Petroleum engineering

This article briefly provides an overview of Petroleum Engineering – its history, nature of work, and the processes involved from the discovery of oil and natural gas reserves. General profiles of career opportunities in petroleum engineering are discussed first, followed by an introductory discussion of the basic concepts in petroleum engineering. This article aims help students decide whether to pursue a career in petroleum engineering by providing them general information and an introduction to the science behind the field.

Introduction

Petroleum Engineering is a multi-disciplinary application of the natural sciences and geology, geodetic, chemical, and mechanical engineering in the discovery, development, and field processing of crude oil and natural gas. Petroleum engineers can be one of three specific professions: reservoir engineers, drilling engineers, or production engineers. Reservoir engineers study and design drilling exploration wells in the discovery structures suited for crude oil and natural gas accumulation. Reservoir engineers determine the best quantity and location of the exploration wells as well as the methods in which maximum recovery is achieved economically. Drilling Engineers execute the plans from the reservoir engineers. Drilling Engineers oversee the design and planning of the drilling of exploration wells. By the time the wells are ready for extraction of crude oil and natural gas, Production Engineers are responsible for the design and implementation of surface production facilities required in the production and treatment of the petroleum extracted. They ensure that the oil and gas fit the standards required for the transportation and refining operations. Petroleum engineers must duly perform their responsibilities in finding the most economical and effective discovery and recovery processes, as well as ensure its compliance to specified environmental standards.

History

In the 1890s in California, geologists were tasked to prevent water from seeping into oil-producing zones by relating water zones and oil-producing zones. Recognizing its potential in the oilfield development, the American Institute of Mining and Metallurgical Engineers (AIME) established a Technical Committee on Petroleum in 1914. Eventually, the AIME changed its name to the American Institute of Mining, Metallurgical, and Petroleum Engineers in 1957.

Driven by the power industry’s need for more fuel energy after the World War I and World War II, schools started offering Petroleum Engineering as a formal course in Pittsburgh in 1910. In 1915, the University of Pittsburgh granted the first degree in Petroleum Engineering. Similarly, in 1915, the University of California in Berkeley began a four-year program in Petroleum Engineering.

The petroleum engineer is expected to develop skills in geology, well drilling technology, formation evaluation, oil and gas production technology, properties of reservoir rocks, properties of reservoir fluids, fluid flow in porous media, and reservoir management . At present, petroleum engineers face the challenge of applying new technology in recovering hydrocarbons from oil shale, tar sands and offshore oil and gas fields. They are also challenged to increase the recovery of oil using new techniques as well as develop sustainable and environment friendly technologies for the exploration and production processes .

Schools and Study Programs

The Campus Explorer reports Texas A&M University as the top Petroleum Engineering School while Access Education , educational consultants based in Delhi, reports the University of Texas at Austin as the top. Other schools that also consistently make it to the list are the Colorado School of Mines, Texas Tech University, University of Oklahoma, University of Tulsa, Louisiana State University, and the West Virginia University. Education-Portal, a California-based company that aims to provide accessible information to education through the internet, listed Stanford University and Marietta College as the best petroleum engineering schools .

The University of Texas at Austin is home to the Center for Petroleum and Geosystems Engineering (CPGE) Research. This center focuses on various researches such as Unconventional Resources such as sandstones and shales, Reservoir, Production, and Natural Gas Engineering, Drilling, Well Completions, and Rock Mechanics and Environmental Engineering. The CPGE also boasts of numerous research achievements in the fields of Reservoir Engineering, Production Engineering, Drilling Engineering, Subsurface Environmental Engineering, and Formation Evaluation .

