Oil extraction: Primary, Secondary & Tertiary

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The development and production of crude oil in U.S. oil reservoirs involve multiple phases, each aimed at maximizing oil recovery from the reservoir. These phases are commonly referred to as primary, secondary, and tertiary (or enhanced).

1) Primary drilling in the context of oil and gas typically refers to the initial phase of drilling operations in the exploration and production of hydrocarbons. This phase involves drilling the first well in a potential oil or gas field. The primary drilling process aims to reach and evaluate the subsurface formations to determine the presence of hydrocarbons, assess reservoir characteristics, and gather geological and geophysical data. About 10 percent of a reservoir's original oil in place is typically produced during primary recovery.

Here are the key steps involved in primary drilling:

Site Selection: Before drilling begins, geologists and geophysicists study the subsurface using seismic surveys and other techniques to identify promising locations for oil or gas deposits.
Well Planning: Engineers and drilling experts develop a well plan, which includes details such as the target depth, drilling trajectory, casing design, and other technical specifications.
Drilling Rig Setup: A drilling rig is mobilized to the selected location. This involves assembling the necessary equipment and infrastructure for drilling operations.
Spud-in: The drilling process begins with the spud-in, where the drill bit is lowered into the ground to start boring the well. The initial drilling phase is crucial for reaching the target formations.
Drilling Operations: The drilling rig uses a rotary drilling method to create a hole in the earth's crust. The drill bit cuts through various rock layers, and drilling fluid is circulated to remove cuttings and cool the drill bit.
Casing Installation: As drilling progresses, steel casing is inserted into the well to prevent it from collapsing and to isolate different geological formations. Cement is then pumped into the space between the casing and the wellbore to secure it in place and prevent fluid migration.
Logging and Evaluation: Logging tools are used to assess the properties of the rock formations encountered during drilling. This information helps geologists and engineers determine the potential for hydrocarbon production.
Testing: In some cases, formation testing may be conducted to assess reservoir properties and the flow potential of hydrocarbons.
Completion: If the well is deemed economically viable, the drilling rig is replaced by a completion rig to install production equipment such as tubing, packers, and wellhead components.

The success of primary drilling is crucial because it determines the viability of the oil or gas field. If the well proves to be productive, additional wells may be drilled to exploit the resource further. If not, the site may be abandoned, and exploration efforts may shift to other locations.

2) Secondary operations or interventions in the oil and gas industry refer to activities conducted after the initial drilling and production phases. These operations aim to maximize well performance, maintain reservoir integrity, and address specific challenges to enhance hydrocarbon recovery, resulting in the recovery of 20 to 40 percent of the original oil in place.

Here are some common secondary operations or interventions:

Workovers:

• Routine Maintenance Workovers: Regular interventions to maintain and optimize well performance, including equipment inspections, cleaning, and replacing worn components.Remedial Workovers: Interventions to address specific issues affecting well productivity, such as perforating additional zones, repairing damaged equipment, or re-stimulating the reservoir.

Well Stimulation:

• Acidizing: Injection of acid into the well to dissolve mineral deposits, scale, or other substances that may restrict fluid flow in the reservoir.Hydraulic Fracturing (Fracking): High-pressure injection of fluids into the reservoir to create fractures in the rock, enhancing permeability and increasing hydrocarbon flow.

Artificial Lift Systems:

• Electric Submersible Pumps (ESP): Installation of electric pumps downhole to lift fluids to the surface, particularly in wells with declining natural pressure.Rod Pumping: Use of a rod pump to mechanically lift fluids to the surface.

Waterflooding:

• Secondary Recovery with Water Injection: Injection of water into the reservoir to maintain pressure and displace oil toward production wells.

Gas Injection:

• Gas Lift: Injection of gas into the wellbore to reduce fluid density, enhance lift, and improve fluid flow to the surface.Gas Re-Injection: Injection of produced gas back into the reservoir to maintain pressure and improve recovery.

Sand Control:

• Sand Screens and Gravel Packing: Installation of screens or gravel packs to prevent sand and other solids from entering the wellbore and causing damage.

Perforation:

• Additional Perforations: Creating new perforations in the well casing to access untapped reservoir sections or improve fluid flow.

Logging and Surveillance:

• Well Logging: The use of downhole tools to gather data on well conditions, fluid properties, and reservoir characteristics.Reservoir Surveillance: Continuous monitoring of reservoir performance using sensors and data analysis to make informed decisions about well and reservoir management.

Sidetracking:

• Drilling a New Borehole: Creating a new wellbore from an existing well to reach different sections of the reservoir.

These secondary operations are critical for sustaining and optimizing hydrocarbon production over the life of a well or field. The choice of intervention depends on the specific challenges faced by the well or reservoir and the goals of the operator in terms of maximizing recovery and economic viability.

3) Tertiary recovery methods, also known as enhanced oil recovery (EOR) methods, are applied in the oil and gas industry to extract additional hydrocarbons from reservoirs after primary and secondary recovery methods have been implemented. Tertiary recovery aims to increase the overall percentage of oil recovery from a reservoir, techniques that offer prospects for ultimately producing 30 to 60 percent, or more, of the reservoir's original oil in place.

