ASPHALTENE DEPOSITION IS ONE OF THE MOST CHALLENGING RESERVOIR ENGINEERING PROBLEMS. IN THIS PAPER A RIGOROUS MODEL CONSIDERING MECHANICAL DEPOSITION MECHANISMS AND ADSORPTION HAS BEEN DEVELOPED TO PREDICT THE ASPHALTENE DEPOSITION AND PERMEABILITY REDUCTION IN POROUS MEDIA BY DISCRETIZING THE GOVERNING EQUATIONS IN SPACE AND TIME. THE MODEL PARAMETERS HAVE BEEN DETERMINED BY APPLICATION OF AN APPROPRIATE OPTIMIZATION TECHNIQUE. THE VALIDITY OF THE DEVELOPED MODEL IS EVALUATED BY COMPARING THE MODEL PREDICTIONS WITH EXPERIMENTAL DATA. THE RESULTS SHOW THAT THERE ARE VERY GOOD AGREEMENTS BETWEEN MODELING RESULTS AND EXPERIMENTAL DATA.

IN THE UPSTREAM ASPHALTENE FLOW ASSURANCE COMMUNITY, BOTH ACADEMICS AND INDUSTRIES ARE ACTIVELY INVOLVED TO PREDICT THE ASPHALTENE DEPOSIT PROFILE IN WELLBORES AND PIPELINES. IN THIS WORK, THE PERTURBED CHAIN FORM OF THE STATISTICAL ASSOCIATING FLUID THEORY (PC-SAFT) WAS APPLIED TO PREDICT THE ASPHALTENE PHASE BEHAVIOUR UNDER HIGH PRESSURE-HIGH TEMPERATURE CO2 INJECTION CONDITIONS. THEN, THE PREVIOUSLY DEVELOPED ASPHALTENE DEPOSITION TOOL (ADEPT) WAS USED TO INVESTIGATE THE EFFECT OF CO2 INJECTION ON ASPHALTENE DEPOSITION PROFILE IN WELLBORE. BASED ON THE OBTAINED RESULTS, WHEN THE INJECTED CO2 CONCENTRATION INCREASES FROM 0 MOL% TO 15 MOL%, THE DEPOSITION FLUX IN WELLBORE DECREASES. BEYOND 15 MOL% INJECTED CO2, DEPOSITION FLUX IN WELLBORE INCREASES. TO JUSTIFY THE TREND OF DEPOSITION FLUX VERSUS CO2 CONCENTRATION, THE SOLUBILITY OF THE MIXTURE WAS CALCULATED USING PC-SAFT. THE CALCULATIONS SHOWED THAT ADDITION OF CO2 TO THE LIVE OIL INCREASES THE MIXTURE SOLUBILITY SINCE THE SOLUBILITY OF CO2, AT SPECIFIC PRESSURES AND TEMPERATURES, IS MORE THAN THE LIVE CRUDE SOLUBILITY. FURTHER ADDITION OF CO2 DECREASES THE MASS FRACTION OF HIGH SOLUBILITY COMPONENTS IN THE OIL, I.E. AROMATICS, RESINS AND ASPHALTENES, AND AS A RESULT THE MIXTURE SOLUBILITY DECREASES AND SO MORE ASPHALTENES PRECIPITATE AND TEND TO DEPOSIT.

