Waterflood System Research Articles

Investigation of the possibility of applying the injection process in the Lokbatan-Puta-Gushkhana field

The study of the Lokbatan-Puta-Gushkhana field development issue showed that all its production facilities from the beginning of development until 1956 were developed on natural reservoir mode. Since 1956 the development was carried out with application of water impact. However, the impact was not conducted correctly. An analysis of the waterflooded facilities showed that the injection process failed to maintain reservoir pressure and there was a significant depletion of reservoir energy during development. The productive formations of the field have large oil reserves. If exploitation is carried out under current conditions, development of these reserves will become impossible. In this work we carried out study of the process of injection of VIIa and VII horizons of the selected certain part of the VI block. In the study, maps of cumulative oil production and maps of area distribution of residual recoverable oil reserves were constructed to estimate the volume of reserves and their location. Depending on the results obtained, it will be possible to apply the injection process in other blocks and horizons of the field. These studies can play a crucial role for the development of a new waterflooding system and suggest a positive effect of the injection process on the development performance of production facilities.

Study on the properties of oil-water interface after the interaction between ionized water and naphthenic acid

The properties of the oil-water interface have a great influence on improving oil recovery. However, there are few studies on the impact of the interaction between ionized water and polar components of crude oil on the properties of the oil-water interface. In this paper, the influence of ionized water and naphthenic acid on the properties of the oil-water interface was investigated by measuring the oil-water interfacial tension, dilational rheological parameters, and interfacial film thickness, and the displacement mechanism of the ionized water flooding system was discussed. The results show that after the action, the interfacial tension of oil and water continues to decrease, and 1/3 ionized water (salinity diluted to 1/3 of the prepared ionized water, 1253 ppm) decreases to a maximum of 50.89%, while 1/5 ionized water (752 ppm) only decreases 14.40%; the thickness of the oil-water interface film decreases with the salinity of ionized water, but the decrease increases after 1/3 ionized water. In addition, the interfacial shear viscosity, interfacial expansion modulus, and interfacial phase angle tangent values all reach the maximum value within 10–15 days and then decrease. The research results of this article will provide a theoretical basis for the application of ionized water in oilfields.

INFLUENCE OF SKIN FACTOR VALUES ON WELL PRODUCTIVITY

For several decades, the problem of increasing oil recovery from reservoirs has been one of the most significant in oil-producing countries of the world. Most oil fields, usually represented by heterogeneous reservoirs, are developed using a waterflooding system. Experience in the development of water-oil zones shows that oil extraction from deposits underlain by bottom water is characterized by a relatively low oil recovery factor. When monitoring the development of oil and gas fields, various research methods are used. One of the main research methods is hydrodynamic testing of wells (HDT). The article discusses the influence of the skin factor on well productivity. Keywords: skin factor, productivity coefficient, mobility, water cut.

ABOUT WATERFLOODING OF LOW-PERMEABILITY RESERVOIRS

The purpose of this work is to analyze the effectiveness of the flooding system on low-permeable reservoirs of the Achimovian formation and optimize its operation taking into account the facial model. Due to the depletion of hydrocarbon reserves in traditional formations with good reservoir properties, interest in hard-to-recover reserves is currently increasing. And the main difficulty in the development of such reservoirs is the efficiency of waterflooding systems. When developing low-permeability reservoirs, various mechanisms of oil displacement during flooding can be identified. When flooding reservoirs with a permeability of less than 1 mD, there is no need to keep a high wellhead pressure. Moreover, with a large accumulated compensation, stopping water injection for up to six months does not lead to a drop in production, which creates prerequisites for the organization of cyclic flooding. This will solve a number of problems that appear in injection wells when working in such conditions. The facial structure of reservoirs sometimes has a decisive influence on wells operation and their mutual influence. The transition to the field development with a complex geological structure, low filtration characteristics of the formation, the existence of geological bodies with different properties, requires not only thoroughness in the formation of a conceptual understanding of the oilfield, but also the creation of detailed digital facial maps taking into account the existence of zones with different sedimentation, as a consequence, creating zones with different filtrationcapacitance properties, requiring different approaches to development.

