EA024788B1 - Method of reservoir hydraulic conductivity determination - Google Patents

Abstract

The invention relates to oil industry, in particular to the hydrodynamic methods of well surveys, and can be used for determination of the reservoir bed parameters. The invention essence is the method of determination of hydraulic conductivity of the oil reservoir bed. The method includes well shutdown at the bottom position of a pump jack plunger. The rate of recovery of bottom hole pressure is monitored with equal intervals, at unstable filtering mode after the well shutdown. The curve of bottom hole pressure recovery is plotted in semilogarithmical coordinates, and for the curve plotting the following formula is used:where P(t) and Pare current bottom hole pressure, and its value at the moment of the well shutdown, respectively; Pis pressure at the reservoir boundary; m, n+1 are constant factors determined using the experimental data. Comparison of the calculated value ξwith the actual value of the reservoir hydraulic conductivity determined using a core shows that the disclosed method allows to determine the reservoir hydraulic conductivity with the maximum error 4.0%.

Description

(57) The invention relates to the oil industry, in particular to hydrodynamic methods for investigating a well, and can be used in determining the parameters of the reservoir. The invention consists in a method for determining the hydraulic conductivity (GP) of an oil reservoir. The method includes stopping the well at the lower position of the plunger of the pumping rock. The rate of downhole pressure recovery is monitored at regular intervals, with an unsteady filtration mode after a well shutdown. The bottomhole pressure recovery curve (CVPC) is built in semi-logarithmic coordinates, and the following formula is used to construct the CVPC:

P (1) = P _k - (P _k -P _s ) exp [- m (1n C) ^{n + 1} ];

where P (1) and P _with - respectively, the current value of the bottomhole pressure and its value at the time of stopping the well; R _to - pressure in the reservoir circuit; w, and + 1 are constant coefficients determined from experimental data. Comparison of the calculated value of ξ ^ρ ερ with the actual value of the hydraulic conductivity of the formation, determined by core, shows that the proposed method allows to determine the reservoir GP with an error of not more than 4.0%.

The invention relates to the oil industry, in particular to hydrodynamic methods for researching a well, and can be used in determining the parameters of the reservoir.

A known method for determining the hydraulic conductivity of a formation (1) is to use a nonlinear theory of the elastic regime of an oil reservoir, which assumes a nonlinear filtration law during unsteady pressure redistribution in the formation and changes in the elastic supply of the formation and fluid associated with starting or stopping a well, changing their operating modes. At the same time, during unsteady filtration in the reservoir, the hydraulic conductivity coefficient changes with a change in the pressure gradient on the well walls and depression on the reservoirs. This method solves the problem of reservoir hydroconductivity (GP) according to the bottomhole pressure recovery curve (HPC) and the curve of the continued flow of fluid into the well, obtained as a result of hydrodynamic research after it has been stopped. In this case, the conditional size of the disturbances in the reservoir region from the well stop is determined depending on the logarithm of the function of the influence of fluid influx into the well on the propagation of the disturbance front in the reservoir, which has a 6th degree polyminal shape. The disadvantage of this method is that it does not show how the GP is determined by HPC.

There is also known a method (2) for determining physical parameters of a formation, in particular a GP, including monitoring the rate of recovery of bottomhole pressure (P _s ) during an unsteady mode of a well after its shutdown, or decrease (P _s ) after putting a well into operation. The method includes recording change P _s at regular intervals, and in accordance with these data, build ARC (Figure 2). Semilogarithmic scale as the plot of increment bottomhole pressure (ΔΡ = P (1) - P _c) against the logarithm of time studies ; where Ρ (ΐ), P _s - respectively, the current value of P _s and the value of P _s before stopping the well from the logarithm of time (1η ΐ) using the tangent method and three points. In this case, the pressure recovery at the bottom of a stopped imperfect well, which is operated before stopping with a constant flow rate, is described by the Horner method (Fig. 1, 2) according to the following formula:

P _{No. 3} = P - u);

where Р „ _з - bottomhole pressure during the well operation time, bar;

P * is the apparent pressure determined by extrapolating the rectilinear portion of the graph P „ _s (ίρ + 4ψί, bar;

t - the slope of the rectilinear section of the graph of pressure changes in the logarithmic coordinates, bar / 1ode, cycle;

Δΐ - current research time, h;

ΐ _ρ is the equivalent production time from the well before closing, h

The main disadvantage of this method is that in most cases, especially for low-production wells, there is no straight section on the final part of the reservoir and pressure recovery is incomplete. This is confirmed by the experimental works presented in the source (4), which are presented in FIG. 3 in the coordinates 1η (ΐ) - ΔΡ, where only a certain section is rectified on the semi-logarithmic HPC. Moreover, the straightening is subjective (Fig. 3, lines 1-3). Referring to FIG. 3, the averaged position of line 1 is just a random result obtained with a given random sample of data. In addition, using only a straight section of the KVD to obtain reservoir characteristics, it is impossible to take into account the influence of the wellbore volume on the process of restoring bottomhole pressure and hydraulic reservoir, which gives an erroneous value ΔΡ, and small 1% errors in determining ΔΡ in zone AB lead to significant errors ξ in determining the hydraulic conductivity of the formation (for example, the spread in the values of ξ is up to 200).

The objective of the invention is to improve the accuracy and reliability of determining GP by HPC.

