Well Experiments
Field experiments were conducted using vibrators located at the Earth’s surface in the vicinity of oil-producing wells. Vibro-energy generated by vibrators traveled down as elastic waves to the oil-bearing formation. The goal of the experiments was to study the effect of elastic waves on the relative permeability to oil and to water, water saturation, oil production rate, and the rate of oil displacement by water. Generally, it was found that the presence of elastic waves increased the relative permeability to oil, decreased the relative permeability to water, the decreased the water cut, and enhanced the oil production. In terms of industry application, the use of vibroenergy for enhancement of oil recovery is acceptable only if the amount of generated vibro-energy is smaller than the amount of energy contained in the additionally recovered oil.
The authors studied the energy balance between the generated vibro-energy and energy contained in the additional oil produced by using vibrators. Calculations show that the amount of vibro-energy applied to one unit of rock volume does not exceed 1.5% of the energy contained in the oil present in this unit volume calculations were based on the fact that the energy content of 1 kg of oil is 4.2 = 107 J. Therefore, for this process to be economically feasible, it is necessary to increase the oil production by a minimum of 1.5% (Vahitov and Simkin, 1985 [36]). To study feasibility of enhanced oil recovery based on the use of vibro-energy, field experiments were conducted in several old oil field in Russia, Uzbekistan, and Kirgizstan.
1.2.2 Mechanisms of Interaction of Fluid Flow With the Vibro-Energy in Porous Media
Laboratory and field experiments demonstrate the dependence of fluid flow and character of oil displacement by water on application of vibro-energy. Results of experiments demonstrate that kro/krw and the rate of water displacement by water increase on application of vibro-energy. The effect of vibro-energy on fluid flow the in porous media is defined by a number of nonlinear factors. Application of vibro-energy causes periodic or quasi-periodic movements of oil and water phases in pore channels with periodically changing directions. Due to these periodic movements, molecules of oil and water stick to a lesser degree to the solid phase. Accelerations of the oil phase and water phase are related to each other as (Kouznetsov and Simkin, 1994 [21]):
where ρo and ρw are densities of oil and water, respectively; xo and xw are distances traveled by the oil droplet and water droplet, respectively; and t is the time.
Equation (1.5) shows that the acceleration of the oil phase, which has a lower density than water, will be larger than the acceleration of the water phase. The lower the density of oil, the higher will be the ratio of acceleration of oil to that of water due to applied vibro-energy. Thus, the time of possible static contact of oil molecules with a solid phase will decrease with decreasing density of oil. In turn, this will lead to a decrease of adhesion of oil molecules to the walls of the pore channels and better mobility of the oil phase. Mobility of the water will also increase, but to a lesser degree than that of the oil.
Periodic movements of the oil and water in pore throats and variable pressure gradient caused by the applied vibro-energy lead to the destruction of water films blocking fluid flow through narrow pore throats. This leads to a general increase of the relative permeability both to oil and to water. The molecules of oil are much larger than those of water. Therefore, destruction of water films sealing pore throats and increasing the size of the open part of pore throats should produce a larger effect on the relative permeability of rock to oil than that to water.
The relative permeability to oil also increases due to reduction in the interfacial tension and contact angle between oil and water on application of vibroenergy. As a result, the size of oil globules decreases.
The results of vibro-stimulation tests for enhanced oil recovery, using powerful surface-based vibro seismic sources, indicate that the rate of displacement of oil by water increases and percentage of non-recoverable residual oil decreases if the vibroenergy is applied to the porous medium containing oil (Kuznetsov et al., 2021 [68]). Tests on sandpacks showed an increase of degassing rate due to application of vibro-energy. Results of both laboratory and field tests of the proposed enhanced oil recovery method showed an increase in the recovery of oil and oil-water ratio. Decrease in water cut is caused by the reduction in the oil-water interfacial tension and increase in the relative permeability to oil and to water.
This proposed vibro-seismic methodology will serve as an additional enhanced oil production recovery technique. Vibro-energy reduces interfacial tension, increases the relative permeability to oil, and increases the produced oil-water ratio. Possibly, this technique can be used in conjunction with other methods, such as thermal recovery, application of direct electric current, and chemical floods.
In the, 1980s, Donaldson, Chilingar, and Yen published two books on Enhanced Oil Recovery (I: Fundamental and Analyses and II: Processes and Operations) (Donaldson et al., 1985 [57]; Donaldson et al., 1989 [58]).
Inasmuch as both acoustic/vibrational and EEOR technologies are used by the authors in revitalizing abandoned oil fields, decision was made to invite the foremost experts on EEOR (Professor’s Donald Hill and Muhammad Haroun) to make contribution to this book.
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