A new generation of LWD density-porosity tools azimuthally measure bulk density (RHOB) and photoelectric effect (Pe) in 16 sectors around the borehole in holes from 5 ¾ to 10 5/8 inches. They can provide formation images with a pixel size of 1.2 inches. These tools can function in conductive water based or non-conductive, oil or synthetic-based drilling muds.
The density images could be used to identify lithology and allow computation of dips for structural analysis. This application is demonstrated in deviated and complex wells in near-shore Gulf of Mexico. Field examples will illustrate the successful application of the density images for structural analysis, basic dip computation, and identification of large stratigraphic features such as folds, unconformities, fractures, and nodules.
Although these tools do not have the same resolution as some wireline deployed imaging tools, they provide an alternative method particularly when operators rely only on LWD for formation evaluation. Thus, they can save rig time associated with wireline runs and their respective wiper trips. They also measure while drilling so that if hole conditions negate the use of wireline tools, the information is already collected. Additionally, these multi-sector tools can be run in highly deviated holes which so often require electric line tools be drill pipe conveyed reducing costs exponentially.
These new LWD tools have also proven that they can deliver image-based information on borehole conditions such as shear and/or tensile fracturing, stress direction, borehole breakout, and borehole shape greatly aiding wellbore stability studies. In brief, the services provided by these new-generation tools are applicable to drilling, geological, geophysical, and petrophysical departments for formation evaluation, borehole stability study, and geo-steering.