Flooding Scheme Research Articles

Reservoir numerical simulation method considering time-varying relative permeability during polymer flooding process

Abstract In response to the abnormal decline in liquid production capacity during the middle and later stages of chemical flooding in Chinese offshore oil fields, in-depth analysis was conducted using reservoir engineering, dynamic analysis, and reservoir simulation methods. Because of the viscoelasticity of polymer solution, the relative permeability curve of oil/water during polymer flooding is different from that during water flooding, including the minimum mobile water saturation and residual oil saturation. In this study, an interpolation coefficient ‘f’ related to polymer solution concentration was firstly proposed for simplicity. Then, reservoir numerical simulation with the self-developed simulator ‘SIMFAST’ were conducted to investigate the influence of the interpolation coefficient ‘f’ on the injector and producer performance and the applications in actual field production history matching. The results indicated that compared with the commercial simulators, the self-developed simulator with the interpolation factor could more reliably describe the characteristic of the injected polymer solution in controlling water cut rise, and more efficiently simplify the combination of parameters on relative permeability curves during polymer flooding in offshore oilfields. Finally, above reservoir simulation method considering the change of the relative permeability curves during chemical flooding, was successfully conducted in the production history matching in J oilfield in Bohai Bay China, in terms of oil rate & water cut parameters. The research results give an efficient method to investigate the fluid seepage behaviour variation and its influence on oil rate and water cut during polymer flooding in China offshore reservoirs, which offers very useful technical support for the accurate design of chemical flooding schemes.

Does flood risk funding protect the most vulnerable? A case study of England

Not only has the frequency and severity of flooding increased under climate change, but which communities are at-risk and how those risks are distributed within communities has changed too. This realisation points to an important interplay between exposure (risk) and social vulnerability. Who is vulnerable? Answering this question is far from straightforward as different vulnerability indicators identify different groups across different scales. This paper addresses this issue. Using the empirical case of England, the spatial distribution of flood risk at different administrative scales is analysed in relation to the Environment Agency (EA) allocation of flood funding between 2015 and 2021. We find that Upper-tier Local Authority Districts with higher levels of both flood risk and social vulnerability received more funding in the period considered. Yet, that is not the scale at which flood scheme funding decisions are made. Flood schemes are decided at the local level, but funding data for smaller administrative scales is not available. Different understandings of vulnerability, the Modifiable Areal Unit Problem (MAUP), and issues around data transparency and availability in flood risk management, need to be urgently addressed.

Optimization of CO2 EOR and geological sequestration in high-water cut oil reservoirs

In terms of the collaborative optimization of CO2 flooding for Enhanced Oil Recovery (EOR) and CO2 sequestration, previous studies have co-optimized both cumulative oil production and CO2 sequestration by various algorithms. However, these solutions fail to optimize the CO2 injection schemes for high-water cut oil reservoirs. This paper presents an optimization methodology for CO2 flooding and sequestration in high-water cut oil reservoirs. The production optimization was carried out by adjusting the injection and production rate. To solve the proposed objective functions, the simultaneous perturbation stochastic approximation (SPSA) algorithm is applied in this paper, and the CMG-GEM module is utilized to simulate the reservoir production performance. A typical high-water cut reservoir in the Shengli oilfield was used to verify the feasibility of the presented methodology. In this paper, the production performance and net present value (NPV) for continuous gas injection under different water cuts were analyzed. The optimal timing of transforming from water flooding to gas displacement for the high-water cut reservoir was optimized. In addition, the optimal water–gas ratios for Water-Alternating-Gas (WAG) flooding were determined. The sensitivity of NPV to gas injection price and carbon subsidy was analyzed. The results show that when the gas price is 0.178 $/m3 and the carbon subsidy is 0.0169 $/m3, the optimal timing of transforming from water flooding to gas injection should be earlier than the time when the water cut is 0.82. Through the combination of NPV, cumulative oil production rate, and CO2 sequestration volume for WAG flooding, the optimal WAG ratio should be 1:2. The presented method in this paper considers various economic indicators and can optimize CO2 flooding and sequestration in high-water cut oil reservoirs efficiently, which can provide some guidance for the design of CO2 flooding schemes in high-water cut oil reservoirs.

