APPLICATION OF HIGH-RESOLUTION LWD BOREHOLE IMAGES FOR RESERVOIR CHARACTERIZATION IN TECTONICALLY AND GEOLOGICALLY COMPLEX RESERVOIRS

摘要

The geology of Papua New Guinea is highly complex, resulting from intense tectonic activity that is attributable to its location at active tectonic plate boundaries. The rugged mountainous terrain makes it very difficult to acquire surface seismic and other geophysical data, which leads to a high degree of uncertainty in the structural geology influencing petroleum basins and fields. Even at moderate wellbore inclinations, a wide range of apparent dip angles and features can be encountered in these complex structures. Because of these uncertainties, a large component of most development drilling is still field appraisal. High-resolution borehole images can identify the presence and orientation of key structural features, such as faults, fractures, bedding, unconformities, and borehole breakouts, which are indicators of the stress field around the borehole. These data are essential in geological mapping and geomechanical modeling. Although high-resolution wireline electrical images could be acquired, the high borehole stresses caused rapid borehole deterioration and borehole instability issues, which often resulted in significantly reduced image data quality. The additional time required to obtain wireline image data also increased the probability that a borehole section would be lost before it could be cased. Recent enhancements to a logging-while-drilling (LWD) imaging sensor have significantly increased its resolution. Although LWD images are not quite as sharp as some wireline electrical images, they provide a significant advantage of 360-degree coverage and improved acquisition conditions and logistics. In addition to the valuable structural information, important stratigraphic and textural details are visible, which promote a more complete understanding of the facies of the various formations. Micro-electrical mages also enable the detailed mapping of fractures and breakouts that are valuable for geomechanical analysis and for updating the stress model. Conductive fractures, indicative of open fractures, can be identified and imaged in greater detail, sometimes pinpointing where a loss of drilling fluid has occurred. This capability enables completion designs that avoid perforating these features, which reduces the potential for gas or water coning.