RU2611097C1 - Method of developing oil deposits at late stage of operation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to the extraction of hydrocarbons, namely to the development of oil deposits at the late stage of operation. The method includes the initial period of operation and the final period of operation, at which the methods of enhancing oil recovery - EOR - are applied. According to the method, determining the criterion of the EOR implementing start is envisaged. To do this, the graphical dependence of the relationship of the volume of initial extracted oil reserves located within the feeding radius of a specific production well to the estimated value of cumulative oil extraction of this well depending on the time of operation (the reference chart) is drawn, then - to the forecast value of cumulative oil production, then - to the value of the actual cumulative production of this well. After that, the resulting graphs are combined. During the well operation, the time point of the beginning of divergence in the graphs of the reference and actual changes in the volume relationships of the initial extracting reserves is established. The graphs divergence point is defined as the time point for introducing an appropriate EOR for the impact on the pitface formation zone to restore the productivity of the selected well. Wherein the following graphs discrepancies of the reference and actual changes of said relationships over time are selected as the basis for the next EOR introduction.

EFFECT: invention provides improving the efficiency of the operation method due to the timeliness of introducing the necessary methods for enhanced oil recovery.

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Description

The present invention relates to the production of hydrocarbons, and in particular to methods for increasing oil recovery in productive formations.

Under the stage of development of an oil field refers to the time interval of the various stages of operation, characterized by different sizes of accumulated production and the rate of change (growth - decline) (V.L. Katsyubinsky, R.Kh. Muslimov. About the stages of development of oil fields. // Oil industry, M., 1996, No. 4, pp. 78-85).

The entire development period according to the known method is divided into the operational stage: in the natural mode - stages I, II and III, and then the artificial operation stage - IV, at the stage of which various technologies for enhancing oil recovery (EOR) are used or the same as enhanced oil recovery methods (EOR).

The known method, which provides for a slightly different staged development of an oil field, in which stage I is distinguished as the initial stage of drilling the area of the field under the grid of production wells, stage II - the operation of the wells due to the formation's own energy due to the pressure of the formation water (elastic pressure mode), or pressure gas cap (elastic gas-pressure mode. According to the well-known classification of stages I and II refer to the initial period of operation. All subsequent stages relate to the decisive period of operation (Yu.A. Gutorov, AM Gareev. On the possibility of implementing a systematic approach to solving the problem of increasing the efficiency of exploitation of oil fields. // Oilfield business. M., VNIIOENG OJSC, 2013, No. 2, pp. 27-29 )

The introduction of the concept of stage-by-stage development allows one to reasonably choose the type of EOR that can give the best effect at a particular stage, being guided by the choice of the dynamics of the average production rate over the years.

An untimely transition to the use of an EOR that is inconsistent with the current state of oil field development can lead to a sharp decline in the productivity of production wells, which in some cases is irreversible, and can lead to irreparable loss of reserves, which will inevitably become difficult to recover.

So, the untimely entry of the EOR regime at stage III can lead to the extraction of only 15% of active reserves, and the untimely entry of the EOR regime based on vibration-shock technologies at the fourth stage can lead to the extraction of only 20% of active reserves (Yu.A. Gutorov, AM Gareev, On the Possibility of Implementing a Systematic Approach to Solving the Problem of Increasing the Efficiency of Oil Field Exploitation, Oil Field Business, Moscow, VNIIOENG OJSC, 2013, No. 2, pp. 27-29).

The disadvantages of this method include the uncertainty of diagnostic criteria that ensure timely commissioning of EOR methods corresponding to each stage of the current state of field development.

The task of the invention is to increase the efficiency of EOR methods due to more timely putting them into action.

This problem is solved by the fact that in the method of developing oil fields at a late stage of operation, including the initial period of operation and the final period of operation, during which oil recovery enhancement methods are used - EOR, in contrast to the known method, a standard graphic dependence is built to determine the criterion for starting EOR input (reference change) the ratio of the volume of initial recoverable oil reserves located within the power radius of a particular production well to the estimated value cumulative oil production of this well depending on the operating time according to the formula:

,

,

where Q _{beg. extract} - the volume of initial recoverable oil reserves located within the radius of the supply of a particular production well, m ³ ;

Q _{acc. calc.} - the estimated value of the cumulative oil production depending on the operating time of a particular production well, m ³ ;

t - well operation time, months;

To _p - coefficient of porosity,%;

To _ol - the coefficient of permeability, μm ² ;

To _us is the saturation coefficient,%;

ΔP is the difference between the pressure on the supply circuit and the bottomhole pressure, MPa;

μ is the viscosity coefficient, MPa⋅s;

R _to - the radius of the power circuit, m;

h is the thickness of the reservoir, m;

r _s - well radius, m;

To _kin - oil recovery ratio,%.

