Asphaltene deposition during flow through pipes: Parametric and inhibition analyses

Asphaltene deposition is known as one of the problematic topics in petroleum engineering which is caused by changing pressure, temperature, and composition. So it becomes important to investigate the effect of different parameters such as precipitant to oil volume ratio, temperature, and flow rate. For this purpose, flow loop deposition set up was constructed and the pressure drop changes along tube were measured during experimental and this enhancement of pressure drop during the time illustrates deposition occurred. the results showed that increasing precipitant to oil volume ratio and temperature causes increasing deposition and as flow rate increases, the mass of deposits decreases because of increasing the shear rate on the wall of the tube. The novelty of this study is using CTAB and Benzoic acid inhibitors in this flow loop setup. It was observed the CTAB has more impact on inhibition of asphaltene deposition through the tube than a Benzoic acid inhibitor.     

Analyzing electrical field effect on asphaltene deposition

Asphaltenes are the heaviest and most complicated fraction in a crude oil sample and consist of condensed polynuclear aromatics, small amounts of heteroatoms (e.g., S, N, and O), and some traces of metal elements (e.g., nickel and vanadium). The main mechanisms of asphaltene deposition are precipitation (formation of asphaltene solids out of liquid phase), aggregation (formation of larger asphaltene particles), and deposition (adsorption and adhesion onto the surface). Asphaltene deposition is a major unresolved flow assurance problem in the petroleum industry, which may occur anywhere in the production system consists of reservoir, wellbore, through flowing and the separator. Asphaltene moieties in crude oil are found to carry residual surface electric charge, so by exerting an electrical field in a specific length of pipe, asphaltenes will deposit and we will have no blockage problem. Determining asphaltene electric charge is an important issue that will be done by static experiment, and then effect of electrical field on asphaltene deposition in dynamic state should be investigated. This paper discusses electric field effect on asphaltene deposition and represents a way to deposit asphaltene moieties in specific location.     

Reversibility of Asphaltene Deposition Under Dynamic Flow Conditions

Occurrence of asphaltene deposition in production formation constitutes one of the most serious problems currently encountered in the petroleum industry in many areas of the world. Reversibility of asphaltene deposition causes crucial argument and controversy in laboratory research of the petroleum industry. A deeper understanding of this phenomenon is the key for treatment of the problem of asphaltene deposition. The major goals of this study were to investigate 1) asphaltene adsorption rate on carbonate rock surfaces under static condition, and 2) asphaltene deposition and its reversibility under dynamic flow conditions. For the sake of achieving these goals, two groups of experiments were undertaken. The first one measured asphaltene adsorption rate under static condition, while the second group was devoted to studying reversibility of asphaltene deposition under dynamic flow condition through actual porous medium. The results of the study indicated that the increase of aging time increases asphaltene adsorption on carbonate rock surfaces under static condition. However, the major part of asphaltene is adsorbed during the first 30 h of contact of oil with the rock surface. The results of dynamic flow experiments showed that asphaltene deposition is a continuous process causing permeability damage and is also partially reversible. Furthermore, the asphaltene deposition causes more damage in low permeability rock than one in higher permeability. The obtained results are expected to have important implications for better formulation of treatments of asphaltene deposition.     

Reversibility of Asphaltene Deposition Under Dynamic Flow Conditions

Abstract

Occurrence of asphaltene deposition in production formation constitutes one of the most serious problems currently encountered in the petroleum industry in many areas of the world. Reversibility of asphaltene deposition causes crucial argument and controversy in laboratory research of the petroleum industry. A deeper understanding of this phenomenon is the key for treatment of the problem of asphaltene deposition. The major goals of this study were to investigate 1) asphaltene adsorption rate on carbonate rock surfaces under static condition, and 2) asphaltene deposition and its reversibility under dynamic flow conditions. For the sake of achieving these goals, two groups of experiments were undertaken. The first one measured asphaltene adsorption rate under static condition, while the second group was devoted to studying reversibility of asphaltene deposition under dynamic flow condition through actual porous medium. The results of the study indicated that the increase of aging time increases asphaltene adsorption on carbonate rock surfaces under static condition. However, the major part of asphaltene is adsorbed during the first 30 h of contact of oil with the rock surface. The results of dynamic flow experiments showed that asphaltene deposition is a continuous process causing permeability damage and is also partially reversible. Furthermore, the asphaltene deposition causes more damage in low permeability rock than one in higher permeability. The obtained results are expected to have important implications for better formulation of treatments of asphaltene deposition.     

