Abstract: The method of fluid loss control is provided for the case of high-rate fluid loss. Two treatment fluids are provided, where a first treatment fluid comprising a carrier fluid, solids and a first polyelectrolyte, and a second treatment fluid comprising a carrier fluid and a second polyelectrolyte. Two polyelectrolytes in both treatment fluids are oppositely charged under the pumping conditions, being taken form the classes of polyanionic and polycationic polymers. Two treatment fluids are pumped separately to the zone with fluid loss. The mixing of two treatment fluids into the well creates low-permeability agglomerates that plugs the fluid leakage channel, preventing or reducing further fluid movement between the wellbore and subterranean formation. The plugging of thief zone can be temporary or permanent.

Abstract: A method for temporary isolation of a well interval is proposed, the method comprising: pumping a first slurry into the well, the slurry comprising a viscous carrier fluid, degradable particulates, and degradable fibers, until a first filter cake is formed; and pumping a second slurry into the well, the slurry comprising a viscous carrier fluid, non-degradable particulates, and degradable fibers, until a second filter cake is formed. The first and the second slurries are not mixed when pumped into the well. To ensure optimum interval isolation, the ratio of the volume of the first slurry to the volume of the second slurry should be in the range 1:5 to 2:1. A method for hydraulic refracturing within an interval with several hydraulic fractures and a non-damaging well killing method are also proposed. The technical result is manifested in no formation damage and degradation of the sealing layer formed.

Abstract: A method for temporary isolation of a well interval is proposed, the method comprising: pumping a first slurry into the well, the slurry comprising a viscous carrier fluid, degradable particulates, and degradable fibers, until a first filter cake is formed; and pumping a second slurry into the well, the slurry comprising a viscous carrier fluid, non-degradable particulates, and degradable fibers, until a second filter cake is formed. The first and the second slurries are not mixed when pumped into the well. To ensure optimum interval isolation, the ratio of the volume of the first slurry to the volume of the second slurry should be in the range 1:5 to 2:1. A method for hydraulic refracturing within an interval with several hydraulic fractures and a non-damaging well killing method are also proposed. The technical result is manifested in no formation damage and degradation of the sealing layer formed.

Abstract: A treatment fluid that comprises a carrier fluid and a degradable material in the form of particles, fibers or both is provided or prepared. The treatment fluid is placed in a borehole such that the treatment fluid contacts a liner, a downhole filter, perforations, natural fractures, induced fractures, or a subterranean formation or combinations thereof. The treatment fluid is allowed to flow into the liner, downhole filter, perforation, natural or induced fracture or subterranean formation such that the degradable material forms at least one plug or filter cake (or both), preventing or reducing further fluid movement between the wellbore and the subterranean formation. The degradable material is then allowed to dissolve after a period of time, causing the plug or filter cake (or both) to weaken, thereby allowing removal of the plug or filter cake (or both) and reestablishing fluid movement between formation and the wellbore.

Abstract: Compositions and methods by which well control may be maintained during well construction, workover or well-intervention operations in a subterranean well without damaging formation are disclosed. A treatment fluid that comprises a carrier fluid, as well as degradable particles, or degradable fibers, or combination thereof is provided or prepared. The treatment fluid is placed in the borehole such that the treatment fluid contacts a liner, a downhole filter, perforations or subterranean formation or combinations thereof. The treatment fluid is allowed to flow into the liner, downhole filter, perforation, natural or induced fracture or subterranean formation such that the particles and fibers form at least one plug or filter cake (or both), preventing or reducing further fluid movement between wellbore and subterranean formation.

Abstract: Fluid compositions comprising water, at least one water soluble polymer, degradable particles or nondegradable particles or both, and degradable fibers have utility as temporary lost circulation prevention systems. The compositions may be placed in a borehole such that they contact perforations, formation cracks, fissures, vugs or combinations thereof. The compositions form a plug or filtercake that minimizes flow between the wellbore and the formation. After completion of the well operation, the fibers degrade and the plug or filtercake weakens and may be washed away, thereby reestablishing fluid flow between the wellbore and the formation.