Maintaining overall asphaltene stability is imperative for a successful flow assurance treatment program. However, complex interactions between the polar asphaltene fraction and other components in crude oil or reservoir minerals makes the stability assessment extremely challenging. These interactions can contribute towards the precipitation and subsequent deposition of unstable asphaltene clusters comprising of impurities such as paraffin, polar organics, and inorganic mineral composites. This study investigates the impact of inorganic salts and minerals on asphaltene stability and inhibitor performance efficiency.
Four problematic crude oil samples having asphaltene deposition issue along with its field deposits were analyzed. Primary characterization of oil samples was conducted by measuring physicochemical properties. Crude oil and deposit samples were further evaluated by performing multiple compositional analyses like Fourier Transform InfraRed (FTIR) Spectroscopy, Carbon Chain Distribution (CCD), and X-Ray Fluorescence (XRF). Furthermore, asphaltene inhibitor performance efficiency was measured by carrying out both dispersion test analyses.
Primary characterization of crude oil samples did not suggest any anomalous behavior indicative of unstable asphaltene fraction. However, the solid field deposition in the production and flow-lines were observed. Therefore, further analyses of the oil as well as the solid deposits was necessitated. The analyses revealed unusually high concentration of inorganic impurities co-precipitating out with the asphaltene fraction. In general, polar nature of asphaltene induces van der Waals force of attraction between permanent dipoles (Keesom), induced dipoles (London dispersion), and permanent with induced dipoles (Debye). Paraffin and polar organic fractions associate with asphaltene through van der Waals forces and reduces the active polar sites available for the inhibitor to interact with. Moreover, presence of ions within the salts and inorganic minerals introduce ion-ion or ion-dipole interactions, which are considerably stronger than the van der Waals forces. Thus, these interactions with ionic salts and minerals interfere with the inhibitor-asphaltene interactions to a greater extent and consequently reduces the inhibitor performance efficiency significantly within laboratory screening methods.
This study, for the first time, highlights detailed contribution of impurities, specifically of ionic salts and minerals originated from drilling and completion fluids or reservoir minerals, on the overall asphaltene stability and inhibitor performance efficiency. The molecular forces arising due to co-precipitation of organic and inorganic minerals were observed to impact the asphaltene inhibitor performance considerably. Therefore, it is important to comprehend the compositional and elemental content of both crude oil and field deposit samples and accordingly select asphaltene testing methodology and modify the asphaltene inhibitor chemistry.
Da Silva de Aguiar, Janaina Izabel (Clariant) | Pimentel Porto Mazzeo, Cláudia (Clariant) | Garan, Ron (Clariant) | Punase, Abhishek (Clariant) | Razavi, Syed (Clariant) | Mahmoudkhani, Amir (Clariant)
Recent studies revealed that solids from lab-generated deposits often exhibit compositional differences from those of field deposits, pointing to a more complex fouling process in field operations. The objective of this work was to understand and apply knowledge from field deposit characteristics in order to design and conduct laboratory experiments which yield solid deposits with comparable compositional fingerprints. This approach allows a more objective and reliable product development and recommendation strategy to be adopted for increased success in the field applications. First, oil and deposit samples from an offshore field was characterized. Second, samples of the asphaltenes extracted from oil (AEO) and from the deposit (AED) were characterized based on solubility using an Accelerated Solubility Test (AST). A customized Asphaltene Dynamic Deposition Loop (ADDL) was used in this study to simulate the precipitation and deposition of asphaltenes from the crude oil. Crude oil used in the tests was from the same well where the deposits were collected. ADDL tests were conducted at high temperature and pressure and the composition of the collected deposit from this test was compared with the deposits from the field. At last, Light Scattering Technique (LST) was applied to screen asphaltene inhibitors (AI). Four candidate chemistries were tested on LST. To confirm the efficiency, the high performer was tested on ADDL under dynamic conditions. Deposits collected from the ADDL were characterized and results showed a high degree of similarity to the field deposit. AI1 was evaluated by ADDL and it decreased the deposition in the filters by 60% and 84% at 1000 ppm. This product was selected to be tested in the field and a plant trial is ongoing.
