Results are discussed for evaluation of effectiveness of the cyclic geomechanical treatment (CGT) on a Tournaisian carbonate reservoir. Analysis of laboratory experiments performed according to a special program to assess permeability changes for Tournaisian samples under cyclic changes in pore pressure is presented. The main conclusion is the positive selectivity of the CGT: an increase in permeability is observed for samples saturated with hydrocarbons (kerosene) with connate water, and maximal effect is related to the tightest samples. For water-saturated samples, the permeability decreases after the CGT. Thus, the CGT improves the drainage conditions for tight oil-saturated intervals. It is also confirmed that the CGT reduces the fracturing pressure in carbonate reservoirs. Using flow simulations on detailed sector models taking into account the results of laboratory experiments, a possible increase in well productivity index after CGT with different amplitudes of pressure variation was estimated. Results of a pilot CGT study on a well operating a Tournaisian carbonate reservoir are presented, including the interpretation of production logging and well testing. The increase in the well productivity index is estimated at 44-49 % for liquid and at 21-26 % for oil, with a more uniform inflow profile after the treatment. The results of the field experiment confirm the conclusions about the mechanisms and features of the CGT obtained from laboratory studies and flow simulations.
Water encroachment of well products at late stages of oil field development leads to formation of oil-in-water emulsion. At water cut of 30-80% three-component emulsions are formed, which lead to rod sticking and, eventually, to rod string breakage. Water-in-oil emulsions differ from crude oil in both viscosity and initial shear stress. The increase in viscosity of water-in-oil emulsions when the rods are mechanically actuated occurs approximately in the first third of the lift string, starting at the pump. At further lifting the viscosity of the mixture increases not so intensively, and its growth is due to the decrease in temperature and pressure during the ascent to the wellhead. In the work measures are proposed to reduce the hydrodynamic resistance to rod movement at load reduction.
