Comparative Studies of Using Aphron Drilling Mud Versus Spud Mud

The complexity involved while drilling troublesome formation where problems like stuck pipe, thief zones and wellbore collapsing exists requires special remedial actions to continue drilling operations. These issues associated with depleted reservoirs can be reduced by either going for underbalanced drilling or by using some special type of drilling fluids which can mitigate the problem of lost circulation zones and differential sticking. Now if we go for underbalanced drilling which requires special equipments that are costly in nature, can make the project economically unviable and hence we have to use some special kind of mud which can extenuate the above mentioned problems. One such type of remedial drilling fluid that can be used in these troublesome formations is Aphron drilling fluid that has inherited properties of high shear-thinning by containing stabilized air-filled bubbles known as aphrons.

This type of drilling fluid provides the property of invasion control specially in highly permeable formation that include permeable and fractured sandstone and limestone formations apart from this it also provides stability in unstable shaly/clay formation. This property of invasion-control drilling is because of the stability of aphrons even at high pressure environment and their tendency to non-coalescing and hence the micro bubbles (aphrons) will move faster as compared to the surrounding liquid phase and will instantly form a layer of bubbles at the fluid front thus slowing down the entry of drilling fluid into the permeable formation and thus helps in building an interface that acts as an internal seal to seal the pore network of the wellbore. If we look at the fundamental level the barrier formed by the micro bubbles and the radial-flow pattern of the fluid will slow it down and causes the LSRV (low-shear-rate viscosity) to increase exponentially, now as the LSRV increases which is assisted by low thixotropy due to micro gel network of the fluid causes the fluid to generate high viscosity rapidly thus protecting the fluid to penetrate in the formation. Apart from this the low adhesive and cohesive nature of aphrons will prevent their sticking to the well bore and thus assist the displacement of produced fluids.