IN THE PRESENT STUDY THE EFFECT OF AC ELECTRICAL FIELD ON ASPHALTENE PRECIPITATION IS INVESTIGATED. AN ASPHALTENIC CRUDE OIL WITH 11.32WT% ASPHALTENE WAS SELECTED TO CONSIDER THE EFFECT OF AN AC ELECTRIC FILED EFFECT ON ASPHALTENE PRECIPITATION. IT WAS SHOWN THAT IN THE PRESENCE OF AN ELECTRIC FIELD, MIXING OF ASPHALTENIC CRUDE OIL WITH HEPTANE LEADS TO ENHANCEMENT OF ASPHALTENE PRECIPITATION. THE PRECIPITATION BEHAVIOR OF ASPHALTENE IN CRUDE OIL-HEPTANE WAS CONSIDERED AT DIFFERENT VALUES OF ELECTRIC FIELDS AND EXPOSURE TIME OF FIELD. THE RESULTS SHOWED THAT AN INCREASE IN ELECTRIC FIELD STRENGTH FOR SMALL EXPOSURE TIME UP TO 5 MINUTES A SINUSOIDAL BEHAVIOR IS OBSERVABLE FOR ASPHALTENE PRECIPITATED VALUE WHILE WITH INCREASING THE EXPOSURE TIME OF FIELD UP TO 30 MINUTES A LOW INCREASING TREND IS OBSERVED FOR ALL THE ELECTRIC FIELD STRENGTH. THIS CAN BE EXPLAINED BY AN INTERACTION BETWEEN THE ELECTRIC FIELD FORCES AND THE CHARGE OF ASPHALTENE PARTICLES. THIS INFORMATION IS USEFUL FOR MANIPULATION OF THE SITUATION WHERE ELECTRIC FIELD IS APPLIED TO ASPHALTENIC CRUDE OILS.

PRECIPITATION OF ASPHALTENES IN RESERVOIRS, WELLS, AND FACILITIES HAS A SEVERE DETRIMENTAL EFFECT ON THE ECONOMICS OF OIL PRODUCTION BECAUSE OF A REDUCTION IN WELL PRODUCTIVITY AND/OR CLOGGING OF THE PRODUCTION FACILITIES. SEVERAL PROCEDURES ARE USED TO REMOVE OR PREVENT ASPHALTENE PRECIPITATION, BUT THE USES OF ASPHALTENE INHIBITORS PROVIDE MOST PRACTICAL AND ECONOMICAL SOLUTION FOR DEPOSITS TREATMENT. IT IS NECESSARY TO KNOW THE PERFORMANCE OF AN INHIBITOR BEFORE ITS APPLICATION IN THE FIELD. IN THIS WORK PERFORMANCE OF FIVE NON-COMMERCIAL INHIBITORS; NAMELY BENZOIC ACID, NONYLPHENOL, PHENANTHRENE, PHTHALIC ACID, SALICYLIC ACID AND ONE COMMERCIAL INHIBITOR NAMELY IR95 IN THE AMOUNT OF PRECIPITATED ASPHALTENE AT STANDARD CONDITION, RESERVOIR CONDITION AND OCCURRING ONSET SHIFTING HAVE BEEN STUDIED. RESULTS OF INHIBITOR TESTS REVEAL THAT AMONG NON-COMMERCIAL INHIBITORS, SALICYLIC ACID WITH HAVING EXTRA HYDROXYL GROUP (-OH) ON BENZOIC RING HAS THE MOST EFFECT ON ASPHALTENE PRECIPITATION REDUCTION AND IR95 HAS THE BEST EFFICIENCY AMONG ALL INHIBITORS.

A POLYDISPERSE THERMODYNAMIC MODEL IS DEVELOPED BY INTRODUCING AN ASPHALTENE MOLECULAR WEIGHT DISTRIBUTION FUNCTION BASED ON FRACTAL AGGREGATION. MODIFICATION THAT IS INTRODUCED INTO POLYDISPERSE MODEL SOLVES THE INSTABILITY PROBLEM OF KAWANAKA MODEL. ALSO CALCULATION OF RESIN CONCENTRATION IS NOT REQUIRED ANYMORE. FLORY-HUGGINS AND MODIFIED FLORY-HUGGINS THERMODYNAMIC SOLUBILITY MODELS ARE APPLIED TO COMPARE THEIR PREDICTIONS WITH PROPOSED MODEL VIA EXTENSIVE SET OF EXPERIMENTAL DATA AT DIFFERENT RESERVOIR PRESSURES AND TEMPERATURES AND GAS INJECTIONS.

