Influence of pore structure heterogeneity on channeling channels during hot water flooding in heavy oil reservoir based on CT scanning

Hot water flooding is an effective way to develop heavy oil reservoirs.However,local channeling channels may form,possibly leading to a low thermal utilization efficiency and high water cut in the reservoir.The pore structure heterogeneity is an important factor in forming these channels.This study proposes a method that mixes quartz sand with different particle sizes to prepare weakly heterogeneous and strongly heterogeneous models through which hot water flooding experiments are conducted.During the experiments,computer tomography(CT)scanning identifies the pore structure and micro remaining oil saturation distribution to analyze the influence of the pore structure heterogeneity on the channeling channels.The oil saturation reduction and average pore size are divided into three levels to quantitatively describe the relationship between the channeling channel distribution and pore structure heterogeneity.The zone where oil saturation reduction exceeds 20%is defined as a channeling channel.The scanning area is divided into 180 equally sized zones based on the CT scanning images,and threedimensional(3D)distributions of the channeling channels are developed.Four micro remaining oil distribution patterns are proposed,and the morphology characteristics of micro remaining oil inside and outside the channeling channels are analyzed.The results show that hot water flooding is more balanced in the weakly heterogeneous model,and the oil saturation decreases by more than 20%in most zones without narrow channeling channels forming.In the strongly heterogeneous model,hot water flooding is unbalanced,and three narrow channeling channels of different lengths form.In the weakly heterogeneous model,the oil saturation reduction is greater in zones with larger pores.The distribution range of the average pore size is larger in the strongly heterogeneous model.The network remaining oil inside the channeling channels is less than outside the channeling channels,and the hot water converts the network remaining oil into cluster,film,and droplet remaining oil.

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.

Low gas-liquid ratio foam flooding for conventional heavy oil

The recovery of heavy oil by water flooding is 10% lower than that of conventional crude oil, so enhanced oil recovery （EOR） is of great significance for heavy oil. In this paper, foam flooding with a gas-liquid ratio （GLR） of 0.2：1 for the Zhuangxi heavy oil （325 mPa.s at 55 ℃） was performed on cores, sand packs and plate model. In sand pack tests, polymer enhanced foam flooding increased oil recovery by 39.8%, which was 11.4% higher than that for alkali/surfactant/polymer （ASP） flooding under the same conditions. Polymer enhanced foam flooding in plate models shows that the low GLR foam flooding increased oil recovery by about 30%, even when the extended water flooding was finished at 90% water cut. Moreover, it was discovered by microscopy that foam was more stable in heavy oil than in light oil. These results confirm that low GLR foam flooding is a promising technology for displacing conventional heavy oil.

Steam Flooding after Steam Soak in Heavy Oil Reservoirs through Extended-reach Horizontal Wells

This paper presents a new development scheme of simultaneous injection and production in a single horizontal well drilled for developing small block reservoirs or offshore reservoirs. It is possible to set special packers within the long completion horizontal interval to establish an injection zone and a production zone. This method can also be used in steam flooding after steam soak through a horizontal well. Simulation results showed that it was desirable to start steam flooding after six steam soaking cycles and at this time the oil/steam ratio was 0.25 and oil recovery efficiency was 23.48%. Steam flooding performance was affected by separation interval and steam injection rate. Reservoir numerical simulation indicated that maximum oil recovery would be achieved at a separation section of 40-50 m at steam injection rate of 100-180 t/d; and the larger the steam injection rate, the greater the water cut and pressure difference between injection zone and production zone. A steam injection rate of 120 t/d was suitable for steam flooding under practical injection-production conditions. All the results could be useful for the guidance of steam flooding projects.

Investigation of feasibility of alkali-cosolvent flooding in heavy oil reservoirs

