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Abstract Due to the economic concerns for asphaltene related problems, chemical treatment of the near-wellbore asphaltene deposition became popular in the oil and gas industry in the past few years. However, due to the complexity and the lack of knowledge on the asphaltene problems, these asphaltene remediation programs are not always successful. Although, the field applications of these procedures have been discussed in the literature, a dynamic model that can handle asphaltene chemical remediation in the reservoir is missing. In this paper, a comprehensive non-isothermal compositional reservoir simulator with the capability of modeling near-wellbore asphaltene remediation is developed to address the effect of asphaltene deposition on the reservoir performance. This simulator has many additional features compared to the available asphaltene reservoir simulators. The simulator can handle asphaltene behavior during primary, secondary, and EOR stages. We model asphaltene precipitation and flocculation using a solid model and a reversible chemical reaction, respectively. In addition, adsorption, entrainment, and pore-throat plugging are considered as the main mechanisms of the asphaltene deposition. Furthermore, we consider wettability alteration and porosity, absolute permeability, and oil viscosity reductions due to asphaltene. Moreover, based on the mechanisms of the asphaltene-dispersant interactions, a dynamic modeling approach for the near-wellbore asphaltene chemical treatments is proposed and implemented in the simulator. We assume that dispersants dissolve flocculated and deposited asphaltenes and transform them to colloidal asphaltenes. Dissolution of asphaltene particles using dispersants is modeled using a two-step process (1) the dispersants are adsorbed on the surface of the asphaltene particles and (2) the interactions between adsorbed dispersant and asphaltene becomes dominant. The first reaction is very fast and the second reaction is the rate-determining step. Finally, we present case studies to investigate the effectiveness of chemical treatment jobs on asphaltene dissolution. The results show that the type of dispersant, amount of dispersant, soaking time, number of treatment jobs, and time period between two treatment jobs affect the efficiency of an asphaltene chemical treatment plan. Therefore, the success of the treatment job requires dynamic modeling. Since the presented asphaltene remediation model is very comprehensive, we can optimize the treatment plan in a field and maximize the revenue by simulation of various scenarios.
Asphaltene deposition has a significant detrimental effect on oilfield production. The key to effective treatment of asphaltene deposition is recognition of the problem. Asphaltenes can be identified and quantified using laboratory methods. In the past physical, mechanical and chemical treatments have been used to control asphaltene deposition in the oilfield. Chemical treatments have included aromatic solvents and low molecular weight dispersants. However, many of these treatments are ineffective.
Recently, technically and economically effective methods to control asphaltene-created production problems have been developed. These applications make problems have been developed. These applications make use of a new polymeric dispersant/inhibitor at clean-up dosages of 1,000 to 10,000 ppm and continuous dosages of 50 to 400 ppm.
As a result of downhole clean-outs and chemical squeezes using the new dispersant/inhibitor, production increases have been achieved and maintained. Tank bottom and interface control has been achieved through continuous feed applications. In one case, an additional benefit of the treatment was increased effectiveness in demulsifying oil/water emulsions and maintaining cleaner discharge water.
Many oil field processes are plagued with problems that are attributable to the precipitation problems that are attributable to the precipitation of asphaltenes. Asphaltenes deposit wherever a change occurs that increases the solubility of asphaltene-stabilizing resins in the bulk oil phase. Typically, this occurs in well bores, jet pump orifices, downhole pumps, tubing, flow lines, treater interfaces or stock tank bottoms.
For example, production losses are sometimes the result of asphaltene precipitation in the formation or in the well bore. This heavy material may reduce the dehydration efficiency of heater treaters to the extent that pipeline specifications for water content of crude oils cannot be met.
Asphaltene-related problems also occur in stock tanks. Precipitated matter can build to several feet in depth, thus reducing storage volume and increasing handling difficulties while producing a potentially hazardous waste product.
This paper describes asphaltenes briefly and discusses case studies using a new polymeric asphaltene dispersant/inhibitor.
Baker Petrolite has developed a new proprietary method of detecting the asphaltene content of crude oil. The method employs a spectroscopic probe detection technique that measures the amount of dissolved asphaltenes in the crude directly without sample preparation. The device is suitable for both discrete or continuous in-process sample measurements. Laboratory and field test data are presented. The new technique compares with traditional methods of asphaltene characterization including IP-143 extraction gravimetric analysis and ADT spectroscopic methods. This technique, combined with asphaltene inhibitor/dispersant injection control, provides a novel method for the control of asphaltene deposition in crude oil production systems.
The deposition of asphaltic material from crude oil is a well-characterized operational problem associated with the production and refining of crude oil. The details of asphaltene characterization, deposition, and deposition inhibition have been reported in numerous references.1,2,3,4 There is a tremendous economic benefit to the continuous inhibition of asphaltene deposition and avoidance of costly mitigation techniques.5
Many inhibitors and dispersants have been developed to prevent the deposition of asphaltenes in well bores and pipelines.2,3,4,5 In the past, the effectiveness of these inhibitors is typically measured by analyzing discrete crude samples with laboratory test methods such as the IP-143 extraction gravimetric test and the ADT spectroscopic test.6 These laboratory methods work reasonably well, but are very time-consuming and labor intensive. None of the current laboratory methods of asphaltene analysis are feasible for field use.
