CASE STUDY: CASED HOLE DENSITY APPLICATION, NORTH SLOPE, ALASKA

This paper provides a case study of the techniques used to acquire, process, and interpret cased hole density data combined with logging while drilling (LWD) resistivity data for completion decisions in a sidetrack well from the North Slope, Alaska. Density data, acquired through 3.5 in. casing, augmented the openhole LWD resistivity and gamma ray (GR) data used to investigate possible water breakthrough and formation water saturation before completing this well. The cased hole density data were critical to this decision because they were not available with LWD; they could not be acquired in an open hole because of borehole conditions; and they were necessary for porosity determination. Formation lithologic effects precluded the use of alternative through casing porosity measurements, such as neutron log data.

After acquisition, the density data were processed to account for casing and cement effects and were then compared with offset density data for quality control purposes. A petrophysical analysis was performed using this processed density with the LWD resistivity and GR information to aid in the completion decisions. The objective of determining if water breakthrough had occurred was met, and this well was perforated and fractured accordingly. Well tests indicated the presence of low water cut and competitive oil rates, which confirmed the petrophysical interpretation.

The ability to acquire accurate formation density data after casing had been set reduces completion decision uncertainty. This added another tool to the completion decision process while this field was developed.