A METHOD AND APPARATUS FOR MEASURING WELL CHARACTERISTICS AND FORMATION PROPERTIES

摘要

The present invention provides for method and an apparatus for determining t he porosity of a geological formation surrounding a cased well. The method furt her comprises of generating neutron pulses that release neutrons into an area ad jacent the well, from a neutron source. Neutrons are sensed and a plurality of neutron detector count rates is acquired using at least two neutron source to neutron detecto r spacings. A timing measurement is acquired at one of the spacings to measure a first dep th of investigation. A ratio of the neutron detector count rates is acquired to me asure a second depth of investigation. An apparent porosity is calculated using the timing measurements and the ratios of neutron count rates. The effect of a well casing on the ca lculated apparent porosity is determined in response to at least one of the ratio of neutron detector count rates and the timing measurement. A cement annulus is computed based o n the ratios of neutron count rates and the timing measurement. A formation porosi ty is calculated by performing a correction to the apparent porosity for the casin g and the cement annulus.