The Oil Mines at Wietze and Pechelbronn

Introduction

After collection of oil from surface outcrops and seeps, mining of oil is arguably the oldest means of exploiting hydrocarbon resources. Heavy oils, used to caulk ships, were hand dug from shallow pits in the Middle East several hundred years BC. (Lyman et al, p 565). In recent times, two oil fields in Europe have become notable for their development through subsurface mining methods. These fields are Wietze, the birthplace of the USE’s oil industry in the 1632 milieu, and Pechelbronn, located in the Alsace not far from the borders with present day Germany.

Wietze Oilfield

Oil seeps and “Teerkuhlen” (tar pits) in northern Germany were known and used from the middle-ages. The first “oil well” was drilled on behalf of the Hanoverian government from the tar pit at Wietze in 1859, the same year that E.L Drake is credited with starting the modern oil industry in North America (Kauenhowen, p. 472-474). Historical production rates for Wietze (Reeves, p 1578) are shown on Figure 1.

Mining operations started up in 1917, as denoted by (E) on the figure. By the time the field was shut in 1963 (G), some 16 million barrels of heavy oil and 2.7 million barrels of light oil were produced. Of these volumes, 2.6 million barrels of light oil and 9.5 million barrels of heavy oil were produced from wells, with the remainder produced from mining operations. Further discussion of well productivity and potential development scenarios for the USE (by drilling) will be the subject of a second essay; for now, the remainder of this essay will focus primarily on mining operations.

Mining at Wietze

Mining operations for oil recovery at Wietze were initiated in 1917, based on successful efforts at Pechelbronn (Bloesch, p 413). Two shafts were sunk in 1917 for the drainage of oil into the mine galleries (Rice et al, p 407). While production was initially achieved by seepage from the reservoir into the mine galleries, the mining operations were later changed to actual extraction of the oil-bearing sands themselves. The mined sand was brought to the surface where it was washed to extract the oil (Torrey p 589).

Underground extractive mining of oil sands uses methods and technologies common to coal mining (Lyman et al, p4). Mining techniques such as “room and pillar” and longwall mining, with which the USE up-timers would be well familiar, can be employed to recover oil bearing sands.

While the exploitation method for Wietze was initially chosen to be the same as for Pechelbronn, the reservoirs themselves are significantly different. While the Pechelbronn accumulation is a stratigraphic trap, consisting of lenticular sand bodies interbedded with (impermeable) limestones and marls (Clapp, p 1098); the oil at Wietze is found in structurally complex, steeply dipping sandstone beds on the flanks of a piercement-type salt dome (Reeves, pp 1560-1561).

By the time mining operations were shut down in 1963, the mines had produced 964 thousand tonnes (6.8 million barrels) of oil (Zander). Taken over the life of the mine, average daily production corresponding to this volume was over 400 barrels per day.

It is worth noting that over 75% of the oil produced from the mines was through drainage rather than actual extractive mining of the sands themselves. In comparison, conventionally drilled wells produced 1.7 million tonnes (12 million barrels) of oil, nearly 80% of which was the ‘heavy’ oil. Ultimately, while oil mining was significant, the conventional production methods proved more viable, even for the shallower ‘heavy’ oil intervals.

Operational Challenges at Wietze

The oil extracted from the mined intervals at Wietze was found to be of heavy gravity, low in content of light ends such as gasoline (Bloesch p 416). Rice (p 307) reported that the miners at Wietze encountered very little gas released from the oil. Because of the low gas content, Wietze did not experience problems with fire danger.

The mining operations were not without challenges, however. Prolific aquifers are present in the shallow strata overlying the mined intervals. When the original shafts were sunk, it was necessary to freeze the area immediately around the shafts until they could be sealed off (likely with masonry) to prevent flooding the mine workings (Rice et al, p 302).

