Drilling fluid losses can pose a significant risk to personnel safety and the environment, complicate drilling and cementing operations, and cause costly delays.

A customer was experiencing mud losses and gas kicks whilst drilling a well with high hydrogen sulphide concentration. All remediation attempts, including mud weight adjustment, had been unsuccessful and mud losses had persisted for several weeks. Chemical, drilling fluid and rig time costs were spiralling upwards so the customer needed to locate the lost-circulation zones quickly and reliably.

TGT recommended its ‘Drilling Losses’ product and ‘True Integrity’ diagnostic system as a reliable means to pinpoint and explain the source of lost circulation.

The True Integrity system utilises methods, measurements and analysis that reveal seal failures throughout the well system, including ‘formation seal’ failures that tend to be the underlying cause of lost circulation. Key to the operation of the diagnostic system is the Chorus platform. Chorus technology records and displays the acoustic energy created by fluid movement throughout the well system. An appropriate diagnostic programme was developed to reveal lost circulation dynamics and Chorus sensors were deployed through the drillstring to survey the well.

The diagnostic system with Chorus revealed four active lost circulation zones, labeled A1 to A4 in Logplot. This explains why the operator was having so much trouble solving the issue.

The operator deployed lost circulation material (LCM) to all four zones and the diagnostic programme was repeated.

The second survey showed that fluid loss had been eliminated in A1 and A2, and considerably reduced but not stopped in A3 and A4.
A second treatment was applied using a different LCM to A3 and A4, and a third survey with Chorus showed that A4 had been sealed, and only minor losses were escaping to A3.