RU2327031C2 - Method of wells finding for side tracking on mature water cut deposits - Google Patents

Abstract

FIELD: oil-gas area.

SUBSTANCE: one chooses all perspective wells in the deposit, in which drainage zones it can be found unrecovered oil. They are predicted by suddenly grew water cut in exploitation wells and in areas of raised contrast in shale-collector between its maximal and minimal penetrating in vertical and horizontal directions, when derivative relation water-oil take on value, more than unit. Then one analyses water cut, relation water-oil, oil recovery factor while water flooding. According to analyses results - oil recovery destruction to finite index of its extraction one defines concentration places of unrecovered oil, their quantity and location. Dimensions of unrecovered oil are taken inversely related to achieved index. According to production decline curve analysis in all wells in concentration places of unrecovered oil and around them one gets dynamic reservoir factors in concentration places of unrecovered oil - deformation index of collector properties of shale-collector and its penetration. This is checked on geological model. One predicts projected uplift of new stem dipping and chooses well, in which new stem dipping will be bored.

EFFECT: extraction increasing and final oil recovery.

5 dwg

Description

The invention relates to the oil and gas field, in particular, to methods for re-development of mature flooded fields in search of pillars of oil in order to increase production and ultimate oil recovery of such deposits.

Mature fields or the so-called “brown fields” are increasingly attracting the attention of exploration and production companies, which return to them and re-evaluate their potential in order to stimulate production and increase oil recovery. To increase production and final oil recovery, the most promising way may be the development of unexplored oil deposits in mature flooded fields. Most of the world's oil reserves are in water areas. Therefore, mature waterlogged fields cover the highest percentage of undeveloped oil deposits.

A known method of seismic exploration, in which the prediction of reservoir properties of reservoirs or oil-saturated thickness of the reservoir is carried out by reflected waves obtained by summing according to the principle of a common deep point. ("Methodology for the interpretation of seismic data in the integrated study of oil and gas reservoirs", A.G. Averbukh. "Geophysics", No. 1, 1998, pp. 13-19). The disadvantage of this method is that the interpretation of the reflected waves does not allow with sufficient accuracy to determine the location of the pillars of oil in mature flooded fields.

A known method of seismic exploration of massive geological rocks, in which the scattered component is isolated by additional suppression of reflected and multiple waves (RF patent No. 2168187). The disadvantage of this method is that when processing data obtained from a random or nonrandom set of scattering points located over a considerable area of space, the selection of regions with oil pillars by interference wave fields does not occur accurately enough, which leads to the loss of information about the studied object.

A known method of seismic exploration of objects (patent RU 2248014), in which such an option is selected for reflected, diffracted and scattered waves, which provides the best selection of objects against interference. An example of the practical application of the method is the search for flooded zones by reduced wave scattering.

However, all of the above methods require complex technical equipment to be implemented and do not allow with sufficient accuracy to diagnose the presence of pillars of oil.

Improving the accuracy of determining wells for drilling new shafts in mature flooded fields is achieved through the use of a new method of analyzing information and applying the principles of technological design of the research object, according to which all promising wells are selected in the field, in the drainage zones of which oil pillars could be predicted for sharply increased water cut of oil in producing wells and places of increased contrast in the reservoir between its maximum and minimum permeability in the vertical and horizontal directions, when the derivative of the water-oil ratio takes values, large units, analyzes the water cut, the water-oil ratio, the oil recovery coefficient during waterflooding, according to the results of the analysis, the places of concentration are determined by the shift in oil recovery to the final oil recovery coefficient of the pillars of oil, their number and location, while the dimensions of the pillars of oil are taken inversely proportional to the achieved coefficient, according to the analysis of the production decline curve in all wells in the places of concentration of the pillars of oil and around them, dynamic reservoir parameters are obtained in places of concentration of the pillars of oil - the coefficient of violation of the reservoir properties of the reservoir and its permeability, which is checked by the geological model, after which the production volume of the planned new well is predicted and the well is selected, from which a new trunk will be drilled.

The proposed method considers unexplored deposits by the example of pillars of oil. Drilling new shafts from existing wells to the location of the pillars of oil immediately increases the production and final oil recovery of worked-up watered fields using available means, due to which this method can be successfully applied.