Performance of geographically restricted flooding for emergency alert applications

ABSTRACT For various emergency alert applications like a disaster, accident, or hazard alert, geographically restricted flooding can prove to be extremely vital, especially considering the absence of any fixed infrastructure and the alert having spatio-temporal boundaries. Among various geographically restricted flooding schemes, in this work, a scheme called floating content is considered. Floating content uses geographically restricted flooding to make a piece of information available within a certain geographic area. In this work, an Android-based emergency alert application is deployed and tested in two different environments. One environment spans over a small geographic area (an office), while the other environment is a university campus. The application is used to log the mobility patterns of users for both the considered environments, and these mobility patterns are thoroughly analyzed. Then the performance of the considered emergency alert application in terms of key performance metrics is evaluated for both of the considered settings by considering single and multiple seeders (alert generators). Moreover, for the prediction of performance, two different analytical models are also evaluated, and the results of these models are compared with the ones obtained from real-world experiments, showing the performance limits of geographically restricted flooding.

Design of the Position of the Blocking Material in a Water-Flooded High-Permeability Interlayer of an Oil Reservoir for a Five-Spot Flooding Scheme

Design of the Position of the Blocking Material in a Water-Flooded High-Permeability Interlayer of an Oil Reservoir for a Five-Spot Flooding Scheme

The Micro-Flow Mechanism of Polymer Flooding in Dual Heterogeneous Reservoirs Considering the Wettability.

There have been some studies conducted about the single factor viscoelasticity of polymer solution or wettability effect on the micro-flow mechanism of polymer flooding. In this paper, the flow mechanism of polymer solution in dual heterogeneous reservoir considering the wettability and gravity was studied. The influences of wettability and rock particle shape on flow characteristics were studied based on the characteristics of saturation and pressure distribution. Compared with the simulation results of polymer flooding in three different rock particle shapes porous media, the oil displacement efficiency of the circular particle model is the highest at 91.57%, which is 3.34% and 11.48% higher than that in the hexagonal and diamond models, respectively. The influence of wettability was studied by the circular particle model. The oil displacement efficiency under water-wet conditions was higher than that under oil-wet conditions. The displacement process considering gravity was affected by the crossflow caused by gravity and viscous force, and the micro-oil displacement efficiency was 9.87% lower than that of non-gravity. Considering the wettability, vertical crossflow will be formed. The oil displacement efficiency under water-wet conditions was 3.9% higher than in oil-wet conditions. The research results can not only expand and enrich the micro-flow mechanism of viscoelastic polymer solution, but also provide reference and guidance for polymer flooding scheme design.

On an Effect of a Simple and Energy-Efficient Flooding Scheme for Multi-hop Full-Duplex Communications

On an Effect of a Simple and Energy-Efficient Flooding Scheme for Multi-hop Full-Duplex Communications

Proposal of Coastal Flooding Scheme Using Smart Balloon Powered by Wind Turbine Generator

Proposal of Coastal Flooding Scheme Using Smart Balloon Powered by Wind Turbine Generator

Study on the Oil Displacement Mechanism of Different SP Binary Flooding Schemes for a Conglomerate Reservoir Based on a Microfluidic Model

The objective of this study is to elucidate the oil displacement mechanism of different surfactant- polymer (SP) binary flooding systems in conglomerate reservoirs and to determine the optimal scheme. On the basis of water flooding, the microfluidic model is used to reveal the oil–water flow law of different SP binary flooding systems and then determine the oil displacement mechanism. The experimental results show that the SP binary flooding solution can enhance oil recovery by enhancing the sweep volume; the oil displacement efficiency of the echelon viscosity reducing (EVR) scheme is better than that of the echelon viscosity increasing (EVI) scheme and the single constant viscosity (SCV) scheme. For the EVR scheme, the oil displacement system with a high molecular weight and high concentration preferentially enters the large-scale pore-throat of the reservoir. After a period of time, a high resistance area can be formed in the large-scale pore-throat along the main flow direction of water flooding so as to reduce the mobility of the displacement solution in the dominant seepage channel and decrease the frequency of water channeling and then improve the oil displacement efficiency in the large-scale pore-throat to enhance the oil recovery. When the molecular weight and viscosity of the SP binary solution are both reduced, the oil displacement solution with a low molecular weight and low concentration mainly produces low-permeability layers by adjusting the displacement path to enhance the sweep volume in the small-scale pore-throat. Through the reconstruction of a pressure field and the redistribution of seepage paths of chemical micelles with different sizes, the displacement mechanism of crude oil in pores and throats shows a changing trend from large-scale pore-throats to small-scale pore-throats. After the viscosity reduction of the SP solution, the lower production limit of the pore-throat radius is reduced to 1 μm and the sweep volume of the small-scale pore-throat is enhanced. The stepwise production of crude oil in pores and throats with different radii is realized so as to enhance the oil recovery of the conglomerate reservoir. Finally, a new model of SP binary flooding suitable for “echelon injection and stepwise production” of a conglomerate reservoir is established innovatively.

