Changes

By using gamma ray log (see figure 3), the user will be able to differentiate the shale (or shaly) or non-shale formation. With the help of spontaneous potential log, the user could give some corrections to the gamma ray log, shale usually has positive SP log reading, when clean (sand, etc.) formation has very negative SP log reading, shaly formation lies between them (not too negative). Resistivity log will also help the user to differentiate the lithology, sandstone or carbonates have high resistivity, the average resistivity value in this well is around 8 Ωm, because of that, formation with higher resistivity than that can be classified as sandstone (if the gamma ray value is low to medium) or carbonates (if the gamma ray value is very low). The last one is the density log (RHOB), with this log, the user could differentiate if the formation is tight or not, also with this log, the user could differentiate between shale-shaly-non shale formation, shale usually has low density when non-shale formation usually has density higher than shale, shaly formation lies between them, if the formation has a very high density log reading, the user may classify that formation as a “tight” formation, when its gamma ray log reading is around 30-50, we may call it as a “tight sandstone” formation, or if the gamma ray log reading is very log (usually below 15 API), the resistivity and density log reading is very high, it could be an anhydrite which is a good cap rock in petroleum system. Table 5 shows the characteristics of some rocks that can be used to differentiate the lithology, but please remember that the reference value is relatively different for every well, so the user should not confused with this issue.

By using gamma ray log (see figure 3), the user will be able to differentiate the shale (or shaly) or non-shale formation. With the help of spontaneous potential log, the user could give some corrections to the gamma ray log, shale usually has positive SP log reading, when clean (sand, etc.) formation has very negative SP log reading, shaly formation lies between them (not too negative). Resistivity log will also help the user to differentiate the lithology, sandstone or carbonates have high resistivity, the average resistivity value in this well is around 8 Ωm, because of that, formation with higher resistivity than that can be classified as sandstone (if the gamma ray value is low to medium) or carbonates (if the gamma ray value is very low). The last one is the density log (RHOB), with this log, the user could differentiate if the formation is tight or not, also with this log, the user could differentiate between shale-shaly-non shale formation, shale usually has low density when non-shale formation usually has density higher than shale, shaly formation lies between them, if the formation has a very high density log reading, the user may classify that formation as a “tight” formation, when its gamma ray log reading is around 30-50, we may call it as a “tight sandstone” formation, or if the gamma ray log reading is very log (usually below 15 API), the resistivity and density log reading is very high, it could be an anhydrite which is a good cap rock in petroleum system. Table 5 shows the characteristics of some rocks that can be used to differentiate the lithology, but please remember that the reference value is relatively different for every well, so the user should not confused with this issue.





Lithology

Gamma Ray (API)

Spontaneous Potential (mV)

Resistivity (Ωm)

[If shale resistivity is 8]

! Lithology !! Gamma Ray (API) !! Spontaneous Potential (mV) !! Resistivity (Ωm) [If shale resistivity is 8] !! Density (gr/cm3)

Density (gr/cm3)

Sandstone

| Sandstone || 30 – 50 || Varies, very negative || 10+ || 2.4 – 2.8

30 – 50

Varies, very negative

| Shaly-sandstone || 50 – 75 || Varies, negative || 8 < Resistivity < 10 || Around 2.4

10+

2.4 – 2.8

| Sandy-shale || 75 – 90 || Varies, negative || Around 8 || Around 2.3

Shaly-sandstone

50 – 75

| Shale || Higher than 90 || Higher than 0 || 8 || Around 2.3

Varies, negative

8 < Resistivity < 10

| Anhydrite || Below 15 || - || Very high, up to 100+ || Up to 2.9

Around 2.4

Sandy-shale

| Coal || Varies || - || Varies || Varies, could be 1.7 – 2.2

75 – 90

Varies, negative

| Crystalline || Below 30 || - || Very high, up to 150+ || Up to 2.9

Around 8

Around 2.3

| Limestone || 20 – 30 || - || Very high, up to 100+ || 2.3 – 2.7

Shale

|-

Higher than 90

Higher than 0

8

Around 2.3

Anhydrite

Below 15

-

Very high, up to 100+

Up to 2.9

Coal

Varies

-

Varies, could be 1.7 – 2.2

Crystalline

Below 30

-

Very high, up to 150+

Up to 2.9

Limestone

20 – 30

-

Very high, up to 100+

2.3 – 2.7

Table 5-Petrophysical properties reference of some sedimentary rocks.

===Petrophysical & Rock Physics Properties Analysis===

===Petrophysical & Rock Physics Properties Analysis===