The Grantville Gazette - Volume 4 Part 35

Europeans first learned of Trinidad's oil in 1510, when Columbus s.h.i.+pped samples back to Spain. Prior to European settlement, Indians used Trinidad's asphalt to caulk dugout canoes, so Sir Walter Raleigh, who used it to repair his s.h.i.+ps on his 1595 visit, was just copying native practice.

The Pitch Lake, now a tourist attraction, is large (95 acres), and 300 feet deep at the center. The asphalt

can be broken out by picks; there is no need to drill.

Of course, there are other, less immediately accessible, sources of oil on the island. Even there, it should not be necessary to drill to great depths to obtain petroleum. In 1857, the Merrimac Company drilled a well to a depth of 280 feet, and struck oil. In 1867, Mr. Walter Darwent found oil on the Aripero estate at a depth of 160 feet. And the next year, the Trinidad Lake Petroleum Company was gratified by the discovery of oil at La Brea at a depth of 250 feet.

In 1902, a well was drilled to 1,015 feet in three months using the "Canadian Pole method of percussion drilling." It produced a small gusher (100 barrels a day).

The first big find was in 1911-12; one well yielded 10,000 barrels per day from a depth of 1,400 feet.

The Trinidadian reservoirs, when intact, have a high gas pressure. That is both good news (initial production can be high) and bad news (the well may blow wild, wasting oil and blasting casing, tools and rocks into the air). It became customary to keep an emergency crew on hand, armed with pumps, shovels and picks.

Venezuela also has a great deal of oil; in 1996 it ranked sixth worldwide in proven oil reserves. Its oil is already known to down-timers; "the first oil exported from Venezuela (in 1539) was intended as a gout treatment for the Holy Roman Emperor Charles." At Guanoco you can find the Bermudez Asphalt Lake, covering 1,100 acres with an average depth of six feet.

In what would have become the United States, were it not for the Ring of Fire, oil and natural gas can be found in the Appalachian mountains (Pennsylvania and West Virginia), in the midcontinent region (Louisiana, Arkansas, Mississippi, Oklahoma, Kansas and Texas), in the Rocky mountains (Colorado and Wyoming), in California, and in Alaska. (There is also oil in Alberta, Canada.) In our own timeline, beginning in 1638, the New Sweden Company established colonies in modern Delaware, New Jersey, Pennsylvania and Maryland. It is possible that a similar venture in the 163x timeline could exploit the petroleum of Pennsylvania and West Virginia, but it is doubtful that it would be economical for them to s.h.i.+p it back to USE. Still, an advantage of an American expedition is that the Grantville Public Library is likely to have specific information (e.g., where and how deep to drill) only about American (especially West Virginia, Pennsylvania and Ohio) oil fields.

Nigeria is also a major oil country (in 1995 it ranked twelfth in proven reserves). In 1632, it was not dominated by any European power, and it is convenient from a transportation standpoint; oil could be s.h.i.+pped by sea all the way from Nigeria to Germany. This isn't as cheap on a per mile basis as pumping it through a pipeline, but it is certainly superior to transporting it by rail from Baku or Ploiesti.

However, an expedition to Nigeria is not for the faint-hearted. The Encyclopedia Americana will tell Grantville residents (and spies) to look for oil in the Niger river delta (first discovered there in the Fifties). What they won't know, until they get there, is that the oil fields are in swampland, and that they will probably need to drill from barges.

Where Is Oil Found?

Oil is a liquid rock. In fact, another name for oil-petroleum-means "rock oil." Oil is formed primarily from marine sediments rich in organic matter (bacterial, plant, and animal remains). These deposits are usually found along the rims of ancient ocean basins, where sea life was most abundant. In these basins, as more and more sediment was deposited, the layers below were compacted, becoming rock. The compaction also resulted in physical and chemical changes in the organic matter, eventually resulting in the formation of oil in the pores of this source rock. Further compaction drove the oil out.

The first criterion for the formation of a useable oil pool is that the oil find its way into a suitable reservoir rock. This must be porous (so it can hold the oil) and permeable (the pore are interconnected, so oil can flow into and out of it). Think of the rock as being like a can filled with marbles. The usual reservoir rocks are sandstones and limestones.

Since oil is lighter than water, it constantly tries to migrate upward and outward. If it not somehow trapped, it will pa.s.s out of the reservoir rock, eventually reaching the surface, evaporating, and becoming lost to the atmosphere. Thus, to have a viable oil reservoir, it is therefore not enough to have a good reservoir rock; one must have an oil "trap."