At the Texas A&M University (TAMU) is the Harold Vance Department of Petroleum Engineering. Undergraduate and graduate programs are offered in this department that tackle topics ranging from Petroleum Engineering Systems and Advanced Drilling Engineering for undergraduates to Advance Reservoir Engineering and Conservation Theory for graduate students . Faculty members from the department also have a wide array of research interests such as Petroleum Geology, Power Generation Processes, Petroleum Reservoir Engineering, Petroleum and Geothermal Reservoir, Unconventional Gas Resources, and Gas Engineering . Aside from Faculty Researches, TAMU is also the host for various research programs such as the Crisman Institute for Petroleum Research , the Center for Energy, Environment, and Transportation Innovation (CEETI) , and the Global Petroleum Research Institute (GPRI) .

In an undated article provided by the Society of Petroleum Engineers written by Darla-Jean Weatherford of the Texas A&M University, a table indicating several petroleum engineering schools and some interesting information was provided. In deciding which school to enter, the following information might be useful:

Figure 1: Petroleum Engineering schools and some interesting information. Source

Compensation

From the Society of Petroleum Engineers, a 2011 Salary Survey showed that there was an overall increase of 5.9% in the average base pay for petroleum engineers. The mean base pay increased by 6.5% from USD139,194 to USD148,301. The Texas A&M University also reports an average of USD81,113 salary for the full-time petroleum engineer with an undergraduate degree. This average includes a low of USD40,200 and a high of USD108,000. Petroleum engineers from the Texas A&M University Graduate program recorded an average of USD93,424 for a full-time engineer, with a low of USD65,000 and a high of USD126,000 .

Figure 2: 2011 Salary Survey Results. Source

Chemistry and Petroleum

Petroleum is a naturally occurring mix of hydrocarbons which may be in the form of a liquid (crude oil) or a gas (natural gas). It may also include compounds of sulfur, nitrogen, oxygen, and other elements. Petroleum literally means ‘rock oil’, which reflects its origin as petroleum is most often found in between rock strata thousands of feet below the earth’s surface. When the mixture is composed of small molecules, petroleum exists as a natural gas at normal temperatures and pressures. Otherwise, the molecules are large, and it exists as crude oil at normal temperatures and pressures. Since petroleum underground is buried deep into the earth’s crust, the increased temperature, known as the geothermal gradient, makes it more fluid and mobile. Likewise, the increased pressure also causes the solution of natural gas in the mixture. The components of petroleum are described in the following figures:

Figure 3: Components of Typical Petroleum Gases. Source	Figure 4: Typical Crude Oil Fractions. Source

Processes

Reservoir

In general, petroleum can be found underground in reservoir traps. Reservoir traps include three main types of rocks: source rock, reservoir rock, and the cap rock. The source rock is a rock of fossilized material which has been compacted over time. This type of rock originates from sedimentary rocks. The reservoir rock is the target of all drilling operations as it is the source of extractable crude oil and natural gas. The cap rock is a layer of impermeable rock that prevents or seals the natural gas from escaping to the Earth’s surface.

Figure 5: Underground source for petroleum. Source

Source of Reserves

Oil and gas are formed underground by the decomposition of organic matter buried deep in the sedimentary rocks. As the temperature rises from the chemical decomposition of these organic matter, oil is generated and eventually, gas.

Figure 6: Oil formed from the decomposition of organic matter flows upward, along the crevices of rocks in the Earth's crust. Source

Upon formation, the oil and gas flow upwards in between the crevices of the compacted rocks until they encounter a dense cover of rock, or the cap rock, which causes them to accumulate. Since oil is formed first, it accumulates first and as the temperature continues to rise, gas accumulates consequently. These traps are often called pools or reservoirs .

The Five Types of Reservoir Fluid

One of the first tasks of the Reservoir Engineer is to determine the type of fluid found in the reservoir. Each kind requires a different method in processing (fluid sampling, techniques of predicting oil and gas reserves, plan of extraction and recovery, etc) and production, which is why correctly determining the type of fluid is necessary. The five types of reservoir fluids are as follows:

Black Oil

Black oils consist of large, heavy, non-volatile molecules. The molecular weight of black oil is typically 70 to 150 in molecular weight with high points at 190 to 210 . They are also called “low-shrinkage crude oil” or “ordinary oil”. Unlike its name, black oil isn’t always black.

