Question

The log data obtained for a particular well section are shown in the following figures. Identify the CORRECT interpretations for different zones.

• A. Zone 1 – shale; Zone 2 – clean sand with oil; Zone 3 – clean sand with gas; Zone 4 – clean sand with water
• B. Zone 1 – clean sand with gas; Zone 2 – clean sand with oil; Zone 3 – clean sand with water; Zone 4 – shale
• C. Zone 1 – shale; Zone 2 – clean sand with gas; Zone 3 – clean sand with oil; Zone 4 – clean sand with water
• D. Zone 1 – clean sand with water; Zone 2 – clean sand with oil; Zone 3 – clean sand with gas; Zone 4 – shale

Hint:

Gamma Ray logs help identify shale content, while Neutron and Density logs are crucial for determining fluid type in clean sands.

Answer 1

The Correct Option is C

In well log interpretation, we analyze the responses from various tools like Gamma Ray, Density, and Neutron logs to characterize the reservoir properties. Based on the provided log responses for each zone, we can deduce the lithology and fluid content in each zone.
Step 1: Interpret Zone 1.
The Gamma Ray log shows high values in Zone 1, suggesting the presence of shale, which is confirmed by the lack of significant response from the Density and Neutron logs. Shale is typically characterized by higher Gamma Ray values and no significant deviations in Density and Neutron logs.
Step 2: Interpret Zone 2.
Zone 2 shows a low Gamma Ray response and a high Neutron and Density response. This indicates a clean sand with gas, where the gas-filled pore spaces cause the Neutron and Density logs to behave in a certain way. The sand is clean with minimal shale content.
Step 3: Interpret Zone 3.
In Zone 3, we observe a typical clean sand with oil response. The Gamma Ray response is low, and the Neutron and Density logs are indicative of oil presence. The high oil saturation causes the Density and Neutron logs to show a specific trend.
Step 4: Interpret Zone 4.
Zone 4 shows a response typical of clean sand with water, as evidenced by the low Gamma Ray and a response from the Neutron and Density logs. The response indicates water saturation in the pores of the clean sand.
Thus, the correct interpretation is Zone 1 – shale, Zone 2 – clean sand with gas, Zone 3 – clean sand with oil, and Zone 4 – clean sand with water, which matches option (C).