Study on Compatibility between Complex Mode Micropore Structure and Polymer Solution of Different Formulation for Conglomerate Reservoir

In this paper, the conglomerate reservoir is selected as the object to investigate the micropore structure and the compatibility of polymer solutions. Firstly, the characteristics of complex mode pore structure are analyzed based on casting thin sections, scanning electron microscope, and capillary pressure curve. Then the conglomerate reservoir is divided into five types by use of the K-means clustering algorithm, and the differences in micropore structure among the different reservoir types are also clarified. Secondly, the dynamic light scattering technology is used to directly determine the hydrodynamic diameter of different polymer formulations. As the polymer molecular weight increases, the average hydrodynamic diameter becomes larger, and with the same polymer molecular weight, the average hydrodynamic diameter becomes gradually larger as the solution concentration increases. Based on the above research results, the matching relationship between five reservoir types and polymer solutions is determined through laboratory experiments. The experimental results show that when the polymer molecular weight is determined, the volume of pore volume that can be effectively swept by polymer hydration molecules gradually decreases as the concentration of the solution increases. When the polymer molecular weight and its concentration are both determined, the pore volume of effective displacement of polymer-hydrated molecules also gradually reduces with becoming worse reservoir pore structure. The scope of application of different polymer formulations becomes progressively smaller as the microscopic pore structure of type I to type V reservoirs becomes deteriorated. The compatibility between the micropore structure of different conglomerate reservoir types and polymer solution is determined to provide the geological basis for the reasonable formulation of the polymer flooding scheme.

Application of CCUS in India: Designing a CO2 EOR and storage pilot in a mature field

Numerous mature oil and gas reservoirs around the world, along with added financial benefit, present a tremendous benefit of CO2 EOR and storage, especially in the regions where tax benefits and policies related to the CCS is limited. This work presents the first effort of CO2 EOR and storage in a mature oil field in India through a comprehensive application of laboratory study, reservoir static modeling, dynamic simulation, pilot design, and techno-economic sensitivity analyses. Through this case study, the technical feasibility of CO2 EOR and associated storage was assured for the first time through a novel approach of combining various subsurface and surface data with laboratory analyses. Almost no analog was available for CCUS on the same-age rock from a young thrust belt setting. The various vintages of core to seismic scale data posed a great challenge for effective integration. The solution approach to these issues included combining flow physics, fluid chemistry, geological concepts and digital modeling with practical engineering data analyses. Temporal change of oil composition in this reservoir due to the long production history had created some challenges for determination of CO2 miscibility. It was estimated through the lab study and modeling that the miscibility can be achieved near 3000 psi due to its altered oil composition resulted by years of production. To arrest the reservoir pressure decline, a pre-EOR water injection was identified as an immediately need to re-pressurize the reservoir and achieve miscibility of injected CO2. Comprehensive analysis of various subsurface and surface data integrating geoscience and engineering techniques have allowed for a consistent and applicable 3D description of reservoir, which was critical to identify suitable areas with appropriate remaining oil saturation, chemistry, and reservoir pressure. The history matching-calibrated-simulation model was utilized to evaluate the performance of various development scenarios of the identified area. Specifically, CO2 injection in a sector of geological model was performed using Todd-Longstaff miscible flood scheme. Upon comparing the proposed scenarios, a CO2 injection pilot in Pattern-1 was identified, with one injector and three producers over ∼60 acres area. This pilot uses 150 Metric Ton/day (MT/D) of CO2 captured and processed from an existing facility and transported about 70 km to the field location. The CO2 will be injected continuously into this pilot area for 5 years, and the well switches back to water injection afterward. Around 1.1 MMSTB incremental oil will be recovered in next 10 years, corresponding to 11.7% of OOIP in the flooded area. Up to 268,275 MT of CO2 will be sequestered in the reservoir. The learnings from this first ever study of its kind in India set the benchmark for data analysis, integration, and case specific approaches. The success and knowledge base from this endeavor will tremendously help and encourage further expansion of CCUS activities in India.