Volatile Oil

Volatile oils are composed of intermediates such as ethane through hexane. They contain more intermediates and fewer heavy molecules as compared to black oil . The molecular weight for volatile oils ranges from 43 to 70. If the petroleum fluid has a molecular weight less than 43, it is then classified as any of the three gases . This type of oil is also called “high-shrinkage crude oil” and “near-critical oil”.

Retrograde Gas

Retrograde gases are also called “gas condensates” or “condensates”. These gases range in molecular weight from 23 to 40, and have white fluorescence which aid in identifying them in reservoirs. This gas is often processed to obtain the intermediates (liquid propane, butane, pentane, and heavier hydrocarbon) abundant in it . These liquids are often called “plant liquids”.

Wet Gas

Wet gas is the type of natural gas containing more ethane, complex hydrocarbons, and less than 85% methane. It is said to contain heavy hydrocarbons from which liquid hydrocarbons such as propane and butane can be liquefied .

Dry Gas

Dry gas is the last hydrocarbon to be generated in the petroleum-formation process. It is the type of gas that does not produce condensate, reservoir liquids, or liquid hydrocarbons . Typically, it is composed of methane and some intermediates. It is termed ‘dry’ as it does not contain enough heavy molecules to produce liquid hydrocarbons at the surface, contrary to wet gas . Shown in the following figure is a summary taken as an excerpt from Table 9.1 in The Petroleum Engineering Handbook by Larry W. Lake.

Table 1: Petroleum Fluids and their corresponding molecular weights and stock-in-tank color. Source

Searching For Oil and Gas

Figure 7: Searching for oil and gas using seismic surveys. Source

In the search for oil and gas reserves, the geologist and geodetic engineer play key roles in the realization of the task. Various quantitative and graphical measures are taken to successfully locate a potential reservoir as well as identify the characteristics of the reserves. First, structural mapping of the site is to be conducted. With this, the faults, folds, synclines and anticlines and lineaments of the site can be determined. It is essential in interpreting structural movements and in identifying potential sources for the reserves. A seismic survey enables the prediction and identification of the presence of hydrocarbons in the subsurface. The seismic survey employs quantified geological and geophysical methods in determining the generation, migration and entrapment of petroleum underneath. In addition, remote sensing enhances data gathered by seismic surveys by mapping the structural elements on the site. It provides invaluable data for the quality, health, safety, and environment for the chosen locations. It provides detailed descriptions of the rock features as well as determining land use, type of vegetation and surface roughness. By using these additional inputs, the corresponding safety measures can be taken in response to the risk factors posed on the surface of the reserve.

Drilling

Drilling a well into a potential reservoir is the only way to determine whether it truly contains harvestable oil, gas, or both. It provides essential information for further exploration methods and field development plans. An oil well is a hole drilled through the surface to gain access to oil and gas from subsurface rock formations. It can be classified into two: offshore and onshore. An onshore well is a drilling system based on land, while an offshore well may either be floating or may be permanently fixed to the seabed.

Drilling typically constitutes a big portion of any oil and gas exploration expenditure. As such, different kinds of technology are being considered to lower the cost while maintaining or improving the drilling execution. One such example is the use of artificial intelligence techniques and cutting image analysis in the monitoring of well drilling.

To begin drilling, an oil rig is set up above a suspected oil and gas reserve. A typical oil rig is illustrated in Figure 6. When drilling, different types of fluid, collectively called “mud fluid”, is pumped downward to push rock cuttings and samples up to the surface. These are then studied and tested for hints of oil or gas which would verify the presence of reserves in the area (refer to Figure 7).

Figure 8: They typical oil rig. Source	Figure 9: Mud fluid going down the well pushes rock cuttings that were drilled up to the surface for testing. Source .

