Experimental and modeling analysis of asphaltene precipitation in the near wellbore region of oil wells

In this work, effect of reservoir temperature (in a range of 50–100°С) on the amount of asphaltene precipitation was determined. Rate of asphaltene precipitation was increased by increasing temperature. Damaged permeability of carbonate core samples was investigated at different asphaltene contents conducting core flood tests. The results showed the experimental and predicted data of damaged permeability ratio due to asphaltene precipitation matched. Moreover, the optimum mass concentration of components of the developed asphaltene inhibitor was determined by measuring interfacial tension on the boundary of oil and inhibitor solution. In addition, the change in the concentration of asphaltene inhibitor was simulated depending on the radial distance to well, production time and type of isotherm.     

Asphaltene precipitation and inhibition in carbonate reservoirs

In this work, the effect of formation water concentration in the emulsion with oil on the amount of asphaltene precipitation was studied. In addition, the effect of flow rate and asphaltene concentration on formation damage of Iranian carbonate core samples was investigated. A new asphaltene inhibitor was used for preventing asphaltene precipitation. Performance of the inhibitor was studied under static and dynamic conditions. The inhibition efficiency reached 77% at a concentration of 3% of asphaltene inhibitor. Also, adsorption rate of the inhibitor was determined at different inhibitor concentrations. The results showed that the adsorption rate is increased by increasing the inhibitor concentration. However, the adsorption rate remained almost unchanged at higher concentrations.     

Experimental and modeling study of asphaltene adsorption onto the reservoir rocks

Abstract

In this work, amount of asphaltene adsorption onto the carbonate and sandstone rock samples was investigated at various initial concentrations of asphaltene in oil. Asphaltene adsorption onto both types of the reservoir rocks was increased by increasing the initial concentration of asphaltene. The amount of asphaltene adsorption onto the rock samples was predicted using Langmuir and Freundlich isotherm models. The results showed that Langmuir model had a better accuracy for prediction of asphaltene adsorption onto the rock samples than Freundlich model. Furthermore, asphaltene adsorption onto the reservoir rocks was studied in the presence of a recently developed asphaltene inhibitor. The inhibitor significantly reduced asphaltene adsorption at any initial concatenation of asphaltene. Moreover, changes in the rock permeability due to asphaltene precipitation were determined in the presence and absence of the asphaltene inhibitor.     

A novel test method for evaluate asphaltene inhibitor efficiency on damage permeability

Asphaltene deposition has a significant detrimental effect on oilfield production. The key to effective treatment of asphaltene deposition is recognition of the problem. Asphaltene and effective treatment can be identified and quantified using laboratory methods. The most commonly way to asphaltene precipitation reduction is applying an asphaltene inhibitor. Most researchers investigate the effect of asphaltene inhibitors on fluid and precipitation reduction in static tests. This study is a coherent approach to measure effect of asphaltene precipitation on reservoir permeability and survey effect of asphaltene inhibitors on damage permeability.     

Choline chloride/monoethylene glycol deep eutectic solvent as a new asphaltene precipitation inhibitor

In this research work, a family of green solvents named deep eutectic solvents (DES) was used as asphaltene precipitation inhibitor for the first time as per our knowledge, i.e., choline chloride:monoethylene glycol acid (1:1). Ultraviolet–visible (UV–vis) spectrometry was used to estimate the precipitation onset point of asphaltene and to evaluate the impact of the DES to increase their resistance against the precipitant effect. A microscopic method was used to monitor the agglomeration trend during titration. The distribution of asphaltene particles monitored by dynamic light scattering (DLS) showed a value of 1,419 nm for inhibitor-free sample, while for sample with the DES was 1,039 nm under similar conditions.     

Optimization Assisted Asphaltene Deposition Modeling in Porous Media During a Natural Depletion Scheme

Abstract

Changes in thermodynamic properties such as pressure, temperature, and composition may result in asphaltene precipitation and deposition in porous media. In addition, asphaltene deposition can cause wettability alteration, permeability reduction, and ultimately a decrease in the productivity of a reservoir. Natural depletion is one of the most common processes of asphaltene deposition in which pressure changes destabilize the dissolved asphaltene in the oil and settle them onto the rock surface.

In this work, natural depletion experiments in consolidated core samples were performed under simulated reservoir conditions to obtain reliable data and analyze the asphaltene deposition mechanisms.

