Long-Barrel Coring Technique for the Mishrif Reservoir in the Garraf Oilfield,Iraq

Due to high permeability,differential pressure sticking and lost circulation are often occurred in the Mishrif Reservoir of the Garraf Oilfield during the course of drilling.In addition,the Mishrif Reservoir contains marl and pyrite,which makes it extremely difficult to ensure desirable core recovery and coring quality.On the basis of analyzing the formation characteristics and coring technical difficulties in the oilfield,a long barrel coring technique appropriate for the Mishrif Reservoir has been developed,nd designed the aluminum alloy inner barrel with pressure relief function,as well as inner barrel stabilizer with protection against back off,which raised the core recovery.Application of the pulley hoisting system and the core gamma scanning technique has resulted in fast and high efficient core processing operations,and performed total coring footage of 309.00 m in three wells of Garraf Oilfield,with average core recovery up to 92.5%.Results of the application demonstrated that the coring technique can effectively solve the technical problem of coring in Mishrif Reservoir of Garraf Oilfield,and provide certain reference of coring operations in Mishrif Reservoirs of the Middle East in the future.