Cutting of Drilling Fluid with Oil, Gas,or WaterWhen the bit penetrates a porous formation, the fluids contained in the formation(gas, oil, or water) escape and mix with the drilling fluid. This is called cutting ofthe drilling fluid. Sometimes, swabbing also causes cutting of the drilling fluid.Cutting drilling fluid (contaminating with low-density formation fluid) reduces thedensity of the fluid in the annulus and causes a subsequent loss of hydrostaticpressure. If drilling fluid cutting is identified to be occurring, proper steps shouldimmediately be taken to remedy the situation. Failure to recognize and deal withdrilling fluid cutting can cause a kick.Kick causes 372.2.6. Loss of Riser Drilling FluidIn Sub-Sea drilling, the drilling fluid in the riser that connects the drilling vessel tothe seabed contributes a significant portion of the bottomhole pressure. If thisriser is accidentally disconnected or damaged, the drilling fluid in the riser will bereplaced by seawater, which is usually lighter than the drilling fluid. This canreduce the bottomhole pressure and cause the well to kick.2.2.7. Ballooning or Charging FormationBallooning or charging of formations occurs when the formation being drilled haseither induced or pre-existing fractures. During circulation, the pressure in thewell is high (due to friction pressure loss in the annulus). Due to high wellborepressure, the fractures open up and store drilling fluid. The wellbore pressurereduces the moment circulation ceases, as the annulus friction pressure loss,which adds to the wellbore pressure, no longer exists. This causes the fractures toclose and return the stored fluid back to the well. If the returning fluid is lighter inweight (original formation fluids, such as gas, oil, or salt water), the bottomholepressure will reduce and the well may kick.