RU2641145C1 - Method of gas dynamic investigation of well for low-permeability reservoirs - Google Patents

Abstract

FIELD: oil and gas industry.SUBSTANCE: method of gas dynamic testing of wells for low-permeability reservoirs comprises measuring Qand bottomhole pressure Pof investigated well at n different modes in the i-th, where i=1, 2, 3, …n at arbitrary time intervals τ, between the i-th and the initial research modes. Formation pressure for investigated well is determined at arbitrary moments of time by measuring formation pressure in nearest well located under observation located in the drainage zone of investigated well.EFFECT: increased efficiency when carrying out gas-dynamic tests due to reduced cost of working time for conducting investigations and improved accuracy of obtained results.2 dwg, 2 tbl

Description

The invention relates to the gas industry and can be used in gas-dynamic studies (GDI) of wells in fields with low filtration-capacitive properties.

от дебита (индикаторные кривые), где Р_пл - постоянная величина во время проведения ГДИ. Коэффициент фильтрационного сопротивления А определяют как отрезок, отсекаемый полученной прямой на вертикальной оси. Коэффициент фильтрационного сопротивления В определяют как тангенс угла наклона прямой к горизонтальной оси. Недостаток данного способа состоит в том, что для определения коэффициентов фильтрационных сопротивлений А и В при исследовании скважин необходимо измерять значения пластового давления, что требует много времени при исследовании скважин, вскрывающих коллектор с низкими фильтрационно-емкостными свойствами. Процесс восстановления пластового давления для таких коллекторов составляет от 1 до 13 месяцев, а экспериментальный материал набирается в течение длительного времени - от 1 до 3 лет.The prior art method for the study of gas wells in stationary filtration modes (Gritsenko A.I., Aliev Z.S., Ermilov OM, Remizov VV, Zotov G.A., Guide to the study of wells. - M .: Nauka, 1995, pp. 186-188), in which, based on the example of a well tested in seven modes, the coefficients of filtration resistance A and B are determined by a graphical method. For each mode of well research, the ratio of the difference between the squares of the reservoir is determined from the obtained values (R _pl ) and bottomhole pressures (P _s ) to flow rate (Q) and plot bridges

from the flow rate (indicator curves), where R _PL is a constant during the GDI. The filtration resistance coefficient A is defined as the segment cut off by the straight line on the vertical axis. The filtration resistance coefficient B is defined as the tangent of the angle of inclination of the line to the horizontal axis. The disadvantage of this method is that to determine the coefficients of the filtration resistance A and B in the study of wells, it is necessary to measure the values of reservoir pressure, which requires a lot of time in the study of wells that open a reservoir with low filtration-capacitive properties. The process of reservoir pressure restoration for such reservoirs is from 1 to 13 months, and the experimental material is collected for a long time - from 1 to 3 years.

A known method of gas-dynamic research of a well (see RF patent No. 2527525 C1, publ. 09/10/2014, class E21B 47/00). According to the known method, current measurements of reservoir and bottomhole pressures and gas production rates are carried out at steady-state well operating conditions, followed by normalization of measurement results by conversion to dimensionless units. The normalized coefficients of the filtration resistance of the study are determined and the correction factor is additionally determined. Calculate the normalized flow rate for each mode by the coefficients of filtration resistance without taking into account and taking into account the correction factor. Calculate the rate of deviation of the flow rate for each mode, analyze the results and make a conclusion about the reliability of the measurements in each mode. If the rate of deviation of the flow rate for each mode does not exceed 5%, then the measurement results are considered reliable. Then normalized coefficients of filtering resistances are brought to dimensional view and studies are stopped. If the rate of deviation of the flow rate for one or several modes exceeds 5%, then the measurement results in these modes are considered unreliable and repeated measurements are carried out in these modes with subsequent processing of the measurement results. The known solution is aimed at increasing the efficiency of gas-dynamic research. The known method has the disadvantage that in order to determine the coefficients of the filtration resistance, it is necessary to know the value of the reservoir pressure, the determination of which, in the case of a reservoir with low filtration-capacitive properties, is problematic, since the process of restoring the reservoir pressure during research is long-term, so repeated measurements will lead to a significant increase in the time of the well study, as well as labor and material costs.

The problem to which the invention is directed, is to develop a method for gas-dynamic study of wells that have opened a low permeability reservoir, devoid of this drawback.

The technical result achieved by the proposed solution is to increase the efficiency of gas-dynamic research by reducing the time spent on research and improving the accuracy of the results.