The trap is formed of a rock which is relatively impermeable to oil. This is sometimes called the cap rock. Shales make excellent cap rocks. Of course, to form a trap, the cap rocks must be positioned to prevent the upward and horizontal movement of the oil in the reservoir rock. This kind of positioning can occur as a result of the folding or faulting of the earth's crust.

The same structures which trap oil can also trap gas, and the same field can produce both fossil fuels.

Prospecting for Oil Even if you know that there is oil in, say, Saudi Arabia, you still have to find it. In searching for oil you must strike a balance between trying to cover a large area and not overlooking any indications that oil might be present.

The simplest approach is that you walk over the land, looking for surface signs of oil or gas. A more sophisticated prospector will make an effort to deduce the subsurface structures by finding places where the underlying rock layers are exposed, such as outcrops, roadcuts, ditches, wells, and mines. By comparing the rock beds at different sites, you build up a picture of how the underlying rock layers are contorted. With enough information, you can identify a potential oil trap. Finally, you can also use geophysical methods to find out what is below the surface. These prospecting methods are discussed in greater detail below.

Oil Signs Early prospectors combed the land for signs of oil, such as oil and gas seeps, mud volcanoes, solid petroleum deposits, burnt clays, and "showings" of oil in water and salt wells. They then drilled nearby. An oil seep or "spring" is a place where oil seeps to the surface. The La Brea Tar Pits in Los Angeles are a good example. The oil may reach the surface in a number of ways. The trap may be eroded to the point at which the reservoir surface "outcrops," that is, is exposed to the surface. Or the oil in a trap may be tapped by a joint (a crack) or a fault in the overlying rock. Either way, the oil reaches the surface and slowly evaporates. Typically, the seepages are tarry (asphaltlike), but a young seepage, or one warmed up by the sun, may become more liquid and flow. In 1864, the chemist Benjamin Silliman, Jr., remarked that in the Rancho Ojai area of California, "the oil is struggling to the surface at every available point and is running down the rivers for miles and miles."

Modern geologists regard oil seeps as proof that an oil-bearing rock is in the region. However, they do not necessarily mark a good place to drill for oil. An oil seep, after all, is a place where the oil is escaping to the surface. It escapes because the trap rock above the oil reservoir has been breached by erosion or faulting. The more prolific the seeping, and the longer it has been going on, the less oil is left to be drilled.

Oil seeps are often a.s.sociated with water springs, possibly because water springs are also formed as a result of outcropping and faulting. The oil forms an iridescent film on the spring water. If the water is stagnant, the oil may acc.u.mulate as a semisolid ma.s.s that remains after the oil evaporates.

Gas can also seep to the surface. Gas seepages are easiest to detect when they occur underwater, forming visible bubbles. Thus, gas seepages are most often spotted in swamps, streams, lakes, and coastal waters. Bear in mind that gas often travels greater distances than does oil.

Escaping oil and gas can catch fire, baking nearby rocks such as clays to give them a burnt appearance. A mud volcano can cover an area of several square miles and be more than a thousand feet tall. It is a cone of mud through which gas escapes, perhaps through cracks in a layer of clay. As the gas rises, it mixes with the clay and ground water to form a mud, which erupts under the pressure of the escaping gas. Mud volcanoes have been found in the Baku region beside the Caspian sea, on the Arakan coast of Burma, on the island of Trinidad, and in Rumania. Gas or oil may be found, not only in a well drilled for the purpose of finding oil, but also in a water or salt well. In major oil producing regions, minor oil showings may be found in nearly every exploratory well. Even if a showing itself is too minor for the well in question to be commercially viable, the driller may hope that the showing indicates that the well is on the edge of a pool.

Anticlines and Geological Mapping Beginning in 1861, geologists speculated that anticlines-rooflike arches (folds) of rock-could, if a layer of impermeable rock (the "trap" layer) overlaid a porous, oil-soaked layer (the "reservoir" layer), prevent the oil from escaping. In 1913, Charles Gould pointed out that all of Oklahoma's big pools lay under anticlines, and the rush to find anticlines began. The Mannington, West Virginia, oil field was one of the first discoveries made as a result of applying this geological knowledge.

