Method for cement evaluation with neutron logs

摘要

Method for evaluating cement integrity in a cased well environment using a logging tool that has a neutron source and one or more neutron or gamma ray detectors. Neutron porosity logs are obtained from the well before (42) and after (41) casing. This log data along with well dimensions and material composition parameters are the input quantities to a multi-parameter database (43) that is constructed by computer modeling or laboratory experiments to relate volume fraction for fluid filled channels in the cement sheath to the input quantities. The channel volume fraction (45) corresponding to the input quantities is identified or interpolated (44) from the multi-parameter database.

主权项

1. A method for evaluating cement integrity in a cased well drilled into a subsurface formation with a cement sheath installed in an annular region between the well casing and the formation, comprising:
obtaining an open hole neutron log and hole dimensions acquired from the well before casing and cementing, and obtaining a cased hole neutron log and related information including one or more of casing size and weight, cement weight, and mud weight, acquired from the well after casing and cementing; with the open and cased hole neutron logs, hole dimensions, and the related information as input quantities, using a mathematical model, operated on a computer, to determine a volume of fluid filled channels in the cement sheath; and estimating the cement integrity based on the fluid filled channel volume.