Degassing Coal Reservoirs
Preliminary degassing of coal reservoirs
The Russian authorities have recently passed a regulation saying that in any new coal mine project where methane content is higher than 9 m3/tons the coal mine reservoir needs preliminary degassing.
The main issue here is safety. Many Russian miners have lost their lives due to underground explosions of methane gas. In May this year on “Black Tuesday a mine blast killed 38 in western Siberia’s Yubileinaya coal mine. Not for the first time grave concerns were raised over mining safety. Both the Russian government and the mining directors are looking for new ways to degas reservoirs.
CBM Partners has the answer.
There has to be a “preliminary degassing of coal bed methane reservoirs”.
CBM Partners has the means and technology to degas the coal beds while at the same time to produce methane gas from the coal bed reservoirs. By drilling wells and producing them we are extracting methane gas and degassing the CBM reservoir at the same time. This of course is happening ahead of mining operations but NOT DURING.
Preliminary degassing of coal bed methane from reservoirs involves three primary steps:
- Step one – Exploratory Analysis
- Step two – Drilling
- Step three – Production
There are many benefits to degassing coal bed methane reservoirs.
- Two products of energy are produced and used for market. Obviously one of them is coal. After a certain period of time (in many cases a minimum of 5 years) coal can be produced, often with the aid of additional gob vents and air blowing techniques. Of course this only takes place after the gas well has extracted its maximum potential for a long a possible, or until a decline in production is seen due to reservoir “falloff”. Reservoir “falloff” is when the well bore shows a significant decrease in methane volume flow rate, and means that the reservoir is ready for mining operations to begin. The first step is to remove any left over methane gas by means of air blowing and gob vents and other mining safety procedures, after which mining operations can begin.
- The second energy product is methane gas.
“Produced” means a product of the reservoir. Example – water, methane, coal dust.
Simultaneous production of CBM and production of “produced water” from the CBM reservoir not only provide methane production for Gas producing companies, but also provide coal mines with two key elements being partially removed ahead of mining operations: methane gas and “produced water”.
Simultaneous production of CBM and the extraction of “produced water” from the reservoirs provide coal mines with the dewatering of the reservoir from “produced water”, degasification of methane gasses, “produced water” that can be used for coal washing, and a dry sweet gas that can be unitized for coal mine usage or sold to others such as steel plants etc…
Safety Issues at Coal Mines
Over the last 80 years, U.S. coal mines have come a long way in increasing safety and decreasing fatalities and accidents. The number of deaths from coal mining in the United States has dwindled over time – from 2,063 in 1930, to 325 in 1960, to 22 in 2005.
Safety recommends the full use of degassing mine reservoirs ahead of mining operations. This is the only known way to assure a better safety environment for mining operations.
Other items to notate:
- Mines need to permit companies such as CBM Partners permission to drill wells “down dip” and ahead of mining operations. In turn this will permit companies such as CBM Partners to place the wells strategically and in the most optimal positions for gas methane extraction.
- Mines need to utilize the extracted produced water for their own usage such as the washing of coal.
- Degassing by drilling CBM wells must be combined with all the other techniques being implemented by law and mining regulations to promote the safest environment possible. Nitrogen flooding would also be considered. Nitrogen could be generated on site and injected into a well near the center of existing wells. The nitrogen would force the methane to other wells for removal. The nitrogen would be lift in the coal and would reduce the chance of an explosion when the mining operation reached that area
- Also, it is important to understand that where the coal bed is going to be mined, then the CBM wells need to be “placed” 5 years ahead of mining operations. Many wells do not produce CBM for one year or more and it takes at least 3-5 years and in some cases 10-20 years to get the most methane extracted from the reservoir. For this reason CBM drilling must be planned well in advance. Careful strategic planning is called for, using a “time-displacement setting.”
- Drilling can be accomplished perhaps with special piping to assist mining operations with the best possible scenarios when reaching the wells area. Other types of tubing and casing can be used even steel casing and tubing with proper mining operation technique on approach and through an abandoned well location.
Pic below shows coal mine – ANTELOPE – and is located within 1000 feet of one of our CBM wells. It’s a real nice picture showing the famous ShipRock Mountain in the background behind the San Juan coal mine!
Apparently these ANTELOPE find our “GREEN GAS” VERY GREEN!
