The Chicontepec basin in the northern region of Mexico has experienced an increase in the application of completion technologies using fracturing sleeves (FSs) activated by baffles in long, extended horizontals. Because of the oil’s high viscosity in that zone and the inherent decrease in initial production, the milling of such FS baffles has become a necessity. Milling jobs have proven to be difficult using conventional coiled tubing (CT) milling methods, tools, and processes. Analysis of previous variables, well constructions, CT strings, and CT equipment led to the development of an unconventional work method that has been applied with success in more than 12 wells in the region.
CT milling operations rely heavily on two variables—the amount of effective weight on bit (WOB) that is applied over the obstruction and the torque generated by the tool. An intervention in a long, extended horizontal using CT implies the following constraints:
Normal force of CT in the extended section.
Friction caused by the previous normal force.
Friction pressure loss resulting from limited CT diameters and lengths.
While observing the long time intervals involved with most interventions and a few events in which the CT became stuck, a new intervention method was developed. Highlights of this method include the following:
Specific bottomhole assemblies (BHAs) for milling and cleaning of debris generated.
Static friction reducers.
Pressure friction reducers.
Staged milling/cleaning work method of the total amount of FSs.
The first deployments of the combined work method were observed with caution and were not fully supported by the customer. The staged milling was supposed to increase the operating times in these interventions. However, by the time the third well was milled using this method, this perception began to change because of comparisons between the time lost during unwanted events, such as the tool becoming stuck and difficulty during milling. Previous events had reduced the occurrence of these issues in the last 12 wells and the use of associated FSs.
The importance of this work method is evident by the observed reduction in overall intervention time, delivering production earlier with no quality issues for the Chicontepec area.