Ways to increase the resource base of the Volga-Ural oil and gas province

In the conditions of one of the most representative groups of facilities containing significant oil reserves, confined to the Tournaisian stage of the Volga-Ural oil and gas province, and characterized by low rates of putting into active development, low recoverable reserves, low profitability of oil production, a study was made of the process of developing reserves under various modes operation. The reservoir energy depletion mode and the use of various in-loop waterflooding systems were considered. The parameters of waterflooding techniques have been established, which determine the oil recovery efficiency, by adjusting which, taking into account the peculiarities of the geological structure of the facilities under study, it would be possible to achieve an increase in the reserve’s depletion degree and a reduction in the cost of production. It is proposed to justify the decisions made to improve the process of developing these low-productive deposits with hard-to-recover reserves based on the obtained geological and statistical models and algorithms by using parameters, determined with minimum permissible errors at the stage of putting facilities into operation as well as using the full range of information at the stage of full drilling of the deposits. Keywords: oil recovery factor; hard-to-recover reserves; carbonate reservoirs; reservoir flooding; development profitability; reserves management.

CALCULATION OF AN ALTERNATIVE DEVELOPMENT SYSTEM FOR THE MAIN DEPOSIT OF THE DANILOVSKOYE OIL AND GAS CONDENSATE FIELD

The article provides a calculation of an alternative development system for deposit 3 (Main deposit ) of the Danilovskoye oil and gas condensate field. At the time of the analysis, this deposit is in the pilot development stage, with six development variants proposed in the trial operation project, which assume a principled arrangement of wells along an areal homogeneous grid. At the same time, due to the need to maintain the energy of the formation (that is, certain values of thermodynamic conditions), three provide for a transition to pressure maintenance, with the resulting four-point scheme of effect on the deposit (intensity 1:2; one well for injection, two for production). In the alternative model under consideration, the development method also involves a subsequent transition to pressure maintenance, but with a more active, five-point waterflooding system (intensity 1:1, equal ratio of production and injection wells), if necessary, as will be shown in the work, easily convertible to a nine-point one. The latter is an objective advantage, since the formation has low permeability and high vertical and lateral heterogeneity, and during waterflooding, zones not affected by the impact may appear, and, consequently, zones with high residual oil saturation. When calculating the characteristics of the proposed alternative method, modeling using the Peaceman method is used. Peaceman’s method is based on determining the well-reservoir connectivity of each individually opened cell, used to calculate flow rates (taking into account different values of average water cut for wells). The method is classical and, although it includes a large number of limiting assumptions, it is applicable everywhere and can provide sufficient justification for the effectiveness of the chosen development variant. General recommendations for the development of the entire field are also given (taking into account the low viscosity and lightness of oil and the properties of reservoir rocks). Such as the use of acid fracturing technology, the use of surfactants, hydrochloric acid treatments (HAT) and a complexing phosphorus-containing reagent — AFC.

Regulation of hydrocarbon production process based on dynamic tracer monitoring of horizontal well inflow profile

This paper presents the results of geological and production analysis of development and reserves of the pilot area using the results of dynamic marker monitoring of horizontal wellbores of production wells using high-precision indicators. As part of the research, the geological structure of the reservoir section was updated, which includes a lithological and facial analysis and geological and hydrodynamic simulation of the reservoir. The energy state of the reservoir was analyzed and the efficiency of the waterflood system was evaluated using dynamic data analysis and correlation analysis. The reasons for changes in the dynamics of inflow profiles over time have been analyzed. By the example of the pilot area the decision-making algorithm for adjusting the process of hydrocarbon reserves extraction, based on the analysis of the relevant geological and technical information, obtained during the long-term dynamic marker monitoring of the horizontal wells operation, has been implemented. A set of recommendations has been developed, which makes it possible to achieve stable dynamics of development indicators, to increase the coefficients of coverage by displacement in the area and the reservoir section, to involve previously undrained areas of oil reserves in the development. The results of the analysis of the efficiency of the implemented geological and technological measures are presented.

