EA032229B1 - Method for determination of oil reservoir permeability - Google Patents

Abstract

The invention is related to oil industry, in particular, to hydrodynamic well surveying, and can be used to determine reservoir filtration characteristics. The essence of the invention is that, for determining oil reservoir permeability, a plot of RP versus volumetric fraction of clay in the reservoir (Z) and a plot of RP versus salt concentration in reservoir water (Z) are modelled and built, optical density of oil (D) is determined, and the RP numerical value is calculated by the following formula:Modelling of the oil reservoir with consideration of a number of affecting features allows higher accuracy in determination of characteristics and a lower degree of the geological risk in substantiation of continuing the development of the reservoir under consideration.

Description

The invention relates to the oil industry, in particular to methods for researching an oil reservoir, and can be used in determining the filtration characteristics of the reservoir. The essence of the invention lies in the fact that to determine the permeability of the oil reservoir model and build a graph of the dependence of the PP on the volume fraction of clay in the reservoir (Ζ _Γ ) and a graph of the concentration of salt in the formation water (Ζ _ο ), determine the optical density of the oil (Add) and numerical value of PP according to the following formula:

Г _g л, d _ol ) = (a - b _{г g} ·) [k ₀ + (K „-K _o ) (1 - exp (~ ^))] ~ b + cD ₀ „

Modeling the formation taking into account the complex of influential features will improve the accuracy of determining the characteristics and reduce the degree of geological risk while substantiating the continued development of the formation in question.

The invention relates to the oil industry, in particular, to methods for researching an oil reservoir, and can be used in determining the filtration characteristics of the reservoir.

There is a method (1) for determining physical parameters of a formation, in particular permeability of a formation (PP), which includes monitoring the rate of recovery of bottomhole pressure (P _s ) during an unsteady mode of a producing well after its installation or reduction of P _s after putting the well into operation. The method includes recording _of changes P at regular intervals, and in accordance with these data build pressure recovery curve (HPC) in a semilogarithmic graphic dependence increment

from the logarithm of the study time (1d 1)

ΔΡ ₂ - ΔΑ

A _R = A ₊ and A + _d1 = ^ - ^ - 1 where _g1 ΐ - rectilinear slope portion of the curve;

And - the segment cut off on the ordinate axis, characterizing the pressure.

Given the obtained value of ΐ determine the permeability by the formula

0.183 @ μ £ ^K M where O is the well flow rate before stopping, m ³ / s;

ΔΡ - pressure increment, Pa;

μ is the viscosity of the reservoir fluid (fluid), Pa-s;

K - permeability, m ² ;

- power (layer thickness), m;

B is the volumetric coefficient of oil.

The disadvantage of this method is that it does not give a reliable assessment of the formation, since it does not take into account the influence on the PP value of the volume fraction of clays in the formation, the salt concentration in the formation water and the thickness of the asphaltenes deposits on the inner surface of the formation capillaries.

A known method for determining the permeability of the reservoir of oil and gas fields (2), including core sampling from reservoir rocks, the use of thermal analysis to identify individual chemical compounds of the reservoir, the establishment of a relationship between the percentage concentrations of minerals and permeability through the use of multivariate correlation-regression analysis to obtain multiple linear correlation equations with subsequent determination of permeability by the following relationship:

K = 1034.0X _x + 80.1X ₂ - 14.4X ₃ + 2.0X ₄ - 1.7X ₅ + 4.8X ₆ - 0.5X ₇ 4-39, ZX ₈ where K is the estimated permeability, mD;

X ₁ - X ₈ - the composition of the deposits, wt.%.

The disadvantage of this method is that it is quite time-consuming and does not give a reliable estimate of the permeability of the formation.

The closest technical solution to the claimed method is a method (3) for determining the permeability of an oil reservoir (PP), including a method for modeling and plotting the dependence of the PP on the volume fraction of clays in the reservoir.

The method allows to evaluate the PP, but only taking into account the volume fraction of clay in the reservoir.

