A Multifaceted Approach for Controlling Complex Deposits in Oil and Gas Production
Authors: Frenier Wayne W. , Ziauddin Murtaza 
Published: February 2011

Deposition of organic and inorganic solids is common in various areas of the oil and gas production operations that include pipelines, wellbores, and the reservoir and surface facilities. Precipitation is the first step leading to deposition and is a necessary but not sufficient step. Deposition must then occur on a susceptible surface to be detrimental. At this point the deposit may be called a "foulant". There is a large literature base on individual deposits (inorganic scales, wax, asphaltene and hydrates), but relatively little on "real" foulant that usually are much more complex. To maintain production (Flow Assurance-FA) it is not enough to control scale or wax or hydrates. Since these materials affect each other and form complex mixtures, the formation of them must be addressed and treated simultaneously. This paper will review the formation, inhibition and removal of complex inorganic/organic deposits. Practical multi-faceted techniques based on the most recent research and developments will be described and then illustrated using case histories to arrive at best practices for control.

The scope of this paper is directed to issues of complex fouling deposition phenomena in the production ("upstream") oilfield environment. This includes the near well bore ("formation damage"), arterial deposits in flow lines, natural or artificial tubulars, subsurface devices, gathering lines and well site surface equipment. From a FA perspective, the biggest problem faced in the offshore developments is the formation of gas clathrate hydrates. The second most important problem is wax damage, followed by asphaltenes. Onshore and especially for low production ("stripper") wells, paraffin deposition is a major production problem. In reality, in both environments, these are usually mixed deposits since corrosion-susceptible steel surfaces are present in contact with unstable brines and mixed hydrocarbons.

The first part of the paper will review current literature on the formation of complex mixtures including scales and asphaltenes in the near well-bore area, "Black Powder" deposits in gas lines and the effect of surfaces on wax and hydrate formation. Since the subject is multi-component deposits, control methods also must be multi-faceted. Chemical and engineering analysis techniques that will be highlighted include down hole/surface fluid (oil/ brine and gas) evaluation as well as methods to analyze the efficacy of remediation and prevention methods. Of particular interest are methods for treating multiple types of problems. These include simultaneous scale/organic removal/inhibition treatments and wax/asphaltene/corrosion control treatments. Application methods reviewed include matrix (squeeze) methods, pig trains and coil tubing placements. The case histories of multiple deposit treatments will be included. The conclusions result in a best practice that starts with fluid collection and ends with a comprehensive plan and implementation of multiple FA strategies.

The economic impact of scales and organic deposits is in the multiple billion dollar range annually. Inorganic scale damage (not including corrosion!) has been estimated at approximately 2 billions of dollars/year. An exact damage estimate for wax, hydrate, asphaltene and naphthenate fouling is not available, however individual producers believe the problems are more significant than the inorganic scale. Another way to look at the problems is by the number of companies (more than 50) who are providing deposit removal/inhibition/analysis services. As reservoirs worldwide age, multiple problems will be caused by inorganic scales and mixed organic deposits. These foulants are an inevitable result of higher water cuts and a need to produce more hydrocarbons from high pressure wells that then pass the fluids through cold seafloor lines. Vigorous, multifaceted FA plans should be implemented now!