Here are some standard tertiary recovery methods:

Chemical Flooding:

• Polymer Flooding: Polymers are injected into the reservoir to increase the viscosity of the injected water, improving the sweep efficiency and displacing more oil.
• Surfactant Flooding: Surfactants are used to reduce the interfacial tension between oil and water, enhancing oil recovery by making it easier for oil to flow.

Thermal EOR:

• Steam Injection: Steam is injected into the reservoir to heat the oil, reducing its viscosity and making it easier to flow towards the production well.
• In-Situ Combustion: Oxygen or air is injected into the reservoir to initiate combustion and create a high-temperature front that helps mobilize and displace oil.

Miscible Gas Injection:

• Carbon Dioxide (CO2) Injection: CO2 is injected into the reservoir, causing the oil to swell and reducing its viscosity. Additionally, CO2 can mix with oil, making it more mobile and enhancing recovery.
• Natural Gas Injection: Natural gas is injected to maintain reservoir pressure and improve oil displacement.

Microbial EOR:

• Microbial Injection: Microorganisms are introduced into the reservoir to metabolize oil components and produce byproducts that enhance oil recovery.

Hybrid Methods:

• Combination of Techniques: Some projects may employ a combination of different EOR methods to optimize oil recovery, such as combining chemical flooding with thermal methods.

The decision to implement tertiary recovery methods is typically made after evaluating the reservoir's performance during primary and secondary recovery phases. This depends on the specific characteristics of the reservoir, including its geology, fluid properties, and the success of previous recovery methods. As technology advances, new methods and improvements to existing techniques may continue to be developed in the oil and gas industry.

Steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS) are thermal recovery techniques used in the oil industry to extract heavy crude oil or bitumen from oil sands or reservoirs with low mobility. These methods involve the injection of steam into the reservoir to reduce the viscosity of the oil, making it easier to flow and be produced to the surface.

Steam-Assisted Gravity Drainage (SAGD):

• Process:
  • Two parallel horizontal wells are drilled into the reservoir—one above the other. Steam is continuously injected into the upper wellbore, heating the surrounding reservoir and reducing the viscosity of the heavy oil or bitumen. As the oil becomes more fluid, it drains by gravity and collects in the lower wellbore. The lower wellbore is then used to produce the mobilized oil to the surface.
• Key Features:
  • SAGD is particularly effective for recovering bitumen from oil sands. It relies on gravity to drain the mobilized oil, which can significantly improve recovery rates. The process is suitable for reservoirs where the oil is too viscous to be economically produced using traditional methods.

Cyclic Steam Stimulation (CSS):

• Process:
  • The CSS process involves repeated cycles of steam injection and oil production. In the first stage, steam is injected into the reservoir for a certain period to heat the oil and reduce its viscosity. The well is then shut in to allow the heated oil to drain towards the production well. After a period of production, the cycle is repeated.
• Key Features:
  • CSS is suitable for reservoirs where continuous steam injection, as in SAGD, may not be practical or economical.It is often used in reservoirs with lower mobility and where the reservoir is not as thick as those targeted by SAGD.CSS can be implemented with existing vertical wells, reducing the need for extensive wellbore construction.

Both SAGD and CSS are considered forms of enhanced oil recovery (EOR) and are commonly applied in heavy oil and bitumen reservoirs, such as those found in the oil sands of Alberta, Canada. These thermal recovery methods help overcome the challenges posed by the high viscosity of heavy oil, allowing for increased recovery rates and improved economic viability of these challenging resources. The choice between SAGD and CSS depends on reservoir characteristics, economics, and operational considerations.

High Recovery Rates:

• SAGD can achieve high recovery rates, allowing for the extraction of a significant portion of heavy oil or bitumen from reservoirs that would be challenging to produce using conventional methods.

Gravity Drainage Mechanism:

• The gravity drainage mechanism in SAGD helps move the mobilized oil towards the lower wellbore, enhancing recovery efficiency.

Continuous Production:

• SAGD operates as a continuous process, providing a steady and continuous production stream over an extended period.

Suitability for Thick Reservoirs:

• SAGD is well-suited for thick reservoirs where the economics of recovery are favorable, and the formation is amenable to the continuous injection of steam.

Reduced Environmental Impact:

• Compared to some other extraction methods, SAGD can have a lower environmental impact in terms of land disturbance, as it typically involves fewer surface facilities.

Versatility:

• CSS is more versatile than SAGD and can be applied in a wider range of reservoir conditions, making it suitable for reservoirs where continuous steam injection may not be feasible.

Existing Well Infrastructure:

• CSS can often be implemented using existing vertical wells, reducing the need for extensive wellbore construction compared to SAGD.

Economic Viability:

• CSS can be economically attractive in reservoirs with lower mobility, where the economics of continuous steam injection (as in SAGD) might be less favorable.

Adaptability to Reservoir Characteristics:

• CSS can be adapted to reservoir characteristics, and the cyclic nature allows for adjustments based on performance feedback, optimizing recovery over time.

Lower Upfront Capital Costs:

• CSS may have lower upfront capital costs compared to SAGD, making it more feasible in certain economic environments.

In both SAGD and CSS, steam injection reduces the viscosity of heavy oil or bitumen, allowing it to flow more easily and be produced to the surface. The choice between SAGD and CSS depends on reservoir-specific conditions, such as thickness, permeability, and economic considerations. Both techniques are crucial in developing unconventional resources, particularly in oil sands and heavy oil reservoirs.