IN THIS PAPER, AT FIRST STAGE THE SOAVE-REDLICH-KWONG (SRK) EOS IS MODIFIED BASED ON PERTURBATION THEORY. THE PARAMETER OF THE NEW CUBIC EQUATION OF STATE CONSIDERED REDUCED TEMPERATURE AND ACENTRIC FACTOR DEPENDENT. THE AVERAGE OF ABSOLUTE DEVIATIONS OF PREDICTED VAPOR PRESSURE, VAPOR VOLUME AND SATURATED LIQUID DENSITY OF 40 PURE COMPOUNDS ARE 0.859, 2.792 AND 5.825 PERCENT, RESPECTIVELY ALSO COMPARISON WITH THE NEW EQUATION OF VAPORIZATION OF PURE COMPOUNDS IS GIVEN (FIG 1, 2, 3, 4).DU,DH,V AND OTHER EQUILIBRIUM PARAMETERS ARE CALCULATED USING MODIFIED EQUATION OF STATE AND WILL APPLIED IN FLORY-HUGGINES (FH) MODEL TO PREDICT WT% OF ASPHALTENE PRECIPITATION DURING SOLVENT TITRATION. AT THE SECOND STAGE THE FLORY-HUGGINES (FH) MODEL IS MODIFIED BY THREE ADJUSTABLE PARAMETERS (A, B, C) TO PREDICT ASPHALTENE PRECIPITATION MORE ACCURATELY. THESE PARAMETERS ARE DEFINED BASED ON MOLECULAR WEIGHT OF ASPHALTENE TO MOLECULAR WEIGHT OF HEAVY OIL RATIO IN FORM OF POLYNOMIAL FUNCTION. THE PHASE BEHAVIOR OF ASPHALTENE WAS EXTENDED BY THESE MODIFICATIONS AND THE PRECIPITATION OF ASPHALTENE IS CALCULATED WHILE ADDING THREE N-ALKANES SOLVENTS. THE COMPARISON BETWEEN PREDICTED AND EXPERIENCED RESULTS IS SHOWN IN FIG 5 TO 10. THE NEW MODEL IS RELATIVELY ACCURATE IN PREDICTING PHASE BEHAVIOR OF ASPHALTENE IN HEAVY OIL.

WHEN DURING OIL PRODUCTION THE THERMODYNAMIC CONDITIONS WITHIN THE NEAR-WELLBORE FORMATION LIE INSIDE THE ASPHALTENE DEPOSITION ENVELOPE OF THE RESERVOIR FLUID, THE FLOCCULATED ASPHALTENES CAUSE FORMATION DAMAGE. MATHEMATICALLY, FORMATION DAMAGE IS A REDUCTION IN THE HYDROCARBON EFFECTIVE MOBILITY, L ( L=KO/M=KKR/ M). ASPHALTENES CAN REDUCE THE HYDROCARBON EFFECTIVE MOBILITY BY A) BLOCKING PORE THROATS THUS REDUCING THE ROCK PERMEABILITY, K, B) ADSORBING ONTO THE ROCK AND ALTERING THE FORMATION WETTABILITY FROM WATER-WET TO OIL-WET THUS DIMINISHING THE EFFECTIVE PERMEABILITY TO OIL, KO, AND C) INCREASING THE RESERVOIR FLUID VISCOSITY, M, BY NUCLEATING WATER-IN-OIL EMULSIONS. IN THE MOST FREQUENTLY ENCOUNTERED CASE OF ASPHALTENE-INDUCED FORMATION DAMAGE WHERE AN UNDER-SATURATED OIL IS BEING PRODUCED WITHOUT WATER, THE MOST DOMINANT DAMAGE MECHANISM IS BLOCKAGE OF PORE THROATS BY ASPHALTENE PARTICLES CAUSING A REDUCTION IN ROCK PERMEABILITY K. THIS PAPER PRESENTS A RATHER SIMPLE, YET REALISTIC WAY OF MODELING ASPHALTENE-INDUCED NEAR-WELL FORMATION DAMAGE CAUSED BY BLOCKAGE OF PORE THROATS BY ASPHALTENE PARTICLES. THE MODEL UTILIZES BOTH MACROSCOPIC AND MICROSCOPIC CONCEPTS OF THE PORE THROAT BLOCKAGES. IT ALSO UTILIZES AN EXISTING ASPHALTENE PHASE BEHAVIOR MODEL. THE NEW ASPHALTENE NEAR-WELL FORMATION DAMAGE MODEL IS APPLIED IN ONE CASE WHERE IT IS USED TO TRACK THE DEGREE OF FORMATION DAMAGE AS A FUNCTION OF TIME AND THE EFFECTS ON NEAR-WELLBORE AND WELLBORE HYDRAULICS. SIMILARLY THE MODEL CAN BE USED TO PRELIMINARY STUDY OF THE ECONOMICS OF DEVELOPING A RESERVOIR KNOWN TO CONTAIN AN UNDER-SATURATED ASPHALTENIC OIL.