Chapter 3: Petroleum Exploration History and Technology

Chapter 3:
Petroleum Exploration History and Technology

From the moment mankind discovered petroleum seeping from the earth's surface we have sought after ways to put it to use - early on as pitch for canoes and fuel for lamps. But modern methods of drilling for oil revolutionized the use of petroleum, and it all began in Titusville, Pennsylvania as a result of the determined efforts of Colonel Edwin Drake.

Cable–Tool Drilling

While petroleum oil was known prior to this, there was no appreciable market for it until it was discovered to be a good source of kerosene. As a result, Drake's employers were on a quest to establish an enterprise that would fuel kerosene lamps if only they could unearth enough oil.

With oil seeping at the surface as an indicator of more below, Drake decided to drill for the oil using an old steam engine to power the drill. In 1857 and again in 1858, Drake had limited success, extracting a maximum of 10 barrels of oil per day. This, however, was not enough to a commercial enterprise. When attempts to dig huge shafts in the ground failed due to water seepage, Drake decided to drill in the manner of salt drillers using a cable–tool system.

In cable–tool drilling, the drill bit is suspended in the hole by a rope or cable. By means of a powered walking beam operated by a steam engine, the cable and attached bit are raised and then allowed to drop. This up and down motion is repeated again and again. Each time the bit drops it hits the bottom of the hole and pierces the rock; however, there were two features of the cable–tool method that were unfavorable. First, the drilling had to be stopped often and the bit pulled up so that cuttings of chipped rock could be removed. Secondly, it could not drill soft rock formations because the splintered rock fragments tended to close back around the bit and wedge it in the hole.

The Drake well was dug on an artificial island on Oil Creek. It took some time for the drillers to get through the layers of gravel. At 16 feet, the sides of the hole began to collapse and despair was setting in. It was at that point that he devised the idea of a drive pipe. This cast iron pipe consisted of 10 foot long joints. The pipe was driven down into the ground. At 32 feet they struck bedrock. The drilling tools were then lowered through the pipe and steam was used to drill through the bedrock. The going, however, was slow. Progress was made at the rate of just three feet per day. On August 27th his drill bit had reached a total depth of 69.5 feet At that point the bit hit a crevice, and the men packed up for the day. The next morning, Drake's driller, a blacksmith named William Smith, looked into the hole. He was surprised to see crude oil rising up the pipe. Drake was summoned and the oil was brought to the surface with a hand pitcher pump. The oil was collected in a bath tub. After Drake's breakthrough success, many flocked to Pennsylvania to drill for oil, and Drake became a fixture in history. The cable-tool drilling method was in common use until the 1920's.

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Rotary Drilling

The first rotary drilling rig was developed in France in the 1860's. However, it was seldom used because it was erroneously believed that most petroleum was under hard-rock formations that could be easily drilled with cable-tool rigs. Then, in the 1880's, two brothers named Baker were using a rotary drill to locate water in the soft rock formations of the Great Plains. They used a rotary drilling system that employed a circulating fluid to remove the rock cuttings. Later, the system was successfully used in Corsicana, Texas where drillers searching for water discovered oil in the unconsolidated soft rock structure.

Rotary drilling operates by pressing the teeth of the drill bit firmly against the rock and turning, or rotating it. Simultaneously, a fluid, usually a liquid including clay and water called drilling mud, is forced out of special openings in the bit at high velocity. This forces the mud and rock chips away from the drill bit and back up the casing and finally out into a holding tank.

In 1899, Patillo Higgins, living near Beaumont, Texas, observed the flammability of the gas springs on his property and concluded there must be oil under the enormous hill on his land Spindletop Lucas oilwell named Spindletop. He placed an advertisement in the paper searching for a driller to find oil on his property. It was answered by Captain Anthony Lucas who made a deal with Higgins to drill. Lucas made a lease agreement in 1899 with the Gladys City Company and a later agreement with Higgins. Using a rotary system, Lucas drilled to 575 feet before running out of money. After securing additional funding, Lucas continued drilling and made history. On January 10, 1901, at a depth of 1,139 feet, what became known as the "Lucas Gusher" blew oil over 150 feet in the air at a rate of 100,000 barrels a day. It took nine days before the well was brought under control. Spindletop was the largest gusher the world had ever seen and catapulted Beaumont into one of the United States' largest oil-fueled boomtowns. Beaumont's population of 10,000 tripled in three months and eventually rose to 50,000. Speculation led land prices to increase rapidly. By the end of 1902 over 600 companies were formed, including ExxonMobil and Texico, and 285 active wells were in operation.

