Data Collection and Analysis
Test and Monitor Existing Ventilation Shafts and Gob Vent Boreholes
A Raven Ridge technician can monitor the total volumetric rate and gas quality of existing vent shafts or gob vent boreholes over time to determine the yearly average rate of methane emissions. This will help to establish a baseline emission rate for possible future greenhouse gas (GHG) emission reduction trading. Monitoring and analysis of the pressure in the shaft or well after shut-in will also provide evidence for characterizing the mine void contacted by the shaft or well and the gas content and permeability of the coal near the mine void.
Manage Coring Program to Determine Existing Gas Content of Remaining Coal
Our Operations Manager can design and implement a core well program to retrieve coal samples at strategic locations relative to the abandoned mine workings that will provide the best gas content characterization over the project area. This is especially important for future (CFD) modeling. Conventional plug testing of other potential gas flow units should also be done at this time.
Determine Gas Content by Canister Testing
The coal retrieved by the core well program must be sampled on the well location and placed in cylinders to determine the methane content of the coal. Raven Ridge can supply the required number of quality control-tested degas cylinders and the expertise to determine the gas content from these samples. Standard coal ultimate analysis is also performed on all samples by an outside laboratory. Gas content samples should be taken at each core hole for all coal seams expected to contribute to the gas production.
Determine the Gas Storage Function with Adsorption Experiments
Fresh samples from the desorption experiments will be used at the Raven Ridge laboratory to determine the gas storage versus pressure function, most commonly expressed in terms of the Langmuir Adsorption Isotherm Equation. One adsorption isotherm should be determined for each coal seam expected to contribute to the gas production.
Determine the Mine Void Volume
Mine void volume can be determined in several ways:
- Mined tonnage kept by the mine operators
- Mined tonnage kept by regulatory agencies
- Analysis of maps of the abandoned workings
- Analysis of ventilation shaft flow data and pressure response after shut-in
- A combination of the above techniques
Our Staff Mining Engineer will determine the mined volume from the existing maps and identify volumes isolated from the main workings by in-mine seals. These areas may have to be exploited individually, therefore a cost effective strategy to optimize the extraction of gas can be developed for the client.
Determine the Extent of Flooding
Areas flooded by water will not yield methane and need to be accounted for when proceeding with resource and reserve calculations. These area affected need to be determined either by drilling and/or hydrologic studies. Documentation by the mine operators may be available relative to the location and rates of water entries and will be incorporated into the study.
Methane Resource Determination
Determine the Volume of Methane Stored in Void Space
The data gathered above will enable our engineering staff to determine the volume of methane stored within the mined-out void space of the abandoned mine.
Determine the Volume of Methane Stored in the Remaining Coal
Raven Ridge geologists and engineers determine the amount of coal remaining in the mined seam(s) as well as the volume of unmined coal likely to be in good pressure communication with the abandoned workings. This is done by reviewing data from the mine operator (exploration data) and other geologic documentation and by reviewing mining methods to determine the possible effect on the remaining unmined coal. This information together with the data gathered on the gas content of the coal seams will provide a reasonable estimate of the original-methane-in-place before establishing a gas recovery project.
Project Specific Production Forecasting
Provide an Initial Estimate of Production Rate and Project Life Using CFD Modeling
A CFD model can be built based on the information gathered in the above procedures. The numerical model can be complex or relatively simple depending on the degree of detail desired. For initial estimates of recovery, a conceptual model that incorporates the coal volume, void volume, current gas content and estimates of coal permeability can be built to estimate the recovery through time given various development scenarios. Because of the large range of uncertainty in these parameter values Raven Ridge recommends that a sensitivity analysis be performed on these variables to determine their effect on the production forecasts of the desired scenarios.
Provide a Refined Forecast of Production Based on Matching Actual Project Performance with CFD Model
Projects that have historical methane production data can use this data to refine the conceptual model by calibrating the production rate and pressure predicted by the model to actual data. This information can help to reduce the uncertainty of the void and coal permeability as well as the size of the void and quantity of coal actually being drained. A more detailed model can also be developed to help understand the effects of known in-mine seals on production.