Negative pressure is one of the metastable states of liquids at which it can be extended up to a certain limit without a gap of continuity. There are numerous experimental studies where a negative pressure up to 40 MPa has been obtained at laboratory conditions. However, these results of the experimental works were not practically implemented, as real liquids both in the nature and the technological processes contain impurities. Under certain kinetic and hydrodynamic conditions the waves of negative pressure in real liquids (crude oil, water, and water-based solutions) were observed. The wave of negative pressure is a turned soliton wave with one negative hump. It is a conservative wave, which maintains its shape and dimensions, and travels long distances with the speed of sound. An advanced technology of generation of the negative pressure wave in real systems allowed creating completely new energy saving technology. This technology based on negative pressure phenomenon has been already used for increasing oil production efficiency during various oil well operations, cleaning of oil well bore, and pipelines from various accumulations. It is shown that a new technology has a lot of potentials for bottom-hole cleaning operations, oil recovery enhancement, pipeline transportation, gas-lift operation etc. Negative pressure is known to be one of the metastable states at which liquids can be extended up to a certain limit. Theoretic evaluations show that in pure liquids negative pressure may reach large values while the liquid may stand significant extending efforts. For instance, the maximum negative pressure that may be sustained by ideally pure water is estimated as −109N/m2. It means that an imaginable rope of completely pure water with the diameter of 0.01m can sustain a huge extending effort more than 105 N. It is evident that the real experimental values of negative pressure are much less than the corresponding theoretic estimations. It is connected with the impossibility of obtaining ideally pure liquids without any “weak places” (gas bubbles, admixture, etc) and with the circumstance that in experience, the rupture often happens not in the liquid volume but on the surface touching the walls of the vessels weakened by the existence of thin films, embryos, etc. There are numerous results of the experimental work of static and dynamic character, where negative pressure has appeared in one or another degree [1]. In laboratory conditions, negative pressure apparently was first revealed in the experiences made by F. M. Donny (1843), who used degassed sulfuric acid and obtained negative pressure only −0.012 MPa. Among the further attempts of receiving bigger negative pressure, it is worth mentioning the experiences made by O.Reynolds, M.Bertelot and J.Meyer. Basing upon a centrifugal method and using mercury, L.J.Briggs obtained the record value of negative pressure (−42.5 MPa). But as a matter of fact, beginning from the first experiences by F. M. Donny, the main condition in the investigations for the appearance of negative pressure has been the homogeneous character of the liquid and high degree of the purity the liquid-vessel system. Significant values of negative pressure has been obtained under those conditions, however these results of a great scientific importance have no effective applications in practice as real liquids in Nature and technological processes are heterogeneous multicomponent systems. A long-term experimental work has been done to generate negative negative pressure in real liquid systems and investigate influence of this state on thermohydrodynamical characteristics of natural and technological processes [2,3]. Basing on the idea that negative pressure can be created due to the sudden character of extending efforts a direct wave of the negative pressure in real liquids (water, oil, solutions etc.) have been obtained experimentally. For impulsive entering into metastable (overheated) zone in a phase diagram “liquid-vapor” the pressure should drop so fast that the existing centers of evaporation (bubbles, embryos, admixtures etc.) would not be able to manifest themselves for this period. In these terms purity of the liquid is not decisive, and herewith there might exist states of an overheated liquid with the manifestation of negative pressure. It was determined that wave of the negative pressure resembling overturned soliton wave with one but negative peak propagates with speed of sound. The typical variation of the pressure in the petroleum stream in pipe is given in Figure 1. Reversed wave of the negative pressure was not recorded during the experiments. Evidently this is associated with considerable structural changes in the liquid after the passing of the direct wave. The arising negative pressure though being a short-term, results in a considerable overheating of the fluid system and leads to spontaneous evaporation and gas-emanation with the further cavitation regime. It was determined that after passing of the negative pressure wave hydraulic resistance in the system becomes much less, and significant increase of permeability of the porous medium and intensification of the filtration process take place. On the base of the investigations it was made a conclusion that any discharge in the hydraulic systems when the drop of the pressure requires much less time that relaxation of the pressure in the system inevitably results in the arising of rarefaction wave, in