Global oil distribution and oil production

The global distribution of crude oil is not an even one, and the volume of oil and natural gas produced in each region is also not proportionate to the size of its reserves. The United States contributes about 16 percent to global oil production while claiming less than 2 percent of the world's reserves. Comparatively, the Middle East claims about 50 percent of the oil reserves but is only responsible for 30 percent of the global oil production.

In 2020/2021, onshore drilling accounted for approximately 70 percent of the crude oil produced, with offshore drilling responsible for the remaining 30 percent. Offshore drilling is considered the more challenging of the two, with increased environmental risk and lower cost-effectiveness. 

Key steps in natural gas and oil extraction

a) Drilling

Percussion drilling is the first method for drilling into the earth to reach for petroleum deposits for oil production. This form of drilling uses a hollow metal pipe with the help of water to improve the surrounding soil condition for penetration. Directional drilling has grown more common over time, assigned to its increased productivity in accessing harder-to-reach oil reservoirs. Directional drilling also allows operators to access multiple reservoirs with a single oil rig, maximizing oil production from a single operation. 

b) Well completion

Casing is the first step of the completion process and prevents the well from closing in upon itself. 

The casing is a solid string of steel pipe or an installation with a wire screen liner, depending on the stability of the well formation. Cementing follows with the pumping of cement slurry into the well. The slurry, consisting of additives and cement, displaces the drilling fluids and occupies the space between the casing and the sides of the drilled well. 

In open-hole completions, drilling continues till the top of the oil reservoir, and the casing is done at the point and left open at the bottom. For cased-hole completions, the casing runs into the oil reservoir and is perforated to create a connection between the wellbore and productive formation. The installation of the production tree is the final step of completion. The production tree provides surface control of the well's subsurface states with casing heads and tubing heads. 

c) Hydraulic Fracturing  

Fracking, in other words, known as hydraulic fracturing, is a technique that blasts fluid to extract natural gas or oil from shale and other forms of 'tight' rock. These less accessible and impermeable geological formations seal in oil and gas, making gas and oil production difficult. The fracking fluid consists of water, sand, and a small number of additives.

The additives include acid used to dissolve minerals to aid fuel flow, biocides to eliminate bacteria, and corrosion inhibitors to prevent damage to the steel parts of the well by the fracking fluid under operating conditions. 

d) Production 

Upon the completion of fracking, production begins with the oil and gas flowing out from the wellbore, and recovery of the fracking fluid. The recovered fracking fluid is either recycled into other fracking operations or safely disposed of according to local or international environmental regulations. 

Scale formation in oil production processes 

Oil field scale formations are costly as they disrupt gas and oil production and damage downhole and topside equipment, prompting frequent replacements. Associated cost also includes the re-drilling of plugged oil wells and other remedial workovers for injection and production wells. 

Mixing incompatible waters during injection operations to maintain reservoir pressure is the primary source of scale formations in oil production fields. Incompatibility occurs when two bodies of water interact chemically and leads to mineral precipitation. An example of incompatible waters mixing is the introduction of seawater with high concentrations of sulfate ions and low concentrations of calcium, barium, and strontium ions, to formation waters with low sulfate ion concentration and high calcium, barium, and strontium concentrations. Mixing of these waters will allow for the precipitation of different sulfate-scale forming species. 

The second principal mechanism of scale formation in oil production wells points to changes in pressure and temperature along the water pathway. A decrease in pressure or increase in temperature of the brine leads to the reduced solubility of minerals that have retro solubility profiles. 

Types of mineral scale formations in oil production wells

a) Calcium carbonate scale formation

In a scale species with retro solubility, the extent of calcium carbonate scale precipitation increases with temperature. Calcium carbonate formation also increases with an increase in the pH of the surroundings. 

The decrease in total pressure around the pumps used in water-flood operations allows dissolved carbon dioxide to escape into the surroundings as carbon dioxide gas. The acidity of carbon dioxide causes an increase in pH and subsequently an increase in the tendency of precipitation. 

CrestoPro™ O870 is a green scale inhibitor (renewable, biodegradable, and ecologically acceptable) that effectively controls calcium carbonate formation. In harsh to extreme conditions where high scaling indices persist, the application of CrestoPro™ O874 is the preferred inhibitive solution for calcium carbonate scale formation. 

b) Barium sulfate scale formation 

Sulfate scale formations are a consequence of fluid incompatibilities, where formation water rich in cations mixes with sulfate-rich seawater. 

Barium sulfate, in particular, is arduous to deal with due to its low solubility in most fluids and low reactivity with most acids. 

Deposition of barium sulfate in a continuous scale surface layer on production tubular reduces the available surface area for treatment. The ideal approach to barium sulfate scales includes retardation to prevent precipitation from occurring. 

CrestoPro™ O870, apart from its inhibitive function on calcium carbonate, also effectively inhibits barium sulfate. CrestoPro™ O868 is the optimum solution for waters of moderate to high scaling indices of barium sulfate, while CrestoPro™ O862 is most effective in dealing with barium sulfate scale formation in severe water conditions. 

c) Iron sulfite scale formation 

Iron sulfide scale formation poses a problem for flow assurance in sour gas and oil production wells. The mixing of incompatible fluids in the sour wells containing a high concentration of iron and hydrogen sulfide gas leads to the formation of iron sulfide scales. 

Iron sulfide scale formations cause operational problems when it accumulates in surface flow lines, downhole tube equipment, and perforations. 

CrestoPro™ O860 inhibits and promotes the dissolution of iron sulfide to prevent scale formation. CrestoPro™ O861 is a higher coverage solution for application when the operational system faces iron sulfide and calcium carbonate scale formation in tandem. 

d) Silica scale formation 

Silica scale formations can arise from Alkaline-Surfactant-Polymer (ASP) flooding operations, a tertiary recovery method in oil production. The lower cost of alkali encourages its use in over surfactants, resulting in the high pH of the ASP flood. 

As the ASP flood moves through the oil reservoir, it dissolves quartz silica and stabilizes the dissolved silica. As the flood progresses upward, the neutralization of the high pH ASP flood by neutral pH connate water near the production well drastically decreases the solubility of monomeric silica, forming colloidal silica. In the presence of polyvalent metal ions such as aluminum, iron, and calcium, there is also an increased tendency for the formation of metal silicate complexes. 

CrestoPro™ O866 effectively disperses and inhibits the formation of colloidal silica and metal silicate complexes, improving operational efficiency and productivity of tertiary recovery operations of oil production wells.