Factors Causing Emulsion Upsets in Surface Facilities Following Acid Stimulation
Authors: Coppel C.P. 
Published: December 2007

Severe emulsion upsets in surface treating facilities following acid stimulation frequently occur after production from the stimulated well is commingled with other production. Preventing such upsets requires using optimum demulsifiers at high concentrations and eliminating, or at least minimizing, the formation of precipitates.

Introduction
Frequently, severe emulsion upsets occur in surface treating facilities following acid stimulation. Such upsets usually occur after production from the stimulated well is commingled with other production from nonstimulated wells. These emulsions have been extremely difficult to treat and have resulted in loss of considerable oil produced as an untreatable emulsion and a reluctance, in some areas, to use acid stimulation.
Results presented in this paper show that acids partially spent on formation solids contain, in solution, potentially precipitable materials. As the pH of the produced acid precipitable materials. As the pH of the produced acid increases upon commingling with other production, fine solids are precipitated; these solids are capable of stabilizing extremely tight emulsions. The stability of such emulsions is far greater than that of emulsions stabilized by fine particles loosened from the formation or by oil-wet formation particles loosened from the formation or by oil-wet formation particles. Preventing upsets in the field requires using particles. Preventing upsets in the field requires using optimum demulsifiers and eliminating, or at least minimizing, the formation of precipitates from partially spent acids. Examples are given for handling such problems in the field. A novel technique for the reproducible formation and the study of emulsions in the laboratory is presented. The use of the technique in selecting optimum demulsifiers for the field is described.

Background
Historically, emulsion treatment has played a significant role in petroleum production. Much of the world's oil is produced with water and, in many cases, stable water in produced with water and, in many cases, stable water in oil emulsions occurs. An entire technology has been developed for treating such emulsions. Types of treatment include thermal, electrical, and chemical treatments. Most oilfield emulsions are stabilized by small amounts of naturally occurring, surface-active materials present in either the oil or the water, and usually can be treated with nominal amounts of chemicals or by other means. Such emulsions generally are observed at the wellhead and are believed to form either in the wellbore or in the formation.
Emulsions observed following acid stimulation are significantly different. First, they do not always show up at the wellhead, but generally form only after production from the acid-treated well is commingled with production from untreated wells. Second, they are extremely difficult to treat requiring either large amounts of chemical demulsifiers or unusually long separation times. Such emulsions are a particularly serious problem in offshore operations, where it is usually impractical to separate production from individual wells and where an entire production from individual wells and where an entire field's production may be commingled before treatment. Emulsion upsets under such circumstances can result in thousands of barrels of nonpipeline-quality oil. The problem has been particularly acute in Gulf Coast fields, problem has been particularly acute in Gulf Coast fields, but also has been noticed recently to a lesser degree in production from offshore California. As more production production from offshore California. As more production comes from offshore and more acid stimulation is used in such areas, occurrence of severe emulsion problems can be expected to increase.
The work reported here was related to sandstone acidizing with HC1-HF acid.
JPT
P. 1060