Method for Evaluation of Plugging of Nano-micron Fractures

Borehole wall destabilization in unconventional oil and gas drilling has been a problem frequently encountered, and it is widely agreed that plugging of the nano-micron fractures in shale is key to the solution of the problem.A new compound cellulosic filter membrane was chosen to do filtration test.This membrane has pore sizes that are compatible with the sizes of fractures found in shales.By comparing of spurt losses of different additives, the plugging effect of these additives on the membrane can be examined.Using this method, limestone of nano-micron particle sizes and silica of the same size distribution are selected and compounded, producing a clay-free drilling fluid with strong plugging capacity.Polyamine and aluminum compound are also introduced into the drilling fluid to render it inhibitive capacity.At low apparent viscosity, this drilling fluid has high YP/PV ratios, and high φ₆, φ₃ readings.These characteristics are advantageous to hole cleaning.The drilling fluid has low filter loss and high percent cutting recovery(almost 100%).It has plugging capacity much higher than that of the conventional polymer drilling fluids, and is suitable for use in tight oil and gas drilling and shale gas drilling.