Published March 2016

Complications appear due to the pressure in osmosis well and their elimination

J.S. Akhundov

In equal values of reservoir and hydrostatic pressure in the well as a result of diffusion, the ions Na+, K+, Ca++ and Mg++ having a high concentration, tend to get into the drilling mud with a low concentration. When drilling permeable formation, mentioned ions unopposed pass into the drilling mud, thereby deteriorating its quality indicators and hydrodynamic functions. While drilling clay formations with highly mineralized water content, due to the absence of permeability, highly concentrated ions can not osmotically get into the drilling mud with a low concentration. The character of ions’ osmotic passage depends on the membrane’s permeability. In poor membrane permeability the diffusion of smaller volume ions may occur, and in impermeable membranes the exchangeable cations create osmotic pressure. It is known that clay rock has a closed porosity, i.e. microcells. Therefore, clay rocks are practically impermeable, as a result of which behind the membrane extremely high osmotic pressure deteriorating natural structural relationships between rock particles occurs and it leads to the caving. For the prediction of above mentioned complications the exchangeable cations are added into the drilling mud and the diffusion process does not take place in equal concentrations of ions in the formation, and the osmotic pressure on the well walls stops.