Numerical Analysis of Chemical Reactions between Shale Formation and Drilling Fluid of Water Base (in One of the Southwest Formations of Iran

Instability in shale layers is accounted as one of the biggest problems in drilling industry and area of gas and oil craft. Yearly, industrialists spend a great deal of money to solve this problem. Connection between drilling fluid water base and shale formation causes the swelling development and an increase of pore pressure in the walls of wells; the continuation of this process during time span will be one of the most important factors for the stability of well walls. The potential difference developed/created between drilling fluid and shale formation will cause changes in pore pressure, swelling pressure, water absorption percentage by the shale and the coefficient of membrane. By using the mathematical methods and numerical modeling of finite difference methods, the physical and chemical reactions developed between drilling fluid of water base and shale formation were studied in this work. The results obtained from the numerical modeling express this fact that using fluids in the studied field, to prevent the instability of well resulted from swellings of shells, creates the necessary efficiency and the potassium chloride fluid shows better performance among them. Therefore, the least swelling pressure and pore pressure have been developed by using it.