REGULATION OF FILTRATION CHARACTERISTICS OF HIGHLY WATERED TERRIGENOUS FORMATIONS USING COMPLEX CHEMICAL COMPOSITIONS BASED ON SURFACTANTS

A signifi cant share of Russian oil fi elds has entered the fi nal stage of development and is characterized by a drop in production. It comes true due to the depletion of active oil reserves, and, as a consequence, an increase in the proportion of residual oil trapped in areas which are not covered by fl ooding, and physically or chemically associated with the formation of oil. An additional factor is the increase in the water content of complex-structured terrigenous reservoirs and their high number of permeable intervals. Development of the considered productive formations is carried out, as a rule, with maintenance of reservoir pressure by means of "cold" fl ooding. Despite the development and relatively low cost, it has its limitations/restrictions. The main reasons why we are not able to achieve complete displacement of oil by "cold" water are the difference between the viscosity of oil and the displacing agent, their immiscibility and hydrophobization of reservoir rocks [14]. All methods of enhanced oil recovery (EOR) used for highly watered oil fi elds with hard-to-recover reserves are aimed at additional recovery of residual oil and achieving the design oil recovery factor (ORF), by optimizing the fl ooding system and upgrading the fl ooding agents. The design ORF can be achieved by increasing the water fl ood displacement effi ciency, by improving the washing capacity of water (displacement agent), or by increasing the sweep effi ciency of the reservoir fl ooding.


INTRODUCTION
There are lots of famous Russian and foreign specialists who has been investigated challenges of theoretical and applied aspects of EOR application: L.K. Altunina Despite some high rates of oil recovery factor, the development of a signifi cant part of oil reservoirs in all countries of the world in terms of the completeness of oil reserves recovery is characterized as unsatisfactory. The solution of the problem of increasing the fi eld development effi ciency with residual oil reserves is associated with the creation of new and improvement of existing physical and chemical methods that provide a better recovery of oil and reduce the volume of associated water production.

