Publications

The pulsed-neutron tool has been used for decades to determine the hydrocarbon saturation, especially in casedhole wells, over time in a producing formation. Pulsed-neutron tools are also flexible in terms of operations in that they can be run with wireline, slickline, or even coiled tubing in both real-time and memory mode. The tool uses an electronic neutron generator to create neutrons with an energy of 14MeV. The neutrons are created in a specific time sequence and at a rate of approximately 1x108 neutrons per second. The neutrons then interact with borehole fluids, casing, cement, and the formations. The interactions create gamma rays with different energies that are then recorded by the tool detectors. The number of gamma rays and the energies can be evaluated to determine the hydrocarbon saturation within the formation. One of the most common problems in old wells is the production of formation water; consequently, borehole diagnostics are needed to determine the water source. The method previously used to accomplish these diagnostics included running a temperature tool; although this method is sensitive to fluids movement, it cannot be used to determine the location of the flow radially. The pulsed-neutron tool enables additional information to be gathered, resulting in achieving better diagnostics. This paper includes an example in which water movement behind the casing that was caused by channeling in the cement was detected. Other examples included in the paper focus on tubing damage, which creates a passage for water coming through from an unwanted formation, and determining packer integrity using pulsed-neutron data with its ability to distinguish fluids. With the successful examples of how the pulsed-neutron tool can be used for water source identification, combined with the flexibility of the tool, this method provides an effective and economical way to solve unwanted water production issues.