New Strategies for Cost Reduction with Depth Correlation in Deepwater Wells

Some completion operation steps, such as perforation and packer seating, require that the degree of uncertainty be limited. The main correlation methods used today are based on tally accuracy, tagging a known element in the well or using wireline gamma ray readings. This paper discusses the development of four alternative depth correlation techniques that aim at avoiding the use of wireline in completion and well testing scenarios. All these methods were implemented in field jobs and demonstrated their efficiency with lower operational cost, higher operational safety and acceptable margin of error for the target job. Two methods are based on gamma ray readings and to send data to surface they use logging while drilling (LWD) and wireless telemetry. Target applications for these two methods are tubing-conveyed perforation (TCP) and well testing operations. The other two methods use casing internal diameter (ID) changes at known depths to determine string depth. One uses a rigid hole-opener to tag a crossover or the top of a liner and the other uses the pressure drop produced by a packer entering into a well section with smaller ID. The main advantages of these new depth correlation techniques are rig time savings and greater operational safety by reducing personnel exposure to dangerous operations.