Geological Structure Features of Carbonate Formations and Their Impact on the Efficiency of Developing Hydrocarbon Deposits

The development of deposits with a complex geological structures is often accompanied by a set of problems associated with optimal decision making. The efficiency of the entire development system depends on the completeness and the quality of the analysis of reservoir parameters. This paper presents methodological approaches for the study of carbonate deposits, and the development of further steps to increase the efficiency of reserve recovery. The secondary transformation of reservoir rocks, resulting in channels of increased conductivity, cracks, and caverns, plays a special role in the nature of the recovery of hydrocarbon reserves from such deposits. Secondary cavernosity leads to violations of the linear laws of fluid filtration in a porous medium, and complicates the field performance prediction based on geological and hydrodynamic modeling. The studied geological structure was detailed using the example of carbonate deposits composed of oil and water- saturated formations, taking into account the results of core studies and the interpretation of geophysical well studies. Furthermore, the parameters of production wells made it possible to confirm that the oil saturated and underlying water saturated formations have hydrodynamic connectivity due to the presence of vertical micro cracks. At the same time, the thickness of the bridge between the reservoirs directly affects the initial water cutting of well production, and further growth dynamics of the water ratio are associated with the structural factors determining the initial oil content of the reservoir. The combination of the obtained dependencies and the distribution model of the reservoir properties along the area made it possible to build a complex map reflecting the predicted development efficiency in certain areas. The integration of the results of various field studies on the injection well stock established that a significant part of the water flows was injected into the water saturated formation, which reduces the efficiency of formation pressure maintenance in the target formation. As a result, in order to reduce the low efficiency injection volume, switching to a more rigid waterflooding system, in terms of the ratio of production and injection wells, is proposed with a further decrease in the injection pressure inside the wells.

Differentiation of exploration and production wells to prevent the breakthrough of water injected into the reservoir

The equations of canonical discriminant functions and distributions were derived for deposits of the Tournaisian age of the Volga-Ural oil and gas province. This enables solution to the problems of increasing the efficiency of implementation of various contour waterflood systems, choosing exploration and production wells for focal waterflood, and estimation of the well grid density at the stage of preparation of the design documents, pressure and injection volumes, as well as making scientifically grounded management decisions for regulating the exploitation process. The method has been proposed to prevent a catastrophic breakthrough of water injected into the reservoir, which is the reason for a significant decrease in the degree of oil reserves recovery.

Simulation of Scale Inhibitor Squeeze Treatments in a Polymer Flooded Reservoir

Summary This study aims to demonstrate the changes to scale inhibitor squeeze lifetimes in a polymer flooded reservoir vs. a waterflooded reservoir. A squeeze campaign was designed for the base waterflood system, then injection was switched to polymer flooding (PF) at early and late field life. The squeeze design strategy was adapted to maintain full scale protection under the new system. During the field life, the production of water is a constant challenge. Both in terms of water handling, but also the associated risk of mineral scale deposition. Squeeze treatment is a common technique, where a scale inhibitor is injected to prevent the formation of scale. The squeeze lifetime is dictated by the adsorption/desorption properties of the inhibitor chemical, along with the water rate at the production well. The impact on the adsorption properties and changes to water rate on squeeze lifetime during PF are studied using reservoir simulation. A 2D 5-spot model was used in this study, which is considered a reasonable representation of a field reservoir under waterflooding (WF)/PF. It was observed that when applying polymer (HPAM) flooding, with either a constant viscosity or with polymer degradation. The study concludes that the number of squeeze treatments was significantly reduced as compared to the waterflood case. This is due to the significant delay in water production induced by the polymer flood. When the polymer flood was initiated later in field life, after 0.5 PV (reservoir PVs) water injection, resulting in 70% water cut approximately, the number of squeeze treatments required was still lower than the waterflood base case. However, it was also observed that in all cases, at later stages of field life the positive impact of PF on squeeze lifetime begin to diminish, due in part to the polymer breakthrough, which results in higher water viscosity in the production near-wellbore region. Preventing the overflush to be as effective transporting the scale inhibitor. This study represents the first coupled reservoir simulation/squeeze treatment design for a polymer flooded reservoir. It has been demonstrated that in over the course of a field lifetime, PF will in fact reduce the number of squeeze treatments required even with a potential reduction in inhibitor adsorption. This highlights an opportunity for further optimization and a key benefit of PF in terms of scale management, aside from the EOR.