Other types of in situ asphaltene monitoring devices have been developed based on acoustic particle size monitors and are described in the literature.7 However, since these devices measure asphaltenes by analyzing deposition, it can be difficult to differentiate asphaltene deposition from other types of deposition such as paraffin, scale, and biomass commonly found in production systems.
Description of the BPC Asphaltene Probe
Due to the proprietary nature and pending patent issues, many of the details of this new technique are beyond the scope of this paper.
The proprietary BPC probe is a fiber optic device that utilizes a special optical crystal that is capable of making measurements in very dense liquids such as crude oil. The probe takes measurements within a few nanometers of the crystal surface. Over a specific spectral range, the probe can determine differences in asphaltene content in a crude sample by direct measurement. These measurements are based on relative differences in absorbance. To determine asphaltene concentrations of specific samples, the probe has to be calibrated to the specific crude with an external empirical method, such as IP-143 or the ADT method.
The novelty of this approach is the direct analysis of the crude oil sample without any laboratory preparation prior to the test. This technique can be used either with discrete samples or as an in-situ, on-line measurement. The probe is designed to withstand process conditions up to 300°F in temperature and up to 3000 psi.
Ovalles, Cesar (Petroleum and Material Characterization Unit, Chevron Energy Technology Co.) | Rogel, Estrella (Petroleum and Material Characterization Unit, Chevron Energy Technology Co.) | Morazan, Harris (Petroleum and Material Characterization Unit, Chevron Energy Technology Co.) | Moir, Michael E. (Petroleum and Material Characterization Unit, Chevron Energy Technology Co.)
Abstract Asphaltenes are blamed for several operational issues throughout the petroleum value chain such as: reducing volumetric production of wells, plugging of valves, pumps, tubing and pipelines during lifting, production, transportation, and storage. During refining operations, asphaltenes can cause heat exchanger and oven fouling and contributing to catalyst poisoning by coke and metal depositions. There are several techniques that can be used to deal with asphaltene precipitation issues: a) control pressure or other operational variables such as oil comingling, b) periodical cleaning (either chemical or mechanical), and c) additive injection to prevent asphaltene precipitation. Specifically, current methods for additive evaluation are time-consuming, rely exclusively on measurements at room temperature and could be very costly if they are carried out at reservoir conditions. Thus, the need for a method for rapid assessment of additives to prevent asphaltene precipitation is necessary to maintain well production and maximize economic benefits. A new analytical technique was developed for screening and selection of asphaltene dispersants at reservoir conditions (<200°C). It is based on the On-Column Filtration method (Rogel 2009 and Ovalles 2015) and can quantitatively measure asphaltene dispersion activity by determining the percentage of reduction of asphaltene content versus the case without additives. It allows performing mass balances, is fast (<50min), repeatable, has small human intervention and uses a small amount of sample. A nonylphenolformaldehide resin (MW = 1600 g/mol) and three commercial additives were tested using gravimetrically separated asphaltenes and a Mid-continent crude oil. Reductions in the asphaltene contents up to 56% were found for the former and 38% for the latter. The mechanism in which asphaltene inhibitors and dispersants interact with asphaltenes depends on the type of additive and asphaltene composition and concentration. Some mechanistic considerations on the action of additives to prevent asphaltene precipitation are presented.
In a Japanese oil field, which applying jet pump (coiled tubing running, standard flow type, produced oil as power fluid containing asphaltenes and waxes) since 2014, unstable power fluid injection pressure has been observed since 2016 due to asphaltene deposition on jet pump nozzle area, which limited power fluid rate and therefore production rate. The objective of this study was to achieve high oil production rate by overcoming the pressure fluctuation due to asphaltene deposition problems.
Asphaltene inhibitors (AI) from various suppliers were tested to measure asphaltene deposition amount as a laboratory screening. The best AI candidate was implemented in a field trial test during which, asphaltene deposition amount in strainers were measured, production oil was collected to measure asphaltene deposition rate under stock tank condition, and operation data was monitored and analyzed. To confirm the new AI efficiency, these data were compared with the ones during the original AI before starting the field test.
This paper presents specific features which were found in the field test. Selected AI was efficient at dispersing asphaltenes. It achieved stable injection pressure and reduced asphaltene deposition amount in production oil sample. However, it became worse again within one month. The main reason was that the new AI worked as dispersant to delay asphaltene deposition so that asphaltenes finally accumulated under jet pump production system which is semi-closed loop. Asphaltene deposition amount on strainers increased during winter, especially shut down periods, because process temperature was close to ambient condition. This temperature-dependent observation means asphaltene deposition was highly influenced by wax deposition. A follow-up laboratory test revealed the asphaltene deposition amount decreased by adding paraffin inhibitor (PI). This field test result revealed the asphaltene and paraffin interaction in field scale.