A FIBER OPTIC PRESSURE SENSOR FOR USE IN WELLBORES

PRESSURE MEASUREMENTS DEEP IN GEOTHERMAL WELLBORES PROVIDE SOME OF THE MOST VALUABLE DATA FOR MEASURING THE PRODUCTIVITY OF GEOTHERMAL WELLS AND FOR ASSESSING RESERVOIRCHARACTERISTICS. WELLBORES HAVE VERY HIGH PRESSURE AND VERY LOW PH, BUT, MOST SIGNIFICANTLY, THEY HAVE VERY HIGH TEMPERATURES (UP TO 350 DEGREES CENTIGRADE) THAT PRECLUDE PRESENT PRESSURE MEASURING INSTRUMENTATION FROM OPERATING ADEQUATELY. INSTRUMENTATION IS NEEDED THAT CAN PROVIDE IMPROVED PRESSURE MEASUREMENT RESOLUTION, ACCURACY, AND RELIABILITY IN HARSH WELLBORE ENVIRONMENTS. TO MEET THIS NEED, A FIBER OPTIC INTERFEROMETRIC PRESSURE SENSOR WITH THE FOLLOWING UNIQUE ADVANTAGES IS BEING DEVELOPED: (1) ACCURACY BETTER THAN 0.01%, (2) RESOLUTION BETTER THAN 0.001%, (3) OPERATION AT TEMPERATURES BETWEEN 150 DEGREES CENTIGRADE AND 350 DEGREES CENTIGRADE DEPENDING ON THE MECHANICAL DITHER EMPLOYED, (4) IN-PLACE CALIBRATION VERIFICATION CAPABILITY, (5) SEPARATION BETWEEN SENSOR AND ELECTRONICS OF UP TO SEVERAL KILOMETERS, (6) PRESSURE SPAN OF 0 TO 10,000 PSI AND ABOVE, (7) NO ELECTRICAL COMPONENTS AT THE SENSING END, (8) IMMUNITY TO ELECTROMAGNETIC INTERFERENCE (EMI), AND (9) LIGHTER WEIGHT AND SMALLER SIZE.