Waterjetting 21c - collection in Gilsonite and steep seams

Picking up the debris from a waterjetting operation can be a more expensive part of the process than actually removing the material in the first place. This is particularly true where the material no longer has any inherent value, but is sufficiently toxic that it has to be collected and then properly disposed of. On the other hand, in most aspects of mining, it is the inherent value that is contained in that debris that makes the whole process worthwhile, and in this latter case requires that as much of the material be initially collected as possible. This can be difficult where, for example, gold particles are being produced, since these are heavy and naturally rapidly sink through the water to settle onto the floor where, if this is rough, they can then lie is natural traps that make it hard to re-elevate them and move them to a desired collector.

If one is to continue to move the particles there must be some mechanism that will continue to move the particles to the point that they can be collected. The very condition that makes it difficult to manually mine coal from steeply dipping beds also serves to carry coal and other minerals from those veins, once the material is broken free from the solid.

Consider, for example, the early mining of Gilsonite, which is a naturally occurring hydrocarbon found in thin vertical veins in places such as Utah. It is named after one of its first developers, Samuel H. Gilson.

Figure 1. Pieces of Gilsonite (Metroexpand )

The problem with mining this material is that the dust is very explosive, and remote, safer methods were needed to get men away from the mining process. In 1957 the major American company, American Gilsonite, turned to the use of hydraulic mining. At first the seam was mined using a series of horizontal lifts, with the washed out material and water being collected in drifts that carried it to a pumping station. However, because of the vertical seam, it was easier to used a drill, with lateral jets so that the rotating waterjets mined and flushed the material down into underlying drifts, where it could be collected.

Figure 2. Method for Mining Gilsonite.

By moving the mining tool along the vein the material could be mined out, without miners at the working face, and without the risks of explosion from the conventional mechanical mining methods.

A recent blimp trip over the Bonanza mine shows the results from years of the mining process, as the seam has been removed.

Figure 3. Mined out seam of Gilsonite at Bonanza, Utah. (J.S. and S.W. Aber)

More recently the mine has returned to a mechanical method for mining the material since the customer wanted a dry, rather than a wet product, and, with demand for the material rising, hopefully they will continue to operate safely – the material is now airlifted to the surface. Mining has been restricted to the top 500-ft of the vein.

The hydraulic mining process demonstrated here shows some of the advantages of the use of waterjets in that there are no workers in the mining area, and that the tool is able to remove the mineral without generating the sparks and explosive dust clouds that can be a danger otherwise.

Figure 4. German coal seam side view, showing thickness and angle of slope. (Benedum, W., Harzer, H., and Maurer, H., "The Development and Performance of two Hydromechanical Large Scale workings in the West German Coal Mining Industry," paper J2, Proc. 2nd Int. Symp. Jet Cutting Tech., BHRA.)

Coal mining has some of the same problems, and in Germany the idea was tried (in a slightly modified version) as a way of mining coal. Rather than operate from a drilling rig at the surface, holes were drilled along a very steeply dipping seam. The process was in two parts, evaluating whether it was better to start at the bottom and drill up, or to start at the top and drill down.

Figure 5. Methods tested for bore and mine coal recovery. (Benedum, W., Harzer, H., and Maurer, H., ibid.)

The method where the drill goes down, and then reams back up turns out to be the better approach. The reason for this is that the coal breaks out along natural planes, and these can produce coal pieces that are large enough to block the drilled hole through which all the material must pass, when drilling upwards. This is not a problem when drilling down, since the coal is falling through a much larger space (the mined out volume). This makes it a little more difficult to recover, since it is not confined where it falls into the lower drift. But, by adding a small monitor in the second drift, the broken coal can be lifted back into a slurry that can then be channeled into a flume, and carried away from the working area.

The process was effective, in that it showed that the coal could be mined from one drift to the next, using the method, but it was difficult, because of the varying conditions of the seam over its length, to make the connecting drill holes at an economic speed, and thus to mine the coal at an economic rate.

Figure 6. Looking down to the lower drift from the upper, after mining, with all the coal removed. (Benedum et al ibid)

Note that in the above picture there is little roof collapse into the mined out cavity. This is either beneficial (since it allows all the coal to be removed) or it can be a disadvantage. Other than the safety factor of having a roof hang up until a very large area collapses at one time (where the air blast can do considerable damage), a continual roof collapse as the coal is mined can provide confinement for the water and, hopefully, enough restriction that the water will carry the coal to a collection point.

This was the idea behind the JPL coal mining worm that they proposed some years ago:

Figure 7. The JPL concept for a horizontal jet mining system (Miller, C.G., and Stephens, J.B., Coal Worm: A Remote Coal Extraction Concept, JPL Report 5010-7, December, 22, 1976, Jet Propulsion Laboratory, Pasadena, CA.)

Unfortunately when a coal mine roof collapse occurs the rock breaks into relatively large pieces so that the water can flow away through the pile, without being confined sufficiently to provide the needed motive force to move the coal to the collection point. For that, the system would still need a steeply dipping bed, and I’ll talk more of this and debris collection in future posts.