Cold production is a challenge in the case of heavy oil because of its high viscosity and poor fluidity in reservoir conditions.Alkali-cosolvent-polymer flooding is a type of microemulsion flooding with low costs and possible potential for heavy oil reservoirs.However,the addition of polymer may cause problems with injection in the case of highly viscous oil.Hence,in this study the feasibility of alkali-cosolvent(AC)flooding in heavy oil reservoirs was investigated via several groups of experiments.The interfacial tension between various AC formulations and heavy crude oil was measured to select appropriate formulations.Phase behavior tests were performed to determine the most appropriate formulation and conditions for the generation of a microemulsion.Sandpack flooding experiments were carried out to investigate the displacement efficiency of the selected Ac formulation.The results showed that the interfacial tension between an AC formulation and heavy oil could be reduced to below 1o-3 mN/m but differed greatly between different types of cosolvent.A butanol random polyether series displayed good performance in reducing the water-oil interfacial tension,which made it possible to form a Type Il microemulsion in reservoir conditions.According to the results of the phase behavior tests,the optimal salinity for different formulations with four cosolvent concentrations(0.5 wt%,1 wt%,2 wt%,and 3 wt%)was 4000,8000,14000,and 20000 ppm,respectively.The results of rheological measurements showed that Type Ill microemulsion had a viscosity that was ten times that of water.The results of sandpack flooding experiments showed that,in comparison with waterflooding,the injection of a certain Ac formulation slug could reduce the injection pressure.The pressure gradient during waterflooding and AC flooding was around 870 and 30-57 kPa/m,respectively.With the addition of an AC slug,the displacement efficiency was 30%-50%higher than in the case of waterflooding.

Characteristics Analysis on Short-Time Heavy Rainfall during the Flood Season in Shanxi Province, China

In order to provide a reference for the correct forecasting of short-term heavy rainfall and better disaster prevention and mitigation services in Shanxi Province, China, it is very important to carry out systematic research on short-term heavy precipitation events in Shanxi Province. Based on hourly precipitation data during the flood season (May to September) from 109 meteorological stations in Shanxi, China in 1980-2015, the temporal and spatial variation characteristics of short-time heavy rainfall during the flood season are analyzed by using wavelet analysis and Mann-Kendall test. The results show that the short-time heavy rainfall in the flood season in Shanxi Province is mainly at the grade of 20 - 30 mm/h, with an average of 97 stations having short-time heavy rainfall each year, accounting for 89% of the total stations. The short-time heavy rainfall mainly concentrated in July and August, and the maximal rain intensity in history appeared at 23 - 24 on June 17, 1991 in Yongji, Shanxi is 91.7 mm/h. During the flood season, the short-time heavy rainfalls always occur at 16 - 18 pm, and have slightly different concentrated time in different months. The main peaks of June, July and August are at 16, 17 and 18 respectively, postponed for one hour. Short-time heavy rainfall overall has the distribution that the south is more than the north and the east less than the west in Shanxi area. In the last 36 years, short-time heavy rainfall has a slight increasing trend in Shanxi, but not significant. There is a clear 4-year period of oscillation and inter-decadal variation. It has a good correlation between the total precipitation and times of short-time heavy rainfall during the flood season.

CO2 assisted steam flooding in late steam flooding in heavy oil reservoirs

To improve the oil recovery and economic efficiency in heavy oil reservoirs in late steam flooding,taking J6 Block of Xinjiang Oilfield as the research object,3D physical modeling experiments of steam flooding,CO2-foam assisted steam flooding,and CO2 assisted steam flooding under different perforation conditions are conducted,and CO2-assisted steam flooding is proposed for reservoirs in the late stage of steam flooding.The experimental results show that after adjusting the perforation in late steam flooding,the CO2 assisted steam flooding formed a lateral expansion of the steam chamber in the middle and lower parts of the injection well and a development mode for the production of overriding gravity oil drainage in the top chamber of the production well;high temperature water,oil,and CO2 formed stable low-viscosity quasi-single-phase emulsified fluid;and CO2 acted as a thermal insulation in the steam chamber at the top,reduced the steam partial pressure inside the steam chamber,and effectively improved the heat efficiency of injected steam.Based on the three-dimensional physical experiments and the developed situation of the J6 block in Xinjiang Oilfield,the CO2 assisted steam flooding for the J6 block was designed.The application showed that the CO2 assisted steam flooding made the oil vapor ratio increase from 0.12 to 0.16 by 34.0%,the oil recovery increase from 16.1%to 21.5%,and the final oil recovery goes up to 66.5%compared to steam flooding after perforation adjustment.

EXTREMELY HEAVY FLOODS AND THEIR CONTROL IN THE TAIHU LAKE REGION

Based on fieldd investigations and relevant literature, this paper expounds on the cause of the extremely heavy floods in the Taihu Lake region in 1991, compares the flood-hit areas of 1954 with those of 1991, summarizes the experience on flood control and presents some useful proposals.