ANALYSIS OF MODERN EOR
Let us consider the fi rst group of methods, based on the increase in water fl ood displacement effi ciency. In oil production, a large number of chemicals (surfac-tants, alkalis, acids, etc.) are widely used, the main action of which is aimed at increasing the oil displacement effi ciency. The application of surfactants is based on improving the oil -washing properties of water by reducing the interfacial tension at the oil -water, oil-formation interface. The effect of using aqueous surfactant solutions is based on 2 mechanisms of surfactant action: 1. due to the reduction of surface tension, less energy is required to create a unit surface of the oil droplet, whereby the droplet is easily deformed and passes through pores of smaller diameter. Which leads to a decrease in pore pressures and a decrease in capillary forces; 2. washing effect of surfactant solutions is manifested in relation to the oil fi lm covering the surface of the rock grains, which leads to rupture of the fi lm and dispersion of oil in the aqueous phase [4,8,12,29,31]. Field experiments and laboratory studies presented by [3,6,15,19,20,22,27,36,45] was found that one of the most effective EOR technologies are physico-chemical methods based on injection a water with the addition of surfactants or mixtures into the formation. The interest of researchers in the study of physical and chemical properties of surfactant-based compositions is caused by synergistic effects (increase in surface activity, decrease in the critical concentration of myceliation, change in the rheology of the solution) observed during laboratory studies and their high technological effi ciency during implementation at the fi eld. A positive result was shown by numerous laboratory studies of the physicochemical, rheological properties of ionogenic and non-ionogenic surfactants together with fi ltration experiments. Confi rmation of laboratory studies was obtained during experimental and fi eld work on the reservoirs of Bashkortostan and Tatarstan Republics [2,3,16,29,32]. To assess the degree of additional oil displacement efficiency from the reservoir is obtained by carrying out pilot testing of nonionic surfactants on Romashkinskoye oil fi eld. In one section of the reservoir, the increase in oil production amounted to 18 thousand tons, or 14% compared to the design production. In the second section of the resevoir after 4 years of injection of 0.025% surfactant solution in two sections, the amount of production was 42.8 thousand tons of oil, or 73 tons of oil per 1 ton of injected surfactant. The effi ciency of the mentioned above technologies decreases with the increase of water cut. Therefore, the volume of their application in the 90th decreased, because most of the oilfi elds are at the fi nal stage of development during this period, characterized by a slow decline in oil production and an increase in the water cut of the overall production of wells to 95-98% (the limit of profi tability of well operation). Currently, fl ooding with surfactant is practically not implemented. As a rule, a combined surfactant-polymer effect is used [40,42,44,45,46,51,52,53]. As noted by the authors of the work [33], despite the positive impact of surfactant during reservoir fl ooding on the current oil recovery and reduction of water production, according to fi eld data, it is diffi cult to assess the effi ciency unambiguously, since the increase in the oil recovery factor does not exceed 2-5%, which indicates the limited possibilities of enhanced oil recovery enhancement methods based only on the principle of reducing interfacial tension. Now let's consider the second group of methods based on increasing the sweep effi ciency. The use of polymer fl ooding contributes to an increase in the sweep effi ciency of the reservoir fl ooding by reducing the ratio of water and oil mobility due to an increase in the viscosity of the injected oil displacing agent. This mechanism is evident because of the polymer adsorption in a porous medium during fi ltration of a polymer solution, leading to decrease permeability of porous media on water even after complete exclusion from them of the polymer solution as the polymer macromolecule, as polyelectrolytes (polyacrylamide), swell in water and increase in size with the formation of inactive hydrated shell. On the mobility of oil macromolecules of polyacrylamide actually do not affect since oil consists mainly of non-polar molecules.
Polymer fl ooding has been used for more than 40 years. During this time, many projects have been implemented in various geological and physical conditions [1,6,8,29,37,41,48,49,51,57]. In the 90thof the last century, the undisputed leader in the fi eld of polymer fl ooding was the United States -in 1986, 178 projects were implemented there. However, the decline in oil prices, as well as new developments that have allowed to solve the technological problems of using gas methods, signifi cantly reduced the number of polymer fl ooding projects. Now the leader in the fi eld of polymer injection is China. Polymer fl ooding is successfully applied in the main fi elds of China, such as Daqing and Shengli. The use of polymer fl ooding only in these two fi elds allowed to obtain in 2004 about 14 million tons of oil, an increase in ORF of 14% was obtained. Twenty years of successful fi eld experience in the application of polymer fl ooding in China has shown that it can be effectively used in fi elds with water content above 95%, giving an increase in ORF up to 10%. It is established that polymers with a molecular weight of 10 to 18 million can be used in most reservoirs, polymers with a higher molecular weight are more effective in high-permeable reservoirs, salt-resistant polymers with a low molecular weight -in low-permeable reservoirs. As for the Russian Federation, one of the commercially available water-soluble polymers that have passed largescale tests in the practice of oil production are various brands of polyacrylamide (PAA) [16,28,33]. At a concentration of polyacrylamide in a solution of 0.01-0.1%, its viscosity increases to 3-5mPa*s, which leads to the same decrease in the ratio of oil and water viscosities in the formation. However, this method has major drawbacks that limit its wide application. As shown in the works [7,8,20,33], the main disadvantages of polymer fl ooding are: 1. a sharp decrease in the intake capacity of injection wells due to an increase in apparent viscosity due to the destruction of polymer molecules in bottom-hole zones; 2. it is ineffective in homogeneous formations containing low viscosity oil (less than 5.0mPa*s); 3. low effi ciency of implementation at the fi nal stage of reservoir development with water cut of more than 70%, due to the formation of extensive washed zones in the reservoir; 4. effi ciency of polymer fl ooding decreases with an increase in permeability of more than 1.5-2.0mkm 2 . The use of polymers, polymer-disperse systems, colloidal-dispersion systems allow to increase the drainage layer by increasing fl uid fl ow resistance in areas of fl ooded oil reservoir. At the same time, water tends to pass into areas not previously covered by fl ooding [1,6,8,29,35,47,50]. Colloidal gels are used as option of polymer fl ooding, in which the rim is reduced to 10000m 3 and below. One option is the BrightWater (Nalco) technology, which is based on the injection of dispersion of ultra-small polymer particles that swell and cross-link after placement in highly permeable water-saturated layers/ rims in reservoirs with high temperature [34,38,56]. Thus, modern research is focused on searching more effective surfactants or their compositions, as well as on optimization of chemical reagents injection methods into the formation, i.e. implementation of new complex technologies (surfactant-polymer, surfactant-polymer-alkaline fl ooding, micellar fl ooding, etc.). According to scientists, the application of technologies with complex action will increase the sweep effi ciency of the reservoir fl ooding and at the same time increase the water fl ood displacement effi ciency.

