Investigation on Casing Damage in Liaohe Du66 Combustion Project

Abstract

The dry In-situ combustion test was conducted for multilayer heavy oil reservoir such as Du66 in Liaohe Oilfield since 2005, in consideration of the limited oil recovery of cyclic steam stimulation for such multilayer heavy oil reservoir with more than 10 layers and the thickness ranging from 1m to 15m. There are more than 90 CSS wells converted into air injection wells operated in geometric well pattern in past 10 years. Field well integrity testing result shows that casing damage such as diameter shrinkage, corrosion, and local destroy, are found in about a fifth of the air injection wells. The casing damage has become one of the largest problems in the in-situ combustion project, and remedial well treatments have to be carried out urgently. It will negatively affect the development performance and also indeed a risky operation under high temperature, backfire and even explosive conditions. In order to effectively prevent the casing damage in air injection process, casing damage in Du 66 project is investigated at first, then performance of field measured temperature and air injection were primarily analyzed combined with numerical simulation of a typical reservoir recovered by an air injection well group. Based on extensive laboratory experiments, temperature and oxidation corrosion on yield strength of different material casing are investigated, furthermore, principles of casing damage in Du66 project are discussed. At last, preventive measures for Du66 combustion project are investigated. The results show that the causes of casing damage in Du66 project involve reduction of casing intensity because of high temperature and corrosion, and stress variation because of large temperature difference between layers, especially local extra high temperature occurring at layer(s) with low air injectivity where burning in the vicinity of wellbore will keep on for a long time. Consequently, downhole electrical ignition other than chemical ignition and self ignition is recommended for its uniformly heating advantage, and separated-zone combustion in sequence, selective separate zone combustion and air conformance control methods are effective to prevent casing damage of such multilayer reservoir as Du66.