In the rush to develop Spindletop, Howard Hughes, Sr. patented a two-cone rotary rock drill bit that revolutionized drilling. It was unlikely that he actually invented the bit, but his law training helped him understand that the patent was the most important part of the financial life of any invention. This design has been improved over the years, but remains the most widely used system today.

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Seismography

Seismic surveys give petroleum explorers details on the structures and strata beneath the surface of the land. Data is collected by creating and then recording vibrations and then depicting them on a seismogram. This data give geologists a dimensional view of the boundaries between rock layers.

While seismographs were in use as early as 1841, they then focused exclusively on measuring earthquakes. Then, during World War I, Dr. L. Mintrop, a German Scientist invented a portable seismograph which he set up in three places facing the Allied lines. When an enemy artillery piece fired, he used the vibrational data to calculate the location so precisely that that the Germans could wipe out the gun with one try.

Chart courtesy of Earth Science World and Exxon-Mobil

After the war, Mintrop reversed the process by setting off an explosion at a known distance and, by measuring the time of subsurface shock wave reflections, he was able to estimate the depth of rock formations. After proving his theories in the field, Mintrop formed Seismos, the first seismic exploration company. Seismos was hired by the Gulf Production Company and quickly proved the effectiveness of the tool in locating likely oil reservoir formations. Later improvements developed in the 1960's allowed 2-D subsurface imaging, and, by the 1980's, 3-D seismic was introduced.

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Well Logging

Some time in the early 1920's, drillers began keeping wells logs to record the depth, kinds of rocks, fluids, and anything else of interest that might occur during the drilling process. Log data is useful for comparison purposes when considering nearby wells that might be drilled later or wells that may have been drilled in the past. More useful are core and cutting logs. This data comes from core samples that are taken during drilling and by examination of the drilling chips that are brought to the surface in the drilling mud. The core sample contains the most information since it is a slender column of rock that shows the sequence of rock layers as they appear in the earth. A special core bit is used to cut and bring up the sample. Once the sample reaches the surface it is packaged and sent to a laboratory for analysis. Core samples can provide a clear understanding of the strata's porosity, permeability, lithology, fluid type and content, as well as geological age. This information helps determine the oil-bearing potential of the sampled beds.

Well log comparison

As technology advanced, electric logging came into widespread use. An instrument called a sonde is lowered into the bore on a conductor line, or electric wire line. The sonde measures and records electrical, radioactive, or acoustic properties of the various drilled formations. The sonde transmits its information up the wire to a recorder.

A Spontaneous Potential (SP) log records the electrical currents that flow in rock formations. Most minerals are non-conductors of electricity when dry. However, some, like salt, are excellent conductors when dissolved in water. As drilling fluids invade a permeable formation, spontaneous potential causes weak current to flow from the un-invaded saltier rock into the invaded rock. The SP log can be visually analyzed to understand formation bed boundaries and thickness, as well as the relative permeability of formations.

Resistivity logging devices measure and record the resistance of a formation to the flow of electricity. High saltwater saturation lowers resistivity, while oil and gas raise resistivity, since hydrocarbons are poor conductors. Common resistivity logs include the lateral focus log, the induction log, and the microresistivity log.

Radioactivity logging devices measure natural and induced radioactivity. Gamma ray logs record the emissions of naturally radioactive elements in formation sediments. Since these elements leach out of porous and permeable rock, a gamma ray logging device can identify impermeable formations such as shale and clay-filled sands. Another type of radioactive log is the neutron log, which emits radiation from the sonde, bombarding the rock around the wellbore. Readings can provide useful information about water, hydrocarbon saturations, salt content, rock types and porosity.

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Acoustic logging devices are also called sonic logs and operate on the understanding that sound travels better through dense rock than through more porous rock. Correlating data provided by several different logging methods can provide a clear picture of the strata of interest.

It's important to note that, due to the expense of logging a well and the overlapping information provided, not all types of logs are run on each well being drilled.

