Module 1

1. Hydrocarbons: Discovery and Production

1.1. What is a hydrocarbon?

Crude oils or petroleum are often referred to as hydrocarbons. A hydrocarbon is a naturally occurring organic compound that is composed of two elements, hydrogen, and carbon. They are the basis of important sources of energy such as coal, natural gas, and crude oils. Methane is a key constituent of natural gas and the simplest hydrocarbon molecule containing one carbon atom and four hydrogen atoms, having a chemical formula of CH4, as shown in Figure 1.

Chemically, hydrocarbons are classified into alkanes, alkenes, alkynes, and aromatic compounds (arenes).

Alkanes are known to be saturated hydrocarbons as their carbon backbone consists of single bonds whereas alkenes, alkynes and arenes are unsaturated hydrocarbons as their carbon backbone consists of double or triple bonds. Alkanes have single bonded carbon atoms, i.e., the carbons are saturated with hydrogen and these alkanes are also called paraffin hydrocarbons, commonly known as paraffins. The general formula for alkanes is 𝐶𝑛𝐻2𝑛+2 where n is the number of carbon atoms. Alkenes, commonly known as olefins, have double bonded carbon atoms present in its structure and their general formula is 𝐶𝑛𝐻2𝑛. Alkynes have triple bonded carbon atoms present in its structure with a general formula of 𝐶𝑛𝐻2𝑛−2 . Arenes, also called aromatic compounds because of their pleasant fragrance, are cyclic unsaturated hydrocarbons. The structure of arenes contains six carbon atoms in a cyclic ring with alternate single and double bonds, i.e., conjugation. The simplest aromatic compound is benzene which has a chemical formula of C6H6 and is the basis for substituent aromatic compounds.

The nomenclature (or naming) of these hydrocarbons is based on the International Union of Pure and Applied Chemistry (IUPAC) Rules. The number of carbons in the parent chain is the prefix, which determines the name of the compound along with the required suffix, depending on the structure of the compound. Alkanes, alkenes, and alkynes have the suffix -ane, -ene and -yne respectively added to the prefix. The table below lists the names assigned by IUPAC for the number of carbon atoms between 1-10.

Table 1: IUPAC names for carbon atoms between 1–10.

1.2. The Origin and Migration of Hydrocarbon

Hydrocarbons are naturally obtained from the decomposition of plants and animals buried deep under the ground in an anoxic environment, i.e., absence of oxygen to prevent the organic matter from being decomposed by bacteria and eventually disappear (Demaison & Moore, 1979). Continuous sedimentation, intense pressure, high temperatures and, advancing geologic age have resulted in the transformation of the planktonic remains to kerogen and lastly to hydrocarbons, that are commonly known as fossil fuels according to the dominant biogenesis theory of the origins of oil.

Planktonic plants (diatoms, blue-green algae etc.) and animals (zooplankton) are the source of most hydrocarbons (Britannica, n.d.). Once these organisms die, they get buried and subsequent sedimentation occurs in anoxic conditions. The organic-rich mud is continuously buried by sediments and forms sedimentary rocks and organic shales. They are called source rocks as petroleum is formed there.

The increasing pressure and temperature transform the organic shale to kerogen. Temperature and time play a crucial role in determining the composition of the hydrocarbons formed from the kerogen. As illustrated in Figure 3 below, if the kerogen is at a temperature greater than 90ºC but lower than 150ºC, the kerogen transforms into oil and gas. The formation of oil occurs in the temperature range 60ºC to 150ºC at 2 to 4.5 km and this is referred to as oil window. At temperatures higher than 130ºC, natural gas is formed. The gas window temperature range is 120 to 250ºC where wet and dry gas are formed (Donev et al., 2019). Wet gas contains liquid hydrocarbons such as ethane, propane, butane and others. and is formed in the depth range of 3 to 5 km. Dry natural gas constitutes of at least 85% methane and is primarily formed in the depth range 5 to 6 km. The drier natural gas results in more the methane (Weaver, 2019). The process of transformation of kerogen to hydrocarbons is called maturation.

Hydrocarbons are formed from sedimentary petroliferous beds, mostly carbonates and shales. The formation of hydrocarbons requires carbon and hydrogen which may originate from the organic compounds present in the subducted sedimentary rocks. Dissociation of carbonates (CaCO3) leads to the formation of calcium and carbonate ions. Carbonate ions act as the source for the required carbon. Additionally, carbon and hydrogen can originate by reducing carbon dioxide (CO2) to carbon (C) and water (H2O), that seeps into subduction zones, rifts, or fractures, to hydrogen (H2) by the oxidation of ferrous iron (Fe2+), using catalysts, that is present in mafic mineral to ferric iron (Fe3+). Hydrocarbons continuously form through such processes eventually resulting in the increase in oil reserves, primarily around subduction, rift zones or deep inside the basement rocks of the crust (Mahfoud, 1995).

