An Investigation of the Effect of Using Foam in WAG Injection in an Iranian Oil Reservoir

The effect of using foam in water alternating gas injection method as an enhanced oil recovery method in one of Iranian oil reservoirs was investigated. The model of under investigation has high vertical permeability in vertical direction, so injected gas front would be breakthrough early times of injection periods. Foam implemented in injected gas phase of water alternating gas injection by decreasing the mobility of the gas phase and improving sweep efficiency of gas phase dominates this problem. In this work foam agent was added in water alternating gas injection method in two manners, with water phase and with gas phase. It was seen higher recovery for adding foam to gas phase in water alternating gas injection method. The results showed that foam increases the resistance of gas phase to flow through high permeable zone. By increasing the concentration of foam agent, total recovery would be increased but the rate of recovery incremental would be reduced after critical foam concentration. To reduce the costs, critical foam concentration must be found.     

The Evaluation of Gas,Water, WAG Injections,and Infill Wells for Improving Recovery of an Iranian Reservoir

Abstract

Increasing demand for energy has forced oil companies to resort to secondary and tertiary methods to increase the recovery from the existing reservoirs. The author investigated enhancing the recovery factor of one Iranian reservoir, which is a naturally fractured reservoir. For this reservoir, it is estimated that 96.5% of oil is contained in the matrix and 3.5% in the fractures. The field is an undersaturated reservoir with no active gas cap and no strong water aquifer. Injections of water, gas, water-alternating gas (WAG), and infill wells on this field were investigated to increase the recovery factor. Eclipse100 was employed to simulate the reservoir. The simulated results showed that gas, water, and WAG injections had nonsignificant improvements on oil recovery. However, it was found that infill wells contribute an appreciable increase in recovery. The amount of increase for drilling 8 infill wells was around 5%. Since development of existing resources contributes a major role on the supply of oil for the future oil market (around 45% by 2030), these results are used to screen the various methods for increasing the recovery of such reservoirs.     

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 on the Applicability of Water-alternating-CO2 Injection in the Secondary and Tertiary Recovery in One Iranian Reservoir

Abstract

The objective of this study was to experimentally investigate the performance of water-alternating gas (WAG) injection in one of Iran's oil reservoirs that encountered a severe pressure drop in recent years. Because one of the most appropriate studies to evaluate the reservoir occurs generally on rock cores taken from the reservoir, core samples drilled out of the reservoir's rock matrix were used for alternating injection of water and gas. In the experiments, the fluid system consisted of reservoir dead oil, live oil, CO₂, and synthetic brine; the porous media were a number of carbonate cores chosen from the oilfield from which the oil samples had been taken. All coreflood experiments were conducted using live (recombined) oil at 1,700 psi and reservoir temperature of 115°F. A total of four displacement experiments were performed in the core, including two experiments on secondary WAG injection and others on the tertiary water and gas invaded zones WAG injections. Prior to each test porosity and permeability of dried cores were calculated then 100% water-saturated cores were oil-flooded to obtain connate water saturation. Therefore, all coreflooding tests started with the samples at irreducible water saturation. Parameters such as oil recovery factor, water cut, and gas-oil ratio and production pressure of the core were recorded for each test. The most similar experimental work with the main reservoir condition, indicated that approximately 64% oil were recovered after 1 pore volume of WAG process at 136,000 ppm brine salinity. Although tests show ultimate recovery of 79% and 55% for secondary and tertiary injection in gas and water invaded zones, respectively, immiscible WAG injection efficiency in the gas and water invaded zones will not be proper. In the similar test to field properties, the average pressure difference about 70 Psig was observed, which shows stable front displacement. These experiments showed that there was significant improvement in the oil recovery for alternating injection of water and CO₂, especially in the secondary recovery process. Water breakthrough time in almost all of the tests shows frontal displacement of injected fluid in cores and produced gas-oil ratio changes a little whenever the injection is miscible and increases rapidly in immiscible processes.     

