Relationships Between Reservoirrock Properties and Surface Activity

Figures 10-17 and 10-18 show correlations between the reservoirrock properties and surface activity in the form of average (orthogonal) regression lines in one graph for two regions: (1) Baku Archipelago and South Apsheron Offshore Zone and (2) the Lower Kura Depression. The correlation coefficient (r) is presented in all cases. The correlation coefficients and criteria of their significance (three times the standard deviation sr) are presented in Table 10-21.

From 32 correlations studied, only one differs slightly from zero at a significance level a = 0.05 (when a = 0.01, this correlation is significant). This correlation is the dependence of permeability on the clay content of the rocks of Lower Kura Depression. All other correlations are reliable enough and have a high statistical stability, i.e., they are controlled by geological factors.

Comparison of data for both regions shows that correlations obtained for Baku Archipelago and the South Apsheron Offshore Zone are more stable in general. The relationships between the (1) weighted and relative clay content and surface activity parameters (Q100 and Ada); (2) Q100 and Ada; and (3) porosity and Ada are the most reliable correlations in the offshore areas. Such correlations validate the determination of porosity and clay content using SP logs. The correlations among reservoir-rock properties are good and depend on the similarity in lithology.

In the Lower Kura Depression, correlations between the clay content and porosity, on one hand, and surface activity parameters, on the other

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Figure 10-17. Correlations between reservoir-rook properties and surface activity parameters of rocks of the Productive Series (Modified after Buryakovsky et al, 1986a). 1—Baku Archipelago and South Apsheron Offshore Zone, 2—Lower Kura Depression. Cs = Csh = clay/shale content; Cc = carbonate content.

Figure 10-17. Correlations between reservoir-rook properties and surface activity parameters of rocks of the Productive Series (Modified after Buryakovsky et al, 1986a). 1—Baku Archipelago and South Apsheron Offshore Zone, 2—Lower Kura Depression. Cs = Csh = clay/shale content; Cc = carbonate content.

Figure 10-18. Interrelationship among the reservoir-rock properties, surface activity parameters, and relative clay content of the Productive Series rocks (Modified after Buryakovsky et al., 1986a). 1—Baku Archipelago and South Apsheron Offshore Zone, 2—Lower Kura Depression. n = see p. 315.

(and also between Q100 and Ada) are quite reliable. In general, however, these correlations are less reliable than in the offshore fields. Among other correlations, relationship between porosity and permeability (controlled by a considerable effect of carbonate cement on both parameters) is the most reliable. This is due to wide carbonate cement content range (up to 44%) in comparison with the rocks of the Baku Archipelago and South Apsheron Offshore Zone (up to 26%).

Figures 10-17 and 10-18 show that for the Lower Kura Depression, with the exception of permeability vs. clay content and porosity, all other correlations have a higher position on the figures with respect to the abscissa. This means that, for example, at the same clay content cu ■

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the reservoir-rock properties (porosity ^ and permeability k) and diffusion-adsorption factor (Ada) in the Lower Kura Depression have higher values than for the offshore areas. The curves of k and Ada vs. Q100 exhibit the same behavior (see Figure 10-15). The relationships between the surface activity parameters of rocks and their porosity and clay content (Q100 and Ada vs. Csh and n curves) and their relationships between each other (Q100 vs. Ada, and ^ vs. Csh and n) are very useful.

The average regression lines were approximated by analytical equations. Sixteen correlations between various variables (reservoirrock properties and surface activity parameters) are presented in Table 10-22. These include: permeability vs. porosity, weighted and relative clay content, cation-exchange capacity and diffusion-adsorption parameter. Included is also the effect of carbonate cement content on reservoirrock properties. These equations can be generalized as the following single model:

Empirical coefficients a, b, and c for two regions studied are presented in Table 10-23.

Table 10-22

Correlations Between Surface Activity Parameters and Reservoir-Rock Properties

Table 10-22

Correlations Between Surface Activity Parameters and Reservoir-Rock Properties

Eq. No.

Equation

Eq. No.

Equation

1

$ = a3 - b3Ccarb + C3Ccab

9

Ada = a9 + b9^Csh

2

lgk = a4 — b4Ccarb

10

Q100 = a 14 — bi4n + Ci4n2

3

$ = ai — bilgCsh

11

Ada = —ai5 + bi5n

4

lgk = a2 — b2Csh

12

lgßi00 = ai0 — bi0$

5

$ = a6 — b6n

13

Ada = an — bii$

6

lgk = a7 — b7n

14

Ö100 = a 12 — bi2lgk

7

lgk = a5 + b5$

15

Ada = a13 — b13lgk

8

Öl00 = a8 + b8Csh

16

Ada = —a16 + b16^Q100

See Table 10-21 for definitions of variables

See Table 10-21 for definitions of variables

Table 10-23

Empirical Coefficients of General Equation of Correlation

Baku Archipelago and South Apsheron Offshore Zone Lower Kura Depression

Table 10-23

Empirical Coefficients of General Equation of Correlation

Baku Archipelago and South Apsheron Offshore Zone Lower Kura Depression

i

a

b

c

a

b

c

1

30.0

1.632

0.0237

31.5

1.355

0.0185

2

3.48

0.194

3.0

0.171

3

36.6

15.8

52.6

23.8

4

3.30

0.113

3.78

0.108

5

0.30

0.300

0.35

0.35

6

4.00

6.67

4.2

6.75

7

2.70

0.242

3.01

0.202

8

0

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0

0.48

9

21.1

9.4

17.5

10.0

10

0

5.1

51.1

0

6.5

57.0

11

15.8

78.8

8.1

81.1

12

1.91

0.061

1.96

0.045

13

68.6

2.86

80.0

2.50

14

14.2

4.37

18.0

6.17

15

29.7

10.3

42.4

11.6

16

18.7

13.3

20.7

14.7

Conclusions can be summarized as follows:

1. Based on a large volume of experimental data, correlations among surface activity parameters, reservoir-rock properties, and grain size and mineralogy of terrigenous rocks of the Productive Series of the Azerbaijan part of South Caspian Basin have been established. Also, the diffusion-adsorption parameter and cation-exchange capacity for different rock types have been determined.

2. Correlation equations obtained may serve as petrophysical models while interpreting SP logs, and also planning and carrying out waterflooding operations.

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