Low Damage Low Density Drilling Fluid Used in Songnan Gas Filed for Lost Circulation Control while Drilling

The igneous rock reservoir in Songnan gas field has low formation pressures and is rich in formation fractures. Time efficiency of drilling operation has been low in this area because of mud losses frequently encountered during drilling. To address this problem, a low solids low damage low density drilling fluid with the ability of controlling mud losses while drilling was formulated based on laboratory experiment. To improve the cuttings carrying capacity of the drilling fluid, a hydrophobic associative amphoteric polymer PAADDC was selected based on the geology and drilling requirement of the gas field. By evaluating the water loss and wall building capacity, as well as pressure penetration property of the drilling fluid, a plugging additive mixed with PB-1 and ultra-fine calcium carbonate of different particle sizes was prepared. A lost circulation material used while drilling was formulated with hollow elastic rubber beads, calcium carbonate particles and hollow elastic micro beads. Evaluation of the drilling fluid shows that this drilling fluid has good rheology, plugging capacity, anti-sloughing ability and capabilities of controlling and preventing mud losses. Use of calcium carbonate makes it easy to minimize formation damage by acidizing job. When used in drilling the Well Yaoping-16, the mud showed stable properties. Mud losses in drilling the low-pressure igneous rocks, which negatively affected drilling time efficiency previously, was successfully resolved. Requirements of drilling operations and reservoir protection were satisfied with this drilling fluid.