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Dujiatai reservoir has an oil bearing area of 37.2km2 with the OIP of 2409×104t, burial depth of -2650~-2960m, porosity of 15.1% and permeability of 37.7×10-3 μm-2. In general, the reservoir is produced initially under natural energy by elastic drive and solution gas drive and development with water injection is tested in the later stage due to fast pressure decline and subsequent substantial production decline. During the water injection field test, although the water to be injected had been filtered to a fine degree, the water injection pressure increased substantially after a short time and water injection became difficult and some of the injectors were forced to be shut in because no water could be injected. The paper introduces the analysis results of the tests on water injection damage to Dujiatai low permeability reservoir. (1) Solid particles entered the reservoir, forming blockage due to the small throats of filtration with the average radius of the throats of about 1.0μm; (2) Because the injected water was not treated against swelling, clay swelled, forming blockage due to the medium to strong water sensitivity of the reservoir; (3) Because of the medium to strong velocity sensitivity of the reservoir, fine particles staying in a unconsolidated manner on the borehole walls or inner surface of the base rocks fell out, migrated and piled up at the throats, forming blockage; (4) The scaling tendency of CaCO3 of the injected water was obvious and the scales adhered to the inner surface of the throats, reducing the filtration radius of the throats; (5) The water injection pipeline was corroded seriously and the suspended particle content at the outlet of the filtering station reached the standard, but it exceeded the standard after going through the water injection pipeline and reaching the wellhead and it was even worse when it reached the bottom of the well. The solutions for the water injection damage to Dujiatai low permeability reservoir are as follows. (1) Acidization or acid fracturing deeper into the formations with weak acids is conducted to erode the unstable migrating particles; (2) Antiswelling agent is added to the injecting water to reduce clay swelling; (3) A secondary filtering unit is set up at the wellhead or the water injection pipeline is replaced with a corrosion prevention pipeline lined with fiberglass. Copyright 2008, Society of Petroleum Engineers.

spe international symposium and exhibition on formation damage control

Case Study: Analysis of the Characteristics of the Damage to Dujiatai Low-Permeability Reservoir by Water Injection and Research of Damage Removal Methods