This is where nitrogen is used as part of the drilling fluid. This is called underbalanced drilling because the weight of the drilling fluid is less than the reservoir pressure. This method avoids a common problem of conventional drilling, where the mud can penetrate into surrounding rock formations and block the channels that allow hydrocarbons to flow into the well bore. Mud penetration can reduce productivity and even cause some reserves to be overlooked entirely.
The process of drilling a well with a fluid column exerting less pressure than is exerted by the reservoir fluids. This process is often performed using gases (eg. nitrogen) to reduce the density of the drilling fluid column.
Occurs when the operator of the site uses specialized mud or gas while drilling to allow for formation fluids to rise to the surface and thus prevent damage to the prospective formation.
Keywords:  unitization