The ability of an anticline to trap oil into a commercially exploitable pool is dependent on many factors. Oil is usually not a.s.sociated with large anticlines, i.e., mountain ranges. If the anticline is small, the amount of oil trapped may be insignificant. If the anticline's slopes are shallow, oil may escape, especially if a.s.sisted by a regional dip or by groundwater movement. If the anticline's slopes are steep, there may be little room to drill. If the anticline has been eroded or fractured, oil once trapped there may have escaped. If an anticline were formed too many millennia after oil entered the reservoir layer, the oil may have moved on before the trap was formed.

If an anticline traps gas as well as oil, the gas will be at the top. That means that the center of an anticline may produce gas, while wells on the flanks yield up petroleum.

A young anticline will form a hill-like surface structure. However, the geologist cannot safely a.s.sume that hills are anticlines and that valleys or plains are not. As a result of erosion, an anticline may be leveled, or even become a valley. For that matter, a syncline (the opposite of an anticline) can become a hill.

Therefore, to be sure whether an anticline is present, one must map the subsurface layers of rock. Mapping the subsurface geology is easiest in hill country (especially the western badlands), where there are numerous outcrops and cliff faces. Mineshafts and road cuts can also be revealing. In farmland, information can be gleaned by descending into irrigation ditches and water wells, as well as by studying occasional outcrops. Pits can be dug, or shallow holes (called "strat" holes) drilled, to gain more information. In forests, swamps, and jungles, of course, the rock formations are well hidden, and digging is also difficult.

If an anticline is fully exposed, you can "walk the bed," that is, trace one of its layers as it rises upward, levels off, and then dips back down. However, it is more likely that only bits and pieces of the structure are exposed. The geologist needs to be able to recognize that a rock layer at outcrop A is part of the same bed as a particular rock layer at outcrop B. Hence, specimens will be collected and carefully compared.

Care must be taken not to confuse two rocks that are similar in appearance but laid down in different geological periods. Fossils can be very useful in dating a rock layer. If the beds are correlated correctly, the geologist can compare the height of a bed, relative to sea level, at different points, and thereby discern whether an anticline is present. Unless distorted by later folding or faulting, the bed will be at its shallowest at the point corresponding to the crest of the anticline, and deeper elsewhere.

The ages of outcrop rocks can be an important clue as to the presence of an anticline. If an anticline is present, and has been eroded down to a plain, older rocks will be exposed at the center of the anticline, and younger rocks on its flanks.

Faulting A fault is a break in the continuity of a stratified rock. If you broke a plank of wood, and then stuck something underneath one half so the plank pieces no longer lined up, that would resemble a fault. Faults can be bad news or good news for the petroleum geologist. The bad news is that a fault can break open an anticline, giving the oil a chance to escape along the gap between the fault blocks. The good news is that the faulting can result in an impermeable rock layer being moved alongside a reservoir rock layer, preventing oil from escaping on that side. They can thus help to form a trap and even, in some cases, form traps all by themselves.

Faults can also break up what would otherwise be a single reservoir into several noncommunicating sections. If so, then each section will have to be drilled by at least one well for the entire reservoir to be drained.

Stratigraphic Traps The term "stratigraphic traps" refers to various kinds of traps that are not formed by folding or faulting.

Paleogeomorphic Traps are aptly named, "buried landscapes," and they are derived from ancient coral reefs and sand bars. Corals are invertebrate sea creatures that form limestone skeletons. When the corals die, their skeletons acc.u.mulate to form hill-like coral reefs. In the meantime, their soft parts decay to

form oil, which permeates the porous limestone. If the reef is buried by fine silt, which is compacted to form a fine-grained (impermeable) sedimentary rock, the oil will be trapped in the reef.

Sand bars are often found offsh.o.r.e. These sand bars can act as oil reservoirs if they, too, are covered

over by silt. Ancient sand bars are the origin of Kansas' shoestring sands.

When one layer after another are laid in parallel, i.e., running in the same direction, they are said to "conform" to each other. If strata are eroded, resubmerged, and then covered with the new sediment, chances are that the new layers will have a different orientation. If the old strata were tilted, and the new

strata are horizontal, oil can be sealed off where the old and new layers meet. This is called an "unconformity trap".

The grain size of sediment can change within a rock layer, leading ultimately to a change in

permeability. This can prevent the oil from spreading out within the layer. If the oil-bearing layer is

capped by an impermeable layer, the "facies-change" trap is complete.

A rock layer will not necessarily have the same thickness throughout. Often, sandstones will have a lenslike cross-section, pinching out at the edges. If the overlying rock is impermeable, it will seal off both the top and the flanks of the sandstone, resulting in a viable "pinch-out" oil trap.

