Behind Pipe Log Evaluation Study: Deepwater Subsea Abandonments in the Gulf of Mexico

摘要

New techniques for well abandonment log evaluations have been under study since 2012 in the Gulf of Mexico (GOM). Legacy practices typically used acoustic methods consisting of cement bond log and ultrasonic scanner devices. The new methods described in this paper consist of adding nuclear sensors to supplement the acoustic measurements and introduce novel processing methods. Behind pipe evaluation techniques (BPET) is the overall solutions package described within the paper. When properly modeled and analyzed, this data has the potential of significantly reducing the cost of removing casing strings during plug and abandon activities. A new development in CBL refracted waveform processing provides relative amplitude mapping within four concentric cylindrical volumes between the CBL transmitters and receivers. These regions extend from the first casing and its annular region and outwards within the wellbore. The density and neutron nuclear sensors allow grouping of detector count rate ratios in data clusters which have been interpreted to be responding to annulus materials spanning from cement, heavier liquids, settled mud solids, lighter liquids, and gas. Neutron responses are useful in trending the relative hydrogen index of the annular contents. Distribution imaging of settled solids from ultrasonic measurements have been helpful in supplementing the interpretation of nuclear and refracted waveform indications.