PREREQUISITES FOR RESEARCH
Most of the up-to-date methods of increasing oil recovery are based on fl ow-defl ecting technologies, technologies of limiting water production and leveling the profi le of injection wells, which allow to achieve effective oil recovery at a fi nal stage of a fi eld development. Currently, sludge-and gel-forming compositions are widely used for selective isolation of water-saturated intervals, but they have disadvantages too. The main one is that the structure of these compounds is almost irreversible. At the same time, part of the oil reserves of the fi eld remains in the isolated area, although it's small, which after isolation becomes almost impossible to be recovered. Since the restoration of the poroperm properties of the interval isolated by such compositions is a rather labor-intensive process, these technologies reduce the fi nal oil recovery factor. Therefore, technologies that allow to temporarily limit or block fi ltration on highly permeable areas are becoming more and more relevant [8]. Reverse emulsions with the addition of surfactants are a promising type of compositions that allow to solve this problem. Today they are used in drilling [11,25] and oil fi eld practice [10,21,23,26], including to increase oil recovery in order to align the displacement front [5,9,13,60,57,38,43,54,55]. They are a thermodynamically unstable dispersion system, the dispersion medium of which is oil and the dispersed phase is water [24,30]. In this case, the emulsion structure has suffi cient rheological properties for selective isolation of watered intervals. Since the dispersion system is unstable in formation conditions, the isolation of well-permeable interlayers is temporary, and after the destruction of the structure of the composition, the adsorption of surface-active components of the emulsion allows hydrophobizing the surface of the pore channels of the formation. Due to this, the phase permeability of the water decreases and the oil-washing capacity of the injected agent increases. This leads to the redistribution of fi ltration fl ows and the inclusion in the work of previously idle intervals of the formation and additional recovery of residual oil using this technology.
Literatureanalysis contains data on laboratory studies and the experience of fi eld tests of new compositions. It shows that for fi elds with a long period of impact on the reservoir by water injection, the most promising methods of increasing oil recovery will be physico-chemical or new combined methods based on chemical compositions. Injection of surfactant-polymer mixtures, microemulsions or micellar solutions will solve problems arising at the fi nal stage of development of highly watered reservoirs. And the main purpose of the application of complex technologies of physico-chemical reservoir stimulation is to achieve design ORF due to the simultaneous increase of the water fl ood displacement effi ciency and increase the sweep effi ciency [17].

RESEARCH PLAN
Authors have developed an emulsion composition with hydrophobic properties based on reservoir water and kerosene (TS-1), emulsifi er of which is YALAN-E2, with the addition of functional components: anionic surfactant (sulfonol) and complex surfactant (hydrophobizer NG-1). The proposed composition is acceptable for the technology of leveling the displacement front within the inhomogeneous permeability objects. According to the data obtained during the laboratory studies of the developed composition, hydrodynamic models were simulated wtithin three approximations: 1. A simple model of a linear section of a layered-inhomogeneous formation consisting of two interlayers of equal capacities and different permeability.