Additional problems arose from the nature of the sands themselves. The oil sands were reported to be “mushy” and unconsolidated, resembling oil quicksand (Rice et al, p 303). Bloesch reported that the mining operations were quite difficult and expensive due to measures required to keep the soft formations from collapsing the works (Bloesch, p 415). Late in the life of the mining operation, the mine was used for research on different recovery mechanisms (Torrey, p 589; Wiesenthal, p 1313). The ultimate result of the research showed that as much additional oil could be produced by various recovery processes using wells drilled from the surface as could be economically mined, leading to the eventual shut-down of the mining operations in 1963 (Torrey, p 589).

Exploitation of the Wietze oilfield in the Ring Of Fire world

When up-timers from Grantville start development of the Wietze field (Flint), one might expect that their natural predisposition would be toward startup of mining operations as soon as possible. However, there are a number of factors which should be given consideration in our speculation of how the USE oil industry would proceed with development of the Wietze field.

First is finding and delineating the oil deposits. It is unlikely that any person in the USE will actually know exactly where the oil deposits lie. True, there are reported oil seeps at Wietze, however these oil seeps apparently do not directly overlie the producing field, as the first wells drilled from the Wietze tar pit were unsuccessful (Kauenhowen, p474).

Furthermore, unless an up-time essay detailing the subsurface geology of Wietze is available; there will be a significant amount of time spent just building an understanding for the complex structure and stratigraphy present in this area. One can imagine the tensions between Quentin Underwood and his geoscientists. (“I’m paying you friggin’ rock doctors to find my oil, not to drill dry holes and collect data for your Imperial University dissertation!”, bellows Underwood). The geoscientists would need to study drill cuttings from each well in order to create cross sections and maps for the various stratigraphic horizons. Each well is like a piece in an incomplete puzzle. Whether the well is dry or oil bearing, each set of data helps to put the three dimensional image into focus.

As exploration / appraisal wells are drilled, some will strike oil zones. It would follow that these would be put into production as soon as facilities are available to process the oil. Given that the Wietze field has been described as being very complex, there will still likely continue to be a significant fraction of dry holes drilled after the initial discovery. (The actual fraction of dry holes or “non-commercial shows” drilled is unknown, but likely to exceed one third of the total wells drilled after the first discovery well. Further investigation will be the subject of discussion in the subsequent essay dealing primarily with drilling and production issues.)

It likely would follow that management would grow increasingly impatient at the rate of discovery and production which would ensue. Eventually, as the geoscientists can obtain data from increasing number of wells, their understanding of the field will improve the odds of any given well finding the oil reservoirs.

Having a good idea of where the oil bearing zones may lie, the USE oil industry may choose at this point to commence construction of a mine. From a modern oil industry perspective, this is likely not the most cost effective approach, as the early development wells will be quite productive as they will penetrate undepleted reservoir intervals. In our time frame, the Wietze field had been under production for four decades by the time mining operations were initiated in 1917 (Kauenhowen, p 476).

Nevertheless, let us suppose that the management of the USE oil industry takes the decision to commence mining operations. Early commencement of mining operations will mean that the Ring of Fire miners will face two challenges not faced by those in OTL.

The first challenge has to do with pressure. The mine shaft will be at effectively atmospheric pressure, but the oil zone will be initially pressurized at or above the regional hydrostatic gradient (typically 0.45 psi/foot, or 9.9 kPa/meter). Unless the reservoir had been significantly depleted through years of production, accidentally mining blindly into the oil reservoir could have dire consequences.

The second challenge has to do with the gas originally dissolved in the crude oil. While Rice reported that there was very little gas associated with the mined oil, his observations were made after decades of production had the opportunity to deplete the reservoir pressure. The miners will need to take precautions against both the presence of explosive gases and reservoir pressure.