particular, the negative pressure wave [4]. The larger is the hydraulic system and the higher is the depression of the pressure, the more intensively the negative pressure wave may manifest itself. In certain terms waves of the positive pressure may be reflected from free surfaces, different obstacles, from contact surfaces between phases in the form of the reverse wave of the negative pressure. On this base there were presented numerous theoretical and experimental works on the simulation of the process, investigation of impact of the negative pressure on certain physical features of real systems [5]. The negative pressure wave may lead to very hard complications: showings of oil and gas leading sometimes to dreadful open fountains, borehole wall collapse, column crushing, gryphon appearance [6]. Analysis of numerous facts of complications, troubles in wells as water-oil-gas showings, crushing of columns, collapses, gryphon formation demonstrates that they arise usually as a result of round-trip operations in drilling of wells and their capital repairs. The negative pressure wave may be initiated by a sudden pulling of pipes or drilling equipment, as well as their sudden braking, quick opening of a valve at the well exit, etc, resulting in metastable extension of the working fluid agent. Though impulse negative pressure manifests itself as a significant dynamic factor, its structural consequences are more dangerous for an oil well. Moving along a well the negative pressure wave results in the spontaneous boiling of the water in the drilling fluid, and as a result of considerable reduction of its specific weight the hydrostatic column is “switched-off’ for some seconds and this may be sufficient for oil and gas showings of the well to be appeared accompanied often by crushing of columns and collapsing of wells due to great destroying energy manifestation. Negative pressure waves may be considered also as one of the dominant factors in geophysical processes, especially, in evolution and appearance of volcanic eruptions and earthquakes [7,8]. Extreme dynamic processes in the underground medium as a matter of fact can be considered as a synergetic manifestation of the negative pressure together with other thermohydrodynamical factors. The waves of negative pressure in the underground environment may be initiated by tectonic dislocations and faults as a result of different dynamic processes, dramatic decrease of pressure during the displacement of fluids and rocks. They may arise also in the form of a reverse waves as a result of reflection of ordinary seismic waves from different underground surfaces. On the basis of received results the method of artificial creation of negative pressure waves has been created [4]. The essence of the method is that negative pressure waves can be generated by means of discharge in hydraulic systems (pipes, wells, etc) when the drop of the pressure takes place during the characteristic time much less than that of pressure relaxation in the system. The greater is the volume of hydraulic system and the higher is the depression of the pressure, the more intensively the negative pressure wave may manifest itself. This method was taken as a basis of elaboration of principally new technologies and installations to increase effectiveness and efficiency of some oil recovery processes. It has been worked out and widely tested in field conditions new technologies on using of the negative pressure phenomenon for cleaning of oil producing hydraulic systems/well bore, pipeline/from various accumulations and increasing of effectiveness of oil producing at different well operation methods. The technology provides generation negative pressure waves in the well using the special mechanisms that leads to the shock depression impact upon the oil stratum, and as a result, to considerable growth in the oil influx, bottom-hole cleaning, accompanied by essential saving both reservoir and lifting energies, elimination and prevention of sandy bridging, paraffin, silt, water, etc. accumulations. For implementations of these technologies corresponding installations have been elaborated, in part, equipments for cleaning out of oil holes from sand plugs, increasing of efficiency and effectiveness of gas-lift well operations and bottom-hole pumping. In cleaning out of oil-holes from sand plugs the most operative and effective liquidation of different sand plugs irrespective of their rheological character is provided, associated with complete bottom-hole cleaning, essential increase of oil recovery and overhaul period. Elaborated equipment is simple and easy to use. Other comparatively advantageous application of the technology provides increase of efficiency of a gas-lift well operation, expressed in considerable reduction of a specific gas consumption associated with essential increase of oil recovery and overhaul period. The design of the equipment is reliable and simple to service. There are different modifications of the equipment for single-row, double-row lifts in packer and packerless designs. The introduced technologies have passed broad test in field conditions. The operative and complete cleaning of numerous oil wells was carried out, where the altitude of sand plugs varied from 20m to 180m; oil output of wells and their overhaul period have been increased and specific gas discharge reduced significantly.

This content is only available via PDF.
You do not currently have access to this content.