Formulation of High Temperature Stiff Micro Foam Drilling Fluid with Strengthened Plugging Capacity

A high temperature stiff foam drilling fluid was formulated on the basis of analyzing the factors affecting the stability of micro foam at elevated temperatures. This drilling fluid has strengthened plugging capacity. A high temperature low molecular weight foam stabilizer was used to form a rigid structural film at the interface of the foams. A wetting agent was used to improve the wettability and osmosis of the foam surfaces, thereby mitigating the evaporation of the micro foams at elevated temperatures. Meanwhile an optimized high temperature filter loss reducer and a low density plugging agent were used to strengthen the pressure bearing and plugging capacities of the micro foam drilling fluid. The density of the stiff micro foam drilling fluid can be adjusted between 0.6 g/cm³ and 1.0 g/cm³. The micro foam drilling fluid has a stable rheology. The half-life of the foam is at least 45 h at room temperatures, at least 35 h at 150 ℃, and at least 120 h at elevated temperatures after optimization of the formulation of the foam, all indicating that the micro foam has excellent stability. The plugging belt formed by this stiff foam is stable; in HTHP sand bed test, the invasion depth of the filtrate was reduced by 82.1%, and the invasion depth of drilling fluid was reduced by 73.8%. The micro foam is able to resist contamination by at least 15% crude oil. No special equipment is required in field application of the micro foam, and it is suitable for use in controlling mud losses in high temperature deep wells penetrating low pressure formations in which mud losses are prevailing. It can be long circulated between the surface and the borehole, and help stabilize the borehole walls. Using this stiff micro foam, drilling fluid costs both on materials and equipment are saved, and borehole walls stabilized.