Experimental study on the enhanced ultra-heavy oil recovery using an oil-soluble viscosity reducer and CO2 assisted steam flooding

Ultra-heavy oil resources have gained extensive attention due to their abundant reserves and the shortage of conventional hydrocarbon resources. In this work, we investigate the feasibility of recovering ultra-heavy oil resources using an oil-soluble dissolver, i.e., a type of viscosity reducer, and CO2 assisted steam flooding (DCS flooding) by studying the impact of those agents on oil properties and EOR performance of this approach. Firstly, the effects of steam, CO2, and the oil-soluble dissolver on the oil properties are investigated by comparing the variations in oil viscosity, SARA (saturates, aromatics, resins, and asphaltenes) compositions, asphaltenes structural parameters, and asphaltenes morphology. Then, the feasibility of DCS flooding in improving ultra-heavy oil recovery is investigated by comparing its performance in core flooding experiments with steam flooding and CO2 assisted steam flooding schemes. Next, the sensitivity of various agents in DCS flooding is analyzed by conducting DCS flooding experiments with different amounts and concentrations of those agents. Finally, the chemical components of the produced fluids are analyzed to further understand the dynamic EOR mechanisms of the DCS flooding. The results demonstrate that the oil-soluble dissolver exhibits the best oil viscosity reduction (56.1%) performance through decomposing the asphaltenes of ultra-heavy oil. Meanwhile, DCS flooding presents promising performance in improving ultra-heavy oil recovery (76.78%) compared with steam flooding (59.6%) and CO2 assisted steam flooding (65.26%). Moreover, DCS flooding is also beneficial to decrease maximum steam injection pressure, control the water cut, and improve steam dryness.

Pilot Test for Nitrogen Foam Flooding in Low Permeability Reservoir

Due to the characteristics of reservoir formation, the producing level of low permeability reservoir is relatively very low. It is hard to obtain high recovery through conventional development schemes. Considering the tight matrix, complex fracture system, low production level of producers, and low recovery factor of M block in Xinjiang oilfield, it is selected for on-site pilot test of nitrogen foam flooding. Detailed flooding scheme is made and the test results are evaluated respectively both for producers and injectors. The pressure index, filling degree, and fluid injection profile are found to be all improved in injectors after injection of nitrogen foam. The oil production, water cut and liquid production file are also improved in most of the producers, with the natural decline rate in the test area become slow. Results show that nitrogen foam flooding technology can be good technical storage for enhanced oil recovery in low permeability reservoir.

An efficient fault-tolerant distributed Bayesian filter based on conservative fusion

This paper proposes a fault-tolerant distributed Bayesian filter for multi-sensor state estimation using a peer-to-peer sensor network with incoherent local estimates problems. The proposed approach uses a Gaussian mixture rather than a single Gaussian distribution to represent the fusion result, which can effectively reduce the negative impact of corrupted local estimates on the fusion results. The resulting filter performs Bayesian recursion via Gaussian mixture. To accommodate a heterogeneous sensor network, we develop a novel arithmetic average fusion employing a set of covariance-dependent weighting coefficients, where the fusion error covariance is effectively reduced in the case of fusing information with different qualities. For intersensor communication, a partial flooding scheme is investigated, in which only valid-likely Gaussian components are disseminated and fused between neighbor sensors. Theoretically, it is shown that under reasonable assumptions, the presented fault-tolerant distributed estimator can guarantee local stability with the exponentially bounded estimation error in the mean square. The effectiveness and superiority of our approach are validated through both simulation and experiment scenarios.