Вычисление перетоков флюида между скважинами в фильтрационной модели разработки нефтяного пласта с помощью линий тока

To analyze the waterflooding system of an oil reservoir and predict the effectiveness of geological and technical measures, information is required on the distribution of injection rate between the reacting production wells and the reservoir boundary. The most reliable methods for calculating these characteristics are methods based on hydrodynamic modeling of flow. Modern commercial software implement algorithms for these purposes based on the construction and analysis of streamlines. At the same time, there are no reliable estimates of the accuracy of these algorithms and recommendations for choosing the optimal parameters in the available literature. In this paper, we propose an algorithm for calculating the proportions of the distribution of the total well flow rate between the surrounding wells and the reservoir boundary using streamlines. Streamlines are constructed on the basis of a finite element solution to the flow problem averaged over the formation thickness and determine the boundaries of the streamtubes connecting the corresponding wells. The flow rate through the flow tubes is calculated by numerically integrating the Darcy velocity field of the indicated two-dimensional problem. The algorithm was tested on idealized examples of waterflooding elements of typical well placement schemes, when the exact distribution of the proportions of fluid injected into the formation is known, and on the example of comparison with the solution of the problem of simulating the injection of a tracer into the reservoir. Recommendations for the selection of starting points for tracing streamlines are presented, which allow achieving a minimum level of error in determining the mutual influence of wells in a wide range of the computational grid resolution of the flow model. A more general application of the described method without significant changes is to equip the high resolution flow model along fixed stream tubes with their rate characteristics.

Optimization Control of Oilfield Waterflooding Systems Based on Different Zone and Pressure

The scrapping of old waterflooding wells and the increase in new waterflooding wells results in mixed flooding of high–low pressure wells in various oil layers in waterflooding systems. In order to meet production operation requirements, the whole system is in a state of high pressure, which leads to an increase in energy consumption and complicates the operation of waterflooding networks. According to the pressure distribution of wells, proceeding with regional accurate waterflooding can reduce operation costs and improve development efficiency. Considering the technical constraints of waterflooding networks, a method was proposed, which can quantitatively optimize classification and zoning for waterflooding of high–low pressure wells according to the pressure of networks and wells. At the same time, the ant colony algorithm and genetic algorithm were fused to form a new adaptive ant colony genetic hybrid algorithm, which can effectively determine the best pumping scheme of the waterflooding station, the pumping flow and optimize the low-pressure area. The K-means algorithm was used to optimize the topology of the pipe network in the high-pressure area to reduce the overall waterflooding pressure. Finally, the method was successfully applied to the large-scale waterflooding system including 2200 wells and 10 waterflooding stations in sites in China. The results show that the method is effective for the operation and reconstruction of waterflooding pipe networks with large-scale and serious mixed high–low pressure.

Study of the predictive ability of the CRM analytical material balance model as a part of a retrospective test on a real field

For solving the problems of operational control and optimization of the waterflooding system, the choice of a model should be based on an understanding of its predictive ability. The article obtained the results of assessing the predictive ability of the CRM analytical material balance model in the framework of a retrospective test at a real field site. In addition to the single-phase representation, classical for the CRM model, special attention is paid to the predictive qualities of the two-phase formulations of the model. Based on the test results, it is shown that the CRM model in a two-phase setting allows predicting oil production at a high level of accuracy with detailing to waterflooding elements.

Особенности проведения гидроразрыва пласта в отложениях с трудноизвлекаемыми запасами