Neither of these challenges are insurmountable. The miners at Pechelbronn successfully developed exploitation methods to mitigate their gas problems; such could also be employed by the Ring of Fire oil miners at Wietze. The main shafts and drifts would be ideally situated outside of the oil bearing zones, within impermeable rock. Under one scenario, drifts (galleries) would be excavated paralleling the oil bearing intervals. Horizontal boreholes, with slotted pipe set in the reservoir zone, would be drilled at intervals along the drift to recover oil and gas and depleting the pressure and dissolved gas until the region of the reservoir rock is safe to enter with a cross drift for excavating the oil sands themselves. In our time line, this practice had been recommended to the miners of Wietze by a mining engineer from Berlin (Rice et al, p. 308)

Safety against fire and explosion danger from methane (and heavier) gases will be critical in the operations. The Wietze miners will need to have access to the Grantville miners’ gas detection equipment. When a section of reservoir is accessed, it will first have to be cleared for gas content, and then periodically re-checked to ensure that the atmosphere stays well below the lower explosive limit.

The structure at Wietze is exceedingly complex, with steeply dipping beds below an unconformity, a major thrust fault plane dipping at 20-30 degrees north through the field, and numerous secondary faults extending from the flanks of the salt dome. It is likely that the miners will face some surprises. There can be instances where a drift may be extended unknowingly across a small fault, into pressurized oil bearing strata.

Assuming normal “drill-blast-muck” operations, the first sign of trouble may be seen when the return from the air drills employed to drill blast holes increases in volume and contains a spray of oil. If the oil flow is noted, and continues after the drill is extracted, it may be necessary to drill a larger exploratory borehole ahead to evaluate and/or drain the interval.

If the drilling of blast holes did not produce notable quantities of oil, and blasting proceeds to open a pressured section of reservoir, the work of the miners will become more interesting. At the mines in which this author has been underground, all blasting was done on a schedule, typically during meal breaks, when all the underground miners were accounted for in safe-haven break rooms. Upon returning to the offending drift, the miners may encounter elevated gas concentrations. (It should be a standard procedure to test for explosive gases when approaching a newly blasted face.) When they reach the site, assuming the gas levels are acceptable, they may find oil flowing into their gallery.

Under such a scenario, the miners will need to rig containment dams and pumps to extract the oil. Additionally, they’ll need to rig ventilation doors and piping to manage any gas which may be present. It will likely be messy, hard, and stressful work until the flow has been properly contained. It will also be likely to divert resources from other mining operations, potentially slowing mine production until the problem area has been secured.

All the while mining operations are proceeding, well drilling and production operations should continue in parallel. Each additional well provides data to better map the sand bodies for future mining. Production will relieve the pressure in the reservoir bodies, reducing the severity and frequency of problems as described above. Additionally, there will be intervals, in particular the light oil zone found in the Triassic below the thrust fault plane (Kauenhowen, p480), which will be more effectively exploited through normal wells’ production. Miners would likely find that zone to be much too gas saturated to safely enter.

The End Products

The hydrocarbons produced at Wietze are moderately-heavy paraffinic-based oils (Rice et al, p302). Fortunately the crudes contain very little asphalt residue, however the downside for the oil quality is that they have very little light ends which may be fractionated into gasoline (Kauenhowen, p 482). Without advanced process techniques such as catalytic cracking, the gasoline production for the Wietze field will certainly be under 5% of the produced volumes.

The bulk of refined products produced at Wietze will likely be kerosene, diesel, lube oil, and fuel oil, based on data presented by Kauenhowen. Using Pechelbronn as an analogue, we can expect that there will be a fair amount of grease and paraffin available from the Wietze production stream as well.

It may be that the low gasoline content of the Wietze crude could motivate the USE to give high priority to oil exploration and / or refining technology. An advantage of expanding through exploration is the option to disperse strategic facilities (refineries and oil fields) to multiple locations.