An Experimental Investigation of Permeability Impairment Under Dynamic Flow Conditions Due to Natural Depletion in an Iranian Oilfield

Asphaltene deposition is an issue that has received much attention since it has been shown to be the cause of major production problems. It leads to permeability reduction under the processes of natural depletion as well as hydrocarbon gas/CO₂ injection. Though a great deal of researches have focused on studying permeability impairment in reservoir rocks, little is known about the asphaltene deposition mechanisms that control the permeability reduction for Iranian reservoirs. In this work, an experimental effort is made to investigate the permeability impairment of core samples of Iranian oil reservoirs. The experiments are performed on both sandstone and carbonate rock types at reservoir temperature and pressure. The mass balance was used for evaluating of porosity reduction during the experiments. The results indicate that the dominant deposition mechanism changes as production proceeds. In addition, it has been found that the primary mechanism in permeability impairment is surface deposition. On the other hand, entrainment of asphaltene particles is manifested when outlet pressure drops from 4,200 to 3,800 Psig for both sandstone and carbonate samples. It can be drawn that asphaltene entrainment dependence to pressure is much more than that to the injected pore volume. This research illuminates the deposition mechanisms and determines dynamic parameters of asphaltene deposition, which are necessary to devise reliable prevention strategies.     

Simulation of Natural Depletion and Miscible Gas Injection Effects on Asphaltene Stability in Petroleum Reservoir Fluids

Natural depletion of petroleum reservoirs as well as gas injection for enhance oil recovery, are unavoidable processes in the oil industry. Foremost, prediction of the problems due to these two processes is very necessary and important. So many field and experimental experiences have shown that heavy organic depositions, especially asphaltene deposition, are principal results during these processes. Results of laboratory simulation of asphaltene deposition during the natural depletion of petroleum reservoirs and also during gas injection and enhanced oil recovery (EOR) processes are reported here. This is achieved through the design of a new experimental setup for the investigation of pressure and composition effects on asphaltene deposition in petroleum fluids at high pressure and high temperature conditions. In this work, asphaltene deposition during decreasing pressure, from pressures greater than reservoir pressure to pressures below the bubble point pressure (natural depletion) and also asphaltene deposition during natural gas injection in reservoir conditions, are studied for three samples—one recombined sample and two bottomhole samples. All of the obtained results from this work conform to theoretical and other experimental works.     

Simulation of Natural Depletion and Miscible Gas Injection Effects on Asphaltene Stability in Petroleum Reservoir Fluids

Abstract

Natural depletion of petroleum reservoirs as well as gas injection for enhance oil recovery, are unavoidable processes in the oil industry. Foremost, prediction of the problems due to these two processes is very necessary and important. So many field and experimental experiences have shown that heavy organic depositions, especially asphaltene deposition, are principal results during these processes. Results of laboratory simulation of asphaltene deposition during the natural depletion of petroleum reservoirs and also during gas injection and enhanced oil recovery (EOR) processes are reported here. This is achieved through the design of a new experimental setup for the investigation of pressure and composition effects on asphaltene deposition in petroleum fluids at high pressure and high temperature conditions. In this work, asphaltene deposition during decreasing pressure, from pressures greater than reservoir pressure to pressures below the bubble point pressure (natural depletion) and also asphaltene deposition during natural gas injection in reservoir conditions, are studied for three samples—one recombined sample and two bottomhole samples. All of the obtained results from this work conform to theoretical and other experimental works.     

Investigation of the asphaltene deposition along the flow of the oil in tubing: Experimental study and a parametric analysis

In this work, a novel experimental setup was designed and utilized to carry out the n-alkane induced asphaltenes for understanding the kinetics of deposition and also effects of oil velocity, oil-precipitant volumetric dilution ratio, and temperature on the rate of asphaltene deposition. As the deposited layer of asphaltenes makes it difficult for the flow of oil along the tube, measurement of the pressure drop across the tube section of setup enabled the measurement of the amount and extent of deposition process at desired condition. The experimental results revealed that increasing the velocity of fluid across the pipe dominance the shear force on asphaltene deposit and cause remobilization of part of the deposit into the flowing fluid in contrary to oil-precipitant ratio, where deposition rate is enhanced with increasing DR ratio. The results of this work elucidate some less-addressed shadows of dynamics of flow blockage in pipelines and could create a better framework for conducting forthcoming experiments     

Application of Fuzzy c-means algorithm for the estimation of Asphaltene precipitation

One of problematic topics in petroleum engineering is Asphaltene precipitation issue which causes problems such as tubing plugging and formation damage due to temperature, pressure and composition changes so the notability of this issue increases. In the present investigation a novel Fuzzy c-means (FCM) algorithm was developed to predict precipitated asphaltene as function of dilution ratio, carbon number of precipitants and temperature for solving the problem. The results showed that this novel approach has great ability to predict precipitated asphaltene in terms of aforementioned parameters. The coefficients of determination (R²) for training and testing steps are calculated as 0.9828 and 0.9387 respectively. This great degree of accuracy expresses that the predicting algorithm has potential to be utilized as software for prediction of asphaltene behavior.     

