Waterflood Efficiency Research Articles

A novel, streamline-based injection efficiency enhancement method using multi-objective genetic algorithm

Water flooding is one of the most important techniques of improved oil recovery. However, two major problems, loss of injected water to the aquifer and unwanted water production, reduce the efficiency of water flooding. An improper allocation of water to injection wells usually is the main reason of these problems. In this paper, both multi-objective genetic algorithm (MOGA) optimization, which is more rapid and accurate than conventional GA, and streamline simulation with the unique advantages of determination of flow path and participation of each injection well in total field oil production, were used in order to appease the mentioned problems. All previous studies have tried to optimize the injection rates based on injection efficiencies that were defined with the application of streamline simulation, while using MOGA optimization and Pareto concept always let us select the best global solutions with regard to the other defined criterions. Final solution in MOGA optimization is a set of correct answers. So, five scenarios, including different restrictions and economic situations were introduced. Best solution was obtained and compared with the common method of water injection optimization exclusively based on improving the efficiencies of injection wells. Results show that MOGA optimization always offers the best solution and all MOGA scenarios have better proficiencies than common optimization methods. Comparison of the proposed methodology in this paper with conventional workflow shows that MOGA, in the best case, can increase total oil production up to 6.5 %, and after considering all limitations, it can increase total oil production up to 4 % and decrease the loss of water to the aquifer to about 26 % in comparison with the common workflows.

Maximizing the Oil Recovery Through Miscible Water Alternating Gas (WAG) Injection in an Iranian Oil Reservoir

In recent years there has been an increasing interest in water alternating gas (WAG) processes, both miscible and immiscible. Microscopic oil displacement and sweep efficiency of waterflooding and continuous gas injection can be improved by WAG injection. In this work, by designing various scenarios of water and gas injection, WAG injection and simultaneously water and gas injection, the recovery and residual oil saturation obtained by implementing these methods are compared to choose the appropriate method of injection. The results showed that simultaneously the water and gas injection method has the highest recovery but from economic view, WAG process is the best enhanced oil recovery method to increase the recovery. In WAG method, the values of gas oil ratio and water cut are the smallest, so in this case, operational and process facilities problems and their costs are the minimum.

An Experimental Study of CO2-low Salinity Water Alternating Gas Injection in Sandstone Heavy Oil Reservoirs

Several studies have shown that oil recovery significantly increased by low salinity water flooding (LSWF) in sandstones. However, mechanism of oil recovery improvement is still controversial. CO2 that develops buffer in presence of water is expected as a deterrent factor in LSWF efficiency based on mechanism of IFT reduction due to pH uprising. No bright evidence in literature supports this idea. Here, a set of core floods including a pair of CO2 WAG and a pair of water injection tests are conducted and, the efficiency of LSWF and high salinity water flooding (HSWF) were compared for each pair. HSWF was followed by LSWF in tertiary mode. Results showed that not only CO2 does not deteriorate LSWF recovery efficiency, but also improves recovery. Since CO2-low salinity WAG showed best performance among types by constant pore volume injected. Positive results in both secondary and tertiary modes with Kaolinite free samples used here showed that Kaolinite release is not the critical phenomenon in LSWF brisk performance. Also different pressure behaviour of CO2 WAG processes in comparison with reported behaviour of LSWF proves that LSWF performance may not depend on how pressure changes through flooding.

Performances of Different Recovery Methods for Orinoco Belt Heavy Oil after Solution Gas Drive

Although foamy oil can improve the performance of solution gas drive in heavy oil, only about 5–15% original oil in place (OOIP) can be recovered under primary production. In this study, a series of micromodel flood experiments and sandpack flood tests were performed to evaluate the performances of water flooding, surfactant flooding, gas flooding, and foam flooding for enhancing the recovery of Orinoco Belt heavy oil after solution gas drive. Water flooding tests show that the sweep efficiency of water flooding was low as a result of the adverse mobility ratio caused by gas bubbles dispersed in the oil; about 10.57% OOIP was obtained in the sandpack study. Surfactant flooding tests indicate that the penetration of the surfactant solution into the heavy oil and the subsequent formation of gas bubbles and emulsified oil droplets in surfactant solution could reduce the mobility of water phase, thereby improving sweep efficiency, and oil recovery of 15.09% OOIP was recovered in the sandpack. Because of the v...

