Ancient man discovered oil and natural gas. By the middle of the 19th century, Russia and the United States had drilled the first oil Wells. The United States drilled the first oil well in Pennsylvania in 1859 and entered commercial development, producing 3 million barrels a year in 1862.

At the end of the 19th century, the world's annual oil production of 150 million barrels, this period mainly depends on oil seedlings in shallow drilling, oil used to refine kerosene for lighting, commonly known as the "kerosene age".

The petroleum industry has grown rapidly since the 20th century. Since 1900, some oil companies have set up geological research departments, began to use petroleum geology theory to guide the search for oil. The key issues are hydrocarbon genesis, hydrocarbon reservoir formation and hydrocarbon distribution.

The basic factors of hydrocarbon accumulation, including source rock, reservoir, cap rock and trap, primary and secondary migration of hydrocarbon generation, are studied. The disciplines closely related to petroleum geology also developed rapidly, such as petroleum geochemistry, which basically determined the organic origin of petroleum and laid the foundation for petroleum geology. At the same time, oil and gas exploration and development technology has been developed. Oil and gas exploration and development from shallow to deep,

From land to sea. By 2000 global oil production was 265 billion barrels and natural gas 85.1 trillion cubic feet. Oil and gas have become the main energy and chemical raw materials, and the world has entered the "gasoline era" and "chemical raw materials era".

The rapid increase in demand for oil and gas has led to the expansion of oil and gas development from high-quality oil and gas to lower-quality, more difficult and more expensive oil and gas.
In 1979, Masters, an American geologist, put forward the concept of trigonometric map of oil and gas resources distribution. Later, some scholars made some modifications to the trigonometric map, but the basic concept remained unchanged. At the top of the triangle is conventional oil and gas, with low technical difficulty and production cost, good quality oil, and a small proportion of total oil and gas resources. Unconventional oil and gas production technology is difficult, the cost of production is high, the quality of oil is poor, but it accounts for a large proportion of total oil and gas resources.

Distribution of types of oil and gas resources

In the near future, both conventional and unconventional oil and gas are likely to be integrated into the oil industry. The petroleum geology is undergoing innovative changes, not only the petroleum geology and its exploration and development technology which take the conventional oil and gas as the object will continue to deepen the development, but also the unconventional petroleum geology and the development of unconventional oil and gas exploration and development technology.

Unconventional oil and gas can be divided into three categories according to their origin. The first is heavy oil and oil sands; The second category is shale oil and gas, tight oil and gas and coal bed gas. The third type is oil shale. (Not finished, this chapter focuses on heavy oil and oil sands)
1. Heavy oil and oil sands

The accumulation mechanism of heavy oil and oil sands is basically the same as that of conventional oil reservoirs, which need hydrocarbon source rock, reservoir, cap rock and trap. Due to the high density and viscosity of heavy oil and oil sands, it is difficult to flow even though most of the reservoirs are high porosity and permeability. Heavy oil and oil sands are difficult and expensive to extract, and require new extraction techniques.

The standards for heavy oil and oil sands around the world are not exactly the same. According to the U.S. Federal Geological Survey's 2007 classification of crude oils according to the weight and viscosity: API greater than 25° is light oil; API greater than 20°, less than or equal to 25° for medium oil; API between 10° and 20°, viscosity greater than 100mPa •S for heavy oil; The API degree is less than 10° and the viscosity is greater than 10000Mpa •S for natural asphalt (i.e., oil sand).
Thus, the properties of crude oil from conventional oil, medium oil, heavy oil, oil sands is continuous change.

The API of most crude oils derived from kerogen thermal evolution is greater than 25°. The formation of heavy oil and oil sands is the result of different degrees of destruction of crude oil before and after reservoir formation.

There are three main factors, one is the tectonic movement in the late period of the basin to control the change of crude oil properties.
Various forms of uplift during basin evolution brought the early formation and its contained oil and gas reservoirs to the surface, bringing air into contact with surface water, releasing the light components of the oil, and washing and biodegradation of the oil. Heavy oil reservoirs below the most conformable surface.

The second is the control effect of cap rock quality on the change of crude oil properties.

The cap rock prevents oil and gas from escaping upward, and the main sealing effect of cap rock is the capillary force of its rock. The best cap rock is salt, but the most widely distributed cap rock is mud shale formation. When the content of silty or even sandy in this cap rock increases, the sealing ability of the cap rock will be reduced, and the oil in the underlying reservoir will be washed and biodegraded, making the oil heavier and thicker.

The third is the action of bottom water. The formation of asphalt pad at the bottom of the reservoir has been found in many oil fields. This is due to the biodegradation of bottom water, which makes the crude oil heavier and thicker. It is difficult for organisms to exist when the temperature is higher than 80℃, and the degradation of bottom water must be at a depth above 80℃.

A prerequisite for large-scale accumulation of heavy oil and oil sands is that there must be abundant source rocks in the basin to produce large amounts of crude oil. In the early stage of basin evolution, passive continental margin basins and craton basins were mainly formed, and the crude oil variation in the late stage was in moderate range.

Otherwise, all the crude oil is destroyed into bitumen. The formation environment of heavy oil is less affected by tectonic movement than that of oil sand. Therefore, oil sands are mostly located in foreland basins, and heavy oil can exist in foreland basins or other types of basins, which are more widely distributed. The relatively favorable locations within a basin are the slope zones of foreland basins and the shallow portions of the frontal uplift. In general, heavy oil and oil sands are relatively shallow.

According to the U.S. Federal Geological Survey, oil sands contain 5.5 trillion barrels of original geological resources. Among them, the western Canada basin accounts for 2.334 trillion barrels and the eastern Venezuela basin accounts for 2.08 trillion barrels, accounting for 80% of the total. The distribution is very concentrated, both of which are foreland basins. The original heavy oil reserves are 3.396 Tb, about 47% of which are located in the Arabian, Eastern Venezuela and Zagros basins. Compared with oil sands, heavy oil is distributed in more types of basins and more widely.

Heavy oil and oil sands oil quality is relatively thick, poor mobility, especially oil sands. Shallow oil sands are mostly mined by open pit mining and roadway mining. Generally, open pit mining can be used when the buried depth of oil sand is less than 120M, and roadway mining can be used when the buried depth is 120-750m.

Production costs have fallen as mining methods have improved. Both heavy oil and deeper oil sands are produced downhole, with a combination of horizontal Wells and steam-assisted gravity drainage (SAGD) currently the dominant method used in Canada. However, the most basic method is steam injection. Under appropriate conditions, such as in Orinoco heavy oil belt, foamed oil mechanism can also be used in the initial cold production of horizontal Wells to improve economic benefits.

By 2012, cumulative global production of heavy oil and oil sands reached 7.38 billion and 17.58 billion barrels, respectively. The world produced 469 million barrels of heavy oil per year in 2012, mainly in eastern Venezuela, Brazil and the Gulf of Mexico, and 602 million barrels per year in the oil sands, mainly in Canada's Alberta Basin. Global heavy oil and oil sands production will reach 5.672 billion barrels per year by 2035, according to HartEnergy's 2011 forecast.

Global heavy oil and oil sands daily production forecast chart 2010-2035

The heavy oil and oil sands that can be produced are mainly found in newer formations such as the Cretaceous, Paleogene and Neogene. It is reported that there are large scale bitumen deposits in eastern Siberia, a large part of which are solid bitumen with old strata, and whether it is economically recoverable remains to be studied. (From the oil view
Observation)