A new plugging-while-drilling fluid of high bearing strength and acid solubility with multifaceted zigzag metal particles as a skeleton material

Abstract

When a high-density and oil-based drilling fluid is used in ultradeep tight sandstone fractured gas reservoirs, the conventional lost circulation materials could not meet the requirements of oil phase dispersion, acid solubility and high pressure in the case of complicated lost circulation. In this paper, the aluminum alloy material with the properties of oil phase dispersion, high rigidity and high acid solubility was introduced to solve the problem. This material is composed of multifaceted zigzag aluminum alloy particles (GYD) and its density is 1.60 g/cm3. The foamed aluminum alloy is ground into 3-80 meshes. Compared with the currently used marble bridge particles, GYD are dispersed completely in oil phase, its Mohs hardness is two times higher (up to 5.0-6.0) and acid solubility is over 90%. According to bridge rules of 1/2 - 2/3 opening degree of formation fractures, laboratory HTHP static and dynamic lost circulation simulation and evaluation were conducted on the slurry which is composed of high-density oil based drilling fluids (as the base slurry), GYD (as the skeleton particles), fiber material and variable filling particles. It is shown that the plugging pressure is over 25 MPa, acid solubility is 65%, the slurry is stable and the density difference (48 hrs.) is less than 0.03 g/cm3 when the dosage of GYD is 8%. This material was tested on site at a certain well in the piedmont zone of the Tarim Basin. The gas reservoir in this well is 7 220 m deep. It is shown that the daily leakage was about 50 m3 when the high-density and oil-based drilling fluid was used. When the GYD drilling fluid was adopted, however, the reservoir is drilled smoothly without any leakage. And thus, the sealing function of "high-rigidity bridge + fiber network + deformable filling" is better exerted on the formation fractures with a high flow resistance and a high loading capacity.