Influence of drilling fluid cooling technology on drilling operations

Drilling Fluid Performance: The plastic viscosity of the drilling fluid decreases as the temperature increases, and the density decreases as the temperature rises. Higher temperatures reduce the carrying capacity of the drilling fluid and decrease the power transmission. To maintain the high-temperature performance of the drilling fluid, various additives need to be added, which increases the cost of the drilling fluid. Additionally, high temperatures make it more challenging to control the drilling fluid due to issues such as the decomposition of some additives and intensified chemical reactions that affect the effectiveness of the additives.

Mechanical Drilling Speed: During the drilling process, there is a heat exchange between the circulating drilling fluid and the formation at the bottom of the well, causing changes in the temperature of the formation. This heat exchange is more intense, especially in deep well drilling where the formation temperature is higher. When the lower-temperature drilling fluid comes into contact with the formation at the bottom of the well, the surface of the rock in contact with the drilling fluid is immediately cooled, causing a decrease in temperature and thermal contraction. However, the internal temperature of the rock remains unchanged, resulting in thermal stress with tensile characteristics on the surface of the rock. As rocks have low tensile strength but high compressive strength, the presence of tensile stress makes it easier for rocks to fracture, thereby improving the mechanical drilling speed. The larger the temperature difference, the greater the impact on the strength of the rock.

Downhole Tools and Instruments: Downhole power drilling tools often use rubber stators, and overheating can significantly shorten the lifespan of the rubber stator. Moreover, higher downhole temperatures will severely affect the measurement accuracy and lifespan of electronic components in geological steering and measurement tools. In some cases, the current downhole drilling tools and instruments cannot be used due to excessively high downhole temperatures that do not meet the temperature requirements. Lowering the temperature of the circulating drilling fluid effectively reduces the environmental temperature for downhole tools and instruments, extends their temperature range of use, improves their reliability, and prolongs their lifespan.

Downhole Stability: The circulation temperature of the drilling fluid is one of the main factors causing instability in the wellbore. In deep well drilling operations, the lower formation layers have higher temperatures, while the upper layers have lower temperatures. During the circulation of the drilling fluid, the temperature of the lower wellbore surrounding rocks decreases, while the temperature of the upper wellbore surrounding rocks increases. As a result of thermal expansion, the tangential stresses in the upper surrounding rocks increase. When the sum of thermal stress and original stress exceeds the strength of the rocks, instability and failure of the upper wellbore can occur.

The relationship between the drilling fluid temperature and the stability of natural gas hydrate wells is particularly significant. Heating-induced decomposition of gas hydrates can lead to a rapid deterioration of the mechanical properties of the formation, resulting in instability. Selecting a low-temperature system drilling fluid and controlling its temperature below the equilibrium temperature of the hydrate phase helps maintain wellbore stability and ensures safe drilling.