Acoustic and Vibrational Enhanced Oil Recovery. George V. Chilingar
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1.1.3 Earth Tides
In the classic book on wettability, Donaldson and Alam (2013) [13] pointed out that Earth tides activate the motion of fluids by continued expansion and contraction as simple harmonic oscillation resulting from diurnal tides. This effect was much greater earlier in geologic history because the moon was much closer to the Earth. Currently, the moon is moving away from the Earth at ≈3 cm/yr. Thus, the Earth tides were more rapid and energetic, resulting in greater dilation and the compression of rocks. According to Donaldson and Alam, in a 10-m-thick reservoir, with a radius of 100 m, an elastic change of porosity of 0.1% will result in an oscillatory motion of 294 bbl of fluid. Such motions could reduce the oil saturation to zero over geologic time, leaving only a trace amount of oil behind.
1.1.4 Compaction
In order to investigate some problems involved in the primary migration of oil, Aoyagi et al. (1985) [3] compacted Na-monmorillonite clay mixed with seawater and crude oil for 25 days under a pressure of 1,000 kg/cm2 and a temperature of 60°C. The proportion of oil in the expelled liquid increased with time. The porosity of the compacted sample decreased from 81% to ≈26%. These authors concluded that the primary migration of oil from source rocks to reservoir rocks occurred chiefly during the late compaction state (ϕ = 10%−30%). Considering the fact that tectonic activity during the primary migration of oil was intense, the oil was simply squeezed out (expelled) from the source rock.
1.1.5 Migration in a Gaseous Form
Kapelyushnikov (1954) [17], Gerber and Dvali (1961) [15], Zaks (1952 [40], 1955 [41]), Zhuze and Yushkevich (1959) [42], and Chilingar and Adamson (1964) [9] studied the possibility of oil migration in a gaseous form. Based on some experimental work, Chilingar and Adamson (1964) [9] concluded that some migration of petroleum could have occurred in a gaseous form in the geologic past at high temperatures.
It is important to remember that with increasing polarity of oil, the relative permeability to oil increases and that to water decreases (water cut decreases) (Sinnokrot and Chilingar, 1961 [32]).
Gerber and Dvali (1961) [15] subjected to extraction four samples of rocks with CO2 at pressures ranging from 100 to 400 kg/cm2 and temperatures of 40°C to 74°−90°C. Their findings can be summarized as follows:
1 The bitumens dispersed in rocks and, having composition related to crude oil, can dissolve in compressed gases and migrate together with them.
2 At 200 to 400 kg/cm2 pressure and temperature of 40°C, in dynamic conditions, CO2 can extract not only oils and tars but also asphaltenes and porphyrins from bituminous shales of Ukhta (Russia).
3 The kerosene and the main oil fraction of bitumens can be extracted from the rocks at pressures of 100 to 200 kg/cm2 and temperature of 40°C.
4 Mobile, syngenetic bitumens in the source rocks can dissolve just as easily in the compressed CO2 gas as does petroleum from oil-saturated rocks.
Kapelyushnikov (1954) [17], who studied the P-V-T relationship of oil, gas, and water at pressures up to 500 atmospheres and temperatures up to 100°C, concluded that gaseous oil/gas mixtures move toward the low-pressure areas, dropping the tars and asphaltenes first, followed by medium and lighter components. He also found that at critical pressures, the water and salts present in the oil-bearing strata are also transported together with the gas toward the low pressure areas.
1.2 Seismic Vibration Techniques
The use of various seismic vibration techniques in Russia resulted in incremental oil production of millions of tons. There are several seismic vibration techniques for transmitting energy into the reservoir, with oscillations over long distance. The area of productive reservoir around the well-being stimulated may be as great as 12 km2. The number of wells simultaneously subjected to the treatment can range up to 50 (depending on the well spacing).
The technique for increasing the oil yield of high water cut and low oil production reservoirs consists of subjecting the reservoir area to cyclic low-frequency (5 to 90 HZ) elastic oscillations within the frequency range corresponding to the reservoir resonance (Kouznetsov et al., 1998 [18]). The results obtained for during seven years of using this seismic vibration technique in different areas in Russia, on the average, annual oil production increased by more than 60%. The duration of the seismic vibration effect was 6 to 18 months and sometimes longer. The vertical reservoir sweep increased by 35%. In some cases, the wells that were producing by artificial lift (sucker rod pumps) retuned to natural flow with almost a tenfold rate increase. The effect was evaluated not only by an increase in the total production rate but also by a decrease in the waste cut. In some wells, the water cut decreased by 30% to 40% (Kouznetsov et al., 1998 [18]; Simkin and Surguchev, 1991 [31]).
1.2.1 Producing 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.