Adaptability Study of Hot Water Chemical Flooding in Offshore Heavy Oilfields

As a new heavy oil development technology, hot water chemistry flooding has great potential in offshore heavy oil fields development. In this paper, the adaptability of hot water chemical flooding was studied based on the typical model of offshore heavy oil fields. The main controlling factors affecting the hot water chemical flooding were analyzed and evaluated by single factor analysis. The technical boundary was established for offshore heavy oil fields. In addition, the hot water chemical flooding scheme was designed by a case study of a well group oilfield D. The results indicate that crude oil viscosity and well spacing have great influences on hot water chemical flooding performance. Hot water chemical flooding is favorable when the crude oil viscosity is between 300 and 1000 mPa·s and well spacing is around 200~400 m. The hot water chemical flooding scheme of the target well group results in 40.2 × 10 4 tons of incremental oil, and 6.3% of recovery factor being enhanced, which shows strong evidence that hot water chemical flooding enables great oilfield development performance.

Molecular dynamics simulation of enhancing surfactant flooding performance by using SiO2 nanoparticles

In this study, four kinds of commonly used surfactants in oil fields, namely anionic surfactant sodium dodecyl sulfate (SDS), cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB), nonionic surfactant primary alcobol ethoxylate (AEO-9) and zwitterionic surfactant dodecyl dimethyl carboxyl betaine (BS-12), were used as the research objects. The oil–water interfacial behaviors at different concentrations were studied by molecular dynamics simulation. Then, silica (SiO2) nanoparticles were combined with surfactant to observe the influence of nanoparticles on the configuration of surfactant monolayer, and to explore the optimal conditions for the synergistic flooding scheme of these nanoparticles and surfactant. The thickness and density of the oil–water interface layer, the radial distribution function (RDF) between the surfactant head group and water molecules, the mean square displacement (MSD) of water molecules around the surfactant head group, the oil–water interfacial tension (IFT) and the surfactant interface formation energy (IFE) were investigated. Surfactant flooding performance of different types and the effect of nanoparticles on surfactants were discussed. The results show that the surfactant with different ionic types have the best concentration in reducing the oil–water interfacial tension, and the interfacial tension is significantly reduced to 7.33 mN/m after adding nano-SiO2 particles in BS-12. After kinetic equilibrium, SDS and CTAB are arranged in an approximately regular manner, non-polar groups are inserted into the oil phase, polar groups extend into the aqueous phase, the long-chain head groups of AEO-9 molecules spread and stack at the interface, and BS-12 is irregularly distributed and some molecules are immersed in the oil phase. After adding nano-SiO2 particles, SDS, BS-12 and nano-SiO2 particles can be observed mutually repulsive in the interface morphology, while CTAB, AEO-9 and nano-SiO2 particles exhibit mutual attraction.

Modeling of microflow during viscoelastic polymer flooding in heterogenous reservoirs of Daqing Oilfield

Viscoelastic polymer flooding has been extensively used in oilfield development as an enhanced oil recovery method. Understanding the microflow mechanism is necessary to promote the polymer displacement effect and design the polymer flooding scheme. Previous studies have investigated polymer flooding mechanisms, such as a favorable mobility ratio and increasing sweep efficiency; however, the elasticity effect on displacement efficiency is still unclear, particularly in a heterogeneous reservoir. Class II reservoirs, which have an effective thickness between 1 and 4 m and a permeability greater than 100 mD, have recently become the target zones of polymer flooding in the Daqing Oilfield. Class II reservoirs are subdivided into type A and B oil layers. Compared with the type A oil layer, type B has a larger permeability contrast, more severe heterogeneity, and worse connectivity. There are considerable differences between types A and B in the actual development of polymer flooding as well as between type B oil layers of different oilfield blocks. Thus, it is necessary to investigate the factors that influence the micro-oil displacement mechanism. In this study, local and global micro-pore models are established based on a computed tomography scan slice of Class II reservoir cores, and mathematical models of the viscoelastic polymer and oil two-phase flow in porous media are established. The log conformation method is used, which can effectively enhance convergence, owing to a high relaxation time inducing high non-linear of equation. The volume-of-fluid method is used to track the interface between the two phases. The governing equations are solved using the OpenFOAM platform, which is open-source software written in C++. Then, the influences of pore structure and polymer elasticity on displacement characteristics are studied. The simulation results revealed that owing to the pore structure, the micro-oil displacement efficiencies of B_GI and B_PII, which belong to the type B oil layer, are lower than that of A_SIII, which belongs to type A, by 26.8% and 10.9%, respectively. The oil displacement efficiency of a commingled production comprising B_PII and B_GI is 4.0% and 15.6% lower than that of single-layer productions of B_PII and B_GI, respectively. The oil displacement efficiency increases by 6.45% when the relaxation time increases from 0.5 to 2 s and decreases when the relaxation time increases from 2 to 10 s. Therefore, by combining the micro-oil displacement efficiency and injectivity of a high-molecular-weight polymer, the optimum relaxation time is determined to be 2 s. The obtained results are significant for the design strata of a commingled production scheme and the optimization of polymer solutions in the type B oil layer of the Daqing Oilfield.

