Coal Geology

In most of the coal reserve study isopach maps are produced based on the “Total Seam” or “Total Coal” thickness.  Isopach mapping using “total seam thickness” is preferred for coal seams with little boney materials. For such seams the difference in thickness between the total seam and total coal is minimal.

Deep Mine Workings

Total Coal Thickness = Total Seam Thickness – Combined Thickness of Shale and Bone layers.

For seams with high partings consisting of bone or shaley material, mapping the “total coal” is a better approach.

Some mining companies prefer maps produced in terms of CLEAN TONS PER FOOT (CTPF) advance. For example, most of the Massey Energy’s reserve maps are produced such way. CTPF maps use the “clean coal thickness” data.

Following is a guide of making Clean Ton Per Foot of 25 feet wide entry (commonly 20 Feet of entry width) advance.

The Clean Ton Per Foot (CFTF) depends of the following parameters:

1. Thickness of the total clean coal (TC) (not the total seam thickness)
2. Entry width of the Deep Mine (W)
3. Seam density (D)
4. Recovery factor (R) (usually 95%, not mine recovery). Some prefer not using the recovery factor or using 100% recovery!

Formula for CTPF calculation: CTPF=TC x W x D x R

Unit Conversion:

• Thickness is commonly reported in feet or inches.
• Entry width is commonly reported in feet.
• Seam density could be reported in various units. Commonly g/cc or Tons/acre-foot.
• Recovery factor is unit-less.

To calculate the CTPF map, all of our length data should be in foot.

Converting coal seam density from g/cc to Tons/Acre-inch to Tons/Acre-Foot:

Convert to Tons/Acre Inch

Tons/Acre-inch= Specific Gravity (g/cc) x 113.325
Example1: for a coal seam with Specific Gravity=1.3
1.3 x 113.325=147.3225 Tons/Acre inch

Example 2: for coal seam with Specific Gravity = 1.47 (Anthracite Coal)
1.47 x 113.325= 166.58 Tons/Acre-inch

Tons/ Acre-Foot = Tons/Acre-inch x 12

Using example 1:
147 Tons/Acre-inch= (147 x 12) Tons/Acre-Foot = 1767.87 Tons/Acre-foot

Tons/Cubic-Feet = Tons/Acre-foot % 43560

So, using the above example,
1767.87 Tons/Acre-foot = 1767.87/43560 (Cubic Foot)=0.04058471 Cubic-foot

Note: So, it is just a matter of unit conversion to get your CTPF map. Many times the client may ask for a CTPF map. Remember to get required information on width of entry and coal specific gravity. Calculate CTPF values for each drill hole location for the particular coal seam you are interested in. Then simply contour either by hand or using some simple contouring program.

Tips: If you have prepared a Total Coal contour map (NOT Total Seam map), your CTPF map should be very similar to that one. Think WHY and let me know if you have found the answer.

Example Calculations

Use the attached EXCEL spreadsheet and modify the seam density as per your need to calculate CTPF.

Also, remember that you can find out the total coal thickness from a CFTF maps if the density and entry width are known.

CTPF-Clean Ton Per Foot

Related posts:

1. Minimum tons needed to call a coal deposit to be deep mineable reserve
2. Gamma Ray Geophysical Logging in Coal Reserve Evaluation
3. Coal Geology Report Preparation: Reserve study projects
4. Topographic Maps and Coal Reserve Study
5. Sino Clean Energy, Inc. Commences Production of New 300,000-Ton Capacity Facility in Guangdong