Lithology Identification From Well Logs

Assignment

You are the petrotechnical professional responsible for determining the lithologies encountered in a recent exploration well. Prioritize, for your colleagues, the most useful well log crossplots which you will be using in conjunction with integrating the other subsurface data acquired to determine the formation lithologies encountered.

Solution

To determine the formation lithology, the following prioritized crossplots would be integrated with all the other available subsurface data and information:

Well Log Crossplots:

1. Density versus neutron
2. M-N plot
3. Matrix identification (MID) plot
4. Sonic versus neutron
5. Photoelectric factor versus sonic

Frequently Asked Questions (FAQs)

1. What are the key well logs used for lithology identification? The key well logs used for lithology identification include gamma ray, resistivity, sonic, density, and neutron logs.
2. What challenges are faced in lithology identification from well logs? Challenges in lithology identification include lithology ambiguities, complex geology, and data quality issues.
3. How is lithology identification beneficial in hydrocarbon exploration? Lithology identification aids in identifying hydrocarbon-bearing formations, reducing the risk and cost of drilling dry wells during exploration.
4. What techniques can be used to improve lithology identification accuracy? Techniques such as machine learning, integration of multiple data sources, and improving data quality and standardization can enhance lithology identification accuracy.
5. Is lithology identification solely based on well log data? Well log data is a valuable source for lithology identification, but it is often complemented by other geological data, such as core samples or seismic data, to improve accuracy and interpretation.

Assessment

1. In what types of reservoirs are multi-mineral analyses most applicable?

A .Aeolian sandstone reservoirs
B .Gas reservoirs
C .Reservoirs of mixed lithologies and mineralogies
D .Homogeneous reservoirs

2. What is the type of well log crossplot where the Y-axis and X-axis are the slopes of the individual lithology lines on the density-sonic and density-neutron crossplots, respectively?

A .M-N plot
B .X-Y plot
C .A-B plot
D .E-F plot

3. What is the technical term for the value of the SP deflection opposite a thick, clean, permeable formation?

A .Clean spontaneous potential (CSP)
B .Permeable spontaneous potential (PSP)
C .Static spontaneous potential (SSP)
D .Formation spontaneous potential (FSP)

4. Which three elements does a spectral gamma ray separately detect?

A .Potassium, uranium, thorium
B .Potassium, quartz, calcite
C .Quartz, dolomite, thorium
D .Potassium, dolomite, sulphur

5. Which well log data, when interpreted or calibrated, can be useful for lithology indication on their own? (Select all that apply.)

A .Array induction log
B .Spontaneous potential (SP) logs
C .Spectral gamma ray
D .Photoelectric factor

6. On what formation matrix scale are the significant majority of neutron porosity logs run?

A .Limestone
B .Sandstone
C .Anhydrite
D .Dolomite

7. What is the significant, unique advantage of M-N plots over standard X-Y well log crossplots?

A .They make full, simultaneous use of all three porosity logs.
B .They can be used in dry gas zones.
C .They are quicker to generate.
D .They can be used in oil bearing intervals.

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