When establishing a decrease in the rate of development of reserves of a specific production well, determined according to the constructed schedule, methods for increasing oil recovery - EOR associated with increasing the surface of the filtration of the bottom-hole formation zone, for example, drilling a horizontal well - hydraulic well or hydraulic fracturing - are used in this well.

Next, build a predictive graphical dependence (forecast change), characterizing the ratio of the volume of initial recoverable oil reserves - Q _{beg. extract} located within the power radius of a particular production well to the predicted value of cumulative oil production - Q ' _{cumulative. prog.} depending on the operating time of a particular production well, subjected to horizontal drilling - horizontal wells or hydraulic fracturing - hydraulic fracturing, according to the formula:

or

where Q _{beg. extract} - the volume of initial recoverable oil reserves located within the radius of the supply of a particular production well, m ³ ;

Q ' _{acc. prog.} - the predicted value of the cumulative oil production depending on the operating time of a particular production well, subjected to horizontal drilling - GS or hydraulic fracturing - hydraulic fracturing, m ³ ;

t - well operation time, months;

To _p - coefficient of porosity,%;

To _ol - the coefficient of permeability, μm ² ;

To _us is the saturation coefficient,%;

ΔP is the difference between the pressure on the supply circuit and the bottomhole pressure, MPa;

μ is the viscosity coefficient, MPa⋅s;

R _to - the radius of the power circuit, m;

L _GS - the length of the horizontal trunk, m;

or

L _grp - fracture crack length, m;

r _s - well radius, m;

To _kin - oil recovery ratio,%.

Then, according to the actual measurements of the productivity of a particular production well in real time, a graphical dependence is plotted in time of the ratio of the volume of initial recoverable oil reserves - Q _{beg. extraction} , located within the power radius of a particular production well, to the value of the actual (current) cumulative production of this well - Qʺ _{cumulative. fact.} (actual change).

Next, combine the obtained graphical dependence (graph) with graphical dependencies constructed according to the formulas (1, 2 or 3), and set the time point for the beginning of the discrepancy between the graphs of the reference and actual changes in the above relations in time, which is defined as the moment for the introduction of the corresponding EOR according to the effect on bottom-hole formation zone to restore the productivity of the selected well, which will correspond to the position of convergence of the graphs of the predicted and actual changes in the above relations s. Further, the basis for the next introduction of the EOR is to choose the subsequent discrepancies between the reference and actual changes in these schedules over time.

The figure shows an example of combined graphic dependencies: reference, forecast and actual changes in relations (dimensionless value) in time (t) of the volume of initial recoverable oil reserves - Q _{beginning extracted} to the estimated value of accumulated production - Q _{acc. calc.} (curve 1), to the predicted value - Q ' _{acc. prog.} (curve 2) and to the value of the actual (current) accumulated production - Qʺ _{acc. fact.} (curve 3).

It is known that the production of oil reserves by production wells in oil fields occurs within a certain “supply radius” - R _k , which limits a certain circular contour around the well, called the “supply circuit” (Sh. K. Gimatudinov / Oil production reference book. M ., Nedra, 1974).

The amount of oil reserves - Q _{beg. zap} within the "power circuit" is calculated using the volumetric method, when, knowing the effective oil-saturated thickness of the reservoir - h, determine its volume within the "radius of power" - R _to , which is multiplied by the porosity coefficient - K _p , and the value of the oil saturation coefficient - To _us.

To determine the share of this volume, defined as the initial recoverable reserves - Q _{beg. extracted} mined using the applied technology, Q _{beg. zap is} multiplied by the coefficient of oil recovery - K _kin , according to the formula:

where Q _{beg. extracted} - initial recoverable reserves, m ³ ;

To _p - coefficient of porosity,%;

R _to - the radius of the power circuit, m;

h is the thickness of the reservoir, m;

To _kin - oil recovery ratio,%;

π is a constant number;

To _us is the saturation coefficient,%.

The daily (current) estimated value of oil production is Q _{add. calc.} from a specific well is calculated using the well-known Dupuis formula (Sh.K. Gimatudinov / Oil production reference book. M., Nedra, 1974):

,

,

where K _CR - permeability coefficient, μm ² ;

ΔP is the difference between the pressure on the supply circuit and the bottomhole pressure, MPa;

μ is the viscosity coefficient, MPa⋅s;

R _to - the radius of the power circuit, m;

r _s - well radius, m;

h is the thickness of the reservoir, m

Current accumulated estimated oil production - Q _{acc. the calculation} will depend on the time t elapsed since the formation was put into operation, according to the formula:

It is known that to compare the pace of development of the field sections located within the power radius of a particular production well, the relationship Q Q _{beginning is used. extracted} - the amount of initial recoverable oil reserves located within the power radius of a particular production well to Q _{accum. calculation} - the current accumulated estimated oil production (D.A. Efros, R. G. Allakhverdieva. Calculation of marginal anhydrous production rates of imperfect wells according to modeling data // Transactions of VNII, M., Gostoptekhizdat, Issue X, 1957).

