Drilling operations in the upstream oil and gas sector are a critical part of the exploration and production (E&P) process, where energy companies work to discover and then extract hydrocarbons (oil and natural gas) from beneath the Earth’s surface. The term “upstream” refers to all activities related to the search for, and the recovery and production of, crude oil and natural gas. Drilling is the primary method by which petroleum and gas reserves are accessed and produced, making it a pivotal operation in the energy industry. In this article we list the key equipment used in this stage of the O&G value-chain: drilling rigs, strings, mud/fluid management, BOP, power supply, hoisting and rotary systems, and well control. A few hints about digital innovations in the field of drilling (digitalization, block-chain, and Internet-of- Things (IoT) are given at the end of the article.
DRILLING EQUIPMENT IN OIL & GAS
WHAT IS OIL & GAS DRILLING
Drilling in the oil and gas sector refers to the process of creating boreholes in the Earth’s subsurface to explore and extract hydrocarbon resources, namely oil and natural gas. This operation is a cornerstone of the upstream segment of the oil and gas industry, which encompasses the search for underground or underwater oil and gas fields, drilling exploratory wells, and subsequently drilling and operating the wells that recover and bring the crude oil and/or gas to the surface.
Modern drilling activities utilize sophisticated technologies and machinery, including drilling rigs equipped with a drill string and bit, to penetrate through rock layers to the hydrocarbon reservoirs below.
The operation involves several critical steps such as site preparation, drilling, casing and cementing the well, testing for hydrocarbons, and completing the well for production. Innovations like directional and horizontal drilling have significantly enhanced the efficiency and environmental sustainability of these operations, allowing for the exploitation of resources with minimal surface impact. Drilling is not only pivotal for producing energy resources but also for assessing the potential and viability of oil and gas deposits, playing a vital role in the global energy supply chain.
DRILLING PROCESS: KEY STEPS
The drilling process for oil and gas wells involves a series of complex and technical steps, each crucial for the successful discovery and extraction of hydrocarbons. The process is meticulously planned and executed, involving a range of specialized equipment and techniques. Here are the key steps in the drilling process:
Site Selection and Preparation
Site selection and preparation are critical initial steps in the drilling process for oil and gas exploration and production. This phase involves choosing a location with potential hydrocarbon reserves based on geological and seismic data and then preparing the site for drilling activities.
Site Selection: Involves detailed analysis of subsurface geological formations through seismic surveys and exploration wells. Geologists and engineers evaluate the area’s potential to host oil or gas reservoirs, considering factors like the type of hydrocarbons, depth, and volume of reserves. Environmental and logistical considerations, such as access to infrastructure, regulatory restrictions, and potential impact on the environment and local communities, also play a significant role in the decision-making process.
Site Preparation: Once a site is selected, it undergoes preparation to support drilling operations. This includes clearing vegetation, leveling the ground, constructing access roads, and setting up water supply and waste management systems. Additionally, the drilling pad is constructed, which involves laying a foundation capable of supporting the drilling rig and associated equipment. Environmental protection measures, such as containment systems for spill prevention, are also implemented during this stage.
Licensing and Permits: Obtain necessary environmental and drilling permits.
Drilling Rig Setup
Setting up a drilling rig is a complex process that involves multiple steps to ensure safety, efficiency, and environmental protection. Here’s a brief overview of all the steps after site has been duly prepared to host the rig:
Rig Transportation: Components of the drilling rig are transported to the site. This includes the mast, drill string, blowout preventers (BOPs), and other necessary equipment.
Rig Assembly: Upon arrival, the rig components are assembled. The process starts with the rig floor and sub-structure, followed by raising the mast or derrick. The drill string, BOPs, and other critical equipment are then installed and tested for operational integrity.
Drilling Preparation: Auxiliary systems like mud systems, power supply, and waste management systems are set up. The mud system circulates drilling fluid to cool the drill bit, remove cuttings, and maintain pressure. Power generators are installed to supply electricity to the rig.
Safety Systems: Safety systems, including BOPs and emergency shut-off systems, are installed and tested. These systems are crucial for preventing blowouts and managing potential emergencies.
Drilling Operations Begin: With the rig fully assembled and all systems tested, drilling operations can start. The drill bit, attached to the drill string, begins to penetrate the earth under careful monitoring to reach the target oil or gas reservoir.
Each step is meticulously planned and executed by a team of skilled professionals to minimize environmental impact and ensure the safety of the crew and surrounding communities. This process can vary slightly depending on the type of rig (land, offshore, etc.) and the specific operational requirements.
