Conversion of XRD Data from Weighting (%) to Volume (%) for Validation of Volume of Clay

 1. What is XRD Data?

XRD data in petrophysics can represent the percentage of mineral types contained in clay mineral groups and non-clay mineral groups. Several types of clay minerals, such as illite, smectite, and chlorite are often found in XRD data. XRD data can be used for more accurate validation when calculating clay volumes.

Example of XRD data validation in clay and shale volume calculation (Yadav et al., 2012)

2. How to Convert XRD Data?

The XRD data in the report is usually in weighted form, therefore it needs to be converted to volume form. The simple basic formula used is:

$\rho =\frac{m}{V}$

$\rho =$ density

$m=$ mass

$V=$ volume 

Sequentially, the steps required to convert XRD data are:

a. Multiplying the percentage of each mineral in weighted form by the total mass of the sample, to obtain the mass of the mineral per type. 

b. Dividing the percentage in weighted form by the density to obtain the volume value

c. Summing up the total volume of clay minerals and the total volume of minerals 

d. Dividing the total volume of clay minerals by the total volume of minerals, to obtain the volume of clay in per cent form

e. Convert the percent value to decimal, ready for use in well data processing applications, such as Interactive Petrophysics.

3. Convert XRD Data

📥 Download XRD Conversion Template

Reference: Yadav, L., Dutta, T., & Sinha, N. (2012). Reconciliation of core and log data analysis in very thin reservoirs of Krishna Godavari Basin, India. Society of Petroleum Engineers. https://doi.org/10.2118/149017-MS

HOW TO MAKE WELLSTICK DIAGRAM?

 A wellstick diagram is a chart that shows the thickness of the markers in each well sorted by interpretation interest. There is a variety of information that we can get from wellstick diagrams such as estimating the direction of deposition and estimating the presence of structures. Wellstick diagrams can be powerful tools for initial geological interpretation. They are often used in reservoir studies, oil and gas exploration, and geological modelling. Usually wellstick diagrams are depicted with stacked bar charts.  

Wellstick Diagram Example

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Customise Wellstick Diagram

Unit of Thickness: Meter (m) Feet (ft)

Number of Wells:

HOW TO DETERMINE GEOTHERMAL GRADIENT?

The temperature beneath the surface increases as the depth increases. The data used to calculate the subsurface temperature includes geothermal gradient, depth, and the surface temperature data from the well being evaluated. The formula used to calculate the subsurface temperature is as follows:

T_d = T_s + (G_g × d)

• T_d = Temperature at a specific depth
• T_s = Surface temperature
• G_g = Geothermal gradient
• d = Depth

However, if the geothermal gradient data is not available, linear regression can be applied to obtain the geothermal gradient value from the temperature and depth data.

Geothermal Gradient Example

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Calculate your Geothermal Gradient and Get the Graph!

Enter the surface and bottom hole temperatures, and depths, to calculate the geothermal gradient and see the graph.

Unit System: Celsius and Meters

Surface Temperature (°C):

Bottom Hole Temperature (°C):

Surface Depth (m):

Bottom Hole Depth (m):

Geothermal Gradient (Celsius and Meter): 14.94 °C/100 m
Geothermal Gradient (Fahrenheit and Feet): 27.19 °F/100 ft