The control of asphaltene precipitation in oil wells

Asphaltene instability can occur in petroleum reservoirs leading to permeability reduction and deposition in transportation pipes restricting fluid flow. In this work, effect of reservoir pressure on amount of asphaltene precipitation was investigated. Two different asphaltene inhibitors (a new developed and an industrial) were used for preventing asphaltene deposition under static and dynamic conditions. Viscosity measurements of the oil, core flooding experiments and transmittance measurement were conducted to understand asphaltene precipitation and deposition behavior as well inhibitor efficiencies. Optimum concentration of the new asphaltene inhibitor was 200 ppm. Experiments show inhabitation efficiency of new inhibitor can reach up to 90% and showed better performance when compared with industrial one. In addition, squeeze lifetime of new inhibitor was 1.86 times longer than the industrial inhibitor in carbonate core samples. In the presence of new inhibitor formation damage and percent of transmittance was lower than in the presence of industrial asphaltene inhibitor.     

Dynamic Pore Scale Modeling of Asphaltene Deposition in Porous Media

Asphaltene deposition in porous medium is one of important factors in reducing the productivity of oil reservoirs. Reduction of permeability is the main factor, which is also due to reduced pores size or complete closure of them. The authors simulate phase one flow of oil in porous medium using a dynamic pore scale network model. Also asphaltene deposition process is considered based on a scaling equation. Because the greatest amount of precipitation occurs at bubble point pressure condition, we considered boundary conditions of the model in this pressure. The hypothetical model is only a very small element of a real reservoir rock therefore we assumed constant temperature in this process, consequently the main reason of asphaltene precipitation is pressure changes in the pores. Permeability reduction simulated was based on these steps: pore and throat pressure changes were due to fluid flow through the network and asphaltene deposited according to scaling equation. Applying a material balance for each pore/throat gives the volume reduction of pores/throats according to the deposited asphaltene. Due to this change in pores size permeability and porosity of the model is calculated. Repeating these steps over the time gives effect of asphaltene deposition on the primary properties of porous medium.     

Prediction of asphaltene precipitation during gas injection

Maintaining the flow of multiphase fluid from the reservoir to the surface has been an important issue with wide economic importance for the petroleum industry. Asphaltene precipitation due to change in temperature, pressure, and composition of oil can adversely affect the oil flow to the surface by reducing the available diameter of the tubing. In this study, the precipitation of asphaltene from an Iranian crude oil was investigated. To do our study, through information about asphaltene instability in the live oil during both natural depletion and gas injection conditions about oil sample from Iranian oil field was gathered. Then, the solid model and scaling model were utilized to predict the weight percent of precipitated asphaltene at a wide range of the pressure and temperature. Results of the work revealed that both models predict the increase in weight percent of precipitated asphaltene when lean gas injected to the live oil at the maximum point of asphaltene instability. In addition, the study showed that both models are capable of predicting the experimental data of asphaltene precipitation; while scaling modeling is more reliable when the gas is injected to the oil.     

原油沥青质初始沉淀压力测定与模型化计算

温度、压力及组成的改变均会造成原油中沥青质产生沉淀,导致储层伤害和井筒堵塞。文中通过自主研制的固相沉淀激光探测系统,用透光率法首次测定了伊朗南阿油田原油样品在不同温度下的沥青质初始沉淀压力;同时利用Nghiem等建立的沥青质沉淀预测的热力学模型对油样沥青质初始沉淀压力进行计算,并与实验结果拟合。结果表明：利用透光率法测定该油田油样,在44,80,123℃下的沥青质初始沉淀压力点分别为42.8,39.7,35.2 MPa;沥青质初始沉淀压力随着温度的升高,在井筒温度范围内呈线性关系。模型计算与实验结果误差不超过15%,所以利用Nghiem模型对原油沥青质的初始沉淀压力进行预测是可靠的。     

A Pipe-Loop Apparatus to Investigate Asphaltene Deposition

A circulating pipe-loop has been designed to measure asphaltene deposition under flowing conditions. Bitumen and n-heptane are combined to induce asphaltene precipitation at the entrance of a test section in which deposition is to be measured. The n-heptane is separated from the bitumen at the exit of the test section allowing the asphaltenes to redissolve in the bitumen before it is pumped back to the test section. In the test section, solid deposits are measured nonintrusively with X-ray tomography using a computer assisted tomographic (CAT) scanner. A segment of the test section is also removable for direct gravimetric measurement and collection of deposits. The pipe-loop is designed to investigate the effect of flow rate, solvent type, solvent-to-bitumen ratio, metal type, temperature, and pressure on asphaltene deposition. The effect of additives can also be assessed. The system is rated for pressures upto 7 MPa, temperatures from 25 to 100°C, and flow rates up to 0.1 m³/h.     

