Discovery of Radioactive Barium Sulphate Scale In PanCanadian Petroleum Producing Operations In Southeastern Alberta
Authors: Krishnan C. , Kopperson D. , Cuthill T. 
Published: March 2010

Radioactive Barium Sulphate scale was discovered in the downhole equipment of a well in Countess "O" Pool during a routine workover. The radioactivity of the scale was determined to be in the range of 140 to 250 Bq/g, exceeding the limit of 75 Bq/g above which it is considered a radioactive waste material. This discovery raised issues related to personnel health, environmental impact, the extent of the problem, prevention, as well as handling and disposal of the scale.

This paper discusses the positive steps taken by PanCanadian in addressing these issues. A brief review of radioactive, materials is provided. PanCanadian's experience with respect to employees' right to know, safe work procedures, radiation monitor selection, radiation surveys, the strategy for barium sulphate scale prevention including inhibitor selection and application is covered in some detail.

Issues such as scale removal methods for pipes, valves and Fittings, as well as transportation, storage and subsurface disposal of contaminated materials are also covered.

Introduction

Naturally Occurring Radioactive Materials, commonly known as NORM, are present in varying concentrations in hydrocarbon reservoirs in a number of areas of the world, specifically the North Sea, Gulf Coast, Alaska, and Western Canada. The petroleum industry has recognized that these materials can give rise to radioactive scale during oil and gas production. The radioactivity of the scale is the result of the co-precipitation of naturally occurring radium from the hydrocarbon reservoir with barium and strontium sulphates. The scale, also known as Low Specific Activity (LSA) scale, emits alpha, beta, and gamma radiation which poses problems when equipment containing radioactive scale has to be handled or removed from service.

Radium is the main contaminant encountered in oil production operations, present in scales deposited in perforations, tubular, wellheads and surface facilities including pipelines and plant equipment. Sludge's present in surface equipment may also contain radium.

Radon is known to be produced with natural gas and has been reported by Gray(l) as a contaminant more prevalent in natural gas production and processing facilities.

The focus of this paper is LSA scale encountered in oil production operations.

FIGURE 1: Radioactive decay or Uranium-238. (Available in full paper)

Fundamentals

Radioactive elements uranium and thorium are present in the earth's crust in varied concentrations. Radium-226 and radium-228 are the decay products of uranium-238 and thorium-232 respectively. These and their daughter products are the materials one expects to encounter in LSA scale in oil operations. The half life of radium-226 is 1,600 years, therefore, if present in scale, it poses a long term problem. Figure 1 shows the radioactive decay path of uranium-238 to the stable lead-206.

Hazards of Scale

The level of radioactivity and the energies of radiation are relatively low for the scales occurring in the petroleum industry. They do not usually present a health hazard to the public or to the majority of employees in the industry unless inhaled, ingested, or absorbed into human tissue. However, during well workovers, equipment maintenance, equipment handling and repair, and vessel entry, employees may have direct physical contact with radioactive scale and sludges.