Effective Dipmeter Logging In Today'S Highly Deviated Wells
Authors: Bigelow E.L. 
Published: October 2008

Diameter logging in highly deviated boreholes has posed problems for well operators and service crews for many years. In the past decade, pipe-conveyed logging techniques improved acquisition capabilities tremendously, but diameter data were still hampered by the inability to obtain good quality resistivity traces on enough pads to make confident correlations to compute dip. Today, a new 6-pad device is being used to effectively log horizontal wells because of a unique 6-arm powered standoff that frees the dip pads and allows them to obtain adequate to superb measurements for correlation purposes.

Dip information remains to be the most detailed borehole information available for reconciling structural geology features, The horizontal attributes of 3-D seismic, along with in-situ dip and depth measurements from a borehole, add a new dimension to reconciling complex geological structures. Important new dip processing concepts provide greater confidence in computed dip results. The evolution of diameter interpretation concepts, aligned with the excellent horizontal coverage of 3-D seismic, leads to significant geological results without requiring a large number of control wells. The economical benefit of describing geological conditions in the early exploitation stages of a reservoir is self-evident.

INTRODUCTION

A 6-arm dip-logging device has been used successfully for the past three years in logging highly deviated and horizontal boreholes. Following more than 15 months of extensive field testing, commercial versions of the tool system have been distributed to Atlas Wireline operating bases throughout the globe. The important features implemented into the tool mechanics are:A 6-pad powered standoff located just below the dip-pad sensorsIndependently controlled pad pressure on each of the six diameter arms that house the sensing elementsPad articulation that pivots within a ±30° radius, permitting each pad face to make optimum contact with the borehole wall.

The powered standoff effectively removes the mandrel weight from the dip-pad section and allows for optimal pad pressure while recording the resistivity traces. The tool scheme employs a dip-pad section that measures independent radii, with independently controlled pad pressure on each of the six arms. This ensures obtaining the best possible correlative resistivity traces from each pads' electrode sensing element. The logging engineer can monitor the resistivity traces, allowing for recording the log while applying an efficient amount of pad pressure. This pad force is typically just enough to make contact with the borehole wall and measure resistivity contrasts in the formation as the tool traverses the well. Dip logs generally require more attention during the logging operation because it is necessary to not only ensure optimum pad contact but also to vary the sensitivity of the recorded log traces as formation characteristics change.

Tool design permits simultaneous recording of an acoustic formation imaging log and gamma ray, which is a particularly effective method for acquiring data in horizontal wells. Synthetic resistivity images can also be created from the six dip-pad traces, thereby permitting a comparison of both acoustic and resistivity images, particularly important for evaluating fracture systems and making thin-bed evaluations. Computed dip results confirm measurement efficiency in highly deviated and horizontal conditions.