It is relatively common for the basic kinds of traps to be combined within a single oil field. An anticline and a fault, or a fault and an unconformity, may work together to trap oil.

Salt Domes Sometimes, a deep-lying bed of salt will be pushed up, perhaps as much as 10,000 feet, to form a great dome. As this salt dome rises, it pushes through the overlying rocks. The rocks to either side will be tilted upward toward the dome, like the wake left by a pa.s.sing s.h.i.+p. Since the salt is impervious to oil, oil rising along one of these tilted layers will stop, and be trapped, when it reaches the dome. Above, the dome, the layers of rock will be folded, forming an upside-down U much like an anticline. Here, too, oil can be trapped.

The first and perhaps the most famous of the salt dome fields was Spindletop, but there are many salt dome fields along the Gulf Coast in Texas and Louisiana. They are also found in the Zechstein basin of Germany.

Geophysical Prospecting In the mid-1920s, gravimeters, magnetometers and seismometers became important tools of the trade. The seismometer is the most effective of these devices, as it can detect a hidden anticline, i.e, one that does not outcrop. To use a seismometer, you must set off an explosion (in effect, an artificial earthquake). When the sound wave strikes the boundary between two rock layers, the sound wave is reflected (and refracted), and you can detect this.

Unfortunately, I don't think seismological prospecting will be practical in the 163x universe within a reasonable time frame. While I have no doubt that a pendulum-type seismograph can be constructed, I doubt that the necessary sensitivity and precision can be achieved.

Even if that barrier is surmounted, we will need to learn how to interpret the seismograms; this is very unlikely to be explained in a public library book. In effect, we will need to rediscover geophysics. It will happen, but not anytime soon.

Percussive Drilling If the oil has seeped to the surface, you may not need to drill a well at all. Depending on whether it is in a liquid or solid state, it can be scooped out or dug out. In percussive drilling, the rock is fractured by repeated "hammer-blows" from heavy cutting tools. Such drilling was first performed in North America in 1808, using a device called a spring pole. This was a sapling bent to hang over the hole. (While the spring pole was initially used to drill for brine, the technique was readily carried over to petroleum extraction.) A rope would be tied to the sapling, hanging over the hole, and the drill would be tied to the free end. A second rope would also be tied to the sapling, but its free end would be tied into a loop. The operator would put his foot in the loop, and kick down, driving the drill into the hole. The natural springiness of the sapling would pull the drill back up, and the operation would be repeated. From time to time, you would replace the drilling tool with a bailer, so you could clear out the acc.u.mulated debris. To facilitate this, a large wooden tripod, with a hanging pulley at the top, was placed over the well hole. This tripod was the precursor of the derrick.

Drilling with a spring pole rig was slow work (one to three feet a day), and spring poles were suitable only for drilling shallow wells, usually less than 300 feet deep. On the other hand, the investment in materials was minimal, and the well could be drilled by one person. This is the drilling strategy that a farmer might use on his or her own land.

Could a spring pole rig be used successfully at Wietze? I can't say for sure, but I think it significant that in 1991, the Petroleum Museum in Wietze issued a commemorative medal that depicts the tripod of a spring pole rig on one side. The spring pole rig was the precursor of the "cable tool" rig, in the sense that both break rock by percussion. The cable tool rig was so called because the drill (the "tool") was at the end of a cable. The cable ran up to a pulley mounted on the cross arm of a mast, and then down to the "tool string" hovering over the well hole. With the cable tool rig, the rock was worn away by the hammering effect of dropping the tool on it. The tool string of the cable rig was raised by animal or steam power. For example, a walking horse or ox could pull a sweep (described by Agricola in 1556) or walk a treadmill. Or a steam engine could turn a capstan. The cable was initially a manila rope, and later steel wire. In 1880, the total weight of the downhole tools was around 2,100 pounds. The drill bit was around four feet long and 140 pounds, and had a chisellike cutting edge. The heaviest tool, the auger stem (over 1,000 pounds), screwed into the bit, and increased the rigidity (and weight) of the drill. Above it were the "jars," which have a lower link that strikes against the auger stem on the upstroke, helping to dislodge (jar") the bit if it is stuck in the rock. The sinker bar, above the jars, has a similar purpose. The topmost downhole tool was the rope socket, which secured the tool string to the cable. The tool string is described in Grantville's copy of the 1911 Encyclopedia Britannica, which also comments on how the different components work together.