The Injection Pattern of Immiscible Nitrogen Displacement After Water Flooding in an Ultra-low Permeability Reservoir

With the nature ultra-low permeable cores from Changqing Oilfield, the simulated experiments of nitrogen drive after water flooding have been accomplished for the ultra–low-permeability reservoir. The injection pattern of nitrogen includes direct gas injection, water/gas alternating injection and pulse gas injection. The results show that direct injection could not develop the ability that nitrogen enters into the local tight area to improve the microsweep efficiency, because the good mobility generates gas channeling in some local high-permeable zone. Subsequent direct nitrogen injection after water drive only enhances the oil recovery ratio by 3.65%. The dispersion degree of oil, water, and gas is much higher for water/gas alternating injection after water injection, and the capillary force is the main resistance to suppress the rapid gas flow validly in local high-permeable zone. Nitrogen is enforced to drive the residual oil in local tight area or micro pore system. Water/gas alternating injection after water flooding enhances oil recovery ratio by 16.37%. Pulsing injection can take advantage of the elastic energy of the high-pressure nitrogen and pressure disturbance effect, which makes pressure redistribution and fluid deallocation between local high-permeability zone and local compact area. With pulse injection, oil in local tight region also can be driven by nitrogen, and the recovery ratio is enhanced by 15.94%.     

The Effect of Nitrogen Injection on Production Improvement in an Iranian Rich Gas Condensate Reservoir

In gas condensate reservoirs, after a decrease in pressure below the dew point pressure, condensate formation would occur. One of the common and practical methods for prohibiting the rapid pressure drop in the reservoir and reduction of liquid dropout is gas injection. In this study, experimental measurement, the full field reservoir model and an economical evaluation have been performed to investigate the effect of nitrogen injection on an Iranian Southwestern gas condensate reservoir. At first, swelling and CVD tests were carried out to determine the swelling factor and changing the saturation pressure by nitrogen. Then, the full field simulation (history matching and prediction) was performed and finally an economical evaluation has been made. The results show that injecting more volumes of nitrogen cause to decrease the liquid dropout, increase the dew point pressure, and condensate ultimate recovery, but this process is not an economical project.     

注入水悬浮固体含量对低渗油藏的敏感性研究

注水是油田稳产的重要措施,注入水的质量直接关系到原油生产。注入水的水质要求有几个方面,其中悬浮固体含量是一项重要指标。针对注入水悬浮固体含量对低渗油藏的敏感性进行岩心流动实验研究,结果表明低渗透油藏对悬浮固体含量的变化十分敏感,一旦悬浮固体含量达到临界值,油藏的渗透率明显降低。     

Experimental investigation of effect of asphaltene deposition on oil relative permeability,rock wettability alteration,and recovery in WAG process

Asphaltene deposition is considered to be one of the most problems during oil productions. This work describes the effect of asphaltene precipitation and deposition on relative permeability of reservoir rock during water alternating gas (WAG) injection process. The main objective of this work is experimental investigating of relative permeability change of reservoir fluid due to asphaltene deposition on application of WAG process by use of core flood setup. Result of this paper investigate the relative permeability change during WAG process with different asphaltene content that help to make better development decisions for a reservoir with fluid with specific asphaltene content.     

Black Oil and Compositional Reservoir Simulation for Increasing the Recovery Performance of an Iranian Fractured Carbonate Reservoir

Abstract

Naturally fractured reservoirs contain a significant amount of world oil reserves. Accurate and efficient reservoir simulation of naturally fractured reservoirs is one of the most important, challenging, and computationally intensive problems in reservoir engineering. Black oil and compositional reservoir simulators have been used to determine the reservoir management and production strategies to increase the oil recovery from a low-porosity, low-permeability fractured carbonate reservoir, with an average matrix permeability of 0.8 md, average fracture permeability of 500 md, and an average matrix porosity of 10%. This reservoir is a candidate for an enhanced oil recovery (EOR) process, because the reservoir production rate has been declined due to increasing the water cut as a result of rising the water oil contact. The injection techniques that have been considered in this study for black oil model include (a) gas injection, (b) water injection, and (c) simultaneous water alternating gas injection and for the compositional model include (a) dry gas injection, (b) CO₂ injection, and (c) N₂ injection. Simulation results show that CO₂ injection has the maximum oil recovery between the EOR scenarios.     

低渗油藏注水井压裂增注

在油田的高速开发中,注水井为地层能量的补充、稳产起到了重要作用.本文针对鄯善油田低渗油藏,从注水井地层现状评估、影响注水井注水量的原因、以及注水井增注的针对性措施这三个方面,论证注水井的压裂增注方法.     