The proposed method of gasdynamic research of a well that has uncovered a low-permeability reservoir is as follows: the flow rate Q _i and bottomhole pressure P _{zi of the} well are _measured at i = 1, 2, 3, ... n different GDI modes during an arbitrary τ _i - time interval between the i-th and initial (at τ ₁ = 0) research modes; formation pressure of the well is assumed identical to the measured formation pressure in the closest observation well located in the drainage zone of the well; the results of measurements of reservoir pressure in the observation well determine the coefficient α _n characterizing the change in reservoir pressure during the well test, solving the equation:

where R _PLN1 - reservoir pressure measured in the observation well at the initial research mode with τ _n1 = 0;

τ _nj is the time interval between the jth (j = 1, 2, 3, ... m) and the initial modes of conducting the well testing of the observation well;

учитывая измеренные дебит Q_i и забойное давление Р_зi, а также что пластовое давление P_плi на i-ом режиме ГДИ скважины равно:coefficient α, characterizing the change in reservoir pressure of the investigated well, is taken equal to the said coefficient

taking into account the measured flow rate Q _i and bottomhole pressure P _zi , and also that the reservoir pressure P _pli in the i-th mode of the well _test is equal to:

,

,

where R _PL1 is the reservoir pressure of the well during the well test in the initial mode (i = 1),

the desired filtration resistance coefficients A and B are calculated.

In FIG. 1, 2 are graphs illustrating embodiments of the invention. In FIG. Figure 1 shows a graph of the calculated values of the logarithm of the reservoir pressure for the observation well of the Astrakhan gas condensate field (lnP _plnj ) versus the time interval between the jth and initial research regimes (τ _n1 ). The measurement results are listed in table 1. In FIG. Figure 2 shows a graph of the dependence of the parameters Y on X, allowing to determine the values of the desired filtration coefficients A and B for well 602 of the Astrakhan gas condensate field. The results of the measured and calculated values obtained during the research are shown in table 2.

When conducting GDI, the assessment of gas inflow to the well under study and flow rate (Q) under stationary conditions is determined from the equation:

where R _PL - reservoir pressure;

P _s - bottomhole pressure;

A and B are filtration resistance coefficients;

Q - well flow rate.

With each mode of operation of the well, as a rule, determine the flow rate, reservoir and bottomhole pressure. Well tests are carried out in several modes, which differ in different flow rates and the corresponding bottomhole pressure values.

The reservoir pressure of the investigated well P _pli for each i-th mode can be represented as follows:

where Q _i - flow rate in the i-th mode;

P _pli - reservoir pressure in the i-th mode;

P _zi - bottomhole pressure in the i-th mode;

i is the mode number, i = 1, 2, 3, ... n of the DRO.

According to the invention, when conducting well tests revealing reservoirs with low reservoir properties, formation pressure is proposed to be determined by measuring it in the closest observation well located in the drainage area of the investigated well.

GDI at the well is as follows.

For the well under study during the well test, the flow rate and bottomhole pressure are measured in n different modes at the i-th arbitrary time intervals τ _i between the i-th and initial research modes. For the initial time interval take the time interval of the first study τ _i = 0. The time interval for conducting studies in each mode is chosen arbitrarily. The number of modes can also be unlimited. For the well under study, a system of equations is compiled that relates the measured flow rates, reservoir and bottomhole pressures:

During the well test, reservoir pressure is also measured in the nearest observation well located in the drainage zone of the well for which the study is being conducted. Measurement of reservoir pressure in the observation well is performed at arbitrary points in time, which may not coincide with the moments of measurements at the well, where the well test is performed. In total, for the closest observation well, m measurements of reservoir pressure Р _{pljj are carried out} at various time points τ _нj .

It is advisable to present the reservoir pressure P _PLJ for the observation well at arbitrary time intervals τ _НJ through the reservoir pressure (P _PL1 ) determined in the first measurement mode (j = 1):

where τ _n1 = 0.

Using the measured values of P _PLJ in time intervals τ _Nj , then determine the value of the coefficient α, which characterizes the change in reservoir pressure of the productive reservoir in the area of the observation and studied wells.

To find the filtration coefficients A and B from the system of equations (3), proceed as follows.

The values of reservoir pressures included in the system of equations (3) are written in the form:

where R _PL1 - reservoir pressure during the study of the well in the first mode (i = 1) in the time interval τ ₁ , taken as the initial (τ ₁ = 0), when conducting well testing;

τ _i is the interval between the i-th and initial research modes.

Substituting in the system of equations (3) the values of R _pli , from the formula (5) we obtain the system of equations:

for which the values of bottomhole pressures P _zi , well flow rates Q _i during studies on each of the n modes of intervals between the research modes τ _i (i-th and first measurements) included in the equations of system (6) are previously measured. The value of the coefficient α is determined based on measurements of reservoir pressure in the observation well and is used to determine the coefficients A and B of the investigated well.