The proposed method is based on a filtration and analysis method based on the principles of technological design, and therefore it is more convenient in determining the concentration of oil in pillars than classical approaches to reservoir research and development technologies.

Most mature fields are over 30 years old. It is difficult to find complete data for any of these deposits. Moreover, in many cases, the source and quality of information remains in doubt. The analysis method, based on the principles of technological design, focuses on the behavior of each well in the production process in order to analyze the oil recovery mechanism. Its implementation requires only data on production dynamics, sporadic pressure values, basic data on the well fluid and the main production parameters, which are most often known. In comparison with this, when modeling reservoir development to adapt to the development history, it is necessary to create a detailed geological model and have detailed pressure data. Consequently, the amount of available data is more suitable for an approach using technological design than for research using a simulation method of reservoir development.

In addition, the method does not require a large investment of time. Compared to studies using the modeling method of reservoir development using a fairly small amount of input data, it is also not necessary to create a complex model and achieve a match between complex modeling and development history. Thus, significantly reduced time spent collecting data and creating a model. Moreover, the approach presented here allows you to filter the most promising areas at the beginning of the analysis. It allows you to combine all available resources in these areas for detailed analysis in the shortest possible time, therefore, the method allows you to achieve results in the shortest possible time.

The proposed method is based on the following steps:

Stage 1: From field level to promising areas

The first stage is the selection of all wells in the field, in the drainage zones of which there could be oil pillars. The zones around such wells are promising.

If oil pillars are in the drainage zone of the well, then a premature breakthrough of water (PW) is observed in the well. The dynamics of changes in production for the well allows you to clearly identify premature breakthrough of water. Based on the foregoing, a filtration method has been developed that ensures the selection of all wells in the field with potential oil pillars in drainage zones.

Stage 2: From promising zones to places of concentration of oil pillars

At this stage, it is necessary to clarify the concentration of pillars of oil in promising areas, to determine their number and location. An in-depth analysis of water production and injection data for all wells of the prospective zone and around it allows us to describe the displacement process. According to the analysis, all places of concentration of the pillars of oil are clarified, their quantity and location are determined.

Stage 3: Parameterization of the concentration of pillars of oil in the reservoir

For further analysis, it is necessary to obtain dynamic reservoir parameters in places of concentration of oil pillars.

An in-depth analysis of the production decline curve in all wells at and around the concentration of oil pillars provides dynamic parameters at the concentration sites themselves.

Stage 4: Forecasting Production

So, based on the parametrization of the place of concentration of the pillars of oil in the reservoir, the production volume of the planned new well is predicted. The initial production rate of a new wellbore can be calculated based on the parameterization of the concentration site of the oil pillar obtained earlier. From the production decline curves of nearby wells, production decline curves can be predicted in the new wellbore. Based on the results obtained, the entire production volume of the new trunk is forecasted.

Step 5: Choosing a Well to Drill a New Bore

In cooperation with well construction specialists, a well is selected from which a new well will be drilled, and work cost calculations are carried out.

Stage 6: Evaluation of project profitability

Finally, a detailed analysis of economic efficiency is carried out, which allows you to resolve all the risks associated with the analysis.

According to the forecasting of the volume of production, initial investment, oil cost and production costs, Monte Carlo simulation was performed at net present value before taxes. Based on the resulting net present value calculated with probability P10 / P50 / P90, the final decision is made to drill a new trunk or reevaluate the project using a detailed autonomous reservoir development model.

1.1. Theoretical basis of the applied data analysis principle

In the proposed method for analysis, the main indicators of the dynamics of production are used to determine wells with possible oil pillars in the drainage zones. To do this, you need to know the following:

- Actually the process of crowding out,

- Relevant production dynamics indicators,

- Ways to identify pillars of oil in the reservoir.

1.1.1. Crowding out process

Buckley and Leverett developed a theory (Buckley S.E. and Leveret, "Mechanism of Fluid Displacement in Sands", AIME, 1942, V.146, p.107) that describes the one-dimensional process of displacing oil and water in a homogeneous rock under constant pressure displacement.