Pechelbronn

That Wietze would be of significance to the USE is clear. Pechelbronn, however, is a recent addition to USE territory. Why then, would this field be important to the United States of Europe? Historically, in our time frame, the Wietze field is linked to Pechelbronn, for the development of the Wietze field by mining was patterned after successful operations at Pechelbronn. In fact, at the time mining operations were initiated at Wietze in 1917, both Pechelbronn and Wietze were operated by the same company, Deutsche Erdöl Aktiengesellschaft (Rice et al, p. 301).

Additionally, Pechelbronn is well known in the USE timeframe. The earliest reported attempt at commercial development at Pechelbronn was in 1627 (Clapp, p. 1099), only five years prior to the Ring of Fire. As of June 1634 it is part of the USE’s Upper Rhenish province. It sits on the western side of the Rhine valley, some 7 miles south of the present day border between France and Germany. Pechelbronn’s location may make it a strategic asset subject to intense trade negotiations, diplomatic wrangling, and possibly even military action.

Full underground development of Pechelbronn began in 1735, the year following publication of a medical thesis written by Jéan Théophile Hoeffel (Musée de Pétrole de Merkwiller-Pechelbronn website). Mr. Hoeffel set up a small refinery for production of what we now call gasoline. Additional development, first by a Graeco-Russian adventurer, then by a French company, followed in the ensuing few years (Clapp p. 1099).

During this initial phase of development, heavy oil was washed out of sands mined from an adit dug into the hillside. (Bloesch, p 410) In 1745 a pit was dug to a depth of 32′ (Musée de Pétrole), followed by others from which galleries were extended and the oil bearing sand was mined (Bloesch).

As the mine was extended deeper, the quality of the oil was found to improve slightly, becoming less viscous and tar-like. Eventually, in 1866, the quality of the oil was such that it would ooze into the mine workings without needing to mine the sand itself. From that point it became more economical to extract the oil which flowed into the mine galleries. (Bloesch p.410)

Bloesch notes that during this period of mining there was no ventilation system installed. Because of a number of ensuing accidents, the method of mining was changed in 1875. Rather than extending the main galleries through the oil bearing zones, new galleries were located above the producing zones, with secondary slopes drilled into the producing horizons.

The first well was drilled at Pechelbronn in 1813, solely for the purpose of delineation of the deposits to be mined (Musée de Pétrole). Further appraisal drilling followed, until in 1882 one of these delineation wells encountered a lighter oil which flowed to the surface (Bloesch p. 410). Another flowing well came in during 1888, after which mining operations were abandoned the following year (Rice et al, p 278) in favor of wells pumping from horizons between 100 and 600m (300′ and 2000′) in depth (Bloesch, Musée de Pétrole).

Between 1889 and 1913, annual oil production (all from wells) steadily increased from 6,500 tonnes to 49,600 tonnes (Clapp, p. 1101). At a typical value of 7 barrels (bbl) per metric ton, this corresponds to 45,500 bbl and 347,000 bbl in 1889 and 1913, respectively. In terms of daily production averages, the annual values translate to 120 bbl/day and 950 bbl/day.

Increased wartime demand for petroleum products led to resumption of mining operations at Pechelbronn beginning in 1916 with the sinking of a shaft to 150m (490′). Production of oil from the mine workings resumed in 1917, reversing the decline in production seen by the wells (Rice et al, pp. 278, 288). The first shaft was sunk into an area considered exhausted by well production: The miners were surprised to find oil draining into the galleries in this depleted area, eliminating the need to mine and wash the sand (Bloesch p.411). Further mining proceeded for the purpose of exposing productive sand face from which oil could flow rather than actually mining the sand itself. From startup in 1917, annual oil production by mining had reached 38,500 tonnes (270,000 bbl) by 1924.

Operational Challenges at Pechelbronn

Rice and Davis describe the mining operation and characteristics of the sand beds in some detail, based on a visit to the mine by Rice during 1923 (Rice et al, pp 289-301). From this description, it is clear that the most significant problems to overcome were all related to gasses which evolved from the reservoir oil as the pressure was depleted.

