RIASSUNTO
SPE Members
Abstract
Nuclear logging provides petroleum exploration and production companies with data that are critical to their decisions and operations. Because this type data is so important, environmentally conscious well-logging and service companies are constantly reviewing the risks to people and environment associated with nuclear sources with the ALARA (as low as reasonably achievable) principle in mind. Opportunities to additionally reduce risks, principle in mind. Opportunities to additionally reduce risks, which can be accomplished only with the active involvement of oil companies, are proposed in this paper.
Introduction
Nuclear sources designed for the oil industry have been used for more than 40 years, and they are widely employed today both in exploration and production work. During this time, the number of accidents and incidents involving both oilfield operators and service companies has been low. Preventive safety programs, coupled with strict controls imposed Preventive safety programs, coupled with strict controls imposed by national and international authorities, have, contributed to this low accident rate. However, in spite of these precautions, accidents involving nuclear sources do occasionally occur and serious risks continue to exist. This paper presents new approaches for reducing the risks associated with nuclear devices.
RISK ASSESSMENT
The principal risks involved in using radioactive sources in the well-logging industry can be summarized as follows. Health hazards to operating personnel resulting from overexposure. - Environmental pollution, if there is uncontrolled release of source material into the surroundings. - ""Loss of control"" of the sources, which can entail serious health risks to unaware persons. Companies having inadequate procedures and programs to reduce risks and prevent accidents involving nuclear sources can experience serious economic losses. These losses can include the cost of recovery and/or remediation of affected areas, cost of litigation and settlement of damages to persons or property, and loss of production in the case of a wellsite accident. With this in mind, priority must be given to reducing the approximately 15,000 isotopic (chemical) logging sources being used today in the well-logging industry. Of this conservative estimate of sources, Schlumberger has a total of 5000; 1400 for density logging, 1600 for neutron logging, and 2000 for tool-check and calibration purposes.
REDUCING THE HEALTH RISK
In line with the ALARA principle, the exposure of personnel involved in field operations with nuclear logging sources is reduced by: - Using sources of minimum strength for the required task. - Providing adequate, secure shielding for isotopic sources and automatic shutdown systems for electronic sources. - Providing safe storage at the operating base and wellsite locations for all sources. - Applying an efficient and safe system of work.
Source Activity
For neutron porosity logging, the 592GBq (16-curie) americium-beryllium (Am-Be) isotopic source is the industry standard. However, in the future, electronically controlled neutron generator tubes will make it possible to substantially reduce the number of Am-Be sources. For density logging, the 63GBq (1.7-curie), cesium-137 (Cs-137) source is widely used, but no electronic equivalent is yet available. However, it has been shown that it is technically possible to create sufficiently energetic X-rays in a downhole tool, using an electron accelerator, to make a good density measurement.
Shielding Technology
Carefully designed carrying shields do provide good protection for personnel using isotopic sources. personnel using isotopic sources. P. 547