The theory describes the passage of water from jet pumps through reservoirs to production wells in front of a shock wave. The shock wave front displaces oil until it reaches production wells and the so-called breakthrough of water occurs. In this and various other related theories, the displacement process is described quite well, and they are widely used in the oil industry.

1.1.2. Key performance indicators

The water cut of the product (OP) and the oil recovery factor during waterflooding (ORF) of producing wells are the main indicators of production dynamics, reflecting the course of the displacement process and the associated effects of missing the pillars.

The method proposed by Welge (Welge, HJ, "A Simplified Method for Computing Oil Recoveries by Gas or Water", AIME, 1952, V.195, P.91), allows to quantify the water and oil saturation of the reservoir during the displacement depending on the properties of the fluid and the formation, as well as the progress of the displacement process. Using this method, all of the above can be linked to the water cut of the product of the producing well.

The effectiveness of the displacement process and inversely proportional to the degree of effects of skipping the pillars are reflected in the SIF achieved during the displacement process.

Thus, the effects of the displacement process can be determined using the main indicators of production dynamics.

1.1.3. Rear Skip Effects

The omission of the pillars is due to the heterogeneity of the rock at the micro and macro levels. Only passing the pillar at the macro level along with the predominant heterogeneity of the rock leads to the appearance of pillars of oil in the reservoir, suitable for drilling new wellbores.

At the microscopic level, oil is stuck in the rock above the residual oil saturation due to the microscopic heterogeneity of the rock. Water only seeps through the rock and holds oil in small pockets. This mainly happens if the displacement rate is higher than critical. Such microscopic pockets of oil do not differ in mobility at the macroscopic level and are the goal of the campaign for oil production by secondary methods, and not the processes of drilling a new wellbore from an existing one, as P.J.Wait described in detail (Wight, GP, "Waterflooding", Society of Petroleum Engineers Textbook Series, Second Edition 1986, ISBN 1555630057).

On figa) it is shown that in this case, oil production is continuously increased until the breakthrough of water. Then it falls due to the instantly increased water cut of the product. CIN is committed to the ultimate CIN. If crowding out occurs below a critical speed, then, in all likelihood, the maximum final recovery factor will be achieved from an economic point of view.

At the macroscopic level, the effect of heterogeneity in the vertical and horizontal directions, as well as gravity, lead to the passage of pillars of oil in pockets, the dimensions of which give enough reason to drill a new branch.

In this case, water mainly displaces oil in regions with high conductivity. It draws channels along high conductivity paths to production wells, displacing oil along these paths and passing it in regions with low conductivity. As a result, water breaks into production wells. After that, the injected water continues to flow along the formed paths of high conductivity, bypassing areas with low conductivity. Thus, oil is not squeezed out of the pockets and remains in the reservoir.

It is important to understand that the greater the degree of heterogeneity in the reservoir from the point of view of parameterization, which means an increased contrast between, for example, the maximum and minimum permeability, the greater is the missed pillar of oil in the reservoir. Moreover, it is important to keep in mind that the greater the degree of heterogeneity in the reservoir from the point of view of oil distribution in it, i.e. the more single places with a certain, for example, permeability, the more single places of concentration of oil pillar.

In a reservoir with heterogeneous parameterization and uniform distribution, water channels along various paths of increased conductivity. The shock wave front of the displacement process is intensively divided depending on the heterogeneity of the rock. Thus, it does not reach the production well with an instantaneous and united front, but spreads over time. As a result, the water content of the product and the recovery coefficient curve in accordance with FIG. 1B) are continuously increased.

Obviously, the final recovery factor is reduced due to the heterogeneity of the rock parameterization. The pockets of the oil pillar are most likely too small for drilling a new wellbore due to uniform distribution.

Compared with a reservoir with non-uniform parameterization and non-uniform distribution, water, and hence the main shock front of the displacement process, moves along the predominant heterogeneity, as shown in Fig. 1C).

In this case, the water follows the so-called premature breakthrough of water mainly due to the prevailing heterogeneity. Thus, the water cut of the product instantly increases, as a breakthrough of water occurs, and the extraction is shifted to the final recovery factor. This indicates the concentration of pillars of oil in the pockets, the dimensions of which are inversely proportional to the achieved oil recovery factor, and gives enough reason to drill a new wellbore.