Production

Once affirmed for oil and gas presence, the location is then prepared for pumping. This phase is taken care of by Production Engineers.

Figure 10: Typical beam-pump system (also called horsehead pump) for oil recovery. Source

There are three systems in the recovery of oil and gas: primary recovery, secondary recovery, and tertiary or enhanced oil recovery (EOR) system.

Primary Recovery

In the primary recovery, the inherent underground pressure is utilized and only 5-30% of the petroleum reservoir is brought to the surface. Fluids under pressure in the rock subsurface cause the expansion of fluids underneath, producing enough pressure to push the oil up the surface for production . Gaseous fuels or natural gas also helps in forcing the oil up by supplying additional underground pressure . The gas caps, or accumulation of natural gas above the oil reserve, can be used in pushing the oil up the wells as well. Simply put, primary recovery uses the inherent energy found in the reserve upon discovery.

Secondary Recovery

When the pressures fall and insufficient underground pressure is available to push the oil up the well, primary recovery isn’t enough to sustain production. As such, additional measures or energy is used to produce crude oil, known as secondary recovery. Secondary recovery systems increase the recovery to 25-65%. Using typical horsehead pump as in Figure 8, a pump barrel in steel rods, known as sucker rods, is lowered into the well. The sucker rods are moved continuously in an up-and-down motion which forces the oil up to the surface. In some cases, energy is added to the system by injecting a fluid. When this fluid is water, the process is called “waterflooding”. If the fluid is a gas, it is called a “gasflooding”. Injection and production pumps are separate infrastructures. By using the injection-method, oil can be forced into the production zone, which enables the production pump to bring oil to the surface. This method is particularly helpful in recovering more viscous crude oil .

Figure 11: Waterflooding to maintain reservoir pressure and push oil up the well. Source

Tertiary Recovery/Enhanced Oil Recovery (EOR)

After the secondary recovery, if a substantial amount of oil still remains, any method employed to extract the remaining oil is referred to as “tertiary recovery”. Any method that proves more effective than gasflooding or waterflooding is called “enhanced recovery”. Figure 10 shows the general schematic of the mechanism for EOR.

Figure 12: General mechanism for Enhanced Oil Recovery. Source

Reservoirs that contain very viscous crude oils yield low amounts of crude oil using secondary recovery techniques. As such, EOR techniques are deemed most useful in these reservoirs . Alternately, tertiary methods can be described as derivatives of the secondary recovery methods designed to improve the sweeping action of the fluid used to push the oil up the well . Such an example is thermal flooding or steam injection wherein steam is used to reduce the viscosity of the crude oil by means of heat, which makes it easier to flow upward. Another variant of steam injection is in situ combustion, wherein a small fraction of the oil is burned to heat the surrounding oil, thereby reducing its viscosity. In general, tertiary recovery techniques work by reducing the viscosity of the remaining crude oil . Other methods used in EOR are the following: chemical methods via polymer, surfactant, and alkaline flooding, carbon dioxide-miscible flooding, and inert gas flooding. Figure 11 presents a summary of the recovery techniques used in relation to the density and viscosity of the oil reserves to be extracted.

Figure 13: Summary of recovery methods for crude oil. Source

Research & Emerging Technologies

In an effort to address environmental concerns posed by the mud fluids during drilling, an environment-friendly mud fluid has been formulated in China last 2011. This fluid uses environment-friendly additives to render the mud fluid less danger when used . Meanwhile in Australia, studies have been conducted on starch as an environment friendly mud additive to protect the marine life environment near the well . Aside from mud technologies, water recycling has also been explored as an answer to expensive refining processes as well as to decrease the volumes of process water used .

The petroleum engineer is also expected to take into account possibilities of oil spills which may greatly affect the immediate environment of offshore drilling operations. In addition, after a reservoir has been spent, infrastructures built for its depletion must be decommissioned to eliminate all possible environmental hazards before abandonment.