Desiccation versus Re-Flooding: Heavy Metals Mobilization—Part 1

From the restoration point of view, heavy metals distribution and seasonal variation were studied in the re-flooded marshes of the Mesopotamia, southern Iraq. As part of the ecological recovery assessment of these newly inundated marshes, it is important to investigate the extend impact of 13 years of desiccation after five years of inundation on the heavy metals mobilization from the marshland downstream into the Shatt Al-Arab River and examine whether these marshlands retain their role of acting as sink of metals. The result shows significant differences between the re-flooded marshes versus the reference marsh, which indicates that desiccation cased changes in environmental variables and divided the one homogeneous system of the Mesopotamia into separated systems. In addition, the special distribution of heavy metals show that Al-Hawizeh and Al-Hammar marshlands were efficient for metals reduction, especially for Ni, while the Central marshland has the major contribution as source to metals. As a conclusion, the recovery potential of three marshlands is strongly controlled by the hydrological status of the marshland and the degree of the desiccation impact. The environmental status of the semidried marshes, Al-Souda north and Um Al-Niaaj, as well as the completely Abu Zarag dried marsh are exhibiting a positive recovery degree than the other monitored marshes in the Mesopotamia in comparison to the reference marsh.

Mechanism investigation of steam flooding heavy oil by comprehensive molecular characterization

Steam flooding is a widely used technique to enhance oil recovery of heavy oil.Thermal viscosity reduction and distillation effect are considered as two main displacement mechanisms in steam flooding process.However,the molecular composition understanding and contribution for oil production are still unclear.In this study,the composition analysis of the heavy oil was investigated in the core scale steam flooding process with the temperature from 120 to 280℃.The crude oil,produced oils and residual oils were characterized comprehensively by gas chromatography and high-resolution mass spectrometry.It is found that steam flooding preferentially extracts aromatics and remains more resins in the residual oil.Viscosity reduction is the dominant mechanism when steam is injected at a low temperature.Large molecular heteroatoms with high carbon number and high double bond equivalent(DBE)are eluted into the produced oil,while compounds with low carbon number and low DBE are remained in the residual oil.As the steam temperature rises,the increased distillation effect results in the extraction of light hydrocarbons from the residual oil to the produced oil.More small heteroatoms with low carbon number and low DBE enter into the produced oil,especially in the none water cut stage.The compositional difference of produced oils is characterized in DBE versus carbon number distribution of the N and O containing compound classes.This work uses a variety of composition analysis methods to clarify the steam flooding mechanism and provides a novel understanding of steam flooding mechanisms with various temperatures and production stages from the molecular perspective.

Numerical Analysis of Settlement Response of Shallow Footing Subjected to Heavy Rainfall and Flood Events

The US and many parts around the world have experienced prolonged periods of heavy rainfall, severe floods, and droughts over the past 50 years. This study investigates the impacts of extreme hydrological events such as heavy rainfall and flood on the settlement behavior of continuous footing installed in unsaturated soil using a coupled Geotechnical-Hydrological finite element software, PLAXIS 2D. Initially, the effect of different degrees of saturation on the settlement behavior of the continuous footing of widths 1.5 m, 3.0 m, and 4.5 m was analyzed by applying a mechanical load. Then the settlement behavior of the footing was analyzed by applying heavy rainfall of intensity 102 mm/day for six days. Finally, the settlement behavior of the footing was analyzed by applying a flood head of 2.5 meters for seven days. The results indicated that the wetting front movement during heavy rainfall and flooding led to the weakening of soil strength and stiffness and induced additional settlements. The additional settlement induced by the flood was significantly higher than the heavy rainfall. The differential settlement was higher when the rainfall was applied on one side of the footing. The rebound of the elastic settlement was uniquely noticed when the flood head receded with time. The results indicated that not all the settlements were induced by the soil saturation but also due to the hydrostatic loading due to the flood head. The settlements induced by the flooding exceeded the allowable settlement of 25 mm, resulting in failure. These additional settlements caused by heavy rainfall and flood will lead to poor serviceability of the structures and cause the failure of the footing.

Quantitative Characterization and Dynamic Law of Interlayer Interference for Multilayer Commingled Production in Heavy Oil Reservoirs by Numerical Simulation

This paper moves one step forward to build?a?numerical model to research quantitative characterization and dynamic law for interlayer interference factor (IIF) in the multilayer reservoir which was heavy oil reservoirs and produced by directional wells. There are mainly four contributions of this paper to the existing body of literature. Firstly, an equivalent simulation method of the pseudo start pressure gradient (PSPG) is developed to quantitatively predict the value of?IIF?under different geological reservoir conditions. Secondly, the interlayer interference is extended in time, and the time period of the study extends from a water cut stage to the whole process from the oil well open to produce?a?high water cut. Thirdly, besides the conventional productivity interlayer interference factor (PIIF), a new parameter, that is, the oil recovery interlayer interference factor (RIIF) is put forward.?RIIF?can be used to evaluate the technical indexes of stratified development and multilayer co-production effectively. Fourthly,?the?effectsof various geological reservoir parameters such as reservoir permeability and crude oil viscosity, etc. on the?PIIF?and?RIIF’s?type curves?are?discussed in detail and the typical plate?is?plotted. The research results provide a foundation for the effective development of multilayer heavy oil reservoirs.