A mass balance equation, momentum equation, asphaltene deposition, and permeability reduction models were applied to model the process of permeability changes as a result of asphaltene deposition. MATLAB programming language was used to calculate the numerical form of the above equations iteratively. A genetic algorithm technique was employed as the optimization tool for history matching and determination of model parameters.

Modeling and optimization results showed an accurate match with measured data. Optimization confirmed that all major deposition processes (surface deposition, entrainment, and pore throat plugging) were effective in permeability changes. Calculation of precipitated asphaltene saturation by the introduced equation provides information on the volume fraction of porous media that was evaded by the precipitated asphaltene particles.     

Laboratory investigation of a new scale inhibitor for preventing calcium carbonate precipitation in oil reservoirs and production equipment

The formation of mineral scale is a complex problem during the oilfield operations. Scale inhibitors are widely used to prevent salt precipitation within reservoirs, in downhole equipment, and in production facilities. The scale inhibitors not only must have high effectiveness to prevent scale formation, but also have good adsorption–desorption characteristics, which determine the operation duration of the scale inhibitors. This work is focused on the development of a new scale inhibitor for preventing calcium carbonate formation in three different synthetic formation waters. Scale inhibition efficiency, optical density of the solution, induction time of calcium carbonate formation, corrosion activity, and adsorption–desorption ability were investigated for the developed scale inhibitor. The optimum concentration of hydrochloric acid in the inhibitor was determined by surface tension measurement on the boundary layer between oil and the aqueous scale inhibitor solution. The results show that the optimum mass percentage of 5 % hydrochloric acid solution in the inhibitor was in the range of 8 % to 10 %. The new scale inhibitor had high efficiency at a concentration of 30 mg/L. The results indicate that the induction period for calcium carbonate nucleation in the presence of the new inhibitor was about 3.5 times longer than the value in the absence of the inhibitors. During the desorption process at reservoir conditions, the number of pore volumes injected into the carbonate core for the developed inhibitor was significantly greater than the volume of a tested industrial inhibitor, showing better adsorption/desorption capacity.     

A Pipe-Loop Apparatus to Investigate Asphaltene Deposition

Abstract

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.     

A novel test method for evaluate asphaltene inhibitor efficiency on reservoir rock

Asphaltene deposits can reduce the productivity of the reservoir as well as foul piping and surface equipment. Current chemical and mechanical methods for treating deposition are only partially effective partly because the deposition process is poorly understood. The most commonly way to asphaltene precipitation reduction is applying an asphaltene inhibitor. In order to investigate the extent of formation damage by asphaltenes in crude oil this work has used electro kinetic technique to study the adsorption of asphaltenes in rock pores. Most researchers investigate the kinetics of adsorption by monitoring changes in the concentration of asphaltene or polymer in a dispersion of adsorbent particles or capillaries. This study is a coherent approach to measure amount of asphaltene adsorption on rock surface and survey effect of asphaltene inhibitors on precipitation reduction in porous media.     

A NOVEL TECHNIQUE OF ASPHALTENE DEPOSITION TREATMENT USING ULTRASONIC IRRADIATION

ABSTRACT

The need for better understanding of asphaltene behavior in the crude oil and treatment techniques of its deposition in porous medium has been recognized but still requires extensive research and experimental activities. The ambitious goals of this study are to investigate: (1) influences of using ultrasonic irradiation on asphaltene behavior in the UAE crude oil, with consideration of solvent and temperature effects; and (2) influences of ultrasonic irradiation characteristics such as frequency and time interval on damaged oil permeability (due to asphaltene deposition) of carbonate reservoir rocks. To achieve the above-mentioned goals, three groups of experiments using ultrasonic irradiation were carried out. In the first group, 18 identical crude oil samples of 2.47 wt% initial asphaltene content were subjected to different time intervals of ultrasonic irradiation of 0, 5, 10, 15, 25 and 30 min and under different temperatures of 25, 40 and 60°C, respectively. Oil viscosity was measured and microscopic images of the centrifugated oil samples of asphaltene clusters were obtained. In the second set of experiments, 12 identical crude oil samples with different toluene concentrations of 5, 10, and 15 vol% were subjected to four different durations of ultrasonic irradiation and under different temperatures. In the third group, seven actual carbonate core samples of damaged oil permeability due to the injection of 60 pore volumes of asphaltic crude oil were subjected to different ultrasonic time interval of 5, 10, 15, 20, and 25 min and frequencies of 10, 15 and 20 kHz, respectively. Both the oil permeability of these samples was measured and the scanning electron microscope (SEM) images were carried out before and after the ultrasonic irradiation process. The results showed that subjection of the UAE crude oil to ultrasonic irradiation decreases the size of asphaltene clusters. Consequently, this effect reduces asphaltene tendency to precipitate at 10 min or more time interval of ultrasonic irradiation. In addition, similar results were obtained with solvent effect, but with more reduction in oil viscosity. The results also indicated that the increase of ultrasonic time interval and/or frequency drastically improve(s) damaged oil permeability.     