Improvement of Water Flooding Efficiency Using Mixed Culture of Microorganisms in Heterogeneous Micro-models

One of the possible methods for reducing unwanted problem of reservoir heterogeneity in flooding processes is the application of microbial slugs for bioplugging of high permeable zones. Objective of this research is visualization of potential of mixed-culture microorganisms as bioplugging agents for improving the efficiency of water flooding in two different heterogeneous micro-models: a glass bead and an inventive etched one. In both micro-models, water flooding removed the oil in high permeable zones while it had little effect on the oil in low permeable areas. Injection of a slug, containing a mixed culture of oil degrading microorganisms was done in glass bead micro-model. The etched micro-model was used to investigate the effect of in situ microbial growth and subsequent water flooding. In both cases the microbial treatment improved the oil recovery in comparison with water flooding in low permeable zone considerably. The results of this study showed that mixed-culture microorganisms have an acceptable potential for bioplugging of high permeable layers of heterogeneous porous media.

Об эффективности заводнения нефтяных залежей в турнейских отложениях (на примере объектов разработки ЗАО «ТАТЕХ»)

Об эффективности заводнения нефтяных залежей в турнейских отложениях (на примере объектов разработки ЗАО «ТАТЕХ»)

The impact of wettability and connectivity on relative permeability in carbonates: A pore network modeling analysis

We use pore network modeling to study the impact of wettability and connectivity on waterflood relative permeability for a set of six carbonate samples. Four quarry samples are studied, Indiana, Portland, Guiting, and Mount Gambier, along with two subsurface samples obtained from a deep saline Middle Eastern aquifer. The pore space is imaged in three dimensions using X‐ray microtomography at a resolution of a few microns. The images are segmented into pore and solid, and a topologically representative network of pores and throats is extracted from these images. We then simulate quasi‐static displacement in the networks. We represent mixed‐wet behavior by varying the oil‐wet fraction of the pore space. The relative permeability is strongly dependent on both the wettability and the average coordination number of the network. We show that traditional measures of wettability based on the point where the relative permeability curves cross are not reliable. Good agreement is found between our calculations and measurements of relative permeability on carbonates in the literature. This work helps establish a library of benchmark samples for multiphase flow and transport computations. The implications of the results for field‐scale displacement mechanisms are discussed, and the efficiency of waterflooding as an oil recovery process in carbonate reservoirs is assessed depending on the wettability and pore space connectivity.

Effects of Brine Composition on the Adsorption of Benzoic Acid on Calcium Carbonate

Most carbonate formations in nature are oil-wet after organic acids have been adsorbed on the grain surface, which lowers the efficiency of water flooding in the carbonate formations. It has been f...

The Study of the Oil Unit Connectivity for Microscopic Displacement Efficiency by CT Scan

In this paper, the main factors that affect the displacement efficiency were experimental studied by means of the physical cylinder model filled with sand, based on the high efficiency of oil displacing water in the process of hydrocarbon accumulation. After eliminating of some factors that affect displacement efficiency, such as viscosity ratio, wettability and reservoir heterogeneity and so on, the research founds that the crude oil unit connectivity, that is continuity of displaced phase, has a significant impact on the displacement efficiency. The experimental results show that the crude oil unit connectivity is more than wettability, and not less than viscosity, as the factors of the impact of displacement efficiency. If the crude oil unit connectivity is serious damaged, even if the wettability of reservoir rocks was changed by improving the viscosity of injected water, its effect of enhanced oil recovery should not be obvious. In fact, this is main reason that the effect of current the EOR method such as polymer flooding, surfactant flooding and stuff was not obvious. It is expected that the research results will be useful in the displacement efficiency of waterflooding that is controlled by the crude oil unit connectivity.

Improve Waterflood Efficiency by Film Treatment Technology

In the process of reservoir water-flooding development, the injected water of sodium sulfate type and calcium, barium and strontium ion in high salinity formation water combine to form slightly-soluble sulfate scale, result in low efficiency of water injection system and reduction of water-flooding swept volume. In view of above problems, nanofiltration (NF) will be a main driver in injection water treatment. It removes SO4 2- in injected water, reduces scale ion content from the source, achieves the purpose of scale inhibition and control, and increases water-flooding efficiency. Lab and field trials indicate that the NF treatment has a favorable result. The removal rate of SO4 2- reaches 85.0%, scale inhibition efficiency is 80.2% and the injection profile of injected well increases 1.95m. The study creates a new way for preventing and treating sulfate scale (especially strontium sulfates scaling), increasing waterflood sweep efficiency and improving injection system efficiency.

