Strengthen a wellbore while drilling is the most effective technique to do to the wellbore before bad losses will be happened. Techniques of wellbore-strengthen are similar to lost circulation concepts. The wellbore-strengthen techniques emphasize on lost circulation prevention, increase in overall formation fracture gradient and elimination of fracture elongation. However, the lost circulation concepts focus on preventing losses of drilling fluid. In the drilling industry, 7 effective ways to strength the wellbore are as follows;
1. High fluid loss slurry – with high fluid loss slurry, the slurry will easily lose liquid component into the formation and leave solid behind. The solid will be pushed into fracture spaces and create impermeable zones.
2. Granular loss-circulation material – By adding the granular loss-circulation material ahead of the time, the material in the drilling fluid will plug off fractures that will result in higher formation strength and stop mud loss.
3. Smear effect – You are able to see this effect when drilling with casing. While rotating, the casing smears filter cake and cutting into the borehole wall. This effect creates a plastic-like sealant at the wall of wellbore that helps prevent the wellbore collapse.
4. Heating the wellbore – By heating up formation around the wellbore, the formation will be expanded and it will increase rock stress. Therefore, the well becomes stronger.
5. Chemical sealant – It acts like an epoxy. When it is pumped into the wellbore, the chemical component will go inside pore spaces and create walls across the fractures in the wellbore therefore the overall formation strength will be greater and loss circulation will be ceased.
6. Ultra-low fluid loss chemical – This particular chemical is mostly utilized to prevent lost circulation in permeable zones. With properly adding into drilling fluid, the chemical will reduce the initial spurt loss of mud therefore a filter cake will be almost impermeable. The impermeable filter cake around the wellbore will prevent losses into permeable formations.
7. Rigid-plug forming treatment – This is a special liquid chemical and when it is mixed with drilling mud, it will create cross-linked polymer just like latex rubber which will plug wellbore fractures in order to prevent lost circulation problem.
Wellbore-strengthening techniques are very important because they will prevent the lost circulation, one of critical problems in drilling operation. Therefore, you need to understand all concepts to achieve drilling free operation.
Reference books: Drilling Fluid Books