engleski

Stress evaluation by breakout analysis at Crnac field

Borehole breakouts determination is one if main and widely used methods for in-situ stress analysis on some field. The breakout analysis can be performed using the information coming from the oriented caliper measurement, usually CBIL (Circumferential Borehole Imaging Log) or STAR (Resistivity) Images, DIPLOG or Oriented 4-Arm Caliper acquisition. CBIL data are very rare but there is enough DIPLOG data available for breakout, therefore in-situ stress analysis. Special methods and computer programs have been developed for evaluation of breakouts and in-situ stress. Results from programs are calibrated with some other methods and complete analyses in Crnac field have been made. Applying created computer programs (STRESS and BOVision) comprehensive breakout stress analysis has been made at Crnac field. Two sources of breakout determination have been used. CBIL and DIPLOG data are analyzed on separate and same wells, and in-situ stress interpretation have been preformed. The data shows that the maximum horizontal stress orientation is northeast- southwest (NE-SW). The stress orientation is almost perpendicular to field anticline elongation. This is also the direction in which drilling induced fractures will propagate. Hydraulically induced fractures have this NE-SW strikes perpendicular to the breakout direction. This suggests that they were formed under the same stress regime. Some of these could be drilling induced. It is therefore recommended that future wellbore traces should be projected in SE-NW direction in order to cross as many as possible fractures. More fractures drilled will give us better permeability of drilled formation.

borehole breakouts; DIPLOG; CBIL; oriented 4-arm caliper acquisition; stress orientation; breakout direction; hydraulically induced fractures

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