из первого уравнения

системы (6) и подставляя данное выражение во все уравнения этой системы, получим:Expressing

from the first equation

system (6) and substituting this expression in all the equations of this system, we obtain:

We introduce the following notation:

where i = 2, 3, 4, ..., n.

System (7) can be written as

where i = 2, 3, ... n.

The system of equations (10) can be solved by the graphical method or the least squares method. The result of the solution is the determination of the filtration resistance coefficients A and B.

The proposed method of well testing of the investigated well, which revealed low-permeability reservoirs, can be illustrated by the example of its implementation, tested on well 602 of the Astrakhan gas condensate field.

To determine the coefficient α, the reservoir pressure P _{plj was measured} in the observation well at various time intervals τ _nj . For the initial time interval taken τ _n1 = 0. The measurement results are presented in table 1.

Logarithm of both sides of equation (4), we obtain

The calculated lnР plnj _values for the observation well are listed in Table 1, which shows the corresponding reservoir pressure measurements P _plj and data on the time intervals between the jth and initial GDI regimes τ _nj .

According to the graph of lnР _plnj versus τ _нj (Fig. 1), the coefficient α _n for the observation well is determined as the tangent of the angle of inclination of the line to the abscissa axis. The value of α _n can also be found, for example, by the least square method (see Instructions for the comprehensive study of gas and gas condensate wells, edited by Yu.P. Korotaev, G.A. Zotov, Z.S. Aliyev. - M .: Nedra, 1971. - 208 p.). For well 602 of the Astrakhan gas condensate field, the value of α was determined (equal to 7.0 × 10 ^-5 days ^-1 ).

For the well under study, GDIs were carried out in various modes at arbitrary time intervals τ _i between the ith and initial research modes. At the same time, P _zi and flow rate of the investigated well Q _i were measured at each of the modes. The coefficient α characterizing the change in reservoir pressure of the investigated well was taken equal to the coefficient α _n characterizing the change in reservoir pressure in the observation well.

Using formulas (8) and (9), taking into account the obtained value of α, we determined the values of X _i and Y _i , which are also listed in table 2.

Then build a graph of the dependence of Y on X (see Fig. 2).

This dependence (10) is linear. The intersection of the straight line (see Fig. 2) with the ordinate axis allows us to determine the value of the filtration coefficient A (in our case, A = 1.01 MPa ² ⋅ days / thousand m ³ ). The value of the filtration coefficient B is determined as the tangent of the angle of inclination of the line to the abscissa axis (in our case, B = 0.0010 MPa ² / ⁽ thousand m ³ day) ² ).

The values of X _i and Y _i given in table 2, taking into account (10) Y _i = A + BX _i according to the graph (Fig. 2) determine the filtering coefficients A and B, which can also be determined by the least squares method.

Thus, the proposed method ensures the reliability of the results of processing the GDI data of a low-permeable, heterogeneous productive reservoir at stationary conditions, in which the possibility of incomplete restoration of reservoir pressure is allowed without determining its value in the wells where the studies are conducted.

Using the proposed method, a reduction in the number of measurements of reservoir pressure is also provided, and the time for well testing at stationary filtration modes is reduced, which is important when conducting well research in fields having reservoirs with low filtration-capacitive properties and complicated by a long recovery period of reservoir pressure.

Claims (9)

The method of gas-dynamic research (GDI) of the well for low-permeability reservoirs, which consists in measuring the flow rate Q _i and bottomhole pressure P _{Зi of the} well for i = 1, 2, 3, ... n different modes of GDI during an arbitrary τ _i - time interval between i m and initial (at τ ₁ = 0) research modes; formation pressure of the well is assumed to be identical to the measured formation pressure in the closest observation well located in the drainage area of the investigated well; the results of measurements of reservoir pressure in the observation well determine the coefficient α _n characterizing the change in reservoir pressure during the well test, solving the equation:

where R _PLN1 - reservoir pressure measured in the observation well at the initial research mode with τ _n1 = 0; τ _nj is the time interval between the jth (j = 1, 2, 3, ... m) and the initial modes of conducting the well testing of the observation well; further, the coefficient α characterizing the change in reservoir pressure of the investigated well is taken equal to the mentioned coefficient α _n ; taking into account the measured flow rate Q _i and the bottomhole pressure P _zi , and also that the reservoir pressure R _pli in the i-th mode of the well _test is equal to:

where R _PL1 is the reservoir pressure of the well during the well test in the initial mode (i = 1), the desired filtration resistance coefficients A and B are calculated by solving a system of equations:

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