Controlling Organic Deposits and Sludge in a Severe Hostile Environment

Abstract

Formation damage, tubing plugging and plugged production equipment caused by the deposition of organic deposits and sludge are inherent in many workover and stimulation operations around the world. This paper describes the methodology followed to improve production through adequate stimulation treatments and control of the organic and sludge deposition existing in the south-east of Mexico. In fact, this is a recurring problem that has existed for many years severely affecting oil production. Evaluation of the results and conclusions derived at different stages of the analysis are discussed. The benefits of emulsifying the acid with an aromatic(external phase), are also presented including the key factor of the iron reducing agent in a ferric iron environment in addition to the required iron sequestering agent. Results of stimulations performed in the area are discussed including well performance months after treatments. Introduction Organic deposits and sludge problems are increasing in the petroleum industry. Their precipitation is a problem that has existed for many years in the south east of Mexico, severely affecting oil production. Oil production in the south east of Mexico is distributed between the tertiary sands, the Cretaceous and Jurassic dolomitic limestone's. These last two are found in the 5,000 to 6,200 meters (m) range with temperatures in the 125–155°C. The reservoir considered in this paper is characterized by natural fractures with a 35° API sludge tendency crude containing asphaltenes in the 10–15% range, paraffin in the 15–20% (High Molecular Weight) and 2-5% (Low Molecular Weight) causing routine deposition in the production equipment, tubing and formation. Until recently, the main approach for resolving the severe deposition of these organics has been remedial; i.e., routine injection of appropriate chemicals to dissolve the deposits. In fact, a good portion of the wells have a0.95 cm capillary tubing which is run with the production tubing for continuous injection of both asphaltene and paraffin dispersants to alleviate the problem. However, the persisting asphaltene-sludge precipitation problem was in need for another approach.