Waterjetting 5c - flow straighteners

One of the advantages that became clear, even in the early days of waterjet use in mining, was that the jets cut into the rock away from the miner. It was thus a safer method of working, since it moved the person away from the zone of immediate risk. Rock has a tendency to fall when the rock under it is removed, and by using the jets to carry out the removal, so the miner is no longer as vulnerable.

But, in the early days of jet use the range of the jet was quite limited. Part of the reason for this is that the water is generally brought to the working place along the floor. It then has to be raised, through bent pipes, to the level of the nozzle, and then turned so that the water in the pipe is flowing in the direction in which the nozzle is pointing.

Figure 1. Sketch of an early Russian waterjet mining monitor

Even though the pressure of the jet is relatively low, the volume flow rates were high, and the bends leading into the nozzle set up considerable turbulence in the jet, so that the range of the jet was quite limited beyond the nozzle. There are a number of different ways of improving the range of the jet, and I will discuss these in later posts, and many of these techniques apply whether the jet is being used at high volume and low pressure for mining, or at higher pressures and lower flow rates for cutting into materials. But today the technique that I will discuss is the use of flow straighteners.

The two most dramatic instances that I immediately recall for their use were at the Sparwood mine in British Columbia, where the collimated jet was able to mine coal up to more than 100 ft. from the nozzle, and in an underground borehole mining application where a Bureau of Mines commissioned system was able to cut a cavity to more than 30 ft. from the nozzle, which was centrally located.

Collimating jets to get better performance is not restricted to the mining industry. A visit to Disney, for example, will find jumping jets that appear to bounce from place to place (video here) (this one shows the start of the surface waves along the jet, known as Taylor instability, which grow and cause the jet to break up; and if you want to make one Zachary Carpenter has two instructional videos on how they are made. (here and here.)

Essentially, as those Youtube segments show, the flow straightness is achieved by dispersing the water – using a sponge – so that it flows through a large number of drinking straws. These straws act to collimate the water flow, and it emerges as a glassy rod, which even acts as a light path so that light shone down it emerges at the far end. This can be used for a variety of different purposes, other than just for entertainment.

This then is the basic idea behind a flow collimator, although for larger mining flows drinking straws are too weak, and the flow volumes need to be larger. There are various designs that have been used for mining applications. Some of the earlier trials were at the Trelewis Drift mine, where the then British National Coal Board set up an experimental operation.

Figure 2. Sketch of Monitor used in the NCB Trials (after Jenkins, R.W., "Hydraulic Mining" The National Coal Board Experimental Installation at Trelewis Drift Mine in the No 3 Area of the South Western Division, M.Sc. Thesis, University of Wales, 1961.)

A number of different designs were used for the flow straighteners that were located at the nozzle end of the straight pipe section leading into the nozzle:

Figure 3. Designs for the initial flow straighteners used at Trelewis Drift (after Jenkins, R.W., "Hydraulic Mining" The National Coal Board Experimental Installation at Trelewis Drift Mine in the No 3 Area of the South Western Division, M.Sc. Thesis, University of Wales, 1961.)

More recent designs, which vary according to pressure, flow rate and pipe diameter, are a combination of those on the left above, and those on the right. It was such a combination that allowed the Canadian miners at Sparwood to achieve production rates of 3,000 tons of coal per shift as an average over the operation of a mining section.

While the use of flow straighteners does not give any gain over having a long straight section of pipe leading into the nozzle, it can bring the flow condition up to that level in places where the geometry (or the resulting unwieldiness of the pipe) would make the long entry impractical.

One of the more interesting applications of this is in the borehole mining of minerals. Simplistically a hole is drilled, from the surface down to the seam of valuable mineral. Then a specially designed pipe is lowered through the hole with the pipe having a nozzle set on the side. Then, as the pipe rotates, and is raised and lowered, the jet mines out the valuable mineral, which flows to the cavity under the pipe, where it is sucked into a jet pump and carried to the surface.

Figure 4. Schematic of a borehole mining operation (George Savanick)

As I mentioned at the top of the article, the jet cut a cavity some 30 ft in radius, with the jet issuing through a nozzle some 0.5 inches in diameter. In order to achieve this range it was important that the jet was properly collimated, yet the nozzle was set so that there could be no straight section.

Figure 5. Section showing the feed into the borehole miner nozzle. Note the vanes in the section leading into the nozzle (George Savanick).

The turning vanes to achieve the flow collimation were designed by Lohn and Brent (4th Jet Cutting Symposium) to produce a jet equivalent to that achieved had the nozzle been attached to a straight feed.

Figure 6. Turning vanes used to achieve a jet capable of cutting coal to 30-ft from the nozzle. (P.D. Lohn and D.A. Brent “Design and Test of an Inlet Nozzle Device” paper D1, 4th Int Symp on Jet Cutting Technology, Canterbury, BHRA 1978)

Tests of the performance of the nozzle showed that it produced a jet that was at least equal in performance to a nozzle with a straight feed, up to a standoff distance of 45 ft.