Formation Test Data

As more wells are drilled and logged in a given field, it becomes easier to predict and determine where the productive petroleum reservoir will extend and end. However, with a new discovery, it is imperative to take some pressure readings to help estimate the lateral extent of the reservoir. Pressure can be taken through a DST or drill-stem test or wireline. Both involve isolating the potential reservoir to recover a sample of fluids and take pressure readings. What is recovered and the pressure data gained from the sample helps determine if a commercially viable reservoir has been found

Offshore Drilling

By the 1930's petroleum exploration companies realized that oil and gas reservoirs existed in shallow waters offshore. But the problem remained how to drill when your drilling rig must float and at the same time stand steady against any heavy wave action. The solution was to create a drilling platform a system of legs or supports that would anchor or hold the platform in place - eventually these type of rigs became know as submersibles.

Drilling Barge The earliest form of submersible rig was a posted barge. It consisted of a barge with several steel posts attached. A deck was laid across the top of the posts, and the drilling equipment was installed on the deck. Posted barges cannot be used in waters exceeding 30 feet. Later improvements on this concept resulted in ship-shaped barges and drill ships. While the ship-shaped barge must be towed into place, the drill ship travels under its own power. In deep waters, drill ships and ship-shaped barges are anchored much like an ocean-going boat may be anchored or may be held into position by dynamic positioning. Here computer-controlled thrusters are used to maintain the ships position.

Another early drilling platform was the bottle-type submersible rig. These have several steel cylinders, or bottles, that when flooded with water come to rest on the ocean floor. When it comes time to move the rig, the water is pumped out, and the rig is moved by tugboats to the new location. Bottle-type rigs are usually designed to operate in maximum water depths of 100 feet, although some have been built that can work in up to 175 feet of water.

Jackup off-shore drilling rig Continuing exploration to further offshore drilling in deeper waters resulted in new submersible designs. The Jackup rig made it possible to drill in waters up to 350 feet with a few operable in up to 600 feet. Jackups are bottom-supported rigs that can be either column- or truss-supported. Columnar legs are steel cylinders while open truss legs resemble a derrick. Both types have water-tight hulls that can float on the surface of the water while being moved into position.

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Today the most common type of offshore rig is the steel-jacket platform. This consists of the jacket, which is a tall vertical section manufactured from tubular steel. The steel jacket is pinned to the ocean floor using driven piles. Additional sections of tubular steel are placed on top of each other. Above the water level are quarters for the drilling crew and the drilling rig. This system has been used to drill wells in up to 1,000 feet of water.

There are other ocean drilling rig designs that are used in special situations, including the concrete gravity platforms used in the North Sea and the steel-caisson platform used in the Cook Inlet of Alaska.

Directional Drilling

Directional drilling techniques began to be employed in the 1970's. Normally wells are drilled vertically; however, there are many occasions when it is helpful to be able to drill at an angle. Directional wells are drilled straight to a predetermined level and then gradually curved. By changing the direction of the drill bit in small increments of no more than 2 to 3 degrees at a time, it is possible to drill many wells into a reservoir from a single offshore platform. Directional wells may also be deflected from a shoreline to reach a reservoir under nearby water. In addition, directional wells are very useful in avoiding fault lines, which can cause hole problems, as well as in instances where it is undesirable to set a rig in a given spot because of an obstruction or for environmental reasons.

Directional well bits can be used to straighten a hole, deflect the hole from the original dry well to intersect a reservoir, kill a wild well that is burning, or sidetrack around a "fish" (an object that has become lodged in the hole and cannot be removed).

Several special tools are available to assist in directional drilling. The most common involves the use of a bent sub and a downhill motor. A bent sub is a short piece of pipe that is threaded on both ends and bent slightly in the middle. It is installed in the drill stem between the bottom most drill collar and the downhill motor. A downhill motor is driven by drilling mud, thus eliminating the need to rotate the drill stem. Shaped like a piece of pipe, the downhill motor can have turbine blades or it can have a spiral shaft that turns inside an elliptical opening in the housing. In the case of the turbine tool, the force of the circulating mud inside the tool turns the turbine blades.

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3D Seismography and 3D Simulation

Beginning in the 1980's, 3-D seismic data collection systems came online. As a result, seismic readings can be gathered in three dimensions allowing the construction of 3-D simulations that literally paint more accurate pictures of potential reservoir formations.

Chart courtesy of Earth Science World and Exxon-Mobil