Study and Application of Reservoir Protection Drilling Fluid Treated with Nano Spheres

Tight sandstone gas reservoirs have special characteristics that make them quite prone to damage, which is very difficult to remove, during drilling. The dry gas reservoir in the Block Linxing, for example, is such kind of reservoirs, with low porosity, low permeability, low abundance, and no sulfur. To protect the reservoir from being damaged, two plugging agents, Micro-ball and CARB, have been used in the drill-in fluids to reduce the API filter loss to less than 5 mL. The Micro-ball is a high molecular weight polymer nano material able to penetrate into the pores in the reservoir formations to form interior mud cakes with ultra-low permeability, thereby to temporarily plug the micro pores. CARB is an acid-soluble inert spherical material with wide range of particle size distribution. CARB has particle sizes greater than the sizes of the pore throats in the reservoir formations, and are thus able to mud cakes on the surface of the formations. CARB has good plugging capacity and forms mud cakes that are easy to remove. The horizontal well LXxx5- 1H, completed with open-hole fracturing, was drilled with this drill-in fluid, which had good inhibitive capacity (shale cuttings percent recovery in hot rolling test is greater than 93%) and good plugging capacity. The improved lubricity of the drill-in fluid helped solve the problems of being unable to exert WOB during horizontal drilling, and balling of BHA. The drill-in fluid is resistant to contamination, has stable property which is easy to maintain, and good flow pattern. The drilling operation has been successful, and the gas production rate obtained after fracturing job is highly satisfactory.