The twentieth century mining efforts involved significant efforts towards ventilation and fire/explosion prevention. No electricity was permitted in the mine workings except for the miners’ battery powered hand lamps. Furthermore, the use of hand picks was replaced with pneumatic hammers, as the former were more prone to creating sparks due to a misplaced blow. Mining was entirely performed without the use of explosives. Fire doors and blast doors are present throughout the workings. Despite the precautions, a number of accidents did occur, the first being documented in 1759 due to an explosion from working with open lights. In late 1919 the mine was shut down for a year after a pair of fires and an explosion. It was reopened after completion of a second escape shaft. (Rice et al, p. 300).

Summary

By the time mining was concluded at Pechelbronn in 1954, a total of 425 km of galleries had been excavated. Some 25,000 drain holes (averaging 2.2m in depth) were drilled in order to drain the oil from the productive intervals.

Oil recovery during the period 1917-1954 totaled 955 thousand tonnes (Musée de Pétrole). In more conventional oilfield units, this approximates 6.6 million barrels. Essentially all of this oil recovery was by gravity drainage from the oil bearing sands (Lyman et al, p 565). Ultimately, the Pechelbronn field had produced 3.3 million tonnes of oil (23 million barrels) of oil by the time of its abandonment (Musée de Pétrole).

Acknowledgements

The author would like to acknowledge predecessors in describing the Wietze field and the potential USE development, Iver Cooper and Detlef Zander. Both of these individuals provided significant information used in preparing this essay.

References

Lyman, T.J.; Piper, E.M., and Riddell, A.W.; “Heavy Oil Mining Technical and Economic Analysis”; Paper SPE 12788, presented at the 1984 California Regional Meeting of the Society of Petroleum Engineers, April 1984; p 565-574

Clapp, Frederick G.; “Oil and Gas Possibilities of France”; American Association of Petroleum Geologists Bulletin, Volume 16 No 11, pp. 1092-1143 (1932)

Bloesch, Edward; “Oil Mining”; American Association of Petroleum GeologistsBulletin, Volume 10 No 4, pp. 405-421 (1925)

Rice, George S. and Davis, John A.; “Mining Petroleum in France and Germany”; Petroleum Transactions, American Institute of Mining, Metallurgical and Petroleum Engineers Volume G-25, pp 278-314 (1925).

Musée de Pétrole de Merkwiller-Pechelbronn (Museum of Petroleum at Merkwiller-Pechelbronn)

http://www.musee-du-petrole.com/site%20anglais/page%201.htm

Kauenhowen, Walter; “Oil Fields of Germany”; Bulletin of the American Association of Petroleum Geologists, Volume 12 Number 5, pp 463-499 (1928)

Torrey, Paul D. “The Oil industry of Germany”; Journal of Petroleum Technology, June 1964, pp 589-594

Reeves, Frank; “Status of German Oil Fields“; Bulletin of the American Association of Petroleum Geologists, Volume 30 Number 9, pp 1546-1564 (1946)

Wiesenthal, Ruideger; “The Effect of Light-Gasoline Injection on Oil Recovery by Water Flooding”; Journal of Petroleum Technology, November 1964; pp 1307-1315

Smith, H. Vernon; “Oil and Gas Separators”, Chapter 11 in Petroleum Production Handbook, edited by Thomas Frick; 1962

Francis, C. K.; “The Refining of Petroleum”; American Society for Testing Materials, Proceedings of the Twenty-Fourth Annual Meeting, June 21-24, 1921; pp 1086-1093; through Google Books

Flint, Eric; 1633, (Chapters 11, 12, 26, 34, 52, 53)

Cooper, Iver; “Drillers in Doublets”; Grantville Gazette Volume 4

Zander, Detlef; “Oilfield Wietze”; Memo outlining production history, summarizing production volumes obtained from DEA (“Deutsche Erdoel Aktiengesellschaft”), and describing possible development scenarios for the field.

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