However, the disadvantage of this method is that it does not take into account the influence on the PP value of the salt concentration in the formation water and the content of asphaltenes on the inner surface of the formation capillaries, which leads to a distortion in the assessment of reservoir characteristics when predicting residual oil reserves.

The objective of the invention is to increase the reliability of assessing the characteristics of the reservoirs for the correct choice of strategies for optimizing oil production.

The essence of the invention lies in the fact that to determine the permeability of the oil reservoir model and build a graph of the dependence of the PP on the volume fraction of clay in the reservoir (2 _g ) and a graph of the concentration of salt in the formation water (Ζ _ο ), determine the optical density of the oil (D _op ) and calculate the numerical value of PP according to the following formula:

where Κ (Ζ ₍ , Ζ _ο , Extra), K ₀ - respectively, the actual value of permeability and its value at zero salt concentration in produced water;

To, - the value of permeability in a saturated solution of produced water;

Ζ _Ρ , Ζ _ο , D _op - respectively, the values of the volume fraction of clay in the reservoir, the salt concentration in the formation water and the optical density of oil;

- the characteristic value Ζ _ο , determined by the given figure using the tangent method;

a, b, c, ά - respectively, the coefficients determined on the basis of experimental data.

- 1 032229

A comparative analysis of the claimed invention and the prototype showed that the claimed invention is characterized by new significant features: the determination of the influence of salt concentration in the formation water and the optical density of oil on the permeability of the formation (PP), as well as a formula obtained empirically based on graphs constructed according to experimental data and reflecting the complex effect of Ζ _Γ , Ζ _ο , D _op on PP.

A comparative analysis of the claimed invention with other technical solutions in this area showed that no solutions were found with significant features that match the features of the claimed invention.

To solve this problem, we analyzed the well-known (3) graph of the dependence of permeability on the volume fraction of clay in the formation (Fig. 1) and compiled a table (Table 1) of the dependence, on the basis of which the mathematical regularity of the change in PP from the volume fraction of clay and the direction of flow was revealed , in accordance with which the permeability, depending on the volume fraction of clay in the reservoir, is determined by the formula

Κ (Ζ _Γ ) = a - bg _r and the coefficients a, b, c, определены are determined (Table 2)

Table 1

κ _ν ^ρ x10 ' ³ calculated k, ^f x10 ' ³ actual % to _b ^p K _L ^f actual % 0,0 437 437 0.8 0.875 0.875 0,0 0.1 84.2 76 10.16 0.764 0.78 2.05 0.2 17,2 16.6 3.19 0.714 0.703 1,56 0.3 4.6 4.4 4.34 0.621 0.627 0.9 0.4 1,5 1.43 4.6 0.53 0.53 0 0.5 0.626 0.67 9.5 0.390 0.4062 3.99 0.6 0.35 0.37 5.7 0.252 0.252 0.79 0.7 0.24 0.28 16.7 0.1272 0.128 0.6 0.8 0.205 0.215 4.9 0,039 0,0567 31,2 0.9 0.19 0.193 0.15 0.0081 0.0081 0 E _C p = 5.95 £ cf ^- 4.11

table 2

B C1 ά a ₂ b ₂ from ₂ s · ⁴ 0.494 18.71 10.16 0.81x10 ' ² 3.79 0.3

According to the graph of the dependence of the permeability of the oil reservoir on the salt content (Fig. 2), also obtained by modeling, the nature of which allows us to describe this dependence in the following form:

K (ΖΑ = K _o + (Koo - K _o ) (1 - ^ex P (- |).

In this case, the value of% c is determined by conducting a tangent at the initial or any point of the approximated curve (Fig. 2) of the experimental data, at both points% c has the same value.

The formation permeability is also affected by the thickness of the asphaltene deposits (s) on the inner surface of the formation capillaries. Depending on the content of asphaltenes (Ζ _α ), the value of which is calculated by the well-known (4) formula k = p + and, using the well-known (5) functional dependence of Ζ _α on the optical density of the oil (D _op ); the thickness of the deposition of asphaltenes is calculated by the formula / 1 = p + d * d ** D _0n = P + b <?;

where p and ς are the coefficients determined on the basis of experimental data.

