Change in viscosity and gravity of crude oil due to dissolved gas. The dissolved gas also has an important effect on the volume of the produced oil. As the gas comes out of solution the oil shrinks so that the liquid oil at surface conditions will occupy less volume than the gas-saturated oil occupied in the reservoir.

Petroleum trap The oil is accompanied always by water and often by natural gas; all are confined in a porous and permeable reservoir rock, which is usually composed of sedimentary rock such as sandstones, arkoses, and fissured limestones and dolomites.

A layer of impermeable rock, called the cap rock, prevents the upward or lateral escape of the petroleum. That part of the trap actually occupied by the oil and gas is called the petroleum reservoir.

A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. Petroleum reservoirs are broadly classified as conventional and unconventional reservoirs.

Therefore, the formation of an oil reservoir requires the unlikely gathering of three particular conditions: first, a source rock rich in organic material (formed during diagenesis) must be buried to the appropriate depth to find a desirable window; second, a porous and permeable (connected pores) reservoir rock is …

Oil doesn’t exist in deep, black pools. In fact, an underground oil formation—called an “oil reservoir” —looks very much like any other rock formation. It looks a lot like…well, rock. The droplets cling to the rock, like drops of water cling to a window pane.

The Ghawar oilfield is the largest oil field in the world. It’s located in Saudi Arabia in the Al Hasa Province. At 280 km long and 40 km wide, it covers a massive area of 11,000 square kilometers and is estimated at approximately 100 meters in thickness.

The most common oil traps are: structural (anticlines, faults, salt dome) and stratigraphic traps (pichout, lens and unconformity traps -see Fig. 1). The poor quality, or lack of a cover- rock, allows the oil to escape and reach the surface (Macgregor, 1993).

The typical reservoir permeability range of 0.001 md (1 μD) to 0.1 md (100 μD) is considered.

Clay is the most porous sediment but is the least permeable. Clay usually acts as an aquitard, impeding the flow of water. Gravel and sand are both porous and permeable, making them good aquifer materials. Gravel has the highest permeability.

Shale oil is a high-quality crude oil that lies between layers of shale rock, impermeable mudstone, or siltstone. Oil companies produce shale oil by fracturing the rock formations that contain the layers of oil….Cons of Fracking

• More flexible.
• Increased productivity.
• Reduced oil and gas prices.

Surface mining of oil shale deposits causes the usual environmental impacts of open-pit mining. In addition, the combustion and thermal processing generate waste material, which must be disposed of, and harmful atmospheric emissions, including carbon dioxide, a major greenhouse gas.

Fracking is a temporary process that occurs after a well has been drilled and usually takes only about 3-5 days per well. Sometimes, wells are re-fracked to extend their production, but the energy each well can produce may last for 20 to 40 years.

According to BloombergNEF’s estimates, U.S. oil producers have cut their average breakeven costs from an average of $56.50 per barrel last year to $45 a barrel now.

The health risks from oil and gas extraction are not limited to air pollution. The drilling method of “fracking” is known for contaminating drinking water sources with chemicals that lead to cancer, birth defects and liver damage.

Oil is a non-renewable source of energy. Burning oil can pollute the air. Much of our oil has to be imported and it is becoming more and more expensive as reserves reduce and imports increase. Producing electricity from crude oil is expensive compared to other fossil fuels such as coal or gas.

Oil: lifeblood of the industrialised nations Oil has become the world’s most important source of energy since the mid-1950s. Its products underpin modern society, mainly supplying energy to power industry, heat homes and provide fuel for vehicles and aeroplanes to carry goods and people all over the world.

(13 May 2021) Brent crude oil prices will average $62.26 per barrel in 2021 and $60.74 per barrel in 2022 according to the forecast in the most recent Short-Term Energy Outlook from the US Energy Information Administration (EIA).