Predicting and optimising the mature Windalia waterflood based on a capacitance-resistance model (CRM)

Waterflood development drilling of the Windalia reservoir on Barrow Island at 40-acre spacing started in 1968, using five-spot and nine-spot inverted drive flood patterns. There was a general conversion to line drive in mid-1970 with various infill and realignment projects. The field comprises more than 220 active injectors and 400 producers. The reservoir is geologically complex, with low permeability and significant heterogeneity. Historically, empirical techniques and fractional flow models were used for forecasting, but these approaches have many inherent limitations; for example, they do not provide individual well performance and they are not sensitive to changes in operating conditions. More recently, a capacitance-resistance model (CRM) that uses historical injection and production data has been used to establish long-term behaviours between water injection and oil production wells, including inter-well connectivity, delay time constants and productivity indices. The evaluation of these behaviours allows direct quantification of waterflood efficiency at well-to-well level and improves identification of opportunities for changing injection patterns and prioritisation of operations and well workovers. Optimisation and forecasting of the Windalia waterflood is performed by maximising cumulative oil production by reallocating the available field wide injection water and evaluating individual injection wells target rates. Numerous optimisation scenarios were built into the models to account for the impact of changing operating conditions such as water availability and aging of wells and processing facilities. CRM is robust and is appropriate for simultaneous optimisation of well rates in a field where water injection and oil production wells are shut-in frequently. The PowerPoint presentation is not available to APPEA.

A Streamline-Based Model of Wuliwan Oil Field Injecting Polymer Microspheres to Enhance Sweep Efficiency of Water Flooding

Polymer microsphere is a deep profile control agent which has been developed in recent years. Microsphere’s excellently elastic property makes it possible to be injected, or to penetrate deep into formation, and plug high permeable layers. Many laboratory investigations have been carried out on polymer microspheres by researchers, and field tests also have been done in some oilfields. The laboratory and field test results show that polymer microspheres can plug pore throats effectively, decrease permeability of high permeable channels, thus force injected water to change it’s direction and enhance water-flood sweep efficiency. In this paper, based on the mechanisms of profile modifying and plugging of polymer microsphere, Streamline models have been build abstractly to simulate the profile controlling progress of polymer microspheres, observe the transformation of streamline field, and analyze its impact on the pressure of water injection wells and performance of oil wells. In the end, the mechanisms of profile modifying and plugging of polymer microspheres have been interpreted based on the streamline field.

Study of Alkaline/Polymer Flooding for Heavy-Oil Recovery Using Channeled Sandpacks

Summary For heavy oils with viscosities ranging from 1000 to 10 000 mPa·s in western Canada, primary production and waterflood together can recover only 8–15% of original oil in place (OOIP) at their economic limits because of the adverse mobility ratio, severe water channeling, low reservoir pressure, and formation voidage. These heavy oils usually have a relatively high content of acids that can react with alkalis to form in-situ surfactants. The loosely consolidated sandstone formations in which these oils are deposited are characterized by high porosity, high permeability, and low reservoir temperature. These reservoir conditions are favorable for polymer application. Therefore, there is a potential to improve waterflood in these reservoirs by applying alkaline/polymer (A/P) flooding. This paper presents the results of a laboratory study of A/P flooding for heavy-oil recovery, including viscosity measurements, flood tests conducted in channeled sandpacks, residual-resistance-factor (FRR) determination, and residual-oil-distribution tests. A heavy oil with a viscosity of 1,202 cp and an acid number of 1.07 (mg of KOH/g of oil) and produced brine collected from a heavy-oil reservoir in Alberta are used in this study. We found that the distribution of the injected chemical solution within the high-permeability channels leads to the diversion of the subsequently injected chemical solution to low-permeability zones with higher oil saturation because of the formation of blockage in the channel zones. Consequently, pressure buildup during chemical-slug injection is the key to the improvement of displacement efficiency. Flood tests also show that A/P flooding is more efficient than either alkaline flooding or polymer flooding. The optimal formulation for the heavy oil used in this study is 0.4% NaOH + 0.2% Na2CO3 + 1000 mg/L polymer, with a tertiary oil recovery of 25–30% of OOIP above that from waterflooding. Analysis of the results of the residual-oil distributions in the channeled sandpacks at the end of A/P flooding show that A/P flooding can effectively improve the sweep efficiency of waterflooding for the heavy oil.