Experimental Study of Asphaltene Deposition During Different Production Mechanisms

Abstract

Sudden changes in key parameters such as pressure, temperature, and fluid composition may result in asphaltene precipitation and deposition, consequently reducing permeability and porosity as well as well injectivity and productivity. Sandstone cores of an Iranian reservoir were studied under high pressure and temperature. Asphaltene deposition was studied in recycled gas injection, CO₂ injection, and natural depletion experiments. The authors observed that these processes could be ranked for the deposition severity viewpoint in the aforementioned order. Qualitatively investigation of cores indicated nonuniform deposition of precipitated asphaltene along a flooded core and reducing deposition from entering core terminal to the core outlet.     

Utilization of RBF-ANN as a novel approach for estimation of asphaltene inhibition efficiency

One of the problematic concerns in petroleum industries is the deposition of heavy fractions of crude oil such as asphaltene fraction during production and transportation. The utilization of inhibitors is known as a relative low cost and effective method for asphaltene inhibition. In this study, Radial basis function artificial neural network (RBF-ANN) was applied to predict asphaltene precipitation reduction in terms of structure and concentration of inhibitor and oil properties. In order to training and testing of RBF-ANN the required data are extracted from reliable sources. The predicted asphaltene precipitation reduction values were compared with the actual data statistically and graphically. The coefficients of determination for training and testing phases of RBF-ANN were determined as 0.995906 and 0.994853 respectively. These evaluations showed that the RBF-ANN as a predictive tool has great capacity to estimate effect of asphaltene inhibitors on reduction of asphaltene precipitation.     

Detection of Precipitation in Pipelines

One of the major unsolved complex problems confronting the petroleum and chemical industries at present is the untimely deposition of heavy organic and other solids dissolved or suspended in the fluid flow systems. The production, transportation, and processing of petroleum can be significantly affected by flocculation and deposition of such compounds in the course of industrial processing systems, including transfer conduits, reactors, and refineries and upgrading equipment, with devastating economic consequences. Heavy organics such as paraffin, wax, resin, asphaltene, diamondoid, mercaptdans, and organometallic compounds can precipitate out of the crude oil solution due to various forces causing blockage in the oil reservoir, well, pipeline, and in the oil production and processing facilities. It is important to producers that the potential organic deposition can be predicted so that the production strategy can be designed to prevent, if possible, or mitigate this problem. Cleaning the pipeline has a common commercial term, pigging. Early detection of precipitation can reduce pigging and, in turn, the maintenance cost considerably. Prediction of why and when precipitations occur has gained much interest in recent years. Most studies focus on the chemical behavior of the crude oil and its contamination. A nonintrusive instrumentation technique for on-line inspection that can yield as much detailed information about the interior of the pipe as possible is highly desirable. In this article, the detection of asphaltene and paraffin wax is studied using various techniques. The techniques include the use of solid detection system by light transmittance measurement for asphaltene detection, the use of photodiode for light transmittance measurement for liquid wax, the use of ultrasound and strain gauge for detecting solid wax.     

CO2驱沥青质沉积对致密储层的伤害机理——以鄂尔多斯盆地延长组长8储层为例

为了揭示CO2驱替过程中沥青质沉积对致密储层的伤害机理,文中基于岩心核磁共振T2谱测试原理,开展了CO2注入压力下的岩心驱替实验,研究了沥青质在岩心中的沉积特征,评价了沥青质沉积对储层的伤害程度。实验结果表明:沥青质沉积量和渗透率伤害率随着CO2注入压力的升高呈现先快速上升后趋于平缓的趋势;在CO2注入过程中,沥青质主要沉积在弛豫时间大于10 ms的大、中孔隙,导致大、中孔隙占比下降,微细、小孔隙占比增加,且随着CO2注入压力的升高,大、中孔隙占比下降幅度增大,微细、小孔隙占比上升幅度增大;此外,沥青质沉积会引起润湿性发生反转,随着沥青质沉积量的增加,润湿反转指数增大,岩心润湿性不断向强油湿方向转变。     

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.     

