TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractPetróleos Mexicanos (PEMEX E&P) and GeoMechanics International Inc. (GMI) worked together to define the potential for fault leakage in the Sihil and Frontal faults of the Cantarell and Sihil Fields, Mexico. Water production with a low salinity content in the northern area of the Akal block in the Field seems to be derived from neighboring blocks of Tertiary age and not from the water leg of the reservoir. Pore pressures in the reservoirs from the Akal block have depleted significantly since production started in the late seventies. Nitrogen injection started in the late nineties and has contributed to pressure maintenance since then. Overpressures in the shale layers above the reservoirs have been identified. A number of studies have shown that shear failure along reservoir-bounding faults can increase fault permeability and compromise fault trap integrity. The orientation of a fault and the magnitudes of the present-day stresses and pore pressure acting on the fault will determine whether the fault has the potential for shear failure and therefore a potential for leaking. The analysis of fault leakage potential was based on a geomechanical model covering the northern area of the Cantarell Field and its changes with time due to reservoir depletion and nitrogen injection. Information from wireline logs, downhole tests and drilling events from eight wells drilled between 1979 and 2005 were used to build the geomechanical models that change with time. The principal effective stress model (the magnitudes and orientation of the principal stresses), and the mechanical properties model were defined and validated with image logs, caliper logs and drilling experiences before their use for fault leakage potential analysis. Specific sectors of the two faults appear to be tectonically active during the production history and therefore had potential to leak. Fault leakage potential may explain water production with low salinity content in the northern area of the Akal Block in the Cantarell field.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractPetróleos Mexicanos (PEMEX E&P) and GeoMechanics International Inc. (GMI) worked together to define the potential for fault leakage in the Sihil and Frontal faults of the Cantarell and Sihil Fields, Mexico. Water production with a low salinity content in the northern area of the Akal block in the Field seems to be derived from neighboring blocks of Tertiary age and not from the water leg of the reservoir. Pore pressures in the reservoirs from the Akal block have depleted significantly since production started in the late seventies. Nitrogen injection started in the late nineties and has contributed to pressure maintenance since then. Overpressures in the shale layers above the reservoirs have been identified. A number of studies have shown that shear failure along reservoir-bounding faults can increase fault permeability and compromise fault trap integrity. The orientation of a fault and the magnitudes of the present-day stresses and pore pressure acting on the fault will determine whether the fault has the potential for shear failure and therefore a potential for leaking. The analysis of fault leakage potential was based on a geomechanical model covering the northern area of the Cantarell Field and its changes with time due to reservoir depletion and nitrogen injection. Information from wireline logs, downhole tests and drilling events from eight wells drilled between 1979 and 2005 were used to build the geomechanical models that change with time. The principal effective stress model (the magnitudes and orientation of the principal stresses), and the mechanical properties model were defined and validated with image logs, caliper logs and drilling experiences before their use for fault leakage potential analysis. Specific sectors of the two faults appear to be tectonically active during the production history and therefore had potential to leak. Fault leakage potential may explain water production with low salinity content in the northern area of the Akal Block in the Cantarell field.