The method is illustrated in FIG. 1 and 2 graphs of the dependence of PP on the volume fraction of clay in the reservoir and the concentration (content) of salt in the formation water.

The method is as follows.

Using a graph of the dependence of permeability on the volume fraction of clays in the reservoir (Fig. 1), determine the permeability by the formula

Κ (Ζ _Γ ) = a - ύΖ _Γ = 1 - 0.91Ζ _Γ

- 2 032229

Then, according to the graph of the dependence of the permeability of the oil reservoir on the salt content in the formation water (Fig. 2), the% value is determined with a tangent drawn at the initial or any point of the approximated curve of the experimental data and the permeability is determined by the formula

Then determine the thickness of the deposition of asphaltenes (I) on the inner surface of the capillaries of the formation depending on the content of asphaltenes (Ζ _α )

Η = ρ + ρ * Ζ _α = -0.05 + 0.047Ζ _α

Using the functional dependence of Ζ _α on the optical density of oil (D _op ) in accordance with the linear dependence given in (5)

Ζ ₃ = 9 ** Extra = 15.67 D _{OP the} formula / ι = ρ + ρ * Ζ _{α is} converted to the following form:

λ = P + <? T * Extra = ρ + ύς = -0.05 + 0.219 D _OD

Taking into account formulas (2) - (4), according to formula (1) with the value Ζ _Γ = 0.1, Ζ _α = 5%, D _op = 0.3, _{ο ο} = 100 g / l, the numerical value of permeability is calculated

K (I _g , g _s , D _op ) = (1 - 0.91 Ζ _Γ ) [zoo + 342 (1 - exp -% -)] + 0.05 - 0.219 D _OD = 364 · 10 ³ μm ² = 364 10 ¹⁵ m ² = 364 mD (milli Darcy)

Comparison of the calculated value of permeability K _p with actual values (see Fig.) Shows that the proposed method allows to determine the permeability of the formation with an error of not more than 5%.

Modeling the formation taking into account the complex of influential features will improve the accuracy of determining the characteristics and reduce the degree of geological risk while substantiating the continued development of the considered formation.

Literature

1. Muravyov V.M. Exploitation of oil and gas fields. - M .: Nedra, 1978, 455 p.

2. RF patent No. 2360108, Θ01Ν 15/08 Method for determining the porosity and permeability of a reservoir of oil and gas fields.

3. Elinbein K., Ringrose F. Modeling of formations taking into account their heterogeneity for optimizing oil production at offshore fields in Norway. // Oil and Gas Technologies, 2006, No. 2, p. 24-28.

4. Markhasin I.L. Physico-chemical mechanics of the oil reservoir. - M .: Nedra, 1977.

5. K.K. 1 §§, Ι.Υ. Ζυο. Mapping and modeling the distribution of viscosity and asphaltenes in deposits with active biodegradation of oil. // Oil and Gas Technologies, 2015, No. 5, 53.

Claims (1)

CLAIM A method for determining the permeability of an oil reservoir (PP), including constructing a graph of the dependence of the PP on the volume fraction of clay in the reservoir, characterized in that it further build a graph of the dependence of the PP on the concentration of salt in the formation water, determine the optical density of the oil and calculate the numerical value of the permeability of the oil reservoir according to the following the formula: where Κ (Ζ ^ Ζ _ο , Extra), K ₀ is the actual value of permeability and its value at zero salt concentration in produced water Ζ _ο ; To _x - the value of permeability in a saturated solution of produced water; - characteristic value Ζ _ς , determined using the tangent method; Ζ _η Ζο, D _op - respectively, the values of the volume fraction of clays in the formation, the salt content in the formation water and the optical density of oil; a, b, c, b - respectively, the coefficients determined on the basis of experimental data. - 3 032229 'Displacement; <Offset vertical flow horizontal flow 0.0 - θ ' ² _. °> ⁴ __0 · θ Y 1.0. Volume fraction of clay (V clay) \ ........... · ........; ........... '___________........ ....... ₂ a ”—1