Once maturation is complete, the process of migration begins because of increasing pressure. The hydrocarbons that were formed from the source rocks start moving to the porous reservoir rocks. Reservoir rocks contain significantly large amounts of hydrocarbons. Migration occurs in two stages as shown below in Figure 4. Primary migration is the expulsion of oil and gas vertically from the source rocks to reservoir rocks. Since the expulsion from the source rocks occurs through pores and fractures that open due to high pressures, it is important that the source rocks can be fractured easily and are porous. Secondary migration is the lateral movement of oil and gas from the source rocks through carrier beds, which are permeable layers (Watts & Eden, 2020).

Once the hydrocarbons migrate, it is essential that they are trapped by impermeable layers of rocks that act as a seal for them to accumulate and form a reservoir. These reservoirs are then drilled to obtain the oil and gas. It is important that the composition of the reservoir is known so that appropriate methods for its production can be adopted. Based on the weight of the hydrocarbon, the least weighed chain makes up gas and with an increase in number of carbon atoms, the presence of gas decreases. In short, if a reservoir contains methane (C-1) in large amounts then it is a gas reservoir. However, if the number of carbon (C) atoms increases (presence of propane (C-3), butane (C-4) etc.) in the reservoir with the least methane, then it may be an oil reservoir but not a gas reservoir.

1.3. Trapping of Oil

Crude oils that are formed deep inside the Earth are trapped within the reservoir. These traps can be upward curves enclosing the oil or angled upwards as a result of stratigraphic and structural processes sealed by highly impermeable rocks like shale or evaporites as seen in Figure 5. Stratigraphic processes involve the formation of different rock layers, also called stratification whereas structural processes involve the de-formation of rock due to geological processes explained below.

The upwardly arch-shaped convex curves that enclose approximately 4/5th of the largest oil reservoirs are called Anticlines. The smooth curve upward is formed due to deformations of the Earth’s crust because of structural processes and are mostly symmetrical in nature. There are also faults that are formed because of movement across the tectonic plates (pieces of Earth’s crust and upper mantle). These prevent oil migration and hence are entrapped within (Smil, 2008). Stratigraphic traps are formed due to the settling of sedimentation rocks in dis-continuous layers. These layers also form the seal that prevents the oil and gas within it from flowing out (Hanania, 2016). The salt dome forms as a result of salt moving slowly upwards which is less dense than the rock above it. This upward movement of salt can break the rock in its journey upwards and oil and gas flowing through the reservoir rock will be trapped (Hanania, 2016).

1.4. Abundance of hydrocarbon in the Middle East

It was in 1901 when William D’Arcy was permitted to search for oil in Persia with his British oil company and after seven years of endless search, oil was first struck in southwestern Iran in 1908. A year later, D’Arcy established the Anglo-Persian Oil Company and by 1935, it was changed to the Anglo-Iranian Oil Company, which was then finally transformed to British Petroleum in 1954. This search for oil paved the way for the successive discovery of oil in the Middle East.

The Middle East is one of the world’s leading producers and suppliers of oil and natural gas. The region is home to a surplus of crude oils and natural gas reserves, primarily due to various geological factors which has led to the abundance of oil, thus boosting the economy of the region.

Crude oil is made up of hydrocarbons that spend billions of years degrading under high temperatures deep under the surface of the Earth. The geological timescale illustrated in Figure 7 highlights the geological era and periods dating to the latest era, i.e., the Quaternary era. Amongst all the geological periods, the majority of oil production comes from younger rocks. It is very rare to find reservoirs dating to late Paleozoic periods (Permian, Carboniferous, Devonian and Silurian). However, 45% of reservoir rocks belong to the Jurassic period within the Mesozoic era and about 35% belong to the Cretaceous period from the same era (Smil, 2008).

The Mesozoic age had a high composition of planktons in the ocean in addition to its tropical climate; this is why 70% of the oil deposits available today were formed in the Mesozoic Era. Around 20% of oil deposits were formed in the Cenozoic Era and 10% of the oil that is available today was formed in the Paleozoic Era (Donev et al., 2019). Consecutive geologic activities led the Arabian Peninsula to break apart from the African continent which resulted in the formation of the Red Sea and the Persian Gulf. Massive amounts of hydrocarbons were found in the subduction zones, rifts, and fractures of the Middle Eastern regions (Distel, 2020). The Middle East hosts 80% of oil and 90% of gas carbonate reservoirs that are rich source rocks (AAPG, 2020). Because carbonate sedimentation occurred continuously in the shallow marine environment that results in thick stacks of multiple carbonates pay zones providing it the necessary storage for the massive amounts of hydrocarbons produced (Sorkhabi, 2010).

