The Shale-Compensated Chlorine Log
- P.F. McKinlay (Texaco Inc.) | H.L. Tanner (Texaco Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- February 1975
- Document Type
- Journal Paper
- 164 - 170
- 1975. Society of Petroleum Engineers
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- 96 since 2007
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Although many chlorine logging systems have been used by the petroleum industry, they never attained widespread popularity. The use of many of these systems was limited by their sensitivity to increasing shale content. A shale-compensated chlorine logging system (SCC) has been developed and evaluated. The SCC log interpretation has proven to be correct in predicting the type of fluid behind the casing more than 80 percent of the time.
The chlorine log was introduced to the petroleum industry in the late 1950's. The primary purpose of this log was to determine the amount of salt water in the formations immediately behind the production casing and to relate this salinity measurement to hydrocarbon content. Although many chlorine logging systems were used by industry,1-4 they never attained widespread popularity. The use of many of these systems was limited by their sensitivity to increasing shale content.
A shale-compensated chlorine logging system (SCC)5 has been developed and extensively evaluated. The recorded log supplies a continuous salinity profile of the formations behind the casing. A specific advantage of this log over other similar logs is that the system compensates for the effect of shale on the salinity measurement. Also, the porosity, lithologic, and borehole fluid effects on the salinity measurement are minimized.
The log has been run in several hundred cased wells. The majority of the runs have been made in wells subject to workover and/or abandonment. New hydrocarbon-bearing intervals have been identified and oil-water contacts in producing reservoirs have been located. The SCC log interpretation has proven to be correct in predicting the type of fluid behind the casing more than 80 percent of the time. Oil production has been obtained in many wells that, before logging, were considered to have little, if any, economic potential.
The SCC log will give reliable results at logging speeds of 20 to 30 ft/min in formations containing high porosity and salinities above 45,000 ppm NaCl. Slower logging speeds are recommended for areas where porosities are low and/or salinities are less than 45,000 ppm NaCl. The possibility of successful completions based on the log interpretation decreases rapidly when porosities are less than 20 percent and formation salinities are below 30,000 ppm NaCl.
The SCC system was specifically designed to minimize the effects of shaliness, porosity, and lithology on formation salinity measurements and water saturation (Sw) determinations.
The system measures thermal neutron-capture gamma radiation in two gamma ray energy ranges: 1.3 to 2.92 MeV, recorded as the NG (Hydrogen) curve, and all gamma ray energies above 3.43 MeV, recorded as the NG (Chlorine) curve. The detector is a 2-in. by 4-in. long NaI(Tl) scintillation detector that is spaced 15¾in. (center to center) from a 2.3 × 107 neutron / americium - beryllium neutron source. Lead is used as shielding material between neutron source and detector.
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