Study and Application on Reutilization Technology of Residual Polymer After Polymer Flooding

There is a large amount of residual polymer existing in the forms of solution, adsorption, and entrapment in formation after polymer flooding. Then the water cut ascends quickly along high permeable channels when displacing water. In order to improve sweep efficiency of water flooding and use residual polymer effectively in formation, the reutilization technology of residual polymer in formation is proposed and developed. When the reutilization agents (including a flocculating agent and fixed agent) are injected, they react with residual polymer to form floc units and cross-linking units that could block high permeability channels and control cross flow. As a result, the sweep efficiency of water flooding and oil recovery could be enhanced. In this article, the optimized flocculating agent is selected through suspension experiments and the fixed effect for polymer is studied in sand pack core models, and the residual resistance factor is used as the evaluation criterion. The experiments show that solid particles can be used as a flocculating agent and the optimal flocculating agent is stabilized sodium clay; the cross-linking agents can be used as a fixed agent and the optimal fixed agent is selected depending on formation temperature and the salinity. This technology has been successfully applied in Henan oilfield, Shengli oilfield, and Daqing oilfield. The water cut and produced polymer concentration decreases dramatically and oil production increases obviously. This technology, which belongs to quaternary oil recovery technology, is a preferred improved oil recovery technology after polymer flooding and has a broad application prospect.

Property Study on Novel Waterflood Conformance Control Gels

In order to improve the sweep efficiency of water flooding in matured oilfield, soft moveable gels (SMG) are developed. The new types of SMG are made of novel, expandable particulate materials. The gels are preformed, stable, size controlled, non-toxic and can reduce water permeability without affecting oil permeability significantly. In this paper, some relevant laboratory methods are carried out for the determination of their main characteristics, including the displacement mechanism, the physio-chemical properties, moblility in porous media and the adjustment of permeability. Furthermore, the properties in bottles and behavior in porous media have also been investigated. The results shows that: 1)the swelling times of SMG are approximately 10, 2)SMG can remarkably improve the efficiency of water flooding, 3)remaining oil startup in low permeability formation, multistage fluid diverting and deep profile control are the main oil displacement mechanisms, 4）the new promising gel system of SMG have extensive application prospects in deep water shutoff and conformance control.

In-depth Profile Control Technologies in China—A Review of the State of the Art

In the process of waterflooding and polymer flooding, the oil displacement efficiency is poor because of the heterogeneity of reservoirs, the conventional profile control and water shutoff technology can no longer satisfy constantly production demand. So, in-depth profile control technology has been developed in recent years, and an obvious effect is obtained in improving development effects of waterflooding and polymer flooding in high water-cut stage. In this article, in-depth profile control technology is widely analyzed, and a development tendency of this technology is proposed; that is, a complete study of in-depth profile control and polymer flooding should be developed based on the sufficient understanding of reservoir status, advantage channels should be controlled and fluids diverted, and the oil displacement efficiency of waterflooding and polymer flooding for high water-cut stage could be improved.

Necessity and feasibility of improving the residual resistance factor of polymer flooding in heavy oil reservoirs

The efficiency of water flooding in heavy oil reservoirs would be improved by increasing the viscosity of the displacing phase, but the sweep efficiency is not of significance due to the low mobility of the vicious oil. On the basis of mobility control theory, increasing the residual resistance factor not only reduces the water-oil mobility ratio but also decreases the requirement for viscosity enhancement of the polymer solution. The residual resistance factor caused by hydrophobic associating polymer solution is higher than that caused by polyacrylamide solution in brine containing high concentrations of calcium and magnesium ions. The results of numerical simulations show that the polymer flooding efficiency improved by increasing the residual resistance factor is far better than that by only increasing solution viscosity. The recovery factor of heavy oil reservoirs (70 mPa·s) can be enhanced by hydrophobic associating polymer solution of high residual resistance factor (more than 3) and high effective viscosity (24 mPa·s). Therefore, increasing the residual resistance factor of the polymer solution not only decreases the requirement for the viscosity of polymer solution injected into heavy oil reservoirs but also is favorable to enhanced oil recovery during polymer flooding.