2. Qatar Oil Discoveries

2.1. Significance of Oil in Qatar

2.2. Discovery of Dukhan Field

The discovery of oil in Bahrain in 1932 by the Standard Oil Company of California (now known as Chevron Corporation) sparked interests in the Qatari land by a British company, the Anglo-Persian Oil Company (APOC, now known as British Petroleum). Their representative, C.C. Mylles was successful in getting a two-year geological exploration license in Qatar. In late 1932, he sent two geologists E.W. Shaw and P.T. Cox to Qatar (Sorkhabi, 2010). The period of January – March in 1933 was spent in a survey where they found similarities between the Dukhan anticline in the southeastern areas of Qatar and the discovery field in Bahrain. The similarity was the presence of Eocene limestone within the surface rocks in the area where oil was discovered in Bahrain (Sorkhabi, 2010). The rock formation found in Qatar can be seen below in Figure 8.

After the mapping of the Dukhan anticline and the conclusion of negotiations on 17 May 1935, APOC was allowed a 75-year oil concession that would cover all the Qatari landscape to explore and produce oil. The first well was recommended in the winter of 1937-1938 by a new group of geologists Norval E. Baker, T.F. Williamson, and R. Pomeyrol. This well was 80 km long with 90 meters of closed structure in the Middle Eocene limestone (Sorkhabi, 2010).  It was completed in January 1940 when the oil well hit the Upper Jurassic Limestone at a depth of 1733m and producing approximately 4,480 barrels of oil per day back then. The limbs of the anticline dip at 2° – 10° at the surface where the oil was trapped.

In 1942, the Dukhan Field was abandoned for a while as it required reconstruction due to the destruction caused by World War II. The operations resumed in late 1947 and in the following years a 120km pipeline was constructed to connect the Dukhan Field to Umm Said Port situated in the east of Qatar (Sorkhabi, 2010). From here, the first shipment of Dukhan crude oils were exported on 31 December 1949 to Europe marking the beginning of a new era for the country’s development and prosperity. The stratigraphic and structural cross-section that was discussed in Section 1.3 can now be understood better in the illustration of Figure 9.

2.3. Development and Discovery of other Oil Fields in Qatar

The production from the Dukhan No. 1 well increased three times by 1954 also increasing the revenue of Qatar to $23 million in the same year. The Petroleum Department of Qatar was overviewing the entire process of production and exploration of new wells until 1953 when the name changed to Qatar Petroleum Company. By 1957, 58 new wells had been drilled in Dukhan from which 48 were producing wells (Sorkhabi, 2010).  As of 2010, the crude oils from the Khatiya, Fahahil and Jaleha stations that were built in 1949, 1954 and 1955 respectively would be pumped to Umm Bab Booster station. The pressure would be boosted for transporting it to the Umm Said port by pipeline.

In August 1949, the Emir of Qatar, H.H. Shaikh Ali Ibn Abdullah al-Thani agreed to a concession to the International Marine Oil Company to explore the offshore areas of Qatar. However, they failed to find any fitting structure where drilling could be done. Due to this, the concession was turned over. Nevertheless, a new concession was granted to the Shell Company of Qatar five years later for 75 years and a 50% partnership in sharing profit after production. A seismic survey began in the waters of Qatar leading to two dry exploratory wells in 1955 and 1956, but in May 1960, Shell discovered the Idd al-Sharqi oil and gas field comprising of the North and South domes (Sorkhabi, 2010). Figure 10 below illustrates the payzones of both the Dukhan and Idd al-Sharqi fields.

In 1963, Shell discovered the Maydan Mahzam offshore field which started production after two years. Together with the Idd al-Sharqi field, the total production increased to 293,000 barrels of oil per day leading to $115 million in 1969. Halul Island was where the first shipment of oil from Idd al-Sharqi was exported on 1 February 1964 (Sorkhabi, 2010).

It was reported in 1981 that new deposits of crude oils near Bunduq Oil Field were found that were of superior quality and sufficient commercial quantity having a gravity of 40 API (Gulf Times, 1981). This finding added to Qatar’s oil reserves that stood at more than 4.7 billion barrels back in the day.