REVERSIBILITY AND INHIBITION OF ASPHALTENE PRECIPITATION IN BRAZILIAN CRUDE OILS

ABSTRACT

A fundamental understanding of the aggregation and precipitation of asphaltenes in petroleum crudes is important for the development of preventive and curative measures for the potential problem of asphaltene deposition occurring during production, transport and refining operations. The question of reversibility of asphaltene precipitation, yet a controversial issue, is crucial for a clear and unequivocal understanding of the precipitation phenomenon, development of mathematical models that describe the behavior of asphaltenes in petroleum fluids, and the design of inhibitors. In this work, the behavior of precipitated asphaltenes in Brazilian crude tank oil samples following flocculant removal and gradual addition of fresh oil was investigated. The results obtained revealed a re-dissolution of precipitated asphaltene particles following flocculant removal and oil addition. On the inhibition of asphaltene precipitation, the capacity of a number of surfactants and block copolymers to inhibit asphaltene precipitation and deposition was also examined. Ethoxylated Nonylphenols and Hexadecyl Trimethyl Ammonium Bromide displayed highest capacity in the inhibition of asphaltene deposition.     

注天然气油井沥青质析出规律研究

目的 解决东河区块原油在注气开采过程中沥青质沉积堵塞井筒问题.方法 采用高温高压固相沉积规律测试装置,基于光散射理论,研究了温度、压力、气油比等因素对沥青质析出特征的影响.结果 温度升高会增加沥青质在原油中的溶解度,促进原油稳定;等温降压过程中,沥青质随着压力降低逐渐析出,在泡点压力附近达到最大析出量,发生沥青质沉积堵...     

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.     

Effect of pressure,temperature, and mass fraction of CO2 on the stability of the asphaltene constituents in crude oil

This paper focus on the main influence factors (temperature, pressure, and mass fraction of CO₂) on the state of asphaltene in the crude oil during CO₂ flooding by using high temperature and high pressure microanalysis system of solid precipitation. For the simulated oil sample – CO₂ system, the state of asphaltene is not affected by temperature within this range of 50°C to 100°C, the particle size of the asphaltene has an increase with the increase of the pressure from 8MPa to 40 MPa. When the mass fraction of CO₂ is less than 35%, the state of the asphaltene has not changed and the asphaltene particles are in a suspension state. When the mass fraction of CO₂ increases to 40%, the aggregation of the asphaltenes occurs and then form precipitation. With the further increase of the mass fraction of CO₂, the particle of the asphaltene aggregates has a significant increase. For the field development project design of CO₂ flooding, the influence of the temperature can be ignored, the appropriate mass fraction of CO₂ is below 35% and the gas injection pressure should maintain a relatively low value. The results can provide a theoretical basis to avoid the asphaltene precipitation during CO₂ flooding.     

The Growth and Development of Asphaltene Aggregates in Toluene Solution

The effect of asphaltene concentrations from 10 to 140 mg/L on particle diameter of aggregates is studied by multiple angle dynamic and static light scattering. The particle diameter of aggregates is increasing with the asphaltene concentration rising. The observed concentration for massive self-aggregation of asphaltene is about 80 mg/L. And the process of growth and development of asphaltene aggregates is studied by measurements of particle video microscopy (PVM) and focused beam reflectance measurement (FBRM) on asphaltene in toluene solution simultaneously. PVM and FBRM provide dynamic images and real-time statistical data of asphaltene aggregates in toluene solution, which can show that asphaltene aggregation is stronger and stronger with the asphaltene concentration increasing. Statistical data demonstrate that small particles are first massively formed in the range of less than 5 μm and 5–10 μm. Then small particles can interact to result in large particles which are in the range of 10–50 μm and 50–80 μm with asphaltene concentration increasing. The number of particles in the range of less than 50 μm is dominant in solution despite asphaltene concentration increasing.