The near wellbore damage due to asphaltenes deposition is one of the major flow assurance issues currently faced by the petroleum industry. This study examines the pore scale flocculation and deposition processes of asphaltenes onto rock matrices. The effect of sand-grain size, clay presence in the reservoir rock, crude oil type, and precipitated asphaltenes type on the depositional behavior of asphaltenes is investigated. The porous media is prepared using sands with two different grain sizes or using sand-clay mixtures. Reservoir rocks were fully saturated with two different oil samples. 8 samples was prepared and they were washed by using either n-pentane or n-heptane, which are known as asphaltene insoluble solvents. In total, 16 experimental samples washed with solvents were subjected to optical microscopy and Scanning Electron Microscopy (SEM) – Energy Dispersive Spectroscopy (EDS) analyses to assess the asphaltene depositional mechanism. For all cases, porosity variations were measured experimentally. Our results suggest that asphaltene-clay interaction can increase the near-wellbore damage due to the strong polar ends in asphaltenes which are attached to clay surfaces and/or asphaltenes that are stuck in clay layers. Porosity of the sand has been found to decrease after the injection of solvents, indicating pore blockage due to asphaltene deposition. While the n-pentane precipitated more asphaltenes than n-heptane, n-heptane asphaltenes occupied more volume and resulted in higher porosity reduction due to higher polarity of n-heptane asphaltenes than n-pentane asphaltenes. Furthermore, the presence of clays and non-uniformity of grain sizes are observed to aggravate formation damage by asphaltenes. The SEM images showed that the interaction of clays with asphaltenes mainly reduces the permeability rather than porosity. The EDS analyses indicate that the impurity content of asphaltenes affect mainly the interaction of asphaltenes and clays.
Asphaltenes and resins are the polar and saturates and aromatics are the nonpolar fractions of the crude oil. The mutual interaction within crude oil fractions results in different overall polarity. With the onset asphaltene precipitation, the overall polarity starts to change drastically and this change affects the asphaltene stability more. This study investigates the crude oil fractions polarity and their individual impact on asphaltene precipitation.
Two crude oil samples with different asphaltene content, API gravity, and viscosity were divided into their Saturates, Aromatics, Resins, and Asphaltenes (SARA) fractions. The crude oils and their SARA fractions were characterized by Fourier Transform InfraRed (FTIR) spectroscopy. The polarity of crude oils and their SARA fractions were determined through dielectric constant measurements by in-house-built capacitance.
The polarity of the individual fractions and bulk crude oil samples were analyzed together to understand how the mutual interaction of crude oil fractions affects the asphaltene stability. The overall polarity of the crude oil is the key to asphaltene stability. Resins and asphaltenes are the polar components of crude oil, thus, resins to asphaltenes ratio affects the overall stability of the asphaltenes. Asphaltenes are soluble in aromatic solvents and insoluble in normal alkanes, thus, while the increase in the saturates fraction in crude oil decreases the asphaltene stability, the increase in the aromatics fraction in crude oil reestablishes the stabilization. The solvent power of saturates and aromatics fractions are controlled by the impurities in saturates and aromatics fractions. Because while saturates and aromatics are known as nonpolar fractions of crude oils, the impurity content of those fractions results in polar sides in both saturates and aromatics fractions. The polar side of those fractions makes the interaction with asphaltenes more pronounced and affect the stability of asphaltenes considerably.
The holistic understanding of the asphaltene stability is achieved by analyzing the polarity of asphaltenes alone and within crude oil. These results are very useful in preventing the asphaltene precipitation and modelling its stability.
Prakoso, Andreas (Texas A&M University) | Punase, Abhishek (Texas A&M University) | Klock, Kristina (Texas A&M University) | Rogel, Estrella (Chevron Energy and Technology Center) | Ovalles, Cesar (Chevron Energy and Technology Center) | Hascakir, Berna (Texas A&M University)
Significant effort has been dedicated to understand the variables affecting asphaltene precipitation. Based on years of research, it is well known how variables such as temperature and pressure can affect the deposition of asphaltenes. However, much less is understood about the effect that asphaltene characteristics have on the tendency towards precipitation of different crude oils. We characterize extensively a series of n-pentane extracted asphaltenes and construct novel correlations with the stability of their corresponding crude oils.
11 different bitumen and crude oil samples are characterized first with API gravity and viscosity measurements, and thermogravimetric and differential scanning calorimetric analyses (TGA/DSC). The weight percentage of the asphaltenes in bulk samples are determined through n-pentane precipitation. The molecular structure of the asphaltenes is investigated with Fourier Transform InfraRed (FTIR) spectroscopy. Asphaltene stability is measured by ?PS and by determining the Asphaltene Solubility Profile. The impact of hydrogen deficiency, heteroatom content and solubility distributions on other properties such as viscosity and aggregation behavior is also explored.
It has been observed that there is weak relationship between the asphaltene content and API gravity or viscosity of the bulk samples. The weight percent of the light, intermediate, heavy, solid, and ash fractions of the asphaltenes, defined with TGA/DSC experiments, indicate that the carbon rich solid component of the bulk samples that can decompose over 550 °C, correlate with the weight percent of the asphaltenes in bulk oil. The ash content of the bulk oil, which is mainly composed of heavy metals like sulfur, nickel, and vanadium, is correlated to the amount of asphaltenes precipitated out of the oil. Moreover, FTIR and solubility profile analyses reveals that the polarity of the asphaltene molecules is affected not only by its molecular composition and structure but also by its interactions with other crude oil components.
This study discusses the impact of the physical and chemical properties of crude oils and their asphaltenes on asphaltene precipitation. Several asphaltene deposition mechanisms are developed and validated for 11 different crude oil and bitumen samples with different asphaltene contents, thereby providing important and fundamental insight into asphaltene related problems.