Introduction. When developing productive deposits containing hard-to-recover oil reserves, the main difficulty is associated with low values of the reservoir properties of the reservoirs and their significant heterogeneity. The use of hydraulic fracturing technology allows solving these problems by increasing the well drainage area, and also as a means of intensifying production. Materials and methods of research. The study of the process of hydraulic fracture development in the deposits of the Bazhenov formation in a vertical well showed that when water is injected, long narrow fractures are formed in the formation, their filling with subsequent supply of a fracturing fluid with proppant leads to an increase in the width and height of the created fracture. Due to the hydrophobic properties and increased brittleness of the rocks of the Bazhenov formation, an effect similar to hydraulic fracturing is also possible during the injection of water into the formation at high pressures, for example, when organizing a waterflooding system. Another direction is multi-zone hydraulic fracturing. The advantage of this method is the greater distribution of fractures over the area compared to point hydraulic fracturing operations. Results and Discussion. On the deposits of the Bazhenov formation, pilot work was carried out to create artificial fracturing by pumping water. The positive effect was expressed in a twofold increase in oil recovery in the pilot area. As a negative side effect, a sharp increase in water cut was noted. The experience of using multi-zone hydraulic fracturing in the conditions of the Bazhenov formation was considered on the example of the deposits of the Surgut arch. The dynamics of flow rates and cumulative oil production by wells during operation is presented. Also, a comparison was made of the main performance indicators of wells with multi-stage hydraulic fracturing with the average indicators of directional wells of the same fields. Conclusion. The pilot work conducted on water injection into the Bazhenov formation deposits unambiguously showed that additional fracturing is formed in the reservoir and the volume of additional fractured capacity is directly proportional to the volume of injected water. The experience of using multi-zone hydraulic fracturing revealed the advantages of this technology compared to directional wells. Under conditions of reservoir reservoir properties uncertainty, the creation of artificial conductivity using hydraulic fracturing may be the only way to ensure well productivity. MSHF in horizontal wells forms a system of fractures in a large volume and seems to be more effective in such conditions compared to conventional hydraulic fracturing.

Improving the carbonate reservoirs development efficiency on the example of the Tournaisian stage deposits

The article deals with the issue of carbonate strata of complex geological structure development efficiency improving. Such facilities, as a rule, have deteriorated reservoir properties, parameter anisotropy and are complicated by secondary cavernosity. All of these factors affect the recovery efficiency and are often reflected in development indicators. On the example of Tournaisian stage deposits an example of a methodological approach to the development analysis which takes into consideration various geological factors is presented. As a result, various dependencies were obtained, which when taken into account determin the most promising areas in terms of development efficiency. The issues of the waterflooding system efficiency and the ways of its efficiency increasing are considered separately. Keywords: oil fields development; carbonate reservoirs; development efficiency; waterflooding system.

Methodological approaches to increasing the flooding system efficiency at the later stage of reservoir development

Based on the analysis of the efficiency of CVI.1 and CVI.2 oil reservoirs development, which partially coincide in structural terms, and the terrigenous strata of the Lower Carboniferous of one of Volga-Ural oil and gas province oil fields, an algorithm for assessing the efficiency of waterflooding was proposed, which takes into account the geological structure of the facility, the results of core and geophysical well surveys, as well as the historical performance of wells. The presented algorithm makes it possible to identify ineffective injection directions for making decisions on waterflooding system optimizing. The effect is the identified potential to cut costs by reducing inefficient injection, as well as identifying areas for the introduction of enhanced oil recovery techniques. Keywords: field development; reservoir pressure maintenance system; waterflooding efficiency; cost reduction.

Evaluation the volume of distribution of the injected water and the interaction between injection and production wells probabilistic and statistical methods

The article describes the application of probabilistic-statistical methods for solving the urgent problem associated with determining the direction of movement of filtration flows. Today, the oil industry enterprises for these purposes use methods of hydrolistening and indicator research. These methods can most accurately assess the direction of movement of the filtration flows, but due to the high cost and duration of these studies in the Perm Krai fields are not often carried out. In this paper, we propose to study the interaction between production and injection wells by correlating the accumulated characteristics of their work. An analysis of the dynamics of the correlation coefficient between the accumulated values of water injection and liquid production performed in this way made it possible to establish qualitative indicators of the waterflooding system within the considered element of the development system. The obtained qualitative indicators of the waterflooding system demonstrate a high reliability of practical application, which is confirmed by the materials of tracer studies, as applied to the carbonate deposits of the Gagarinskoye field. Keywords: tracer studies; oil production; water injection; filtration flows; correlation coefficient; angular coefficient; carbonate reservoir.

