1. n. [Drilling Fluids]
A coring fluid formulated with components that are not likely to alter the wettability in the pores of the rock sample and that has low dynamic filtration characteristics. These qualities help retain the core's native properties and can retain some (or all) of the reservoir's fluids [water, oil and gas (gas only if kept under pressure)]. Bland water-based fluid is formulated to make the filtrate resemble the connate water in the reservoir. Keeping ionic composition and especially the pH matched to the reservoir water is most important. Thus, strong alkaline agents and clay deflocculants are avoided when designing bland coring fluids. Bland oil-based fluids should contain no water phase, and the base oil should resemble the reservoir oil. (Reservoir crude is used in some cases.) Amine, amide, phosphonated and sulfonated emulsifiers, and the powerful oil-wetting agents are also avoided. Fatty acid soaps are chosen to emulsify the trace of water that is likely to be encountered. Additives that minimize dynamic filtration rate must be chosen. Setting mud density and bit hydraulics to give equivalent circulating density close to the reservoir pressure helps avoid filtrate invasion into the core. Designing core bits to core as fast as possible also limits filtrate invasion ahead of the bit.