Obtaining Porosity and Density in Cased Holes for Formation Evaluation in Nigeria

Mohammed Doghmi¹, Parijat Mukerji¹, Luca Zanichelli², and Francesco Zanin^2
1 Schlumberger Oilfield Services, PortHarcourt, Nigeria
² Nigeria Agip Oil Company Ltd, Port-Harcourt, Nigeria

When drilling new wells, operators often encounter conditions that make openhole logging difficult. Borehole stability issues dictate changes in plan and sometimes require the section to be cased before acquiring open hole data. To meet the challenge of obtaining formation evaluation data in cased holes, a new suite of services has been developed to offer operators an alternative to open hole logging that presents unacceptable risks. Cased hole logs can be used to obtain formation evaluation information or to complement logs acquired while drilling. In areas where open hole logging is difficult, preplanning for cased hole logging operations can save time and costs.

This paper presents a field example demonstrating the use of these new services in a Niger Delta well that was cased before open hole logs were obtained. The logging program included standard devices to evaluate cement quality, and density and porosity tools to evaluate the formation. The operation was executed without problems. The porosity and density logs obtained behind casing closely matched the openhole logs from overlapping intervals and other offset wells. Logging while drilling resistivity and gamma ray measurements were combined with the cased hole logs to perform a complete evaluation in a well section where other alternatives did not exist.