Radiological Assessment of Petroleum Pipe Scale Waste Streams From Dry-Rattling Operations

Abstract

Petroleum pipe scale consists of inorganic solids, such as barium sulfate. These solids can precipitate out of brine solutions that are pumped out of oil wells as part of normal oilfield operations. The precipitates can nucleate on down hole pipe walls, causing the buildup of hard scales in some tubulars in a pipe string, while leaving others virtually untouched. Once the scale buildup is sufficient to restrict flow in the string significantly, the tubulars are removed from service. Once removed, tubulars are transported to storage yards for storage, subsequent inspection, and possible recycling. Many of the tubulars are never returned to service, either because the threads were too damaged, pipe walls too thin, or the scale buildup too thick. Historically, the tubular refurbishment industry used primarily one of two processes, either a high-pressure water lance or a dry, abrasive “rattling” process to ream pipes free of scale buildup. The dry rattling process was primarily for touching up new pipes that have rusted slightly during storage; however, pipes with varying levels of scale were reamed, leaving only a thin coating of scale on the inner diameter, and then returned to service. Chemically, radium is an analog for barium, and radium is present in parts-per-million quantities in the brines produced from downhole pumping operations. Thus, some of the scales contain radium salts. When the radium-bearing scales are reamed with a dry process there is the possibility of generating radioactive aerosols, as well as bulk waste materials. At Texas A&M University, and under the university’s radioactive materials broad scope license, an outdoor laboratory was constructed and operated with dry rattling equipment restored to the “as was” condition typical of historical pipe cleaning yards. A battery of measurements were obtained to determine the radiological and aerodynamic properties of scale-waste products liberated from the inner surfaces of a variety of tubulars acquired from working oilfields. Four dose pathways were analyzed: inhalation of scale dust released during dry rattling, ingestion of same, external exposure from uncleaned pipes, and external exposure from pipe scales dispersed on the ground in the natural discharge pattern of the rattling machine for given, recorded meteorological conditions. For the aerosol dispersion research, dust (mass) loading, and the respirable size-fraction component of generated dusts was determined. Additional research revealed the pulmonary solubility class of respirable scale aerosols, as well as the radon emanation rate of bulk scale materials.