Abstract

Removal of scale depositions from wellbore tubulars has always posed a challenge to operators. Traditional methods to do so have included chemical treatments, mechanical methods, or even removal of affected tubulars. All of these methods have varying degrees of success, as well as varying cost to operators depending on the type and amount of deposition in the tubulars.

Barium Sulfate scale removal has traditionally posed the greatest challenge to operators and service companies alike. Chemical soaks have been developed and applied as well as mechanical methods, usually meeting with limited success. As a result of these failures, a dependable, engineered and cost effective approach has been developed. The process combines the use of traditional coiled tubing operations and a high-pressure rotary jetting tool to remove the Barium Sulfate scale - without use of solvents. The process has been successfully utilized to completely remove over 9,000' of Barium Sulfate scale in subject wells that have not been effectively cleaned when tradition methods have been tried.

This paper will look at well conditions conducive to the formation of barium sulfate scale, as well as why it is such a difficult material to remove. Coiled tubing solutions will be discussed, culminating in a collection of case histories where a unified mechanical / jetting program has had best results.

Introduction

Barium sulfate scale is one of the most problematic scales that oil and gas operators have to deal with.With no known chemical treatments for rapid dissolution of the material, other removal techniques are typically called upon, usually incorporating some mechanical rather than chemical solution.

Mechanical methods have, however, limitations which prevent them from either succeeding, or removing 100% of the scale.Therefore a "unified approach" has been adopted - with positive results.This unified approach incorporates two different CT operations, one following right after the first.The first run involves using an appropriately sized drilling motor and bit, the second uses a unique high energy rotary jetting system. This methodology has proven itself to be very effective in field applications.

Barium Sulfate Scale

Barium sulfate scaling occurs in oilfield wellbores throught the world, and has been identified at least as far back as 1914, in the Saratoga Field, Texas(1).Of all the various wellbore deposits, barium sulfate tends to be the most problematic due to its relative insolubility in most known solvents, and its strong mechanical properties.Progress has been made in the development of specialized chemicals addressing barium sulfate dissolution, but typically, these require long soak periods to be effective.Depending on the location and configuration of the scale, as well as a number of well details, operations requiring extended fluid contact time often are just not practical.Therefore, removal methods usually have to involve an aggressive mechanical solution.

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