Interpretation of interwell connectivity tests in a waterflood system

This study is an extension of a novel technique to determine interwell connectivity in a reservoir based on fluctuations of bottom hole pressure of both injectors and producers in a waterflood system. The technique uses a constrained multivariate linear regression analysis to obtain information about permeability trends, channels, and barriers. Some of the advantages of this new technique are simplified one-step calculation of interwell connectivity coefficients, small number of data points and flexible testing plan. However, the previous study did not provide either in-depth understanding or any relationship between the interwell connectivity coefficients and other reservoir parameters. This paper presents a mathematical model for bottom hole pressure responses of injectors and producers in a waterflood system. The model is based on available solutions for fully penetrating vertical wells in a closed rectangular reservoir. It is then used to calculate interwell relative permeability, average reservoir pressure change and total reservoir pore volume using data from the interwell connectivity test described in the previous study. Reservoir compartmentalisation can be inferred from the results. Cases where producers as signal wells, injectors as response wells and shut-in wells as response wells are also presented. Summary of results for these cases are provided. Reservoir behaviours and effects of skin factors are also discussed in this study. Some of the conclusions drawn from this study are: (1) The mathematical model works well with interwell connectivity coefficients to quantify reservoir parameters; (2) The procedure provides in-depth understanding of the multi-well system with water injection in the presence of heterogeneity; (3) Injectors and producers have the same effect in terms of calculating interwell connectivity and thus, their roles can be interchanged. This study provides flexibility and understanding to the method of inferring interwell connectivity from bottom-hole pressure fluctuations. Interwell connectivity tests allow us to quantify accurately various reservoir properties in order to optimise reservoir performance. Different synthetic reservoir models were analysed including homogeneous, anisotropic reservoirs, reservoirs with high permeability channel, partially sealing fault and sealing fault. The results are presented in details in the paper. A step-by-step procedure, charts, tables, and derivations are included in the paper.

Transport of oil/water partitioning components during water injection

The oil/water partitioning components such as alkylphenols and aliphatic acids naturally exist in crude oil compositions at different initial concentrations of hundreds or even thousands of ppm depending on the location of the reservoir compared to the site of original rocks. During contact with sweeping injection brine, those compounds diffuse from oil phase to water phase due to oil/water partitioning behaviours. As a result, their concentration in oil contacting with water will be attenuating during water injection. Their concentration profile in water injection history contains the information related to diffusion in oil and water phase, interstitial velocity of water and oil saturation. This paper presents the research results of theoretical model and numerical model of the washed-out process of alkylphenols in the late stage of water injection. The research results have proposed approximate analytical expression for concentration of alkylphenols at the late stage of water flooding. In this regard, at the sufficient large injection volume the alkylphenol concentration attenuates exponentially and the attenuation rate depends on parameters such as partitioning coefficient, oil saturation and interstitial velocity of water and oil and diffusion coefficients. The simulation concentration results obtained from UTCHEM simulator for the 5-spot model showed a good match with analytical calculation results. The research results can be used as the basis for developing methods to assess water flooding systems as well as oil saturation. The results can also be used for study of transport of non-aqueous phase liquid (NAPL) in environmental contamination. Keywords: Residual oil saturation, waterflooding, tracer, partitioning organic compounds, enhanced oil recovery.

To the issues of retrograde condensate extraction

The features of the formation of retrograde condensate in the reservoir and the method of its extraction are given. In order to improve the development of gas condensate fields and to reduce condensate losses under the reservoir pressure drawdown below the pressure of the beginning of condensate precipitation, the issue of the possibility of its extraction after precipitation in the reservoir by water or gas-water mixture displacement has been considered. The results of laboratory, analytical and field studies indicate that the retrograde condensation of the hydrocarbon mixture has a negative effect on almost all technological processes of condensate production. Reservoir condensate losses during the development of gas condensate fields in depletion mode are on average 60-78%. As an alternative to the cycling process, the use of a unified waterflooding system for the recovery of condensate from the reservoir has been considered. The results of laboratory studies are presented and the directions of the implementation of gas-water repression at gas condensate fields have been substantiated. The possibility of using reservoir gas available in the reservoir has been considered. In this case, the condensate was first flooded with water, and then, before the water broke out of the model, the system was degassed, reducing the pressure by 25% below the pressure of the onset of condensation, and again continued to displace the condensate with water. This procedure makes it possible to extract about 50% of the condensate dropped out in the reservoir.