A similar effect can be observed in a homogeneous reservoir if the injected water flows below the oil due to gravity.

This clearly shows how the heterogeneity of the rock leads to the passage of water to the pillars of oil. In addition, this shows that it is possible to distinguish between different effects of heterogeneity in the presence of a general idea of the geological situation and in detail the main indicators of production dynamics analyzed.

1.2. Filtration principle

The filtering program searches for signs of oil pillar among indicators of production dynamics in all wells in order to determine promising zones. First, the water cut of the product is analyzed. The water content of the product indicates a breakthrough of water and a predominant heterogeneity. Then, the water-oil ratio (IOD) is analyzed. The water-to-oil ratio (IOD) allows you to clearly check the breakthrough of water and the source of flooding. Finally, the CIN is analyzed. This allows you to identify the concentration of pillars of oil and determine their quantitative characteristics.

1.2.1. Water cut product

In the process of oil displacement by water, a sharp increase in the water cut of the product in the producing well to the level of the shock wave front of the displacement process indicates a water breakthrough, as described above and described in detail by Buckley and Leverett.

From the capillary pressure curves in the reservoir, the motion curves of the individual phases in the reservoir can be derived. The method proposed by Welge allows you to generate the expected saturation of the shock wave front and the related water cut of the product. Since any premature breakthrough of water occurs in a zone with a predominant heterogeneity, as mentioned above, it is important to calculate the motion curve of the individual phases for the maximum estimated water mobility. Thus, the water cut of each well that has experienced a water breakthrough should be equal to or greater than this value.

In case of water breakthrough, the water cut of the product in the well also increases rapidly. The derivative of OP (OP ') shows this in the best way. From the results of a study of several fields, it can be seen that in the event of a water breakthrough, the water cut of the product increases by more than 50% points per year (the value varies depending on the state of the field). The fact that a breakthrough of water occurred with a high probability is indicated by the value of the derivative from OP greater than 1.5 · 10 P ^-3P per day.

Thus, the final OD equal to or greater than the OD associated with the shock front and the maximum OD value of more than 1.5 · 10 P ^-3P per day clearly indicate a breakthrough in water. However, it is unclear whether this is a premature breakthrough of water or the result of the displacement process due to the prevailing heterogeneity or, for example, an annular water inflow.

1.2.2. Water-oil ratio

The water-oil ratio and its derivative (OVN ') allow us to establish the reasons for the high values of water cut of the product and water breakthrough. The water-oil ratio and its derivative, plotted on a double logarithmic scale, are widely used in diagnostics in conditions of water cut, as indicated by Bailey et al. (Bailey B., Crabtree, M., Tyrie J., Elphick J., Kuchuk F., Romano C., Roodhart L, "Water Control", Schlumberger Oilfield Review, Q1 / 2000, p.30). IOD and IOD 'allow a distinction to be made between the causes of water breakthrough, such as water displacement, annular water inflow and the formation of a watering cone according to K.S. Chan et al. (Chan KS "Water Control Diagnostic Plots", SPE 30775, Dallas, Texas, 2225 October 1995).

The displacement along the prevailing heterogeneity ultimately leads to a sharp increase in the water-oil ratio during the breakthrough of water with a maximum WHR value greater than unity, as described by I.S. Yersos et al. (Yortsos YC, Choi Y., Yang Z., Shah PC , "An Analysis and Interpretation of Water-Oil-Ratio in Waterfloods", SPE 38869, San Antonio, Texas, 5-8 October, 1997).

\\ A completed watering cone could also indicate oil pillars, which would serve as a basis for drilling a new branch according to Hill et al. (Hill D., Neme E., Ehlig-Economides S., Mollinedo M., "Reentry Drilling Gives New Life to Aging Fields ", Schlumberger Oilfield Review, Q3 / 1996, P.4). From the very beginning, the cone shows an increase in IOD and a decrease in IOD '. If the cone completes its formation to the extent that it restrains the prey, then its effect is similar to the effect of a water breakthrough.