Experimental study on constant pressure of polymer flooding in second-class reservoirs

At present, the second-class oil layer has become the main polymer flooding replacement layer in the Lamadian Oilfield. The second-class oil layer has low permeability, low connectivity and serious heterogeneity. The results of the polymer flooding laboratory experiments are quite different from the field flooding effect. Polysystem design provides better guidance. Based on theoretical and field data analysis, this paper adopts constant pressure injection method. After the experimental injection fluid is seepage through a 1.5m long core, the core flooding experiment is carried out, that is, the problem of excessive pressure rise in polymer flooding is controlled, so that the injection fluid is closer to the oil layer. state of the injected system. The constant pressure polymer flooding experiment was used to establish the matching relationship between the polymer system and oil layers with different permeability, which effectively guided the design of the on-site polymer injection system. At present, indoor polymer flooding core experiments generally adopt the constant speed mode, without controlling the injection pressure. However, due to the influence of permeability, connectivity and other factors, the injection pressure increases greatly, and the reservoir water absorption is difficult, which leads to a great difference between the experimental results and the field effect. In order to make the indoor core experiment closer to the actual field injection state and better guide the design of polymer flooding scheme, it is urgent to optimize and improve the experimental method.

Robust CPHD Fusion for Distributed Multitarget Tracking Using Asynchronous Sensors

This paper studies the multitarget tracking problem based on an asynchronous network of sensors with different sampling rates, where each sensor runs a cardinalized probability hypothesis density (CPHD) filter. To fuse the filter estimates obtained at different sensors conditioned on asynchronous measurements, an arithmetic averaging approach is recursively carried out in a timely manner according to the network-wide sampling time sequence. The intersensor communication is conducted by a so-called partial flooding scheme, in which either cardinality distributions or intensity functions pertinent to local posteriors are disseminated among sensors. The fused results may not feedback to the filter, which will avoid communication delay to the local filters cased by intersensor fusion at the expense of reduced information gain. Furthermore, an extension of the proposed multi-sensor CPHD filter based on the bootstrap filtering algorithm is given to accommodate unknown clutter rate and detection profile. Numerical simulations are performed to test the proposed approaches.

Flood season segmentation and scheme optimization in the Yellow River

Abstract River flood season segmentation is a significant measure for flood prevention. This study aims to carry out theoretical analysis on flood season segmentation methods and put forward a framework for proper flood season segmentation through comparison between different segmentation methods. The studied framework consists of a Fisher optimal partition method for determining the optimum numbers of the sub-seasons, an ensemble approach for segmenting a defined flood season, and a nonparametric bootstrap combined with a fuzzy optimum selection method (NPB-FOS) for testing the rationality of the flood season staging schemes. The present research findings show that different methods could result in different staging schemes. It is proved through rational analysis that the staging scheme obtained by probability change point (PCP) is superior to others. The flood season of the downstream reach of the Yellow River can be segmented into three sub-seasons, i.e. early flood season (01 June–20 July), main flood season (21 July–28 September), and late flood season (29 September–08 November). The segmentation results of the flood season should play an active role in flood prevention.