and wettability of the media on both displacement mechanisms as well as oil recoveries. This experimental study illustrates the successful application of glass micromodel techniques for studying enhanced oil recovery (EOR) processes in a five-spot pattern, and also provides a useful reference for understanding the displacement mechanisms involved in a polymer flood process at different pore morphologies and wettabilities of porous media.     

A mechanistic analysis of viscous fingering in low-tension polymer flooding in heavy-oil reservoirs

Modeling of the low tension polymer flooding (LTPF) in heavy oil reservoirs suffers from the paucity of detailed knowledge of viscous instability or fingering effects. Major limitations of previous approaches for studying viscous fingering in immiscible displacements are that the reported experiments have been conducted utilizing the linear displacements schemes in the media with high, single-phase permeabilities. Consequently, viscous instability has not been studied in low-permeability media and using the displacement schemes similar to the oil-field patterns (e.g., five-spot). To help understand viscous fingering in LTPF in heavy oil reservoirs and to overcome the limitations of previous studies, we conducted experiments in the low-permeability, one-quarter, five-spot patterns. New insights into the main driving mechanisms for viscous fingering are proposed. In summary, the mechanisms of spreading, splitting, coalescence, and microscopic crossflow drive the finger growth. In addition, the viscous fingers are readily initiated in the porous medium, but they can be damped out before traveling very far. This damping of the viscous fingers is due to the flow of the two phases in a direction transverse to the direction of bulk fluid movement as a result of dispersive processes such as stream splitting. Also, the initially-developed fingers may deteriorate over the time of displacement. This depends on the distance between the injector and producer and width of the porous medium. The presence of instabilities that look like fingers and stable displacements behind the unstable front were discovered. The results also indicate that a stable zone exists and progresses at varying velocities. Finally, we reveal three different types of displacements that occur in LTPF: stable displacements, displacement with macroscopic viscous fingering, and displacements with both macroscopic and microscopic viscous fingering.     

An Experimental and Numerical Investigation of Solvent Injection to Heavy Oil in Fractured Five-Spot Micromodels

Abstract

In this work a series of solvent injection experiments was conducted on horizontal glass micromodels at several fixed flow rate conditions. The micromodels were initially saturated with heavy crude oil. The produced oil as a function of injected volume of solvents was measured using image analysis of the continuously provided pictures. In order to investigate the macroscopic behavior of the process in different media, several fractured, with constant width, and nonfractured five-spot micromodels were designed and used. The measured data have also been used for verifying and developing a simulation model that was later used for sensitivity analysis of some parameters that affect oil recovery. The results show that when the fracture spacing increased, the oil recovery decreased. In contrast, as the fracture orientation angle (the angle with the mean flow direction) or solvent viscosity increased, the oil recovery increased. A critical value for the ratio of connate water saturation to the oil volume has been found that, beyond that the solvent injection process, loses its efficiency. The final recovery of a water alternating solvent (WAS) injection process in fractured medium in the presence/absence of connate water saturation was considerably greater than that obtained either by continuous solvent injection or water injection alone. Good agreement was observed between experimental and simulation results when a dual permeability model was used in our simulation.     

Asphaltene Precipitation Prediction Using a Micellization Model Based on Experimental Data

Abstract

Thermodynamic modeling is a promising tool for prediction of asphaltene precipitation. However, most thermodynamic models do not consider the micellar nature of petroleum fluids and the interaction between asphaltene-resin molecules. In addition, the accuracy of the predictions from the Peng-Robinson equation of state (PR-EOS) depends on the mixing rule. In this work, a thermodynamic framework based on the micellization model is used to describe the structure of asphaltene micelles as well as asphaltene precipitation in crude oil and the Wong and Sandler (1992) Wong, D. S. H. and Sandler, S. I. 1992. A theoretically correct mixing rule for cubic equations of state. AIChE J., 38: 671–680. [Crossref], [Web of Science ®] , [Google Scholar] mixing rule also is applied. The results show that the model predictions are matched well with the generated data for two Iranian crude oils.     

Experimental and Modelling Investigations of Asphaltene Precipitation During Pressure Depletion and Gas Injection Operations

Asphaltene precipitation problems manifest themselves in different stages of oil reservoirs production. Experimental and modeling investigations are, therefore, employed as promising tools to assist in predictions of asphaltene precipitation problems and selection of proper production facilities. This study concerns experimental and modeling investigations of asphaltene precipitation during natural production and gas injection operations for a heavy Iranian crude oil at reservoir conditions. First, with design and performance of high pressure–high temperature experiments, asphaltene precipitation behavior is comprehensively investigated; the effects of pressure and temperature are fully studied during pressure depletion tests and the role of injection gas composition on precipitation is described in gas injection experiments. In the next stage, the obtained experimental results are fed into a commercial simulator to develop the asphaltene precipitation model. The results for the pressure depletion experiments indicate that the maximum amount of asphaltene precipitation takes place at fluid bubble point pressure. Increase in the temperature, as seen, causes to reduce the amount of precipitation for the entire range of pressures. For gas injection experiments, the onset of precipitation for CO₂, associated, and N₂ gases takes place at around 0.20, 0.28, and 0.50 gas to mixture mole ratios, respectively. Carbon dioxide shows the highest asphaltene precipitation values and nitrogen has the lowest amounts for the whole range of gas mole fractions. Finally, the results for modeling indicate successful asphaltene precipitation predictions for both pressure depletion and gas injection processes.     