Thus, all cases of water breakthrough caused by water displacement along the prevailing heterogeneity or the formation of a watering cone can be clearly established using the analysis of the RH and RH '.

1.3. Oil recovery and oil recovery ratio (CIN)

And finally, it is necessary to analyze the dynamics of production in order to clarify the possibility of drilling a new branch for the extraction of whole oil. The analysis is based on volumetric calculation, which uses the main parameters of the formation of each well.

According to the foregoing, the oil recovery factor depends on the total recovery and oil recovery under the conditions given to the wellhead. The deviation of the oil recovery factor to a constant value indicates the size of the oil pillar, inversely proportional to the volumes produced so far. A value close to zero for the derivative CIN, (CIN ') allows you to determine the deviation of the CIN in the direction of a constant value. In order to be convinced of the significance of the reserves of crude oil, the final recovery factor must be less than a certain limit, which is the residual current reserves, large enough for economically viable drilling of a new branch.

It is important to understand that in the drainage zones of two or more wells there may be oil pillars that form one promising area for drilling a new branch. Thus, it is advisable to combine the calculation of the maximum oil recovery factor and the correction factor, which takes into account this effect.

Consequently, oil recovery factor and oil recovery factor allow, ultimately, to determine the oil production process, which was limited, and to select only those wells, the extraction of which is entirely oil from which would be economically feasible. This makes it obsolete the question of whether the water breakthrough was premature. Moreover, with its help it is possible to determine the volume of pillars of oil for each well.

Thus, as can be seen from Figure 2, in the drainage zones of all wells filtered in the field according to these criteria, in all likelihood, concentrations of oil pillars may be observed. The areas around them are therefore considered promising.

1.4. Analysis method

The presented analysis method is a step-by-step approach by which the presence of oil pillars is clarified, their volume and location in promising zones are determined, followed by the determination of the concentration of oil pillars. This is achieved by analyzing the displacement process of interest:

- The main geological situation,

- The sources of water and the paths along which it passes by the pillars of oil,

- Inaccessible zones.

In addition, a technique is presented for obtaining dynamic reservoir parameters for determining the locations of the concentration of pillars of oil mainly by in-depth analysis of the production decline curve.

For this, from the point of view of profitability, it is advisable to classify wells or a group of wells by the potential value of the pillars of oil. Next, conduct an express analysis of the oil recovery factor of the concentration sites in order to identify cases when the reserves of one well would or would have been extracted through a neighboring well. And finally, study the history of each well and rule out special cases that are not worth analyzing.

1.4.1. Geological situation

A correct understanding of the existing geological situation of the promising zone allows you to determine the most likely ways of water movement.

Water tends to concentrate in an area with high conductivity, due to the favorable formation properties of the reservoir. Display on the plane of various parameters of the formation, for example, porosity, permeability, effective thickness of the formation and the initial water saturation, allows you to establish the presence of such areas and evaluate the preferred paths of water movement. Logging data makes it possible to understand the vertical structure of a promising area, including interbedding and discontinuous occurrence of rocks, as well as to evaluate vertical relationships in this area. Combining the results of the analysis in these two planes, we can develop a model of the existing geological situation.

Particular attention should be paid to such geological objects as the discontinuous bedding of rocks, which affects the path of water movement, along with the parameterization of the reservoir. In addition, attention should be paid to places in which water probably flows under the oil due to heterogeneity of the formation and / or due to the gravitational effect.

1.4.2. Crowding out process

The combination of the existing geological model and the relationship of water sources and waterlogged wells allows us to determine the paths along which displacement is most likely to occur.

For this, the dependence of the water cut of the product (OP) on the time for the promising zone is built. Based on this, it is possible to establish where and how the water passes within the perspective zone, as shown in FIG. 3.

It must be borne in mind that such graphs are obtained on the basis of studying the prospects of wells. They show the values obtained by interpolation, and not channels, but areas with a high concentration of water depending on time for injection and production wells are detected.

Next, a flow analysis is carried out that links the water injection wells to the production wells. Based on the results of the analysis, single injection and production wells are interconnected in terms of the history of injection and production and the relative position of the wells. Thus, the directions in which the displacement process took place is established more precisely in areas of increasing water saturation.