Drilling the Well
Drilling a well, particularly in the context of oil and gas exploration, involves several critical phases, from the initial groundbreaking to the completion of the main hole. This process is technically detailed, with safety and efficiency being paramount at every step.
Spudding In
“Spudding in” marks the beginning of drilling operations. This phase involves the initial penetration of the ground surface with the drill bit. It’s a crucial step where the exact location for drilling is confirmed, and the drill bit begins to create the pilot hole. The rig’s equipment is all set and ready, marking the transition from setup to actual drilling.
Drilling the Main Hole
After spudding in, the drilling of the main hole begins. This involves using a larger drill bit to deepen the hole to the desired depth. The process is conducted in stages, known as “drilling intervals.” Between intervals, casing pipes are inserted into the drilled sections to stabilize the wellbore and prevent the hole from collapsing. Each casing string is cemented into place to ensure a tight seal.
Circulating Drilling Fluid
One of the critical aspects of drilling is the circulation of drilling fluid, often referred to as “mud.” This fluid serves multiple purposes: it cools and lubricates the drill bit, carries drill cuttings to the surface, and helps maintain hydrostatic pressure to prevent well-blowouts. The composition of drilling fluid is carefully controlled and adjusted based on drilling conditions and the geology of the drilled formations.
Adding Drill Pipes
As the drill bit deepens the hole, additional lengths of drill pipe are added. This process, known as “making a connection,” involves stopping the drill, disconnecting the drill pipe from the top drive, adding a new section of pipe, and reconnecting the assembly to continue drilling. This is a routine procedure repeated numerous times throughout the drilling operation.
Logging and Testing
Throughout the drilling process, various logging and testing techniques are used to analyze the geological formations penetrated by the drill bit. This includes taking core samples and employing electronic logging tools that are lowered into the wellbore to measure properties such as electrical resistivity, porosity, and hydrocarbon presence. These data are crucial for evaluating the potential of the well and guiding further drilling operations.
Reaching the Target Formation
Once the drill reaches the target geological formation, containing the anticipated hydrocarbons, detailed evaluation begins. This may involve further logging, as well as tests to assess the reservoir’s pressure and fluid content.
Each of these phases is critical to the success of drilling operations, requiring careful planning, execution, and continuous monitoring to ensure safety, environmental protection, and the efficient discovery and extraction of oil or gas resources.
Casing and Cementing
Well completion is a critical phase in the drilling process, marking the transition from drilling the well to producing oil or gas from it. Two of the most crucial steps in well completion are casing and cementing, which ensure the well’s structural integrity, isolate the production zones, and protect groundwater resources.
Casing
Casing involves the installation of steel pipes inside the drilled well. These pipes serve multiple purposes: they stabilize the wellbore, preventing it from collapsing; isolate different underground layers to prevent cross-flow of water, oil, gas, or other fluids; and provide a conduit for the production of oil and gas from the reservoir to the surface.
The process of casing a well is done in stages, with multiple layers or “strings” of casing installed at different depths. The first string, known as the “conductor casing,” is installed shortly after drilling begins to stabilize the topsoil. Successive strings, such as the surface casing, intermediate casing, and production casing, are installed as the well is drilled deeper. Each string serves a specific purpose, ranging from protecting freshwater aquifers near the surface to providing a pathway for hydrocarbon production from the reservoir.
Cementing
Cementing is performed after each casing string is placed in the wellbore. It involves pumping cement into the gap (annulus) between the casing and the borehole wall. The primary objectives of cementing are to:
Bond and Support the Casing: Cementing secures the casing in place and prevents it from moving or buckling under the pressures encountered during well operations.
Isolate Formation Zones: Properly cemented casings help isolate different underground layers, preventing the migration of fluids from one layer to another. This is crucial for avoiding water contamination and ensuring that hydrocarbons are produced efficiently.
Protect Against Corrosion: Cement provides a barrier to corrosive fluids that may be present in the formation, thus protecting the casing and prolonging its lifespan.
Seal the Wellbore: By filling the annulus, cementing seals the wellbore, preventing leaks of hydrocarbons to the surface or into other formations.
The cementing process starts with the selection of a suitable cement mix, designed to withstand the specific temperature, pressure, and chemical conditions of the well. The cement is then mixed with water and other additives to enhance its properties and pumped down the casing. It flows to the bottom of the casing string and up into the annulus, filling it from bottom to top. Once the cement sets, it forms a solid seal, providing structural integrity and isolating the production zone.
Casing and cementing are critical for the safe and efficient operation of oil and gas wells. They ensure the structural integrity of the well, protect water supplies, and optimize the production of hydrocarbons, laying the foundation for a successful well completion and the commencement of production.