The formula for this relationship is:

,

,

where Q _{beg. extract} - the volume of initial recoverable oil reserves located within the radius of the supply of a particular production well, m ³ ;

Q _{acc. calc.} - the estimated value of the cumulative oil production, depending on the operating time, m ³ ;

t - well operation time, months;

To _p - coefficient of porosity,%;

To _ol - the coefficient of permeability, μm ² ;

To _us. - saturation coefficient,%;

ΔP is the difference between the pressure on the supply circuit and the bottomhole pressure, MPa;

μ is the viscosity coefficient, MPa⋅s;

R _to - the radius of the power circuit, m;

h is the thickness of the reservoir, m;

r _s - well radius, m;

To _kin - oil recovery ratio,%.

The graphical dependence constructed according to the formula (1) is a hyperbola, which in the attached figure is designated as a curve - 1.

This dependence characterizes the minimum rate of production (depletion) of oil reserves within the radius of the supply circuit R _{to the} reservoir of a particular production well.

The generally accepted practice of increasing oil recovery in productive formations - EOR is to increase the surface of the formation filtration, which is achieved using modern technologies for drilling horizontal shafts - GS (A.G. Kalinin, B.A. Nikitin, K.M. Solodky and others. Drilling of inclined and horizontal wells. // M., Nedra, 1977) or by using hydraulic fracturing technology - hydraulic fracturing (RD Kanevskaya. Mathematical modeling of oil and gas field development using hydraulic fracturing. // M., Nedra, 1999). (And also: Yu.A. Gutorov, LR Fursova. Technology of enhanced oil recovery through hydrodynamic effects on a productive reservoir: Textbook. Oil and Gas Business., Issue No. 3, 2013).

In cases where these technologies are applied, oil production increases by so many times how many times the length of the horizontal well - L _gf or the length of the fracture fracture - L _{hf is} greater than the thickness h of the reservoir.

Accordingly, when replacing the value h in the formula (6) to the value L _n or L _frac obtain large value Q _{'nakopl.dob. f-cast} - predictive value of cumulative oil production depending on operating time, as many times, how many times the value of _n L or L h _fracturing more power producing formation.

In this case, formula (6) takes the following form:

or

.

.

Substituting the obtained values (8) or (9) into the formula (1), we obtain a dependence characterizing the ratio of the volume of initial recoverable oil reserves - Q _{beg. extract} located within the power radius of a particular production well to a larger predicted value of cumulative oil production - Q ' _{cum. progn} depending on the time of well operation after the application of hydraulic fracturing or hydraulic well according to the formulas:

or

where Q _{beg. extract} - the volume of initial recoverable oil reserves located within the radius of the supply of a particular production well, m ³ ;

Q ' _{acc. progn} - the predicted value of cumulative oil production in the well after hydraulic fracturing or hydraulic well depending on the operating time, in m ³ ;

t - well operation time, months;

To _p - coefficient of porosity,%;

To _ol - the coefficient of permeability, μm ² ;

To _us is the saturation coefficient,%;

ΔP is the difference between the pressure on the supply circuit and the bottomhole pressure, MPa;

μ is the viscosity coefficient, MPa⋅s;

R _to - the radius of the power circuit, m;

L _GS - the length of the horizontal trunk, m;

or

L _grp - fracture crack length, m;

r _s - well radius, m;

To _kin - oil recovery ratio,%.

Horizontal wellbore length - L _n is defined by the technical specification of the horizontal well wiring and the crack fracture length - L _SRC with fracturing or determined by calculation according to the well of Geophysical Research - GIS.

The graphical dependence constructed by formula 10 or by formula 11 is a hyperbola, which is indicated in the attached figure as curve - 2, which reflects the predicted dynamics of oil production of a particular production well from hydraulic wells or hydraulic fracturing.

In practice, the actual accumulated production is Qʺ accumulated production _{. the fact} in the process of quite a long- _term operation of the reservoir is significantly different from the value of the forecast cumulative oil production - Q 'accumulated production _{. prog.}

Such a discrepancy is explained by irreversible changes occurring in the bottomhole formation zone — the bottomhole formation zone under the influence of mudding processes and formation cooling, which requires the necessary EOR to affect the bottomhole formation zone in order to restore the initial permeability — K _pr and oil viscosity — μ.