The invention consists in a method for determining the hydraulic conductivity of an oil reservoir. The method includes stopping the well at the lower position of the plunger of the rocking machine. The rate of downhole pressure recovery is monitored at regular intervals, with an unsteady filtration mode after a well shutdown. A downhole pressure recovery curve is constructed in semilogarithmic coordinates and the entire HPC is described by the following formula:

from until

where Ρ (ΐ) and P _with - respectively, the current value of the bottomhole pressure and its value at the time of stopping the well;

P |. _: - pressure in the reservoir power circuit;

t, η are constant coefficients determined from experimental data.

A comparative analysis of the claimed invention and the prototype showed that the claimed invention is distinguished by new significant features: the method of stopping the well, namely, the position of the plunger of the rocking machine and the method for determining GP, in which the formula developed by the inventors describes the whole HPC. It is known that the volume of the wellbore operated by the pump of the rocking machine affects the process of restoring bottomhole pressure and gas pressure, which leads to the curvature of the pressure transducer built in semilogarithmic coordinates. In all technical solutions known in this field, only the final linearized part of the pressure measuring device is used for calculating the hydraulic reservoir and its non-linear part is neglected, which reflects the influence of the borehole volume on the process of pressure recovery and determining the hydraulic reservoir. Since the value of the bottomhole pressure of the well directly depends on the volume of its borehole and the skin factor of the bottomhole zone of the well, the authors of the invention, in order to increase the accuracy and reliability of determining the wellbore, it was proposed to take into account the influence of the volume of the well and for this purpose a formula for describing the entire pressure drop, which describes and its curvilinear part, i.e. the part that takes into account both the volume of the wellbore and the skin factor of the bottomhole zone of the well. Stopping the plunger of the rocking machine in the lower position allows you to stabilize the filtration process in the wellbore at the time of its closure. With these new significant features, there is no need to use the tangent method or other additional calculations to determine the characteristics of the formation and, in particular, the hydraulic conductivity of the formation.

The invention is illustrated in FIG. 1-4.

FIG. 1 is a Horner graph of a typical HPC well located in a limited formation.

FIG. 2 - curve of ΔΡ versus 1§ §.

FIG. 3 - semi-logarithmic CVD.

FIG. 4 - comparison of experimental data on the HPC with the calculated HPC according to the claimed method.

The method is as follows.

After stopping the well at the lower position of the plunger at equal intervals of time, the experimental data of the change in the bottomhole pressure are taken. The derivative ΔΡ (ΐ) of 1η ΐ is determined.

6Ρ (ί) _ С equating 'Ή ¹¹¹ ) ^4π ^, determine the hydraulic conductivity ξ of the oil reservoir:

_ _ <? _ pg ³

4π (1ηΙ) ^η exp [-nr (1n £) ^{n + 1} ] ω ⁶ PaC '

An example implementation of the method.

At the Kyurovdag field, the Kyursangi OGPD δΑΤΥΛΝ О1ЬЬТО, at well No. 1049, after its shutdown, the experimental points of the bottomhole pressure change were taken to construct the pressure-drop coefficient by the proposed method (Fig. 4).

When the value of P _to -P _with = 2.85 MPa; P _to = 12.5 MPa; η = 2; t = 0.02, it turns out

P (1) = 12.5 - 2.85 exp [- 0.02 (1η ί) ³ ];

Obtaining the derivative with respect to 1η ΐ, there is ά (1ηΐ) = 2.85 · 0.02 · 3 1η (ΐ) 'exp [1.02 (1nG) ³ ] = 0.171 [(1η С) ² ] exp [- 0, 02χ3 (1ηί) ^: taking into account the actual flow rate of well No. 1049 15 m ³ per day, and <ДР (1) _ (2 ₌ 13 910 ~ ⁶ ύ (Ιηί) 4πξ ξ

Thus, the hydraulic conductivity];

= 0.171 (Ιηί) ² exp [- 0.02 (Ιηί) ³ ].

8.13 10 ’

1η (ΐ) 2 exp [- τη (1η ί) ^{η + 1} ] 10 ^b for

1η ΐ = 1 ξ = 8,13 10 ^'11 Ιηί = 2 ξ = 3,22 10 "

1ηί = ξ = 2,09 3 10 ^'11 Ιηί = 4 ξ = 2,47 10'

Ιηί = 5 ξ = 5.53 10

Ιηί = 6 ξ = 23.0 10 ' ₌ 36D2 11 _{= m} ³ / PaS.

κ ^ρ ₆ '

Comparison of the calculated value of ξ ^ ^ρ with the actual value of the hydraulic conductivity of the formation (ξ * 6.02-10 ^-11 ), determined at μ = 5-10 ^-3 Pa-s; B = 10 m; to - determined by core 30.01-10 ^-15 m ² , shows that the proposed method allows with an error of not more than 4.0% to determine the GP of the reservoir.

Claims (1)

CLAIM A method for determining the hydraulic conductivity (GP) of an oil reservoir, which includes shutting down a well, in an unsteady filtration mode after shutting down a well, monitoring the rate of bottomhole pressure recovery at regular time intervals, constructing a bottom-hole pressure recovery curve (CVC) in semilogarithmic coordinates, and determining a GP characterized in that the well is stopped at the lower position of the plunger of the rocking machine and the following formula is used when constructing the HPLC: where Ρ (ΐ) and P _with - respectively, the current value of the bottomhole pressure and its value at the time of stopping the well; R _to - pressure in the reservoir circuit; t, η are constant coefficients determined from experimental data.