CRUDE OIL CONSISTS OF FOUR MAIN HYDROCARBON GROUPS: SATURATED HYDROCARBONS, AROMATICS, RESINS AND ASPHALTENES. ASPHALTENES ARE DEFINED AS THE CRUDE OIL FRACTION THAT PRECIPITATES UPON THE ADDITION OF AN N-ALKANE (USUALLY N-PENTANE OR N-HEPTANE) BUT REMAINS SOLUBLE IN TOLUENE. ASPHALTENE PRECIPITATION AND DEPOSITION IS ONE OF THE MOST IMPORTANT ISSUES IN DIFFERENT STAGES OF PETROLEUM PRODUCTION. IT CAUSES THE PLUGGING OF WELLBORE, PIPELINES AND PRODUCTION EQUIPMENT. TO MAINTAIN THE PRODUCTION OF WELL AND AVOID PRESSURE REDUCTION DUE TO ASPHALTENE DEPOSITION, SO MANY MECHANICAL AND CHEMICAL METHODS HAVE BEEN APPLIED. THESE METHODS ARE EXPENSIVE AND NEED SUFFICIENT TIME, THEREFORE IT WOULD BE BETTER TO FIND A CONDITION TO REDUCE POSSIBILITY OF ASPHALTENE PRECIPITATION. THERE IS A STABLE CONDITION AMONG ASPHALTENE, RESINS AND MALTENES AND IT DISTURBS ACCORDING TO VARIOUS CHANGES IN TEMPERATURE, PRESSURE OR COMPOSITION. THIS PRESENT STUDY INVESTIGATES THE ASPHALTENE PRECIPITATION DUE TO PRESSURE DEPLETION FOR A GIANT IRANIAN OIL RESERVOIR AND THROUGH UNDERSEA PIPELINES. IN THIS METHOD THE SOLID THERMODYNAMIC MODEL PRESENTED BY NGHIEM ET AL. (1993) WAS UTILIZED WHICH WAS THEN TUNED USING THE PVT DATA AVAILABLE FOR THIS OIL RESERVOIR. THE MODEL WAS ABLE TO SIMULATE ASPHALTENE PRECIPITATION IN THIS RESERVOIR UNDER DIFFERENT PRODUCTION SCHEMES. TO STUDY THE EFFECT OF PRESSURE DEPLETION ON ASPHALTENE PRECIPITATION, SOLID MOLAR VOLUME WAS USED AS THE MOST IMPORTANT MATCHING PARAMETER. ALSO, INTERACTION COEFFICIENT BETWEEN PRECIPITATING COMPONENTS AND LIGHT COMPONENT WAS FOUND TO INFLUENCE THE AMOUNT OF ASPHALTENE PRECIPITATION ESPECIALLY BELOW THE SATURATION PRESSURE.

INTRODUCTION: CRUDE OIL IS A COMPLEX MIXTURE. IT CONSISTS OF FOUR MAIN HYDROCARBON GROUPS: SATURATED HYDROCARBONS, AROMATICS, RESINS AND ASPHALTENES. ASPHALTENES ARE DEFINED AS THE CRUDE OIL FRACTION THAT PRECIPITATES UPON THE ADDITION OF AN N-ALKANE (USUALLY N-PENTANE OR N-HEPTANE) BUT REMAINS SOLUBLE IN TOLUENE. ASPHALTENE PRECIPITATION AND DEPOSITION IS ONE OF THE MOST IMPORTANT PROBLEMS IN DIFFERENT STAGES OF PETROLEUM PRODUCTION. IT CAUSES THE PLUGGING OF WELLBORE, PIPELINES AND PRODUCTION EQUIPMENTS. TO MAINTAIN THE PRODUCTION OF WELL AND AVOID PRESSURE REDUCTION DUE TO ASPHALTENE DEPOSITION, SO MANY MECHANICAL AND CHEMICAL METHODS HAVE BEEN APPLIED. THESE METHODS ARE EXPENSIVE AND NEED SUFFICIENT TIME; THEREFORE IT IS BETTER TO FIND A CONDITION TO REDUCE POSSIBILITY OF ASPHALTENE PRECIPITATION.