Experimental Investigation of Matricaria chamomilla Extract Effect on Oil-Water Interfacial Tension: Usable for Chemical Enhanced Oil Recovery

Recently, natural surfactants had been studied for chemical enhanced oil recovery as opposite to synthetic surfactants due to environmental problems associated with synthetic surfactants. In this study a new plant based natural surfactant, Matricaria chamomilla, is introduced. For this purpose, the interfacial tension values between natural surfactant solution and oil are measured by using the pendant drop method. The results show that Matricaria chamomilla decreased the oil-water interfacial tension values from 30.63 to 12.57 mN/m. Results confirm surface chemical activity of Matricaria chamomilla in comparison with other natural surfactants.     

A novel random mutagenesis approach using human mutagenic DNA polymerases to generate enzyme variant libraries

The in vitro MutaGen procedure is a new random mutagenesis method based on the use of low-fidelity DNA polymerases. In the present study, this technique was applied on a 2 kb gene encoding amylosucrase, an attractive enzyme for the industrial synthesis of amylose-like polymers. Mutations were first introduced during a single replicating step performed by mutagenic polymerases pol beta and pol eta. Three large libraries (>10(5) independent clones) were generated (one with pol beta and two with pol eta). The sequence analysis of randomly chosen clones confirmed the potential of this strategy for the generation of diversity. Variants generated by pol beta were 4-7-fold less mutated than those created with pol eta, indicating that our approach enables mutation rate control following the DNA polymerase employed for mutagenesis. Moreover, pol beta and pol eta provide different and complementary mutation spectra, allowing a wider sequence space exploration than error-prone PCR protocols employing Taq polymerase. Interestingly, some of the variants generated by pol eta displayed unusual modifications, including combinations of base substitutions and codon deletions which are rarely generated using other methods. By taking advantage of the mutation bias of naturally highly error-prone DNA polymerases, MutaGen thus appears as a very useful tool for gene and protein randomisation.     

A Comparison of Natural Depletion and Different Scenarios of Injection in the Reservoir From the Beginning of Oil Production

This research comprises natural depletion, associate, and CO2 gas injection with regard to asphaltene precipitation and permeability reduction. For the sake of achievement these goals experiments were undertaken by core flood and asphaltene static apparatus. Natural depletion was performed at 4500, 3050, 2250, 1450, and 900 Psig and it has been seen maximum amount of asphaltene precipitation located at saturation pressure. The results demonstrate that asphaltene precipitation during natural depletion was higher than CO2 and associate gas injection. Also it was seen asphaltene precipitation rate during CO2 and associate gas injection was lower than natural depletion. Based on results, amount of asphaltene precipitation was differing according to type of gas. The results of the study indicate asphaltene precipitation during CO2 injection was more than associate gas injection. Finally it was seen the permeability reduction during associate was less than CO2 and natural depletion for this kind of Iranian carbonate sample.     

Injection Efficiency and Water Loss Optimization Using Streamline Simulation in Water Flooding Process

This work has used a novel method for injection efficiency optimization following water flooding management. This method is based on individual streamline simulation ability to describe well allocation factor for injection and production wells. In addition, the well allocation factor can provide the amount of attributed fluid to each injector-producer pair and water loss amount, so it is possible to define injection efficiency. Optimization of injection efficiency is based on increasing the injection rates in efficient injectors and decreasing them in inefficient injectors.

In this study, we used streamline simulation for injection efficiency and water loss optimization with the aim of increasing oil recovery. The current study includes two parts. Firstly, we identify well injection rates based on mathematical relationships and, secondly, we increase injection efficiency and oil recovery by decreasing water loss to the aquifer. By using this method and with the same amount of injected water, in the first and second part injection efficiency increased from 46 to 53% and 53 to 57%, respectively, in a 3-year simulation. It was determined that this method is suitable to identify and optimize injection rates, reduce water loss to the aquifer, and subsequently increase oil recovery.     

Phase Behavior Modeling of Asphaltene Precipitation for Heavy Crudes: A Promising Tool Along with Experimental Data

Thermodynamic modeling is known as a promising tool for phase behavior modeling of asphaltene precipitation under different conditions such as pressure depletion and CO₂ injection. In this work, a thermodynamic approach is used for modeling the phase behavior of asphaltene precipitation. The precipitated asphaltene phase is represented by an improved solid model, while the oil and gas phases are modeled with an equation of state. The PR-EOS was used to perform flash calculations. Then, the onset point and the amount of precipitated asphaltene were predicted. A computer code based on an improved solid model has been developed and used for predicting asphaltene precipitation data for one of Iranian heavy crudes, under pressure depletion and CO₂ injection conditions. A significant improvement has been observed in predicting the asphaltene precipitation data under gas injection conditions. Especially for the maximum value of asphaltene precipitation and for the trend of the curve after the peak point, good agreement was observed. For gas injection conditions, comparison of the thermodynamic micellization model and the improved solid model showed that the thermodynamic micellization model cannot predict the maximum of precipitation as well as the improved solid model. The non-isothermal improved solid model has been used for predicting asphaltene precipitation data under pressure depletion conditions. The pressure depletion tests were done at different levels of temperature and pressure, and the parameters of a non-isothermal model were tuned using three onset pressures at three different temperatures for the considered crude. The results showed that the model is highly sensitive to the amount of solid molar volume along with the interaction coefficient parameter between the asphaltene component and light hydrocarbon components. Using a non-isothermal improved solid model, the asphaltene phase envelope was developed. It has been revealed that at high temperatures, an increase in the temperature results in a lower amount of asphaltene precipitation and also it causes the convergence of lower and upper boundaries of the asphaltene phase envelope. This work illustrates successful application of a non-isothermal improved solid model for developing the asphaltene phase envelope of heavy crude which can be helpful for monitoring and controlling of asphaltene precipitation through the wellbore and surface facilities during heavy oil production.