Study of steam heat transfer enhanced by CO_(2) and chemical agents: In heavy oil production

Steam flooding with the assistance of carbon dioxide (CO_(2)) and chemicals is an effective approach for enhancing super heavy oil recovery. However, the promotion and application of CO_(2) and chemical agent-assisted steam flooding technology have been restricted by the current lack of research on the synergistic effect of CO_(2) and chemical agents on enhanced steam flooding heat transfer. The novel experiments on CO_(2)–chemicals cooperate affected steam condensation and seepage were conducted by adding CO_(2) and two chemicals (sodium dodecyl sulfate (SDS) and the betaine temperature-salt resistant foaming agent ZK-05200).According to the experimental findings, a “film” formed on the heat-transfer medium surface following the co-injection of CO_(2) and the chemical to impede the steam heat transfer, reducing the heat transfer efficiency of steam, heat flux and condensation heat transfer coefficient. The steam seepage experiment revealed that the temperature at the back end of the sandpack model was dramatically raised by 3.5–12.8 °C by adding CO_(2) and chemical agents, achieving the goal of driving deep-formation heavy oil. The combined effect of CO_(2) and SDS was the most effective for improving steam heat transfer, the steam heat loss was reduced by 6.2%, the steam condensation cycle was prolonged by 1.3 times, the condensation heat transfer coefficient was decreased by 15.5%, and the heavy oil recovery was enhanced by 9.82%. Theoretical recommendations are offered in this study for improving the CO_(2)–chemical-assisted steam flooding technique.

A method of monitoring gas saturation in carbon dioxide injection heavy oil reservoirs by pulsed neutron logging technology

A method is proposed to characterize the fast neutron scattering cross-section ( s f) quantitatively by the combina-tion of inelastic gamma rays and captured gamma rays, so as to realize the gas saturation evaluation of CO_(2)-injected heavy oilreservoirs based on the three-de tector pulsed neutron logging technology. Factors influencing of the evaluation effect of thismethod are analyzed and the effectiveness of this method is verified by a simulation example. By using the Monte Carlo simu-lation method and the physical model of bulk-volume rock, the relationship between s f and CO_(2) saturation is studied, and thesaturation interpretation model is established. The influences of formation temperature and pressure, heavy oil density, bore-hole fluid and reservoir methane content on the evaluation results of CO_(2) saturation are analyzed. The results show that thecharacterization of s f by the combination of secondary gamma information can eliminate the influence of formation lithology,borehole fluid and methane content are the main factors affecting the quantitative monitoring of CO_(2) saturation, and the ef-fects of formation temperature and pressure and heavy oil density are negligible. The simulation example verified the feasibilityof the method for evaluating the CO_(2) saturation of CO_(2)-injected heavy oil reservoirs.

THE SYNTHETIC ANALYSIS OF THE VERY HEAVY RAINSTORMS IN GUANGDONG

Twelve very heavy rainstorms that caused severe floods in Pearl River drainage basin from 1949to 1994 are analyzed here. It is found that the rainstorms can be divided into three kinds. and they have differentcharacteristics in circulation and physical quantities. Rainstorms that caused floods in the Xijiang River andBeijiang River usually happen during the first flood season of the year (Apr.-Jun.). They last long. cover largeareas and cause severe disasters. There are Stable circulation backgrounds and complete tyontal precipitationsystems, and large stratification instability fields. Rainstorms often cause floods in coastal rivers and small tributaries during the second floods season (Jul.-Sept.). They happen suddenly, last a short time but have strong raillfail intensity. They are always caused by tropical cyclones but show significant instability only in rainstorm fields.The characteristics of rainstorms causing floods in the Dongjiang River or other main tributaries are similar to thetwo above. That is, they may be connected with fronts or tropical cyclones, and its stability degree is between thepreceding two kinds.