A complex model of a linear section of a layered-in-
homogeneous formation consisting of 10 interlayers of different capacities, permeability and water saturation. 3. A hydrodynamic model of the reservoir (section of the reservoir), adapted to the current fi eld indicators of development.

RESULTS OF HYDRODYNAMIC SIMULATING ON A SIMPLE MODEL OF A LAYERED-INHOMOGENEOUS RESERVOIR
The model was a layered-inhomogeneous layer with lithologic-facies and poroperm properties similar to the upper Devonian layers (Figure 1). The properties of the fl uids saturating the reservoir were also taken from studies of oil and reservoir water of the fi elds under consideration.
Interlayers with the permeability of the lower 0.120mkm 2 and the ratio of permeability of the lower to the upper interlayer, equal to 1:1, 1:3, 1:5, 1:7 and 1:10 were selected to the further experiments. In one case, the reservoir was fl ooded without the use of special agents, the simulation of the model was carried out until the water cut of the produced products was equal to 96%. In the simulation of oil recovery using the developed re    : Displacement front on the model of layered-inhomogeneous reservoir according to the second simulation option verse emulsion, the reservoir was fi rst fl ooded without the use of agents until the water content of the produced products was 85%, then the emulsion rim was pumped for 100 days (Figure 2). Further fl ooding was carried out, as in the fi rst case, to the water cut up to 96%. Results of laboratory studies and 3D hydrodynamic simulations determined the optimal conditions of applicability of the developed technology, as the degree of inhomogeneity of the object and the maximum value of reservoir permeability [18]. It is important to note that according to laboratory fi ltration studies, close to the reservoir conditions, the developed emulsion composition has stability in reservoir conditions and does not break down when interacting with reservoir water. Also, the emulsion composition has selectivity and can be recommended for use in conditions of signifi cant heterogeneity. However, when simulating a hydrodynamic model with a layered-inhomogeneous formation, the lower limit of permeability was set as constant, and only the upper limit was changed. Due to the high permeability of the upper interlayer, the emulsion screen breaks, which is refl ected in the results (the effi ciency drop during the simulation is 1:10 (Table 1, Figure 3)). Stability criteria for emulsions in the reservoir were developed based on rheological studies of emulsions and laboratory fi ltration experiments.Results of these experiments showed that we can recommend this technology for implementing within the permeability of fl ooded reservoir not more than 0,6 -0,8mkm 2 , which corresponds to conditions of the object.
That is, it can be argued that the use of the technology is recommended for a difference in permeability of more than 5 times, but, at the same time, the most permeable interlayer should have a permeability of not more than 0.6 -0.8mkm 2 to retain the emulsion rim in the formation.

RESULTS OF HYDRODYNAMIC SIMULATING ON A COMPLEX MODEL OF A LAYERED-INHOMOGE-NEOUS RESERVOIR
Authors decided to investigate the impact of geological and physical characteristics of layer-by-layer heterogeneity on the effectiveness of the technology of displacement front alignment with the use of emulsion composition [18] after providing studies of the oil displacement on the simplest hydrodynamic model. To solve this challenge, a model of the productive layer (represented by 11 layers) was simulated. The condition of vertical equilibrium of pressure is fulfi lled. The thickness of the net pay zone is 33.2m; distribution of the permeability is random, without any regularities. Residual oil saturation is 0.27 unit, the formation oil volume factor is 1.475 m 3 /m 3 , water -1.103m 3 /m 3 . Viscosities of water and oil correspond to viscosities of the considered geological objects -0,5 mPa*s and 5mPa*s respectively. Geometric dimensions of the linear section of the reservoir: width -300m, length -1500m. The properties of the emulsion are determined on the basis of physico-chemical and rheological laboratory studies. Figure 4 shows the moment of the onset of advanced fl ooding, namely the water breakthrough on one of the  interlayers. In turn, fi gure 5 already shows the advance of the front in the second option of the simulation (fl ooding with edging emulsion). The effect of the displacement front alignment after injection of the emulsion rim is obvious from the comparison of fi gures 4 and 5, due to slow migration of the water through the highly permeable layers (on the same date the front in a second option of fl ooding smoother).