Well Evaluation and Testing
Well Logging
Well logging is a primary method used for well evaluation. It involves lowering measurement instruments into the wellbore to collect data on the physical, chemical, and other properties of the rocks and fluids in the subsurface. Logs can be taken at different stages of drilling, including while drilling (LWD – Logging While Drilling) or after a section of the well has been drilled (Wireline Logging).Common types of well logs include:
Resistivity Logs: Measure the resistivity of the rock and fluids, which helps in identifying hydrocarbon-bearing formations.
Porosity Logs: Determine the porosity of the rock, indicating its ability to hold hydrocarbons.
Acoustic Logs: Measure the speed of sound through the rock, providing information on its density and elastic properties.
Gamma Ray Logs: Detect natural radioactivity to distinguish between different rock types and identify shale and sandstone layers.
Imaging Logs: Produce detailed images of the wellbore wall, helping to identify rock texture, fractures, and other geological features.
Core Sampling
Core sampling involves retrieving a cylindrical sample of rock from the well. Cores provide invaluable direct evidence of the reservoir rock’s properties, such as porosity, permeability, and fluid content. They allow geologists to visually inspect the strata, perform detailed laboratory analyses, and better understand the reservoir’s characteristics.
Well Testing
Well testing is conducted to evaluate the reservoir’s performance by temporarily producing oil or gas through the well. It helps in determining key parameters such as reservoir pressure, production rates, and the composition of the produced fluids. Tests can range from initial flow tests, where the well is allowed to flow or is tested with a temporary completion, to longer-term tests that provide more comprehensive data on the well’s behavior and the reservoir’s characteristics.
Pressure Transient Testing: Involves changing the pressure in the well and observing how it changes over time to assess permeability and the extent of the reservoir.
Production Testing: Measures the flow rates of oil, gas, and water, providing direct information on the well’s productivity and the reservoir’s characteristics.
Formation Evaluation
Formation evaluation combines data from logging, core samples, and well tests to build a comprehensive picture of the reservoir. This includes understanding its geometry, the distribution of hydrocarbons, and the properties of the reservoir rocks and fluids. This information is crucial for making informed decisions about the well’s development, including the placement of production wells, the design of the completion strategy, and the planning of field development. Well evaluation and testing are foundational to the successful development of oil and gas fields. They provide the data needed to make informed decisions about how best to exploit a reservoir, ensuring that resources are developed efficiently, safely, and with minimal environmental impact.
Well Completion
Well completion is a crucial phase in the process of drilling oil and gas wells, signifying the transition from drilling to the production stage. It involves a series of technical procedures to make a well ready for production — essentially preparing the well to extract hydrocarbons (oil and gas) efficiently and safely. This phase is meticulously planned based on the data gathered during the drilling process, such as the depth and pressure of the reservoir, the characteristics of the oil or gas, and the geological conditions.
Key Components of Well Completion
1. Casing and Cementing: After drilling is finished, steel pipes (casing) are inserted into the well to stabilize the wellbore and isolate different subsurface layers. Cement is then pumped down the casing and up the gap between the casing and the borehole wall (annulus) to permanently fix the casing in place and prevent fluid migration between subsurface formations.
2. Perforating: In cased-hole completions, once the cement has set, the casing opposite the reservoir section is perforated. This involves using a perforating gun to create holes in the casing and cement, allowing oil or gas to flow from the reservoir into the wellbore.
3. Installing Production Tubing: A smaller diameter pipe, known as production tubing, is inserted into the well through which the oil or gas will flow to the surface. This tubing isolates the fluid flow to the well’s interior, offering better control over production and reducing corrosion in the casing.
4. Installing Wellhead and Christmas Tree: The wellhead is installed at the surface to provide the structural and pressure-containing interface for the drilling and production equipment. The Christmas tree, an assembly of valves, spools, and fittings, is mounted on the wellhead after completion. It provides the control valves necessary to manage the flow of oil and gas from the well.
5. Stimulation: Many wells require stimulation to enhance hydrocarbon flow. Hydraulic fracturing (fracking) is a common method for shale formations, involving the high-pressure injection of fluid to create fractures in the rock. Acidizing, another form of stimulation, uses acid to dissolve rock and improve permeability.
6. Well Testing and Evaluation: After completion, well testing is performed to evaluate its productivity, determine the reservoir’s characteristics, and plan the production strategy. This includes measuring flow rates, pressures, and fluid composition.
Types of Well Completions
Open Hole Completion: Involves leaving the reservoir section without a casing, suitable for stable rock formations.