It must be borne in mind that the analysis of the main flow does not concern the existing geological conditions, unless a special task is set for this. Therefore, the combination of the relationship of water sources and waterlogged wells with the existing geological model depends on the application of forces and knowledge of the engineering staff.

By combining the two approaches, it becomes possible to distinguish between the main water sources, for example, aquifers (light) and injection wells (dark), and determine their displacement efficiency in zones with high conductivity to the main producing wells (Figure 4). This allows you to check for the presence of pillars of oil and already gives an indication of their location.

1.4.3. Inaccessible areas

Identification of inaccessible zones is necessary for the final determination of the location and quantification of reserves in oil pillars.

Consequently, the inflow zone in the producing reservoir of producing, and hence injection wells, is depicted as a circle under the assumption that the reservoir conditions are homogeneous (in the case of known anisotropy, it easily transforms into an ellipse).

The construction of inflow radii and their combination with established flow paths and schedules of residual reserves allows you to finally establish the concentration of oil pillars.

The size of the pillars of oil is determined by combining the unexcited reserves calculated for each well during filtration, since it is expected that all of them contribute to the pillar of oil located between them.

1.4.4. Reservoir parameterization

To predict the potential productivity of a new branch, it is necessary to determine the main parameters of the concentration zone of the pillars of oil. The main dynamic reservoir parameters, such as the dynamic coefficient of reservoir disturbance and permeability, are required along with the main parameters of the fluid and the reservoir. They can be obtained by in-depth analysis of the production decline curve and analysis by the method of nodal potentials.

At the first stage, an in-depth analysis of the production decline curve makes it possible to derive the main dynamic reservoir parameters from the main production dynamics and pressure data by comparing them with special type curves, as T.A. Blasingham and J.S. Palacio described in detail (Palacio JC, Blasingame TA "Decline Curves Analysis using Type Curves: Analysis of Gas Well Production Data", SPE 25909, Denver, Colorado, April 12-14, 1993). The quality of the in-depth analysis strongly depends on the uniqueness of the match, which is mainly indicated by the correctness of the derived radius of the drainage zone, as well as on the accepted ratio of the vertical to horizontal permeability of the formation.

According to Doublet et al. (Doublet LE, Pande PK, MeCnIltIm TI, Blasmgame TA "Decline Curve Analysis Using Type Curves-Analysis of Oil Well Production Data Using Material Balance Time: Application to Field Cases", SPE 28688, Mexico, 10- October 13, 1994) without an exact match of the drainage radius, a clear in-depth analysis of the production decline curve is impossible. Thus, the results of the analysis of the production decline curve can be accepted only with the proper drainage radius. A sufficiently good approximation of the drainage radius can be obtained from the calculation of the material balance or from a simple volumetric calculation. Moreover, an idea of the radius of drainage is provided by the grid of wells.

The ratio of vertical to horizontal permeability of the formation can be derived from logging or coring data, as well as general assumptions regarding geological conditions or rock type.

Then, the obtained parameters must be checked on the same software that was used to forecast production in order to ensure a systematic correspondence between the compared and predicted production.

The setup for each well and the comparison of actual production indicators are used to verify the obtained parameters. Only if such compliance is achieved, forecasting the initial steady-state oil recovery rate will correspond to the actual indicators.

And, finally, based on the results of an in-depth analysis of the production decline curve, a model check and a basic geological model, the dynamic permeability of the oil pillar zone can be derived.

The values of the dynamic permeability of the rock in all the wells surrounding the concentration of oil pillars are compared with the geological model, their values are averaged for the concentration of oil pillars relative to the model.

Similarly, you can calculate the dynamic coefficient of violation of reservoir properties of the reservoir. It is necessary to break down the coefficient of violation of reservoir properties of the formation into components related to opening the reservoir, perforations and damage to the reservoir. Only the coefficient of disturbance of reservoir properties of a formation caused by damage to a productive formation can be predicted based on the dynamic coefficients of disturbance of reservoir properties of a reservoir of wells surrounding the site of concentration of oil pillars. The reservoir disturbance coefficient due to the opening of the reservoir and perforation is calculated for a new branch based on the planned opening of the reservoir and perforations.

