Wellbore Strengthening
Reducing lost circulation costs through fracture prevention.

The Challenge
Wellbores “break down” when the hydraulic pressure in the wellbore exceeds the breakdown pressure of the weakest formation exposed, causing induced-fracture lost circulation. Lost circulation is the most costly mud-related drilling problem, and induced-fracture lost circulation is one of the most common types. A huge potential benefit exists if induced fractures could be prevented from starting or propagating.

The Answer?
One possible solution is Wellbore Strengthening, which is defined as any treatment that increases the pressure at which the wellbore breaks down.

Option 1
One technique is the addition of special granular loss prevention material (LPM) to the mud, which has recently been used on several ConocoPhillips wells, resulting in significant savings.

The basis of the effect comes from granular materials of a certain size, physical character and concentration added to the mud. When these granular materials lodge near the tip of a newly forming fracture, the extension of the fracture is greatly inhibited. In theoretical terms, the pseudo-fracture toughness is greatly increased, preventing further growth of the fracture. These granular materials, along with the other smaller particles in the mud, form a plug, or dehydrated zone, in the fracture that prevents hydraulic pressure from reaching the fracture tip.

Option 2
Another method of Wellbore Strengthening, a high fluid loss, high solids content squeeze, has been very successful in Nigeria and Alaska. In this method, a fluid designed to have a very thick filter cake is pumped into an existing induced-fracture lost circulation zone, and allowed to deposit a very thick filter cake in the fracture. Once the fracture is fully filled with hard filter cake, the wellbore is stronger than before the fracture was initiated. A successful application on an exploration well in Nigeria resulted in considerable savings.