An Experimental Study of Secondary WAG Injection in a Low-Temperature Carbonate Reservoir in Different Miscibility Conditions

Abstract

This experimental study is aimed at evaluation of the performance of secondary WAG injection in carbonate cores at different pressures. To do so, a comprehensive series of high-pressure high-temperature (HPHT) core flooding tests are conducted. The fluid system includes reservoir dead and live crude oil, CO₂, and synthetic brine while the chosen porous media consists of a number of fractured carbonate core samples. Parameters such as oil recovery factor, water and oil production rates, and pressure drop along the core are recorded for both dead and live oil. According to results, at first increasing pressure improves the oil recovery, but this improvement after MMP is not as significant as it is before MMP. Also recoveries of dead and live oils at same pressure show different values due to differences in miscibility condition of injected gas. Then as the graphs demonstrate, relative permeability reduction due to hysteresis effect has dominant effect on pressure drop curves. Finally, as the production rate curves show, nearly all of the remained oil after breakthrough is produced as the gas is being produced and almost no oil can be recovered during water production portions.     

The Experimental Investigation of Nitrogen and Carbon Dioxide Water-alternating-gas Injection in a Carbonate Reservoir

Abstract

Floods were conducted using rock–fluid systems consisting of carbonate cores from Binak reservoir, which is located in southwest of Iran, oil and brine. The coreflood protocol consisted of a series of steps including brine saturation, absolute permeability determination, flooding with oil to initial oil saturation, endpoint oil permeability determination, and, finally, nitrogen and carbon dioxide water-alternating-gas (WAG) injections. The effect of slug size on oil recovery was investigated using immiscible nitrogen (N₂) WAG injection and the amount of oil recovered was compared with continuous injection of N₂. Experimental results show that ultimate oil recovery is not very sensitive to changing the slug sizes for N₂ WAG injection, although the slug size of 0.15 pore volume (PV) injection is better than others. As less PV is injected, a higher oil production rate is achieved. Also, N₂ WAG flood appeared to be better in performance than continuous gas injection (CGI) of nitrogen. Carbon dioxide (CO₂) injection was performed in three modes, including CGI, WAG injection, and hybrid WAG. Experimental results show that for optimization of oil recovery in CO₂ floods, a continuous gas slug of 0.4–0.5 PV followed by 1:1 WAG needs to be injected.     

河86地区生物灰岩油藏注水水源评价及储层伤害研究

注入水与地层水的配伍性和水质对地层的伤害是影响低渗透油藏开发的重要因素。在五敏实验研究的基础上，通过结垢趋势计算、室内流动实验对河86生物灰岩油藏注水水源进行了系统评价；通过膜滤实验、岩心堵塞实验、细菌堵塞实验等对注水水质控制指标进行了研究。研究结果表明，郝现联合站、史南联合站污水经处理后是理想的注水水源，并给出了主要水质控制指标。     

低渗气藏滑脱效应研究现状及认识

滑脱效应作为影响低速渗流规律的一个重要因素, 已引起人们的重视。国内外学者在滑脱效应影响因素及受滑脱效应影响的渗透率参数测量方面进行了大量的研究, 但是研究结论仍然存在分歧。概述了目前国内外在滑脱效应方面的研究工作, 提出了现存的问题, 对研究低渗透气藏的低速渗流规律及准确测定低渗气田开发中相对渗透率等参数有一定的指导意义。     

纳米驱油剂在增注驱油中的作用

为分析纳米驱油剂在低渗储层增注驱油中的作用,评价了以硅烷偶联剂改性的纳米SiO2为主要成分的纳米驱油剂的基本性能,通过枣湾区块长6储层天然岩心和微观模型驱替实验研究了纳米驱油剂的流动特征和驱油特征.结果表明,纳米驱油剂中的纳米颗粒粒径较小,具有较低的油水界面张力、良好的亲水性及一定的静态吸附能力.30℃下,0.1％纳米...     