THE RESULTS OF HYDRODYNAMIC SIMULATING ON THE RESERVOIR MODEL IN CONDITIONS CLOSE TO THE OIL FIELD
Laboratory studies of the developed emulsion composition on the physical model of the layers showed that after it's fi ltration through the layer, it increases the fi ltration resistance just for water-saturated interval, thereby further fi ltering the water phase is slowing down. In this regard, it can be argued that the use of the developed technology for regulating fi ltration fl ows in hetero- Maxim Korolev, et al geneous terrigenous oil reservoirs will align the front of oil displacement by water and, as a consequence, will increase the effi ciency of oil recovery from highly watered terrigenous reservoirs due to additional extraction of oil from previously involved areas in the development.
According to the data obtained in the laboratory studies of the developed composition, hydrodynamic models of fl ooding at two objects were simulated [18]. Two reservoirs of the Samara region were considered, the fi rst one was a section of a large development object, and the second one was a whole multi-layer development object, since the reservoir is average in reserves. At each of the considered objects some wells were selected in the areas with weakly drained interlayers (Figures 6 and 7). The effect of the technology was evaluated: at the fi rst site for three production wells per injection well; at the second site as a whole for the operation of fi ve injection wells. The lithologic-facies and poroperm properties of the models are similar to those of the upper Devonian and lower Carboniferous strata. The properties of the fl uids saturating the reservoir were taken from studies of oil and reservoir water of the oil fi elds. The simulated reservoirs are at a fi nal stage of development. The degree of depletion at these sites is about 85% of the recoverable reserves.
As an example, let's consider the results of hydrodynamic simulating of the considered multilayer object of the fi eld No. 2 in two design forms: without the use of technology alignment displacement front (for project development) and with the injection of the composition. According to the second option, the developed emulsion composition was pumped into injection wells for a month with a fl ow rate of 100 t/day per well. At the same time, the total volume of injection was -15500 thousand tons. After that, the composition was forced into the formation of the previously pumped water of the reservoir pressure maintenance system [61; 62]. Evaluation of the effi ciency of the considered technolo-gy was evaluated according to the accumulated production for the years of development, as well as the change in the average water cut. The results are presented in graphs (Figure 8-9). The graphs show that after the start of injection of the developed emulsion composition, we get a decrease in water cut by 10%, and an increase in oil production from the fi rst year of implementation of the technology. Additional production at the facility amounted to 35,368 tons of oil over 10 years. Accordingly, we can consider the effect of the application of technology about 0.7 thousand tons per well operation per year. It was also noted that the reduction of water cut achieved by involving in the work of previously not covered by fl ooding areas of interlayers. Additional production was about 2 % at both sites, which indicates a good correlation of the effi ciency of the developed emulsion composition.

CONCLUSION
Thus, the results of the research allowed to draw the following conclusions: 1. Features of the terrigenous reservoirs development at the fi nal stage are high lithological heterogeneity of the layers containing the main oil reserves, and advanced fl ooding of highly permeable interlayers or one layer in a multi-layer object, which leads to uneven development of reserves in the area. Therefore, technologies that allow to temporarily limit or block fi ltration in high-permeable areas are becoming more and more relevant. 2. The developed reverse emulsion is applicable for the technology of leveling (alignment) of the displacement front of inhomogeneous permeability objects. 3. The dependence of the possible achievement degree of the oil recovery factor using the developed emulsion on the degree of the terrigenous formation heterogeneity is established. 4. The implementation of the developed technology of fi ltration fl ows regulation in heterogeneous terrigenous oil reservoirs will align the front of oil displacement by water and, as a consequence, will increase the effi ciency of oil recovery from highly watered terrigenous reservoirs due to additional production oil from previously involved areas to the development process.