Pulsed neutron logs (PNL) are being used similar to production logging instruments to qualitatively identify gas, oil, and water entry into the wellbore. Gas, oil, and water entry are identified with the pulsed neutron log by measuring flowing and static early-time gamma ray and background gamma ray data in combination with conventionally recorded saturation data.
The PNL's best application for production logging is in difficult logging conditions—multiphase flow in highly deviated or non-conventional wells where quantitative measurements are difficult to interpret using conventional production log data. In multiphase flow conditions, the PNL can usually characterize non-uniform flow profiles, which yields similar results to those of conventional production log measurements. In non-conventional wells where flow conditions are further complicated, the PNL data are an excellent supplement to a suite of conventional production logs.
Use of the PNL for production logging offers a useful addition to conventional wellbore surveillance logging. Gas-, oil-, and water-entry data can be simultaneously acquired with conventional PNL saturation data and channel detection logging data. ‘ Simultaneous data acquisition leads to better remedial work decisions, accomplished by ensuring that all major parameters (e.g., gas-oil contact, oil-water contact, potential for cement channeling, and production entry points) are considered before making a remedial work decision.