Asphaltene Precipitation During Different Production Operations

Asphaltene precipitation due to enhanced oil recovery (EOR) methods or natural depletion is a serious technical problem at petroleum industry. The authors present the result of asphaltene precipitation during associated gas injection, CO₂ injection, and natural depletion in reservoir condition. In addition, the effect of variations in operation pressure, injection gas concentration, and production rate on asphaltene precipitation and difference between slope of precipitation graph due to various method of EOR or natural depletion were investigated. The results revealed that temperature has an efficient role on result of asphaltene deposition through associated gas and CO₂ injection. By decreasing temperature, the amount of asphaltene precipitation due to associated gas injection was increased. In fact, recovery of gas injection was decreased at lower temperatures, hence; solubility has an important rule on asphaltene precipitation.     

页岩储层CO2驱沥青质沉淀特征及影响因素分析

为明确CO2在页岩储层纳米孔隙中的流动机理及其对沥青质沉淀的影响,采用自主研发的高温高压过滤容器和复合纳米滤膜,进行纳米滤膜过滤实验,模拟了单(多)层岩石切片作用下的CO2驱替过程,开展储层参数和注入参数对CO2驱替效果及沥青质沉淀的影响研究.研究结果表明:CO2驱会引发沥青质沉淀,导致剩余油中的沥青质含量远大于产出油...     

Mechanism of the reversibility of asphaltene precipitation in crude oil

Asphaltene precipitation and deposition occur in petroleum reservoirs as a change in pressure, temperature and liquid phase composition and reduce the oil recovery considerably. In addition to these, asphaltene precipitates may deposit in the pore spaces of reservoir rock and form plugging, which is referred to as a type of formation damage, i.e. permeability reduction. In all cases above, it is of great importance to know under which conditions the asphaltenes precipitate and to what extent precipitated asphaltenes can be re-dissolved. In other words, to what extent the process of asphaltene precipitation is reversible with respect to change in thermodynamic conditions. In present work, a series of experiments was designed and carried out to quantitatively distinguish the reversibility of asphaltene precipitation upon the change in pressure, temperature and liquid composition. Experiments were conducted in non-porous media. Generally it was observed that the asphaltene precipitation is a partial reversible process for oil under study upon temperature change with hysteresis. However, the precipitation of asphaltene as a function of mixture composition and pressure is nearly reversible with a little hysteresis.     

A new rigorous two-phase kinetic model for accurate prediction of the asphaltene deposition rate during the oil flow in porous media of petroleum reservoirs

Asphaltene formation and deposition in oil reservoirs are the most important problems in petroleum industry. A new rigorous two-phase kinetic model for simulation of flow behavior considering the asphaltene deposition process is presented in this work. All governing equations considering the proposed new adsorption kinetic model are solved by finite difference method. The presented model is validated using the most accurate available data and different oil samples. The proposed approach can be used for accurate evaluation of the effect of asphaltene deposition on the oil flowing condition in porous media of petroleum reservoirs.     

Prediction of asphaltene precipitation using non-isothermal compositional network model

In this paper a comprehensive flow model which incorporates compositional and non-isothermal effects is proposed to investigate asphaltene precipitation onset conditions in advanced well completions. The focus is on precipitation induced by pressure and temperature conditions, particularly in flow restrictions used in wells to delay unwanted break through of water/gas. A network model is used with a non-isothermal black oil fluid model to predict the distribution of pressure, temperature, flow rate and phase fractions in all components of the well completion. The network geometry consists of a production tubing (or liner) and an annulus between the reservoir and the tubing. This geometry will allow for flow between the annulus and the tubing through inflow control devices which are commonly used for zonal control. An asphaltene precipitation envelope is used to identify locations in the well completion at risk. Subsequently, a fully compositional and non-isothermal model is invoked at these locations. This detailed model uses a Finite Difference representation of conservation of mass, energy and momentum. Furthermore, it uses an isenthalpic pseudo-three-phase equilibrium model to predict if asphaltene precipitation actually will occur inside the restriction. A case study is presented in which the proposed model was successfully used to predict physical flow parameters and asphaltene onset conditions. It was found that asphaltene precipitation may occur in flow restriction due to large pressure drop. Furthermore, it was found that the use of isothermal modeling to predict asphaltene precipitation may lead to underestimation of the precipitation. It is concluded that the details of the well completion must be represented in the flow model since pressure and temperature may vary non-monotonically from toe to heel in advanced well completions.