Percussive drilling techniques were known down-time. In the Artois region of France, a water well was drilled in 1126 by hammering down a rod with a chisel edge at the other end. (Gies, 112). A similar technique had previously been developed by the Chinese to drill both brine and natural gas wells, and it is a matter of scholarly debate whether the French were innovators or copycats.

I have not found a record of pre-ROF spring pole drilling in Europe. However, spring pole lathes were used in the Renaissance so, once a down-time engineer had the incentive to drill, this would not be a tremendous intellectual leap. However, the spring pole rigs would probably be used only by farmers on their own property, or on long distance expeditions on which you don't want to transport a full drilling rig yet expect that the oil will be found at a shallow depth.

Can the USE build cable tool rigs right away? I a.s.sume that cable is available, but if it isn't, you can still use a st.u.r.dy rope. Grantville residents know how to construct steam engines, which could provide the motive force. But animal power is an alternative. Then you need a connecting mechanism, such as a walking beam, to translate the steam engine's action into a pull-and-relax on the cable. This is well within down-time engineering skills (there are mills in pre-ROF Europe). Finally, you need the parts of the tool string. I believe that if you can cast cannon, you can cast the cable tools.

There are two basic problems with cable tool drilling. First, one has to stop every few feet to replace the tool string with a bailer, to haul out the debris. Second, the tool string could come loose inside the well hole. One then has to fish it out, which is easier said than done. As a result of these factors, the average pre-1940 cable tool drilling rate was about three feet per day, and the maximum rate, about ten feet a day. (Williamson I, 97; Oil Century, p. 93) A modern cable rig can pierce sixty feet a day (Anderson, 129).

It is often stated that cable tool rigs can be used to drill only to 2,000-4,000 feet. However, in 1953, a cable tool rig plumbed a depth of 11,145 feet.

Rotary Drilling In the 1890s, oil drillers began experimenting with a "rotary rig." In this rig, the rock was worn away by the cutting action of a spinning bit. The bit is attached to a hollow drilling rod, and, as the drilling progresses, you attach additional rod sections so you can reach ever further down.

Early in the development of rotary drilling, water was used to remove cuttings and lubricate the bit. It was discovered that the water mixed with the unconsolidated material to form a mud, and that this mud had advantageous effects, such as preventing fluids from flowing into the well and causing a blow out. Consequently, drillers began to deliberately formulate "drilling muds" for use in areas where the local materials were inadequate.

In soft and loose rocks, the rotary rig was much faster than the cable tool rig. For example, in Roaring Twenties East Texas, it averaged about 150 feet a day. Its maximum rate is perhaps 2000 feet a day. However, the cable tool rig remained the only practical equipment for use when exploring hard rock formations, until Howard Hughes, Sr., developed a special hard rock bit for rotary drilling.

Until the USE reinvents the Hughes technology, it could deploy a combination rig, i.e., one that could switch between cable tool and rotary drilling depending on what formations you encountered. In our history, combination rigs became available at the turn of the century. However, to operate a combination rig, you usually need a pair of drillers, one with expertise in cable tool operation, and the other knowledgeable in rotary drilling.

Can we teach down-timers how to do rotary drilling? We might not need to. Mark Kurlansky says that Europeans began using rotary drilling in the salt industry in the sixteenth century. In 1640, he adds, the Dutch drilled 216 feet under Amsterdam, using a rotating bit attached to extension rods, to obtain fresh water (p. 310).

Contemporary Chinese Drilling Techniques In the medieval Chinese version of cable tool drilling, a cast iron drill bit was suspended by a bamboo cable from a derrick. The cable was attached to a rocker (typically twelve feet long); it was lifted when the operator jumped on to the rocker, and dropped back when he jumped off. (Essentially, a human-operated walking beam). The Chinese were sufficiently sophisticated to use both "jars" and fis.h.i.+ng tools.

Chinese borings were on a ma.s.sive scale; in 1089, there were 160 brine wells just in the province of Cheng Tu. There is no doubt that, pre-Ring of Fire, the Chinese drilled wells of respectable depth, although there is some dispute as to just which depth milestone was reached when. A tenth-century source is quoted as saying that Lin-chiung has a "fire" (natural gas) well which is over 600 feet deep. James and Thorpe say that even during the Tang Dynasty (AD 618-906), the wells drilled in this manner were as deep as 850 feet. (Pp. 405-6). In 1944, a drilling engineer, M.T. Archer, was told that at the TzuLiu-Ching field in southwest China, wells over 2,000 deep were drilled "at least 200 years before Drake spudded in," i.e., before 1659. Typical progress was one to three feet a day. According to the sinologist Joseph Needham, the traditional Chinese drilling technique, which was still used in the nineteenth century, could reach a depth of 4,800 feet. The adaptations that the Chinese made to deep drilling included tall derricks, double stranded bamboo cable, and giant rockers. The latter provided synchronized aerobic exercise for six laborers at a time. (Temple, 51-54).

