This paper discusses the detrimental effects of sludge formation during acid Stimulation treatments, and our experience in preventing the problem. Acid sludging in some oils in the US, particularly in California and the Rocky Mountain Region, has been reported in the literature in the mid 60's. In the early 1980's, when incidents were reported independently in the company's three different fields in central Alberta, we began to investigate the extent of the problem.
Our tests show that crude oil from all the company's fields, scattered across western Canada, has strong tendencies to form sludges when the crude is in contact with a strong acid such as 15% HCl, and the conventional anti-sludge additives are ineffective in controlling it. Sludging is especially severe when Fe is present in the acid. The major source of Fe is corrosion and mill scales in the tubing.
Both field and laboratory observations indicate that sludging can cause serious plugging in the formation, leading to ineffective acidizing. Effective sludge control was difficult in the early days, as the technology was new to the industry. However, with close co-operation with the service industry, notable progress has been made, and currently, sludging can be controlled economically in the presence of up to 40,000 ppm Fe in HCl up to 28%.
Improvement of acidizing success rates has been a continuing interest at the company, as it has been the most frequently used stimulation technique in the field. Evidence of sludge formation during acid stimulation treatments has been reported in the company's oilfields in central Alberta since the early 1980's.
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