A Comparative Study of the Numerical Simulation of the 1998 Summer Flood in China by Two Kinds of Cumulus Convective Parameterized Methods

The NCC T63L20 model of the National Climate Center, China Meteorological Administration is employed to simulate the 1998 summer flood, which mainly occurred in the region of the Yangtze River and Northeast China. For this study, two kinds of cumulus convection parameterized schemes are employed in this model respectively. The simulations show that the Gregory parameterized scheme, which is still used in the United Kingdom Meteorological Office routine model, simulates more reasonable rainfall amount and distribution compared to the Kuo-type scheme. Moreover, the Gregory scheme better simulates the tendency of general circulation than the Kuo-type scheme. On the whole, the Gregory scheme provides a good simulation of the main features of the seasonal precipitation and general circulation in China, although the simulated result still exhibits some departures from the observations.

广东省阳春市潭水河“9.21”特大暴雨洪水分析

广东省阳春市潭水河"9.21"特大暴雨洪水是广东省粤西地区罕见的特大暴雨洪水,通过调查研究本场特大暴雨洪水的成因、规模与特性,计算分析出潭水河的水文特性和参数,对流域内的洪水预报、防汛抗洪、河流的规划治理等具有重要意义,也为其他特性相似的流域规划、防洪决策等工作提供参考依据。

Adaptation of Resilience against Disaster— Case Study of 2000 Tokai Flood and 2011 Flood in Shonai River, Japan

In this study, the application of the resilience concept of the flood event depending on progress of the time is analyzed as the hazard occurrence, the disaster risk, the damage risk, and the evolution of the damages. Flood disaster is defined as the occurrence of an inundation in an exposed area. The human exposure (loss of life, injury, …), structural (buildings, roads, …) and functional (economic, political, … functions of an area) economic exposure cause high risk of damage if the area in which the hazard occurs is at low resilience. Furthermore the damage will increase without adequate response against disaster. The flood disaster risk is decreased by flood control measures, reducing structural and functional exposure. Non-structural measures, such as appropriate prior-evacuation, decrease the human exposure to flood disaster. This study reviews the events of 2000 and 2011 floods in the Shonai River basin in Japan to help assess resilience to flood disaster. These two events had the same type of hazards in intensity and location, allowing the study in terms of adaptation to flood disaster in the river basin to focus on the structural and nonstructural effort to increase resilience of the disaster depending on progress of the time.

Simulation of Heavy Rainfall Events during Retreat Phase of Summer Monsoon Season over Parts of Andhra Pradesh

The main aim of this paper is to simulate monsoon heavy rainfall episodes that caused floods across some parts of Andhra Pradesh (AP) state, India during 29th September through 2nd October, 2009. A heavy rainfall quantity of 21 cm was observed near Amaravathi station (16.15°N;80.5°E) in Guntur district due to a meso-α low pressure system extended from the Bay of Bengal and widespread rainfall episodes were also appeared to many adjoining places in other three districts namely Mahaboob Nagar, Kurnool and Krishna in AP state simultaneously on 29th September. The rainy situation continued till 2nd October and caused floods over above districts of AP state which lead to a death toll of 33 people and heavy crop loss. To quantify the above catastrophic monsoon heavy precipitation events a high resolution (9 km) Weather Research and Forecast (WRF-ARW) model is centered at Amaravathi station to simulate rainfall episodes over the study region. In the present case study the simulated sensitive experiment highlights the dynamical characteristics of the meso-α system interms of circulation changes at different levels. Secondly, the thermodynamical characteristics for the generation of convective activity of this meso-α event in terms of Convective Available Potential Energy (CAPE) and Convective Inhibition Energy (CINE) are also simulated. Dynamical and thermodynamical simulated results support heavy rainfall episodes due to a low pressure system around Amaravathi station. Thus circulation changes, high CAPE and low CINE magnitudes have well defined not only the strength of meso-α system, but also quantum of rain-fall to a tune of 19 cm near Amaravathi station on 29th September. The observed rainfall was 21 cm on 29th September and thus this model underestimates rainfall about 9.5% not only at Amaravathi station, but also at other stations as well. Similar results are noticed over the study region on other three days. In this numerical study heavy rainfall events are better represented by Kain-Fritsch (KF) scheme than Betts-Miller-Janjic (BMJ) and Grell-Deveneyi (GD) schemes. Finally simulated circulation features and rainfall quantities are validated with observed rainfall of the India Meteorological Department (IMD) and satellite derived datasets of KALPANA-1, while CAPE and CINE quantities are checked against available Wyoming University observations. The results are promising.