纯化油田注入水中细菌堵塞岩心实验研究

岩心流动实验装置全系统灭菌;地层水和注入水过滤、灭菌;储层岩心洗油、饱和地层水;用注入水接种培养,制备低、中、高含菌量的驱替用水,其中TGB、SRB、IB菌总菌数分别为1.06×102、1.49×103、1.29×104个/mL。用低、中、高含菌量的3种含菌水驱替岩心,注入量分别为70、70、64PV,岩心对地层水的渗透率分别由9.06×10-3、15.93×10-3、11.84×10-3μm2变为10.16×10-3、1.45×10-3、0.72×10-3μm2,对岩心渗透率的伤害分别为-12.1%、90.9%、93.9%,岩心流出液中总菌数分别为0、4.0×100、4.1×101个/mL。讨论了注水过程中细菌在岩心孔隙中的截留和岩心堵塞。认为纯化油田砂岩油藏注入水中各种细菌的总数应控制在1×102个/mL以下。图3表4参2。     

An Investigation of and Comparison Between the Simulation of Miscible and Immiscible Gas Injection in an Undersaturated Fractured Reservoir in the South of Iran

M-Reservoir is a dual porosity fractured reservoir having active aquifer and heterogenous production zones. It had had only a total oil recovery of 8.4% with the total production of 240 MMSTB up to 2008. By simulation of slime tube experiment using Eclipse 300 software, minimum miscibility pressure of 3700 psia was obtained, which was below its average pressure. Production optimization and final recovery increment were performed via analyzing and matching of fluid reservoir, history matching of past reservoir performance, and investigating on different location of gas injected well. The best location of injected well was selected based on the recovery coefficient and gas injection method of miscible and immiscible at various rates and were compared with natural depletion in selected locations. The results represent that the miscible gas injection has more recovery coefficient than natural depletion and there is somewhat recovery coefficient in comparison with immiscible gas injection.     

A laboratory study of hot WAG injection into fractured and conventional sand packs

Gas injection is the second largest enhanced oil recovery process,next only to the thermal method used in heavy oil fields.To increase the extent of the reservoir contacted by the injected gas,the gas is generally injected intermittently with water.This mode of injection is called water-alternating-gas(WAG).This study deals with a new immiscible water alternating gas(IWAG) EOR technique,"hot IWAG" which includes combination of thermal,solvent and sweep techniques.In the proposed method CO2 will be superheated above the reservoir temperature and instead of normal temperature water,hot water will be used.Hot CO2 and hot water will be alternatively injected into the sand packs.A laboratory test was conducted on the fractured and conventional sand packs.Slugs of water and CO2 with a low and constant rate were injected into the sand packs alternatively;slug size was 0.05 PV.Recovery from each sand pack was monitored and after that hot water and hot CO2 were injected alternatively under the same conditions and increased oil recovery from each sand pack and breakthrough were measured.Experimental results showed that the injection of hot WAG could significantly recover residual oil after WAG injection in conventional and fractured sand packs.     

Investigating the Effect of Capillary Number on Performance Prediction of an Iranian Fractured Gas Condensate Reservoir

Abstract

Gas condensate reservoirs are one of the most complicated reservoirs in which the special thermodynamic behavior of reservoir fluid leads to condensate buildup instead of gas expansion, when the reservoir pressure drops below dew point pressure. To justify the phase behavior of such reservoirs, several models have been proposed. One of the models is a capillary number model that has a considerable effect on the shape of relative permeability curves. Taking account of capillary number is shown to improve the performance prediction of gas condensate reservoirs that otherwise is poorly predicted. In pressures below dew point pressure, velocity and surface tension between gas and oil increases more rapidly in the vicinity of the well compared with other parts of the reservoir, which results in condensate saturation reduction and gas relative permeability improvement. The authors model a fractured gas condensate reservoir with and without taking capillary number into consideration; the performance prediction results are compared to the actual results. The model with capillary number included is shown to be able to predict the performance with a greater accuracy than the case without capillary number.     

复杂断块油藏细分注水开发方案优化研究

东辛油田营13复杂断块油藏构造破碎,地下油水关系复杂,油水井多年来一直是合采合注,层间矛盾日益加重。针对以上问题,运用数值模拟等技术研究剩余油分布规律,实施细分注水方案,采取合采分注的开采方式,改善油藏水驱效果,提高油藏采收率。