The pic below is one of our coal wells located on our Turks Toast Play and is one of the many wells degassing the methane from the coal mine CBM reservoir. It is located within about ONE MILE of the San Juan Coal mine efforts.
Pic of a well workover near the San Juan Coal Mining operations.
The picture above is a photo of a CBM well located on the Turks Toast Play. This play involves a series of wells which are degassing CBM ahead of San Juan Coal mining operations.
Below is an explanation showing charts, diagrams, and graphs using echometer sound wave technology to show the progress of such wells. The progress shows the rate of extraction of CBM, dewatering reservoir stats and much more.
To follow is an acoustic fluid level sound wave from the well is the Cutie Patutie # 90 S which is located on the Turks Toast Play – A play of wells degassing CBM ahead of mining operations. The well was acquired March 16, 2006. The well was and is being rod pumped. As you can see in the figure below, a pulse of CO2 was fired into the well-bore on 6/27/2006 generating an acoustic pulse represented in the black line in the figure. The peak of the wave is the firing of the CO2 into the well bore. As the sound travels down the casing and is reflected back.
The figure below shows the casing annulus and its comparison to the liquid level in the well bore. The fluid level was 926’ from the surface which turned out to be 323’ above the pump intake.
Here is the Dynamometer card taken from the same session. This next figure below demonstrates what the “down-hole” pump is doing: The results show a full card, running at 6.04 SPM (strokes per minute), with a pump displacement of 156 b/d, and getting 99 % pump fillage.
Next, is an additional test taken on the same well four months later. The fluid level is 829’ from surface that turned out to be 420’ above the pump intake.
The reason for the increase of the fluid level is because of a restriction in the pump.
The card below demonstrates how the pump is not working. The standing valve closes and the pump runs and the traveling valve does not open until it hits some fluid and causing it to close. You are only getting about 8 % of pump fillage, so in turn your pump displacement goes down to 15 b/d of fluid, running at 6.9 SPM.
The next test taken on the same well occurred on 8/16/2007; the technician on the well advised that production had fallen and he had thought there maybe a hole in the tubing. The fluid level was at 999’ from the surface 250’ above the pump intake.
Now the card shows that there is trouble with the well. We have good pump displacement 159 b/d, running at 6.1 SPM, and 99 % pump fillage, but there is not much net lift and our peak pump load is only about 753 lbs, in other test it had been running at 1,102 lbs.
Notice your net lift is not as much as it had been in the past, so it shows as a hole in the tubing. The rig pulling unit was called in to repair the tubing and discovery showed a hole in joint # 37 out of 38 joints, so the pump was working but it was only lifting the fluid slightly above the hole and it would pour back into the casing annulus.
Here is the data from the Cutie Patutie # 90 S, as of August 21, 2007. The well is making 150 mcf/d and 172 b/d of fluid at the time of the shot, the gas had been climbing since the rig got off the well (it had a hole in the tubing). This is a methane gas extraction rate of 54750 mmscfd per year from the reservoir, and a produced water extraction rate 62780 barrels per year from the reservoir.
The fluid level was at 989’ from the surface, 250’ above the pump intake, I used collars to locate the fluid level.
The figure above is a sound wave as is passes through the collars in the tubing of the well. Each echo is the reverberation or echo as the sound wave went by the collars and repeated back to the computer. This wave was traveling at 1,315 ft/sec, this is what we call the acoustic velocity of C02 in methane, in different gasses the speed of sound varies, in most of our coal seam well it ranges from 1,350 ft/sec to 1,450’ ft/sec, and we average the length of each joint and how many collars and determine the fluid level.
The graph below lacks some data it has not been updated and is about 6 to 7 months behind. The well was acquired on 3-16-06. Although missing some current data extraction rates of natural methane gas and produced water show a steady increase. The conclusion shows a distinct amount of gas and fluid being extracted from the reservoir ahead of mining operations. At the current rate of extractions the San Juan Coal mine can expect significant amounts of the gas and water to have been extracted by the time mining operations meet up with the well. It is expected that over 70% of the gas and produced water to have been extracted from the reservoir at current production rates.
Casing Annulus is a term used to describe the bottom hole pipe casing.
Pump fillage is a term used to describe how full the pump gets with produced water when pumping. The greater the pump fillage – the more productive the well.