A water-based drilling fluid having a polymer latex capable of providing a
deformable latex film on at least a portion of a subterranean formation
has been discovered to provide reduced drilling fluid pressure invasion
when used to drill in shale formations for hydrocarbon recovery
operations. A precipitating agent such as a silicate or an aluminum
complex (e.g. sodium aluminate) is preferably used in conjunction with the
polymer. Typically, the water present contains a salt to form a brine,
often to saturation, although the invention may be practiced with fresh
water. If a salt is employed, it is often helpful to additionally employ a
surfactant, such as a betaine, for example.
