Formation, Effect and Prevention of Asphaltene Sludges During Stimulation Treatments

Formation of asphaltic sludge during acid stimulation has been a serious problem in many areas for several years. Such sludges have had adverse effects on the results of treatments in many reservoirs of the U.S., particularly in California and the Rocky Mt. region. Recent studies have shown that sludge may also affect results in many areas where it has not yet been recognized as such. These studies indicate the following: (1) Sludge is a precipitate of colloidal materials present in crude oils; (2) the precipitates occur due to changes in environmental conditions of the crude by addition of materials such as acid; (3) once formed, sludge is insoluble in most treating chemicals; and (4) sludge can be prevented or controlled by use of stabilizing agents in treating fluid or by use of certain solvents as the outer phase of acid-in-oil emulsions. How and why sludge is formed and how it can be prevented or controlled are discussed. Simple laboratory tests are given for determining the probability of sludge formation prior to treatment. (13 refs.)