Abstract

Logging While Drilling (LWD) and conventional wireline log data were acquired in 12 wells. The measurements included resistivity, gamma ray, neutron, density, and photoelectric factor. In general, the LWD data were comparable to the half-foot sampled wireline logs. Differences occurred:

• in washed-out boreholes, where LWD logs recorded prior to the wash-out are of better quality than the wireline logs,

• in gas sands, where invasion has diminished the gas effect on wireline logs,

• in shales, where the LWD shallow resistivity is lower than the deep resistivity because of the high dielectric constant of the shale, and

• in intervals with high resistivity contrast, where the LWD readings appear to be limited to a specific range.

LWD tools are reliable. However, LWD requires more depth-alignment editing than wireline logs, and real time data transmission problems were encountered when the mud motor was in use. With few exceptions, the resolution of LWD logs is similar to that of half-foot sampled wireline logs.

LWD logs complemented, rather than replaced, wireline logs. Real time correlation, accurate picking of casing- and coring-points, and early hydrocarbon zone recognition were significant benefits of LWD. On several occasions, when severely washed-out boreholes or difficult drilling conditions were encountered, LWD logs were the only logs acquired.