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In recent years, around the world there is deterioration in the structure of hydrocarbon reserves. Many oil companies are forced to take measures to increase the flow of oil to the producing wells. The most popular method is the method of hydraulic fracturing. One of the key characteristics of the effectiveness of hydraulic fracturing is the conductivity of the resulting fracture.
Practice has shown that there are a number of factors negatively influencing the fracture conductivity, one of which is the formation of a filter cake on the fracture surface, which can lead to a significant reduction in well production rates. In this connection it is necessary to conduct laboratory studies to assess the impact of the magnitude of the filter cake on the conductivity of the fracture.
During fracturing operations fracturing fluid in the fracture is under much greater pressure than in the reservoir, so it leaks and breaks the seam. However, since the cross linked guar molecules are too large and can not enter into the pore matrix, the polymer forms a dense cake on the fracture surface. Furthermore, when after the fracturing operation the pressure is reduced, the crack closes creating a tight proppant packing. When cracks close additional displacement of water from the formation of the polymer network occurs, resulting in even more increased concentration of the polymer. If the polymer remains undisturbed, the super viscous gelatinous mass is formed blocking the pore space of the fracture.
This article discusses a negative influence factor on fracture conductivity – the formation of a filter cake on the surface of the crack, which can lead to a significant decrease in well production rates. Also, the technique of calculating the coefficient of instantaneous loss and wall-building coefficient. Were obtained according to changes in recovery coefficient, coefficient of instantaneous loss and wall-building coefficient from permeability of a core.
AN APPROACH FOR FRACTURE ZONES IDENTIFICATION BASED ON SEISMIC ATTRIBUTES ANALYSIS, SHELYAUR AREA, TIMAN-PECHORA BASIN
Oil and gas industry has reached a stage when most traditional porous type reservoir, developed to near with depletion level. Thus, main attention is increasingly paid to the reservoirs, where porosity and permeability are presented by a system of natural fractures. This trend has given an incentive to grow in research of various methods for natural fractures systems identifying and analyzing as well as subsequent related to it permeability prediction. Study and prediction of natural fracture systems from seismic data is a difficult and actual challenge, because this can significantly influence the choice of oil field development strategy. At present, a wide range of seismic attributes is developed, which can help engineers perform such analysis, but they have limitations with size of structures that could be recognized on traditional seismic resolution, and from the point of view of their cost. The proposed method of multi-attribute data analysis through orthogonal decomposition, developed by I. Priezzhev, can be an effective approach to the study of fracture corridors, and the calibration with real data showed high reliability of the results. Within the study area zone with high anomalies content were identified that can be related with tension stress in the formation, which is often associated with naturally fractures of rock. The results of this study can be used in adjacent areas, where a large amount of data for calibration exists, for predicting the high permeability zones.
The article describes the nature of the influence of pore structure on the channel conductivity parameter model of the core sample. Computational experiments the dependence of the pressure drop on the faces of the sample from the steady flow thus obtained for each structure curve hydraulic characteristics. Dependence apparently is not clear, due to the formation of a particular structure of the pore channels. Indeed the same number, length and diameter of the pore channels (flow tubes) in a plurality of rock samples can be observed different ratios permeability and porosity, pore structures due to the uniqueness of the channels in each sample. In this connection, it is impossible to build a reservoir model models the relationship between microstructure and properties of the pore channels macroparameters (ratio of open porosity and permeability).
Of course, it is theoretically confirmed the absence of the permeability depends on porosity, but most interestingly shows macroparameter permeability dependence on the structural characteristics of the pore space, which anyway can be assessed for different rock reservoirs. However, the uniqueness of the structure of the pore space for core samples composed by the same species, determines the absence of an explicit dependence of permeability on porosity. If it were possible to study the structure of the pore channels, the simulation elements formations would be significantly more accurate. If we define the boundary conditions of uniform distribution of pressure on the faces of the elements of the formation, it is possible to build a global structure of the hydraulic system composed of subsystems, which will also be described structurally similar to the global structure. Thus, the hierarchy in the structure matures, reflecting the relationship between elements of the simulated formation of different levels and spatial detail.
It is known that during the filtration of oil and water or any other fluids other than the classical patterns of interstitial viscous friction (Darcy’s law) raises a number of effects that require the description of additional laws. The movement of the two media is accompanied by:
– Their mixing and interaction at the level of the intermolecular forces and mutual viscous friction;
– Interaction of different media with the material of the walls of the pore channels at the molecular level in the form of van der Waals forces;
– Mechanical resistance of the pore channels of small flow cross section of the medium molecules having comparable dimensions to them (eg oil molecules and microtubules in a size smaller than 0.001 mm);
– Structuring of interstitial flow in the form of emulsions;
– Intermittent change in the nature of the displacement of the piston to the jet and mixed.
Unfortunately at the moment the theory of two-phase (or more) filtering limited to the description of the above phenomena in the form of curves relative permeabilities, the beginning of the gradient filter and capillary pressure curves. Last often one way or another are duplicated in the relative permeabilities.
When conducting computational and laboratory experiments found that non-linearities filtration laws appear at both high and at very low filtration rates. Identify functions relative permeabilities also requires modeling at the micro level. Filtration law, which is, in fact, by law, unifying viscous friction, the friction against the walls of the channels, the molecular interaction forces, adhesion, the effects of the conversion of hydraulic energy into thermal energy, etc.., Requires justification computational experiments at microcapillary models. In turn, this requires the solution of equations similar to the Navier-Stokes equations (with modification) and the revision of the law of viscous friction Newton flow conditions in microcapillaries
It is known that in a situation where a horizontal well is not fulfilling the project purpose to develop oil reserves, mining companies carried out a set of actions for the stimulation. To him in particular applies to hydraulic fracturing, held in the horizontal well by different technologies. The urgency of predicting the effectiveness of hydraulic fracturing in the horizontal well associated with the practical results of its application. The article studies comparison of different models of efficiency of a formation hydraulic fracture depending upon a well location in the system of production and injection wells. The studies resulted in getting very close showings of oil removals and essentially different showings of pressure. So, it was suggested to carry out modeling of a formation hydraulic fracture on the basis of an alternative model. The article considers substantiation of choice of a well-known software package under the name of "Tempest-More" for hydro-dynamic modeling in order to assess effect of a formation hydraulic fracturing, carried out in various conditions, on the amount of oil recovery. The article also presents methods of initial data preparation for numerical studying (properties of oil, gas, water, phase permeability) as well as technological criteria for production and injection wells. Using a formation model, studies effect of a formation hydraulic fracturing technology on amount of oil resources recovered from a deposit by means of application of numerical method and with account of operation of nearby production wells. It is proved that effect of a formation hydraulic fracturing, after being implemented in a well, breaks and affects showings of the nearby wells, where volume of oil removals decreases insufficiently, while volumes of produced water increase, thus minimizing economic efficiency of water removal technology.