Caliper is a fundamental measurement of wellbores. It has significant impacts on decision making regarding well completion and monitoring operations. Traditional Calipers are measured mechanically, thus can not be performed while drilling since they will not be able to survive the harsh conditions of drilling while the bottom hole assembly (BHA) rotates. With logging while drilling (LWD) measurements, several methods have been developed over the years to derive borehole calipers or hole shape indicators from LWD logs. In this paper, we will compare the LWD derived calipers with that obtained from wireline (WL) and summarize the developments, utilizations, and limitations of LWD derived calipers. Factors affecting LWD calipers will also be discussed to help operation petrophysicists for better log data quality control.
Examples will also be shown for using LWD calipers to identify borehole washout, elipticity, breakout, and spiral-hole conditions. Knowing these borehole conditions in real time can help to make action plans to improve drilling practices and reduce drilling risks. After drilling, LWD calipers are used to correct LWD logs for borehole size effects and guide well completions.