For the timely commissioning of the EOR to restore the initial properties of the PPP, in the process of operating a particular well according to the actual measurements of production of this well in real time, a graph is plotted of the ratio of the volume of initial recoverable oil reserves located within the power radius of a particular production well - Q _{beg. extracted} , to the value of the actual cumulative production of this well - Qʺ _{cumulative. fact} , which is a curve indicated on the attached figure pos. 3.

To restore the initial permeability - To _pr and the oil viscosity - μ in the PPZ of a particular well, measures are taken to implement the EOR, the time for which is selected based on the data presented on the graph with curves 1, 2 and 3 plotted. To do this, during monitoring of changes in Qʺ _{acc. the fact} , which is carried out in real time with actual instrumental measurements of well productivity, establishes the moment of divergence of curves 3 and 1 (the dot is marked “b” on the graph), which is a sign of the onset of irreversible changes in permeability - K _pr and oil viscosity - μ under the influence of processes and reservoir cooling in the bottomhole formation zone, as a result of which well productivity decreases. The EOR measures carried out at this point in time allow to restore K _pr and μ, as a result, the well productivity increases, which will lead to the convergence of curves 2 and 3 at point “c” on the graph.

With the further operation of a particular well, the mudding process leads to a repeated decrease in K _ol and μ, which is reflected in the graph by the divergence of curves 2 and 1 at point “g”, which is a sign for repeated EOR in order to restore well productivity. A sign of the success of the EOR is the subsequent convergence of curves 2 and 3 at point “d”.

With the further operation of a particular well, the process of divergence of these curves will be repeated at some point “e”, which serves as a sign for the start of the next EOR activities.

Thus, the stages of the divergence and convergence of the curves reflecting the actual and predicted productivity of the well will be repeated during the further operation of the well, which allows timely implementation of EOR measures to restore the properties of the PPP of a particular production well and increase their technological efficiency.

Claims (22)

A method of developing oil fields at a late stage of operation, including the initial period of operation and the final period of operation, which use oil recovery enhancement methods - EOR, characterized in that to determine the criterion for the start of EOR input at each of the selected stages, a reference graphic dependence of the volume of initial recoverable oil reserves located within the power radius of a particular production well to the estimated value of the cumulative oil production of this well Depending on the time of operation, according to the formula:

where Q _{beg. extract} - the volume of initial recoverable oil reserves located within the radius of the supply of a particular production well, m ³ ; Q _{acc. calc.} - the estimated value of the cumulative oil production depending on the operating time of a particular production well, m ³ ; To _{p -} coefficient of porosity,%; To _kin - oil recovery ratio,%; To _us is the saturation coefficient,%; h is the thickness of the reservoir, m; R _to - the radius of the power circuit, m; μ is the viscosity coefficient, MPa⋅s; r _s - well radius, m; To _ol - the coefficient of permeability, μm ² ; ΔР is the difference between the pressure on the supply circuit and the bottomhole pressure, MPa; t is the well operating time, months, when establishing a decrease in the rate of development of reserves of a specific production well, determined according to the constructed schedule, EORs are used in this well associated with an increase in the filtration surface of the bottom-hole formation zone, for example, drilling a horizontal well or hydraulic fracturing, then construct a predicted graphical dependence characterizing the ratio of the volume of initial recoverable reserves oil - Q _{beg. extract} located within the power radius of a particular production well to the predicted value of cumulative oil production - Q ' _{cumulative. prog.} depending on the operating time of a particular production well, subjected to horizontal drilling or hydraulic fracturing, according to the formulas:

or

where Q ' _{acc. prog.} - the predicted value of the cumulative oil production depending on the operating time of a particular production well, subjected to horizontal drilling or hydraulic fracturing, m ³ ; L _GS - the length of the horizontal trunk, m; L _grp - the length of the fracture rupture, m, then, according to the actual measurements of the productivity of a particular production well in real time, a graphical dependence is plotted over time of the ratio of the volume of initial recoverable oil reserves - Q _{beg. extraction} , located within the power radius of a particular production well, to the value of the actual cumulative production of this well - Q '' _{accum. fact} . and combine with previously obtained graphs by the formulas (1, 2 or 3), then establish the time point for the start of the discrepancy of the reference graphs constructed according to formula (1) and the actual change in the ratio of the volume of the initial recoverable oil reserves - Q _{beg. extraction} , located within the power radius of a particular production well, to the value of the actual cumulative production of this well - Q '' _{accum. fact} in time, and which is defined as the moment for the introduction of the corresponding EOR for the impact on the bottomhole formation zone to restore the productivity of the selected well, which will correspond to the position of convergence of the forecast graphs constructed according to formula (2) or (3) and the actual change in the above relations, this basis for the next introduction of the EOR, the subsequent discrepancies in the schedules of the reference and actual changes in these relations over time are chosen.

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