Strengthening Depleted Wellbores Using Nano Particulates
Authors: Addagalla A. , Pietrangeli G. , Mesa S. 
Published: August 2024

Abstract
Drilling various depleted formations to enter the reservoir at the right location to extract the maximum gain is becoming more frequent and regular. In most cases, the overbalance reaches 1000 psi across various zones and is sometimes observed exceeding 5600 psi. Wellbore instability, deep fluid invasion, differential sticking, and mud losses are a few of the problems that need to be addressed when designing the fluid, irrespective of type of mud system (water-based or non-aqueous fluids). Also, casing isolation might not always be possible and can be very expensive. Therefore, it is necessary to identify a solution from the fluid's perspective that designs a suitable fluid mitigating the above concerns and makes the drilling easier, safer, and more efficient.
With appropriate bridging, a good seal across the formation help maintain the wellbore stability and stop the fracture propagation. The seal that forms should be thin, effective, and have low permeability that can minimize the pore pressure transmission (PPT) into the formation which causes the formation to destabilize. Initially these fractures in the formation are in nano-size levels and typical products available in the market cannot bridge these properly which can lead to bigger fractures and ultimately end up in causing heavy mud loses, well control situations, and formation damage leading to lost production. Bridging software helps to predict the right combination of products required and also determines the requirement for any other, bigger particles.
The latest developments in nanotechnology help in resolving the above concerns and can be used in the drilling fluids without having any adverse effect on the mud and environment. The technology features of the subject nano-sized solid particles allow them to be mixed in aqueous or non-aqueous drilling fluids and in any type of salt phase. Specific fluid design will depend on the application: whether it is to address shale stability, or overbalance or bridging requirements at the target well application with minimal material usage compared to conventional products that are presently used in the industry. The nano-sized particles are free flowing polymer particles (D50 between 100 - 200 nm) and are deformable. They can seal and mechanically plug the micro-fractures and pore throats, thus forming a semi-permeable membrane. This prevents fluid penetration and provides support to enhance hole stability. Nanotechnology helps in minimizing the overall product consumption and waste generation which can be a huge cost savings to the operator and significantly reduce the costs related to transportation movement and number of mixing hours which is indirect savings to the operator.
This paper presents a detailed laboratory analysis of the product over a broad range of conditions at high overbalance pressures. Return permeability data shows the product is not damaging to reservoir, with minimal lift-off pressure and is beneficial to use for better production and improved return on investment. Due to its unique nature, it may be possible to forego breaker fluids, thus decreasing both the cost of operation and the rig time spent on each well. The product has seen great success in fields across the world and several applications were produced successfully.