Oilfield Scale---Can We Handle It?
Authors: Vetter O.J. 
Published: December 2007

This paper is an analysis of the present knowledge of the formation, removal, and prevention of scale. This examination of the state of the art is presented to indicate the limits of current knowledge of oilfield-scale problems and to instigate additional research into these problems. problems. Introduction

This paper** deals with three distinctly different scalecontrol problems in oil and gas fields: prediction, removal, and inhibition. An attempt is made to analyze the state of the art and to show the narrow limits of our present knowledge. This attempt is undertaken to present knowledge. This attempt is undertaken to indicate these limits to operating people and to stimulate additional research.

All the known prediction methods have many shortcomings. Hardly any predict the actual amount of scale formed under a given set of conditions. Instead, they determine scaling tendencies. We can say that the scaling tendency of barium sulfate (BaSO4) is the easiest to predict and calcium sulfate (CaSO4) is much harder to predict and calcium sulfate (CaSO4) is much harder to predict. Presently, we do not have a workable method for predict. Presently, we do not have a workable method for predicting calcium carbonate (CaCO3) scaling. predicting calcium carbonate (CaCO3) scaling. The removal of each type of scale is technically possible, though perhaps not very practical. CaCO3 scale is possible, though perhaps not very practical. CaCO3 scale is the easiest to remove. CaSO or gypsum, is much harder to attack, and BaSO4 is by far the hardest to handle.

Scale inhibition is an art and is successful only in less seven: cases of scaling. We do not know of scale inhibitions that are very effective when the temperature is much higher than 350 deg. F, or when large amounts of scale per barrel of produced water are formed. The application of the inhibitors may also cause problems in the field. Some inhibitors may cause more problems than they solve: the formation of pseudoscales and extreme emulsion problems may be observed under certain conditions. problems may be observed under certain conditions. How Much of a Problem Is Scale?

Anyone who is vaguely familiar with oilfield operations has heard about the scale problem. However. there seems to be confusion about the extent of the formation and wellbore damage caused by scale in oil fields. To some, scale is not much of a problem because one seldom has a chance to see or physically examine actual samples of these deposits. Many scale deposits are, of course. located outside the well within the oil-bearing formation, where they are invisible. On the other hand, despite these analytical difficulties, some people think that scale is one of the major enemies in our daily oil- and gas-field operations.

I belong to the latter group, and I sincerely believe that there are few wells that do not suffer flow restrictions from scale deposits within the drainage radius inside the formation. within the wellbore, or in the surface equipment. If we try to estimate the loss of revenue caused by flow restrictions due to scale, we come up with astronomical figures. I have reason to believe that oil- and gas-field scale costs on the order of $ 1 billion/year in the U.S. alone. This sum should be considered a minimum.

I also believe that the scale problem is increasing. As our oil and gas reserves are depleted, we must produce these hydrocarbons under increasingly severe production conditions. More water production will favor many of the scale-forming conditions. In addition, we "pull" harder on our wells as less oil is being produced, thus favoring again all the scaling conditions. This means that the revenue losses resulting from plugging by scale will consume an increasing portion of our income as we deplete our reservoirs.

P. 1402