Another field off the northeast coast of Qatar in the Persian Gulf, lies the Al Shaheen Oil Field above the North Gas Field. It was initially discovered in 1992 but started producing in 1994 by Maersk Oil. It was in this field that a horizontal well was drilled incident-free up to a measured length of 12,290 m (40,320 ft). This was drilled by Transocean for Maersk Oil and held a world record for completing the longest drilled well of 10,900 m (35,770 ft) in just 36 days as of 2008 (Cantwell, 2008; Guinness World Records, n.d.). However, this world record was broken by the Sakhalin-1 well in Orlan platform at Chaivo field in the Sea of Okhotsk that drilled a well of 15,000 m (49,212 ft) (Robson & Haslam, 2017). Al Shaheen Field is now one of the largest oil fields in the world and the largest producing field in Qatar that produces around 300,000 barrels of oil per day (bbl/day).

3. Qatar Gas Discoveries

3.1. Discovery of the North Field

Back in the 1940s, when more wells were drilled in Dukhan close to well No. 1, gas was discovered in Dukhan No. 4 whose lithology was comprised of limestone (Sorkhabi, 2010). After the end of World War II, non-associated gas, i.e. naturally occurring gas not dissolved in crude oils, was discovered from the Permain Khuff formation at a depth of 3000m during 1959-1960. Exploration engineers discovered natural gas (occurring naturally and comprising mostly of methane) in the northeastern coast of Qatar in 1971. The depth of Khuff formation lies between 2835m – 3262m and is about 116m thick (Sorkhabi, 2010).

The Iranian extension of Qatar’s North Field, South Pars has approximately 46 Tcfg reserves present. The Khuff formation which is one of the most difficult stratigraphic carbonate reservoirs in the Middle Eastern part of the world, comprises of five cycles of carbonate and evaporite deposits (Bashari, 2016). The reason lies in the rapidly evolving sedimentary conditions and varying diagenesis that resulted in a mixture of rock types – limestone, anhydrite, dolomite and little amount of shale. Comprising of five thick units known as K1, K2, K3, K4 and K5, K4 belongs to the lowest zone of Upper Khuff and is known to consist of approximately 55% of the original gas in place reserves, making it the primary gas producer. This is the thickest and richest zone with respect to condensate formation and has the lowest concentration of H2S present (Bashari, 2016).

With more than 900 Tcfg recoverable reserves and with 15 appraisal wells drilled over 14 years, Qatar’s North Field was ranked as the largest non-associated natural gas field in the world (Qatargas, n.d.). Additionally, it is the largest holder of proven gas reserves (14% of the world’s natural gas reserves) after Russia and Iran (GECF, n.d.). This field has been the most valuable and critical find in the history of oil and gas development in Qatar.

3.2. Processing of Gas produced from the North Field

3.3. Overview of Oil and Gas Fields in Qatar

Qatar has major oil and gas fields that have been contributing to its overall hydrocarbon production and economic growth. Figure 14 below indicates all the oil and gas fields located inside Qatar and around it. The major oil and gas fields of Qatar have been discussed in the previous sections but this section will provide an overview of the geological formations of these fields.

Geological time periods that are important for Qatar’s oil and gas are the Permian (the oldest period that is more than 250 million years ago) followed by Triassic through the Jurassic to the youngest period which is the Cretaceous period (about 70 million years old) (Al-Siddiqi & Dawe, 1998). The formations are dated based on the fossils found. It is imperative that rocks can be characterized based on the depositional environments and the changes it goes through within the surface of the Earth. This is because they provide an insight on the sorting of sand particles, the grain size of these rocks, lithology and etc. that will be used to determine their petrophysical properties.

For example, when considering the Arab Formation, it is sub-divided into four major intervals mainly A, B, C and D. Arab D is predominantly a carbonate reservoir and is one of the most productive reservoirs followed by Arab C which also has carbonates but is mainly comprised of dolomites. Therefore, these four intervals are separated and distinguished by a thin impermeable seal of anhydrites. These intervals belong to the same formation but they are not very similar in terms of their lithology or productivity. Arab A and B are both non-carbonate reservoirs and consist of heterogenous dolomitic limestone but are not very productive because of very low porosity (a measure of accumulation of hydrocarbons within the tiny spaces/pores in the rock) and low permeability (ability of hydrocarbons to flow). The Arab formation is sealed by the Hith formation (cap rock). Figure 15 below gives a general stratigraphic layout for the overall geology of Qatar.

