An extensive fracture analysis was performed in a highly deviated to horizontal well drilled in the basement of the Clair discovery, U.K.C.S. Fracturation is the key factor for the well productivity since the oil is produced through fractures connecting the horizontal drain to the overlying and adjacent oil bearing Old Red sandstones of Devonian age.

The main objectives of this study was first to determine and characterize the fracturation pattern along the well, and then to establish the relationship between the fracturation pattern and the possible producing zones identified from the production log interpretation.

The fracturation methodology which was adopted for the fracturation analysis is described in the paper and is based on the descriptions of cores and on the interpretation of openhole logs comprising classical logs, full waveform acoustic log, borehole televiewer log and production log The high resolution televiewer information was calibrated to fracture characteristics determined from the seven cores taken in the Basement and extended to the scale of the well by use of the Full Waveform acoustic log information.

The fracture system in the basement is characterized by several patterns of different scales. The major fractured intervals, spaced between 100 and 150 m, were interpreted to be interacting with a secondary fracturation pattern more closely spaced around 15 to 40 m. These fractured intervals correlate well with the producing zones identified from the production log interpretation.

To complete the fracturation analysis, a comparison between the determined fractured intervals and drilling parameters (ROP, downhole torque and gas shows) was done. It is found that at least two of these parameters respond as the same time to fractures during drilling.

It is believed that detection of the major fracture zones can be possible during the drilling phase of any well drilled in the basement.

The application of the described methodology is highly recommended on future wells with similar objectives.

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