Cased Hole Completion: The more common type, where the wellbore is fully cased and cemented, offering greater control over the reservoir and the production process.
Importance of Well Completion
Well-completion is designed to maximize oil and gas production in a safe, efficient, and environmentally responsible manner. Proper completion ensures the integrity of the well, prevents the contamination of freshwater aquifers, allows for the effective management of the reservoir, and facilitates the repair or modification of the well to extend its productive life. The specific completion process chosen depends on a range of factors, including the type of hydrocarbons, the properties of the reservoir rock, and the economic considerations of the project.
Production
The production stage in the oil and gas industry is the phase where hydrocarbons are extracted from the ground and processed for delivery to the market. This stage follows the exploration and drilling phases, where the presence of oil and gas has been confirmed, and the wells have been drilled, completed, and are ready to begin the process of extraction. The production stage is critical for the economic viability of an oil and gas project, involving several key activities to optimize the flow of hydrocarbons from the reservoir to the surface and ultimately to the consumer. Here’s an overview of the production stage:
1. Initiating Production
The production stage begins with well completion, which prepares the well for production. This involves casing, cementing, perforating, and sometimes stimulating the well to enhance fluid flow. Once the well is completed, production equipment is installed, including the wellhead (often referred to as a “Christmas tree” in the case of gas wells) which controls the flow of oil and gas from the well.
2. Primary Recovery
Primary recovery uses the natural pressure of the reservoir to bring hydrocarbons to the surface. This can be achieved through the natural rise of oil and gas or by using pumps to increase the flow rate. However, primary recovery typically only recovers a small portion of the reservoir’s oil and gas, often around 10-15%.
3. Secondary Recovery
As the reservoir’s natural pressure depletes, secondary recovery methods are employed to maintain production. The most common technique is water flooding, where water is injected into the reservoir to displace oil and gas towards the production wells, increasing the pressure and stimulating production. Secondary recovery can extract 20-40% of the reservoir’s oil.
4. Enhanced Oil Recovery (EOR)
Enhanced Oil Recovery, or tertiary recovery, involves using advanced techniques to further increase oil and gas extraction from the reservoir. These methods include thermal recovery (injecting steam to reduce the viscosity of heavy crude oil), gas injection (using CO2 or natural gas to pressurize and displace oil), and chemical injection (pumping surfactants to lower the surface tension and improve oil flow). EOR can recover an additional 15-25% of the reservoir’s oil.
5. Production Decline
Over time, all wells experience a decline in production as the reservoir depletes. Managing this decline to extend the life of the well and ensure economic viability is a key aspect of production. Techniques include workovers (repairing or modifying the well), infill drilling (drilling additional wells within the same reservoir to access more oil), and installing artificial lift systems (like pump jacks) to increase flow.
6. Processing and Transportation
Once oil and gas are brought to the surface, they must be processed to remove water, gas (in the case of oil wells), and other impurities. The processed hydrocarbons are then transported to refineries (oil) or to pipelines and processing facilities (gas) for further treatment before being made available to the market.
The production stage is a dynamic and technically complex phase of the oil and gas lifecycle, requiring continuous monitoring, adjustment, and application of engineering solutions to maximize recovery and manage the declining production of wells efficiently. It encompasses a wide range of disciplines, including reservoir engineering, production engineering, and facilities engineering, to ensure the optimal extraction and processing of hydrocarbons.
Well Abandonment and Site Reclamation (if applicable)
Well abandonment and site reclamation are crucial final steps in the lifecycle of a drilling project, aimed at safely closing a non-productive or depleted well and restoring the site.
Well Abandonment: This process involves permanently sealing a well to prevent the migration of fluids between underground formations and to the surface. Steps include:
- Removing Equipment: All production equipment is removed from the site.
- Plugging the Well: The well is sealed with cement plugs at various depths to isolate the production zones and protect groundwater. The top of the well is also sealed.
- Cutting and Capping: The wellhead is removed, and the casing is cut below the surface level. A cap is placed over the top.
Site Reclamation: After the well is abandoned, the site is restored as closely as possible to its original condition. This includes:
- Removing Infrastructure: Any remaining infrastructure, like access roads or pads, is dismantled.
- Soil Remediation: Contaminated soil is treated or removed to prevent environmental damage.
- Revegetation: Native plants are reintroduced to stabilize the soil and restore the ecosystem.
These steps ensure environmental protection and safety, adhering to regulations and minimizing the impact of drilling activities.
Each of these steps is critical to the success of the drilling operation, requiring specialized knowledge, skills, and technology. The process is subject to strict environmental and safety regulations to minimize the impact on the environment and ensure the safety of all personnel involved.