As seen earlier in Section 3.1, the Khuff formations, mainly K1, K2, K3 and K4 are home to non-associated gas. The Khuff formation is sealed on one end by the Sudair formation in the Triassic formation as depicted in Figure 15. It can also be noted that the Khuff formation is shared in two geological periods, Permian and Triassic (called Permo-Triassic). Not just in Qatar, but in the Middle East, the Hith, Arab and Diyab formations of the Jurassic period result in a majestic combination of source, reservoir and seal. This triplet is the reason for the creation of the world’s richest hydrocarbon reserve in the region.

4. Qatar Hydrocarbon Value Chain

4.1. Value Chain

The entire process concerned with the creation of a product while considering the procurement of raw materials, required technological development, human resources management, infrastructure and marketing is called the value chain (Tardi, 2021). The oil and gas industry value chain are organized into three processes: upstream (onshore and offshore activities including exploration, drilling, production etc.), midstream (processing, transportation, storage etc.) and downstream (refining, product preparation, marketing, retail etc.). Figure 16 briefly summarizes the common activities involved in each of the processes involved in the hydrocarbon value chain.

Qatar is home to the world’s largest non-associated gas reservoir, The North Field, which was discovered in 1971 but was developed in the 1990s. London-based “Middle East Economic Digest (MEED)” estimated QAR 8564 m ($2,231m) worth of revenue of the Qatar government’s mainly from the crude oil recovery (Gulf Times, 1979). 

The first export by Qatar was crude oil in 1949 after World War II and the first oil fields discovered were Idd Al-Sharqi and Maydan Mahzam in 1960 (QP History, n.d.). The first Liquified Natural Gas (LNG) shipment was exported to Japan in 1997 and since then, Qatar has invested in scaling up, integrating downstream and finalizing deals with international oil companies to become a reliable supplier and flexible partner (Ibrahim & Harrigan, 2012). Followed by the success of LNG, Qatar focused on converting lean gas to clean burning gas-to-liquid (GTL) fuels in the late 1990s. Currently, Qatar is one of the largest exporters of LNG and GTLs across the world. Figure 17 illustrates the integrated LNG model created to develop production, liquefaction facilities, manage gas reserves and shipping (Ibrahim & Harrigan, 2012).

4.2. Refining the Hydrocarbons Produced

The oils discovered are taken out by drilling in the oil wells. This oil is called crude oil, which means ‘unprocessed’ and is rich in hydrocarbons with varying chain lengths. As the chain lengths increase, the boiling point of the hydrocarbon also increases. This principle is applied for the separation of the crude oil components by fractional distillation. Heavier components will settle at the bottom whereas the lighter components (volatile) rise through the distillation column.

However, the products coming as the outlet stream from the column need to be further processed and treated before being sold into the market. The fractions obtained are thus chemically processed via cracking, unification, or alteration (Freudenrich, 2000). Once the fractions are processed, they are treated to remove the impurities followed by blending to make final products. Figure 18 summarizes the separation process of crude oils in an oil refinery.

4.3. Qatar’s Oil and Gas Industry

4.3.1. Liquified Natural Gas

Liquified natural gas (LNG) is a natural gas that has been liquified for ease in transportation as well as to maintain safety measures in cases of pressurized gases. The liquification of natural gas, primarily methane and some amount of ethane, occurs at a cooling temperature of -162ºC and is transported at 25 kPa. Qatargas is the world’s largest producer of LNG, supplying 77 million metric tonnes annually across the globe. The production of LNG takes place across its seven ventures – Qatargas 1, Qatargas 2, Qatargas 3, Qatargas 4, Ras Laffan 1, Ras Laffan 2 and Ras Laffan 3, with its headquarters located in Ras Laffan, Qatar. Ras Laffan Industrial City is the prime LNG and GTL production site in Qatar. The natural gas is supplied to Qatargas from the North Field. The LNG produced is transported via a subsea pipeline. LNG is exported to countries by LNG carriers such as ships or tankers as seen in figure 19 below.

4.3.2. Ethane

4.3.3. Commercialization of hydrocarbons in Qatar

Natural gas primarily contains the following:

C1 – Methane (CH4)

C2 – Ethane (C2H6)

C3- Propane – (C3H8)

C4 – Butane – (C4H10)

C5 – Pentane – (C5H12)

These are processed in Qatar to obtain products that can be commercialized. The following flowcharts show the various products that can be obtained from the processing of each of these hydrocarbons. The compounds in yellow boxes are commercialized in Qatar namely, methanol, ammonia, urea, low-density polyethylene (LDPE), high density polyethylene (HDPE), MTBE (methanol) etc.