Requirements for Drilling Mud

　　Requirements for Mud

　　① Meet the requirements of the drilling circulation

　　Drilling circulation places the following requirements on drilling fluids: low pump pressure (low viscosity), strong cuttings-carrying capacity (high dynamic shear stress), low start-up pump pressure (low static shear stress), good lubricity, low friction, and minimal wear (due to a low solids content).

　　② Maintain wellbore stability

　　When drilling through formation intervals, the hydrostatic pressure of the drilling fluid must be balanced against the formation pressure, and the drilling-fluid density must be kept stable. During drilling in oil- and gas-bearing formations, the hydrostatic pressure of the drilling fluid must counteract the formation pressure; therefore, the drilling-fluid density must be appropriately adjusted. Moreover, the drilling fluid must possess properties that can mitigate the effects of unstable formations—for example, mudstone swelling upon water absorption, which can lead to wellbore collapse; gravelly and volcanic rocks that may experience sloughing or collapse upon contact with water; and salt formations that can develop solution cavities when exposed to water—thus necessitating the use of drilling fluids with tailored characteristics for different formation types.

　　③ Protect the oil and gas reservoir

　　After penetrating the oil and gas formation, the drilling fluid comes into contact with the formation. To prevent damage to the formation, the drilling fluid is required to exhibit low fluid loss, a thin mud cake (formed by solid particles under differential pressure after fluid loss, which then create a mud cake annulus on the wellbore wall), low solids content, and minimal hydration of the filtrate (i.e., minimal chemical interaction between the filtrate and formation fluids upon entry into the formation).

　　④ Protecting the environment and ecology

　　Drilling fluids often contain crude oil, diesel, various oils, and substantial amounts of chemical treatment agents. To prevent potential environmental and ecological impacts, it is imperative to use drilling fluids that are harmless and non-toxic.