Experimental and Numerical Study of Improving Heavy Oil Recovery by Alkaline Flooding in Sandpacks

Abstract Chemical flooding has great potential for enhancing heavy oil recovery, especially for reservoirs where thermal methods are not feasible. It has been shown that the formation of emulsions during chemical flooding can effectively improve sweep efficiency and, consequently, increase heavy oil recovery. The mechanism of flow of oil-in-water (O/W) emulsion in porous media has been extensively studied and simulated using the filtration theory. Few studies have been done for the modelling of water-in-oil (W/O) emulsion flow in heavy oil reservoirs. This study experimentally investigated the effective viscosity of W/O emulsion in porous media. Alkaline flooding tests were performed in channelled sandpacks to demonstrate the effectiveness of sweep efficiency improvement by the in-situ produced W/O emulsions. High tertiary oil recoveries were obtained for all these tests. The alkaline flooding process was simulated by including the observed flow behaviour of extra resistance to water phase flow caused by the formation of W/O emulsions, as well as the adsorption of chemicals, interfacial tension reduction, and in-situ generation of W/O emulsions. These laboratory results and the developed simulation technique are proposed as an improvement to the simulation and design of the field-scale projects of chemical flooding for heavy oil recovery. Introduction Many heavy oil reservoirs in Western Canada are not suitable for steam injection techniques due to thin pay thickness. Both field and laboratory results demonstrate that waterflooding of heavy oil reservoirs can only achieve a very low oil recovery. The main causes for the poor sweep efficiency of waterflooding for these heavy oil reservoirs are very adverse mobility ratio, natural area and vertical reservoir heterogeneity and heterogeneity induced by primary production(1,2). Therefore, improving mobility ratio and blocking water flow through channels are essential for improving heavy oil recovery. The in-situ formation of emulsions during alkaline flooding has been recognized as one of the efficient methods to improve sweep efficiency for heavy oil recovery(3,4,5). The effectiveness of alkaline flooding for acidic crudes was recognized as early as in the 1920s(6). Jennings et al.(3) proposed the mechanism of emulsification and entrapment for alkaline flooding. They carried out caustic flooding tests using a heavy oil. Their results showed that the in-situ produced O/W emulsions tended to plug water fingering and channels, resulting in improved sweep efficiency. Johnson(7) summarized possible mechanisms of alkaline flooding to improve oil recovery: dispersion and entrainment, wettability reversal, and emulsification and entrapment. The formation of W/O emulsions was also observed as a mechanism of improving oil recovery(8,9).

Elastic turbulence under polymer solutions flow in microchannels with variable cross-section

The flow of a dilute solution of a high-molecular polymer in channels of variable cross-section at low Reynolds numbers exhibits elastic turbulence accompanied by an increase of the hydraulic resistance by several times in comparison with water although the viscosity of the solution is only 10-20% higher than the viscosity of water. This phenomenon was studied in models of glass balls by James and McLaren (1978), in channels of variable cross-section by V.N. Kalashnikov (1987). In described experiments the flow field was visualized in the flat and volumetric models of variable cross-section and in the complex channel structure representing the core section of the oil reservoir. An increase of hydraulic resistance was observed in all types of flow at low Reynolds numbers, pulsations in a flow with a frequency of 5-10 Hz were detected. Competent use of elastic turbulence will significantly increase the efficiency of waterflooding during oil production.

Study of a plugging microbial consortium using crude oil as sole carbon source

A microbial consortium named Y4 capable of producing biopolymers was isolated from petroleum-contaminated soil in the Dagang Oilfield, China. It includes four bacterial strains: Y4-1 (Paenibacillus sp.), Y4-2 (Actinomadura sp.), Y4-3 (Uncultured bacterium clone) and Y4-4 (Brevibacillus sp.). The optimal conditions for the growth of the consortium Y4 were as follows: temperature about 46 °C, pH about 7.0 and salinity about 20.0 g/L. The major metabolites were analyzed with gas chromatographymass spectrometry (GC-MS). A comparison was made between individual strains and the microbial consortium for biopolymer production in different treatment processes. The experimental results showed that the microbial consortium Y4 could produce more biopolymers than individual strains, and the reason might be attributed to the synergetic action of strains. The biopolymers were observed with optical and electron microscopes and analyzed by paper chromatography. It was found that the biopolymers produced by the microbial consortium Y4 were insoluble in water and were of reticular structure, and it was concluded that the biopolymers were cellulose. Through a series of simulation experiments with sand cores, it was found that the microbial consortium Y4 could reduce the permeability of reservoir beds, and improve the efficiency of water flooding by growing biomass and producing biopolymers. The oil recovery was enhanced by 3.5% on average. The results indicated that the consortium Y4 could be used in microbial enhanced oil recovery and play an important role in bioremediation of oil polluted environments.