Zero-invasion acidic drilling fluid
View Patent ↗A drilling fluid system using retarded acid systems such as gelled acid (VES or polymer) and/or emulsified acid to drill carbonate formations (calcite and dolomite). Foamed acid may be used in low abnormal pressure carbonate reservoirs. The drilling fluid system permits drilling a target hydrocarbon-producing formation with zero-invasion of the drilling fluid system. A method for using the drilling fluid system for fluid loss control during drilling operations.
1. A method of drilling a well present in a hydrocarbon producing formation, comprising:
drilling a hydrocarbon producing carbonate rock formation with a drilling fluid system to form the well in the hydrocarbon producing carbonate rock formation, wherein the drilling forms carbonate rock cuttings which are suspended in the drilling fluid system,
contacting a face of the well with the drilling fluid system comprising the carbonate rock cuttings,
wherein the drilling fluid system further comprises:
an aqueous acidic solution;
a silicate; and
a hydrocarbon-based isolation fluid;
wherein the aqueous acidic solution, the silicate and the hydrocarbon-based isolation fluid are in the form of an emulsion;
wherein during the drilling the emulsion breaks when contacted with the hydrocarbon producing formation to initiate interaction of the aqueous acidic solution and the silicate to form a gel and thereby form an impermeable filter cake layer on the face of the well in the hydrocarbon producing formation,
wherein, during the drilling, the concentration of the silicate in the drilling fluid system is effective to form an impermeable filter cake layer on the face of the well and has a silicate concentration of: 5 weight % when the hydrocarbon producing carbonate rock formation has a permeability of between 1 to 100 md, 10 weight % when the hydrocarbon producing carbonate rock formation has a permeability of between 100 to 300 md, or 15 weight % when the hydrocarbon producing carbonate rock formation has a permeability of between 300 to 500 md,
wherein the filter cake layer formed on the face of the well in the hydrocarbon producing formation comprises the carbonate rock cuttings, and
wherein the filter cake layer is formed only on the face of the well, has a thickness of about 1 mm, and has zero infiltration volume.
2. The method of claim 1 , further comprising delaying interaction of the aqueous acidic solution and the silicate until the emulsion is broken.
3. The method of claim 1 , wherein the filter cake layer is formed in an amount effective to overcome exerted pressure during pumping of the drilling fluid system.
4. The method of claim 1 , wherein the aqueous acidic solution comprises an emulsified acid or a gelled acid, and the emulsified acid is diesel and the gelled acid is a viscoelastic surfactant based gelled acid or a polymer based gelled acid.