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Information Seminar Paper

Title

OPTIMIZATION OF N2 INJECTION OPERATION WITH COILED TUBING: A CASE STUDY IN ONE OF THE SOUTHERN IRANIAN OIL FIELDS

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Abstract

 NITROGEN LIFTING WITH COILED TUBING (CT) IS COMMONLY USED TO ENABLE A WELL TO FLOW INITIALLY OR BRING A PREVIOUSLY FLOWING WELL BACK ON PRODUCTION. THIS IS ONE OF THE MOST TYPICAL COILED TUBING OPERATIONS CARRIED OUT IN THE IRANIAN SOUTH OILFIELDS. THE LIMITED NUMBER OF CT TRUCKS AND LARGE NUMBER OF WELLS WHICH REQUIRE UNLOADING WITH N2 INJECTION AFTER WORKOVER OR ANY OTHER REMEDIAL JOBS, HIGHLIGTHS THE SIGNIFICANCE OF THE TIME SPENT FOR UNLOADING OF EACH WELLS. SOME OPERATIONAL PARAMETERS SUCH AS INJECTION RATE, INJECTION DEPTH, CT OD ARE COULD AFFECT DURATION AND COSTS OF UNLOADING OPERATIONS. IN IRANIAN OILFIELDS, THESE PARAMETERS ARE USUALLY ESTIMATED BASED ON PERSONAL EXPERIENCE OF OPERATION MANAGERS DURING OPERATION AND THEIR FIELD OBSERVATION THAT IS NOT AN EFFICIENT MANNER. THIS PAPER PRESENTS A NITROGEN LIFTING OPERATION FOR A WORKOVERED OIL WELL LOCATED IN A SOUTHERN OILFIELDS OF IRAN THAT IS UNLOADED WITH 7000 TO 14000 GAL OF NITROGEN GAS WITH 10 TO 20 GAL/MIN INJECTION RATE WITHOUT ANY PREDESIGN OR SIMULATION OF OPERATING CONDITIONS. THIS RESEARCH CONDUCTS AN ANALYSIS TO DETERMICE THE OPTIMUM VALUE FOR THE N2 INJECTION PARAMETERS. THE APPLIED METHODOLOGY COMPRISED OF SIMULATION OF THE WELL AND CT SYSTEM USING A STEADY STATE MULTIPHASE FLOW SIMULATION SOFTWARE, MATCHING MODEL OUTPUTS WITH REAL WELLTEST AND FLOWING TEST DATA, SIMULATION OF N2 INJECTION OPERATION WITH SENSITIVITY ANALYSIS ON VARIOUS DETERMINANT OPERATION PARAMETERS AND OBTAINING THE OPTIMUM VALUE OF THESE PARAMETERS. SIMULATION RESULTS INDICATED THAT INJECTION WITH A SMALLER DIAMETER COILED TUBING STRING ALLOWS HIGHER UNLOADING RATE WITH MINIMUM INJECTION RATE. THE RESULTS OF SENSITIVITY ANALYSIS ON N2 RATE INDICATED THAT INCREASING INJECTION RATE TO SOME EXTENT, LOWERS HYDROSTATIC PRESSURE LOSS IN THE ANNULUS AND BOTTOMHOLE PRESSURE BUT FURTHER INCREASE OF THE N2 RATE BEYOND A CERTAIN THRESHOLD VALUE WOULD INCREASE THE FRICTION PRESSURE LOSS IN THE ANNULUS AND CONSEQUENTLY INCREASE BOTTOMHOLE PRESSURE AND DECREASE UNLOADING RATE. SIMULATION RESULTS WITH SENSITIVITY TO INJECTION DEPTH INDICATE THAT AS GAS INJECTION DEPTH INCREASES, THE MAXIMUM ATTAINABLE UNLOADING RATE INCREASES.COMPARING THE OPTIMUM DESIGNED NITROGEN LIFTING OPERATION WITH THE REALTIME FIELD OBSERVATIONS PROVIDES THAT THE N2 INJECTION RATE IS EXCESSIVELY HIGHER THAN THE REQUIRED RATE IN THIS WELL. AS N2 INJECTION IS A TYPICAL FORM OF UNLOADING PROCEDURE AT NISOC, OPTIMIZATION METHOD WHICH PRESENTED IN THIS RESEARCH, COULD MAKE THE UNLOADING OPERATIONS MORE ECONOMIC BY REDUCING THE ROUTINE TIME AND COST OF THESE OPERATIONS.

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