Study on anti-sloughing drilling fluid technology for oil and gas reservoir protection.

To maintain a stable hole and to keep the reservoir from damaged, several engineering factors are involved, of which the drilling fluid is an important one. Drilling fluid is the first working fluid that opens oil and gas reservoir, and its properties affect both drilling performance and formation damage control. The density of drilling fluid is an important property index which has direct influence on drilling pressure differential. According to the drilling pressure differential, drilling fluids can be classified into two types: positive and negative pressure different drilling fluids. In this paper, from the point of formation damage control, the relationships between driling fluid density and well bore stability, and drilling fluid density and oil/gas reservoir protection were firstly analyzed respectively;secondly the mechanism of the damage of drilling fluid to oil and gas reservoir was analyzed and the methods for formation damage control and anti-sloughing were proposed, that was, when a problem of well bore stability was dealt with, not only the drilling fluid, but also other factors of the well such as geology, engineering and hydraulics etc.should be taken into consideration. Finally the new anti-sloughing drilling fluid technologies for reservoir protection at home and abroad including dilute silicate drilling fluid, polycol drilling fluid and synthetic base drilling fluid were introduced.