What are the advantages and limitations of using well logs for sequence stratigraphy?

2 How to use well logs for sequence stratigraphy?

One of the main goals of sequence stratigraphy is to identify and correlate key surfaces that mark changes in relative sea level, sediment supply, and basin dynamics. These surfaces include sequence boundaries, maximum flooding surfaces, and transgressive surfaces. Well logs can help to recognize these surfaces by showing changes in gamma ray, resistivity, or other properties that reflect variations in lithology, facies, and diagenesis. For example, a sequence boundary may be indicated by a sharp increase in gamma ray due to a change from marine to non-marine deposits, or by a decrease in resistivity due to an influx of fresh water. A maximum flooding surface may be marked by a peak in gamma ray due to a high organic content or clay content, or by a minimum in resistivity due to a high salinity or hydrocarbon saturation. A transgressive surface may be shown by a gradual increase in gamma ray due to a fining-upward trend, or by a decrease in resistivity due to a marine transgression.

3 How to build a sequence stratigraphic model using well logs?

To build a sequence stratigraphic model using well logs, you should first select the appropriate logs for your study area and objective. Quality control and calibration of the well logs may be necessary to correct for borehole effects, environmental factors, or measurement errors. You may also need to calibrate the well logs with core data, seismic data, or other sources of information. It is important to identify and correlate the key surfaces using crossplots, histograms, or other techniques to enhance the contrast and resolution of the well logs. Additionally, biostratigraphic or chronostratigraphic data can be used to constrain the age and correlation of the surfaces. After that, you should interpret and map the depositional sequences and systems tracts using facies analysis, paleoenvironmental reconstruction, or other methods. Integrating the well log data with seismic data, outcrop data, or other types of data can improve the spatial and temporal coverage and accuracy of the model.

4 What are the advantages of using well logs for sequence stratigraphy?

Using well logs for sequence stratigraphy has several advantages, such as providing high-resolution and continuous data along the borehole, which can reveal changes and details in the stratigraphy that may be missed by other sources. Additionally, well logs are relatively inexpensive and widely available, particularly for mature basins with many drilled and logged wells. Furthermore, well logs can be used to calibrate and validate other data sources, such as seismic data, core data, or outcrop data. Finally, they can be used to quantify and characterize the reservoir properties and potential of the sequences and systems tracts, such as porosity, permeability, fluid content, and net-to-gross ratio.

5 What are the limitations of using well logs for sequence stratigraphy?

Using well logs for sequence stratigraphy also has some limitations and challenges that need to be considered. Factors such as borehole conditions, drilling mud, tool response, environmental noise, or measurement errors can obscure or distort the stratigraphic signal and require careful quality control and calibration of the well logs before interpretation. Additionally, local variations and heterogeneities in the rocks and fluids can complicate the identification and correlation of key surfaces across different wells and locations, introducing uncertainty and ambiguity in the interpretation. Furthermore, well logs are limited by the spatial distribution and orientation of the wells, which may not capture the full extent of basin geometry and fill. They may also miss important features or events that occur between or beyond the wells, such as faults or unconformities. Lastly, well logs are dependent on availability and accessibility of data which may be restricted by proprietary or regulatory issues, or by data quality or completeness.