In simpler applications the designs do not need to be that complicated, for many simple spraying nozzles, for example, the straightener is made up of a simple piece of folded metal.

Figure 7. Simple flow straightener for use in low pressure and flow applications.

The water has now reached the nozzle, but that is not the end of the story of the feed system, as I will start to explain, next time.

OGPSS - The heavier oils of California's Kern Valley

The Kern River field was first found by a wood cutter and his son, after being asked to drill a well on the Means property, who began digging with a 3-inch auger, below a seep on the Kern River shore; they found oil at a depth of 13-ft. They then dug out a larger hole, using a pick and shovel to create a larger access from higher up the river bank down to that oil level, and then drilled down an additional 30-ft after having fixed the auger to the end of a section of connected pipes. (This was done by manually turning the auger). The well then started flowing, filling the excavation at around three bd. That oil was then taken and used as boiler fuel to power a more conventional drill that, nineteen days later, reached another producing horizon at a depth of 256 ft. and became the first commercial well in the field. By 1904 the field was producing 17.5 million bbl/a year, at which it peaked.

It is important to distinguish the different fields in the region, since there are many fields around Bakersfield, each having different histories and projections for the future. The Kern River field, for example, has produced roughly 2 billion barrels of oil since that first well, with about 476 million barrels estimated as being still available.

Oil Fields in the Kern Valley around Bakersfield, CA with the Kern River field (the first) and the Midway- Sunset (the largest) further identified. (CA Conservation )

The Kern Valley as a region rapidly became the largest oil producing region in the state, particularly since the arrival of the railroad in 1902 made it possible to develop the adjacent Midway-Sunset field, which remains the largest oilfield in the State. As a result of this, by 1904, California was producing more oil than Texas. Times have changed a bit since then, and while the Midway-Sunset claims to remain the largest oil producing field within the lower 48 states (not that this doesn’t include the offshore Gulf), the largest operator in the field now only produces some 29,000 bd.

Gail Tverberg visited the production facilities at the Kern River field back in February 2009 and gave a more detailed description of the field and the work Chevron is doing than I plan to cover today. (There is no point in trying to compete with her excellent report, though the reference to the video of the tour is now here, and the API picture record of her visit seems to have vanished. The oil in the field is heavy, and so steam has been injected through one set of wells, in an increasingly refined operation, to heat the oil in place, so that it will flow more easily to other collection wells where it can be pumped to the surface.

Kern River production process (from Chevron via Gail Tverberg )

The impact of the steam flood on production was dramatic, and has become the main method of production since it was introduced

Impact of steam flood on oilfield performance (Chevron via Gail Tverberg )

Gail also then posted a comment by Jean Laherrère on his estimate of future production from the field, showing its future decline, even with an increased number of wells , to a final estimate of production for the field.

Cumulative oil production estimate (Jean Laherrere )

My own visit to Bakersfield looked at a different way of producing the oil. The Bureau of Mines (as then was) brought large borehole mining equipment to Bakersfield and used pressurized jets of water to mine the oil and sand from around a well in the McKittrick field at a depth of 350 ft, bringing the mix to the surface, where the oil was removed, and the sand then re-injected back into the cavity. (This process was also successfully applied in mining small pods of uranium ore in Wyoming). The method has the advantage of getting all the oil from the formation section that was mined, with relatively little environmental impact, but the closure of the Bureau shut down this program. (Though I retain slides of the operation).

Some of the sand is even closer to the surface, as the initial well showed, so that strip mining of the region to produce the oil in the same way as in Alberta may be economic for the upper layers of some of the fields, were it not from the emissions that would come from the exposed oil and have a negative impact on local air quality.

The continued search for more efficient methods to extract a greater proportion of the remaining oil in place continue through the present. Methods have been proposed where the steam is generated using solar power to heat the steam. A small pilot plant was opened at the beginning of this year to demonstrate the feasibility of the technique, though as yet on too small a scale to produce a significant amount of oil. Higher temperature steam has been generated at other power plants using the same technological concept and so there may be a path forward for this development.

In the same way there are some experiments to use the injection of oxygen and steam as a way of increasing production. The process is claimed to be able to work below the 2,000 ft limitation of conventional steam flooding to a depth of perhaps 3,500 ft. The claim is also that the costs are down at $4/bbl capital cost and $15/bbl operating cost to achieve this enhanced recovery. The process sounds a little too good to be true in the simple form in which it has been presented to date, but it illustrates the possible potential for improving absolute recovery levels above those

Unfortunately the research budgets for finding enhanced ways of producing fossil fuels are not seen as having the critical importance that they may well have. The greater emphasis on advancing renewable forms of energy, and Washington power struggles have meant that energy research is not the hot topic it once was and the interest in developing new techniques to obtain more oil from existing fields is often subsumed by the desire in companies to grow reserves, even if only by purchase instead of discovery or development.

The debate over energy supply and the environmental impact of different sources of power continues to make it difficult to find satisfactory ways to supply California with the energy that its population needs. With the confines within which the oil and gas industry currently work in the state it is hard to see any future gains in production over the levels of today, and the greater likelihood of declining production.