Deposition of organic and inorganic solids is common in various areas of oil and gas production operations that include pipelines, wellbores, and reservoir and surface facilities. Precipitation is the first step leading to deposition. However, for deposition to actually occur (and be detrimental to operations), a susceptible surface must be available. 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, more commonly experienced, complex foulants. To maintain production (Flow Assurance-FA) it is not enough to control scale, or wax, or hydrates. Because these materials affect each other and form complex mixtures, the formation of them must be addressed and treated simultaneously. This paper reviews the formation, inhibition and removal of complex inorganic/organic deposits. Practical multi-faceted techniques, based on the most recent research and developments, are described and illustrated using case histories to arrive at best practices for control.

The scope of this paper addresses issues of complex fouling deposition phenomena in the production ("upstream") oilfield environment. This includes the near-wellbore ("formation damage"), arterial deposits in flow lines, natural or artificial tubulars, subsurface devices, gathering lines and wellsite surface equipment. From a FA perspective, the most severe problem facing offshore developments is the formation of gas clathrate hydrates. The second most significant problem is wax damage, followed by asphaltenes. Onshore, and especially for low production ("stripper") wells, paraffin deposition is a major production issue. In reality, in both environments, these are usually mixed deposits because corrosion-susceptible steel surfaces are in contact with unstable brines and mixed hydrocarbons. The economic impact of scales and organic deposits runs into the multiple billion dollar range, annually. Inorganic scale damage (not including corrosion) has been estimated at approximately 2 billion dollars per year. An exact damage estimate for wax, hydrate, asphaltene and naphthenate fouling is not available. However, individual producers believe the problem is more significant than the inorganic scale.

This paper reviews current literature on the formation of complex mixtures, including scales and asphaltenes, in the near-wellbore area, "Black Powder" deposits in gas lines and the effect of surfaces on wax and hydrate formation. Because the subject is multi-component deposits, control methods also must be multi-faceted. Chemical and engineering analysis techniques that are highlighted include downhole/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 coiled 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.