It is presently unclear just how much early seventeenth-century Europeans knew about the Chinese drilling methods as a result of reports from merchants, missionaries and diplomats. If the Chinese knowledge is even hinted at in any of the books that would logically be consulted by someone starting an oil company, it would be wise to question these travelers closely and perhaps even ask them to send agents to China to study the local practices, which might help fill in any gaps in up-time knowledge of drilling.

Drilling Operations Beginning in the late 1800s, oil well supply companies provided plans for rigs, as well as all the necessary parts. They s.h.i.+pped the parts to you, and you a.s.sembled them at the site. If a piece broke, you ordered a replacement by number.

Alternatively, you could buy a portable drilling rig. The early ones were hauled, while some of the later ones were self-propelled. My guess is that a USE oil company will begin by drilling for natural gas locally. Once they have mastered the techniques, they can disa.s.semble the successful rig, and s.h.i.+p all the parts, or at least the essential ones that can't be made locally, to the new site. Before long, the parts of these rigs will be standardized, and the USE will have its own oil well supply companies.

There will usually be several crews, working either three eight-hour s.h.i.+fts or two twelve-hour s.h.i.+fts. A typical drilling crew, for working a single s.h.i.+ft, comprises four workers: the "driller" (the s.h.i.+ft supervisor), the "derrickman" (posted at the top of the derrick), and two "roughnecks" (on the derrick floor). The roughnecks do the grunt work and can be hired locally; the driller and the derrickman need training or experience. Sometimes a rotary rig will have additional crew members, such as a "mudman" to monitor and adjust the drilling mud, and a "motorman" to maintain and operate the power drive. Thus, a rotary drilling crew is often larger than a cable tool one. Indeed, a cable tool rig can be operated with as few as two people (the driller and a "tool dresser"), if need be.

Drillers were expected to keep track of the formations they were drilling through. Even if the well were dry, the information gained from a well log-especially when compared to other well logs and to other geological information-could help locate an oil pool. Well logs were supplemented by occasionally taking "cores": actual samples of the rocks being drilled through. Logging is easier if the well is drilled using cable tools, because the rotary drill bit pulverizes the rock.

Some of the German and Dutch fossil fuel fields are on tidal flats, and so we may have to experiment with near offsh.o.r.e drilling techniques. Piers were used as drilling platforms as early as the 1890s. At Huntington Beach, California, in 1929, directional (slant) drilling was used to reach offsh.o.r.e oil from derricks situated on the beach. Also in the Twenties, dredges were used off the Gulf Coast to create artificial islands for use as drilling platforms, and certain lakes were drilled from barges.

When the drillers are done, they must "complete" the well, that is, the well hole must be "cased" so that it is not infiltrated by water from the formations above the "pay" layer. (In soft formations, you case as you go along rather than wait until you're done. If you fail to strike oil, you then pull up the casing rather than let it go to waste in a dry hole.) If the oil is gus.h.i.+ng out, a manifold called a "Christmas tree" is attached to the wellhead, so that the flow of oil can be regulated. If the reservoir lacks sufficient driving force (gas or water) to push the oil up to the surface, the wellhead will be connected to a pump, which then provides the lifting force. It is not unusual for a single pump to be connected to multiple wells.

Gathering lines collect the fluid from several wells, to a tank battery, in which gas, oil and water are separated. Clean oil is then stored in a stock tank. If you are drilling additional wells nearby (see below), you can use some of the oil as fuel for a suitably equipped drilling rig.

The first well drilled in a "virgin" oil field is called the "discovery" well. Once oil is found, "step out" wells are drilled to determine the limits of the productive territory, and then "development wells" are drilled to a.s.sure efficient exploitation of the discovery.

The ideal s.p.a.cing is such that there is one oil well for every forty acres, or one gas well for every 640 acres. Otherwise, there is "well interference"; one well pirating oil or gas from another. In addition, it is not a good idea to run the wells "wide open"; the total production is reduced.