It is necessary to calculate the initial / low / high value of dynamic permeability and reservoir failure coefficient of the reservoir to detect all the uncertainties associated with the analysis of forecasting production volume.

1.5. Production forecasting

Based on the given and derived parameters, it becomes possible to predict the volume of production in the planned branch using the nodal potential method and an empirical analysis of the production decline curve.

In the 40s of the last century, J. Arps (Arps, J.J., "Analysis of Decline Curves", AIME, 1945 V. 160, p. 228) developed the basic principle of modern empirical analysis of the production decline curve. In this model, the dip curve indicator empirically expresses the nature of well depletion versus time.

When analyzing the performance of the exponential decline in production in a promising area, it is necessary to take into account different periods of production. The periods mainly differ from each other due to the total flow rate and injection in the analyzed area. To predict the depletion of a new branch, data should be used only for those periods that reflect the production conditions when it is drilled.

In addition, a guide to determining the exponent of the decline in production is a comparison of the main methods of field development and the results of the study of various fields, which are widely discussed in the specialized literature. Developing scenarios for a base / low / high value reveals any uncertainties at this stage of the analysis.

Compared to this empirical approach, using the calculation of material balance to describe the depletion of a new branch would introduce uncertainty about the boundary conditions. It is also difficult to collect data on the effect of water injection into a promising zone on the analysis of the behavior of a single well. Thus, the empirical seems to be the most suitable method for analyzing production decline.

And, finally, a combination of various initial steady-state values of well production and flow rate drop indicators allows you to obtain a baseline / low / high scenario to predict the total production.

1.6. Selection of a well for drilling a new branch

Drilling a new branch from a well, indicating the presence of a pillar of oil, is not always cost-effective. Therefore, the question - from which well to drill a new wellbore to a selected location of oil pillar concentration, must be decided separately for each case, taking into account the requirements in accordance with which the construction of the well was planned. At the initial stage of selection of promising wells, candidate wells are determined on the basis of the obtained characteristics of nearby wells:

- The maximum distance to the target,

- Well condition and economic prospects,

- Geological structure and prospects for well completion,

- Operations to increase well production and production history.

1.7. Economic justification

When assessing the economic efficiency of the project, all the uncertainties of the analysis are taken into account, and on this basis a final decision is made on drilling or re-evaluating the project through detailed offline modeling, which is based on additional data, for example, new logging charts. For this, Monte Carlo simulation is used at the net present value of the project before taxes.

Thus, the proposed method is intended for the selection of wells in the drainage zones of which could be oil pillars, the purpose of which is to refine, determine the number and placement of such pillars of oil. In addition, an approach to predicting the flow rate of a well in potential branches is described. And finally, he links the analysis of the economic efficiency of the planned branch with the Monte Carlo simulation, which allows you to resolve all the risks associated with the analysis. To carry out the analysis, a minimum of input data is required, as a result of which in many cases it is more convenient and does not require a large investment of time in comparison with classical approaches to the technologies of research and development of reservoirs (Figure 5).

Claims (1)

A method for determining wells for drilling new shafts in mature watered fields, according to which all prospective wells are selected in the field, in the drainage zones of which there could be oil pillars, which are predicted by sharply increased oil cut in production wells and places of increased contrast in the reservoir between its maximum and minimum permeability in the vertical and horizontal directions, when the derivative of the water-oil ratio takes values, large units s, analyze water cut, water-oil ratio, oil recovery coefficient during water flooding; according to the analysis results, the concentration of oil pillars, their quantity and location are determined by the shift of oil recovery to the final oil recovery coefficient, while the sizes of oil pillars are taken inversely proportional to the achieved coefficient, by analyzing the production decline curve in all wells in the areas of concentration of oil pillars and around them, dynamic reservoir parameters are obtained in places of concentration of oil pillars - to the coefficient of violation of the reservoir properties of the reservoir and its permeability, which is checked on the geological model, after which the production volume of the planned new well is predicted and a well is selected from which a new well will be drilled.

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