100 1 e1 covers fm Hydraulic Fracturing—Well Integrity and Fracture Containment ANSI/API RECOMMENDED PRACTICE 100 1 FIRST EDITION, OCTOBER 2015 Special Notes API publications necessarily address probl[.]
Terms and Definitions
For the purposes of this document, the following definitions apply
The space between the borehole and tubulars or between tubulars
A subsurface formation that is sufficiently permeable to conduct groundwater and to yield economically significant quantities of water to wells and springs
A component or practice that contributes to the total system reliability by preventing liquid or gas flow when properly installed
A small injection treatment, performed prior to the main hydraulic fracturing treatment, to acquire job design and execution data
The wellbore intervals in a well that are cased with casing and/or a liner
A mechanical device mounted on the casing's exterior aids in running the casing to the desired depth and helps center it within the wellbore.
These devices are engineered to make contact with the wall of the hole during casing installation, ensuring proper centering of the casing within the well and preventing it from touching the wellbore wall.
NOTE 2 These can be either bow spring, rigid, or solid body devices (see API 10D-2)
The completion string, primarily made up of production tubing, incorporates essential components like gas lift mandrels, chemical injection and instrument ports, landing nipples, and packer assemblies This string is installed within the production casing to facilitate the extraction of fluids to the surface.
Casing that supports unconsolidated sediments providing hole stability for initial drilling operations
NOTE 1 This is normally the first string set and provides no pressure containment
NOTE 2 This string can also provide structural support to the well system
Wells where the zone to be fracture stimulated is close to the base of useable quality groundwater
Casing accessories equipped with check valves are essential components of the lower section of a casing string, designed to prevent the reverse flow of cement after it has been placed in a wellbore annulus.
The fluid present within the pores, fractures, faults, vugs, caverns, or any other spaces of a formation
The formation fluid can exist in liquid, gas, or both states and encompasses various types, including hydrocarbons, fresh or saline water, carbon dioxide, and hydrogen sulfide These fluids may occur naturally or be injected into the formation.
Formation integrity test is similar to a leak-off test (LOT) except that fracture pressure is not exceeded
NOTE See definition of leak-off test
Water generally characterized by having low concentrations of dissolved solids
NOTE Multiple regulatory agencies and legal definitions of this term exist and should be checked for applicability to a specific situation
The formations that have the properties to contain fluid pressure generated by the hydraulic fracturing process
The propagation of fractures in rock layers occurs through the use of pressurized fluids, chemical additives, and physical proppants, aimed at facilitating the extraction of petroleum, natural gas, and other valuable substances.
Some regions with water-sensitive shales utilize energized fluid jobs, such as N2, CO2, LPG, or LNG, without chemical additives, as an alternative to traditional water-based fluids Additionally, certain hydraulically fractured operations are conducted without the use of proppant.
The casing that is set when geological characteristics or wellbore conditions require isolation before drilling to the target formation can be continued
NOTE These conditions include, but are not limited to, prevention of lost circulation, formation fluid influx, or hole instability Multiple intermediate casing strings maybe run in a single well
The instrumentation used to control or take an engine offline or disengage a pump when a certain pressure has been reached or a safety feature to avoid an overpressuring event
A procedure used to determine the fracture pressure in the open or exposed formation, usually conducted immediately after drilling below a new casing shoe
A liner is a casing string that does not extend to the top of the well or to the wellhead
NOTE The liner can be fitted with special components so that it can be connected or tied back to the surface at a later time
A device used to attach a liner to the internal wall of a previously set casing string or liner
Conventional liner hangers are secured to the last casing by using slips that grip the inner wall of the previously set casing string, while expandable liner hangers achieve attachment through the expansion of the hanger against the inner wall of the existing casing.
A subset of physical barriers that consists of mechanical component(s)
NOTE Set cement or a hydrostatic fluid column are not considered mechanical barriers
A well that is inactive and where no responsible or liable party has been identified
A device that can be run into a wellbore with a smaller initial outside diameter that then expands externally to seal the wellbore
The ratio of the proportional decrease in a lateral measurement to the proportional increase in length in a sample of material that is elastically stretched
The components including valves, piping, and stacks that protect equipment from overpressure conditions during operations
The innermost casing or casing and liner that is designed to withstand completion and production loads
A liner that is set through the productive interval
The tubing that is run inside the production casing and used to convey produced fluids from the hydrocarbon-bearing formation to the surface
NOTE Tubing can also be used for injection
The determination of quantitative and qualitative (or both) value of risk related to a situation that has a recognized hazard
The joints of casing located at the bottom of the casing string, typically situated between the guide shoe or float shoe and the float collar, are crucial for enhancing cement quality in the annulus outside the casing's base by preventing cement displacement.
The casing run to isolate shallow formations and designed to meet the necessary regulatory requirements for isolating useable quality groundwater
The casing that can be run from a liner hanger back to the wellhead after the initial liner and hanger system have been installed
A cement placement operation performed from the surface by top filling the annulus from surface
General term that includes drill pipe, casing, or tubing
Subsurface water suitable for consumption by humans or animals with or without treatment
NOTE The intent of this term is to define water that is protected by regulation
Ensuring the structural integrity of a well involves implementing effective technical, operational, and organizational measures These solutions are designed to maintain competent pressure seals and minimize the risk of unintended subsurface movement or uncontrolled formation fluid release.
The string of tubulars used to perform service work or to convey stimulation treatment
A measure of elasticity, equal to the ratio of the stress acting on a substance to the strain produced.
Acronyms and Abbreviations
APB annular pressure buildup bpm barrels per minute
DFIT diagnostic fracture injection test
IADC International Association of Drilling Contractors
MOC management of change ppa pounds proppant added ppg pounds per gallon psi pounds per square inch
SPE Society of Petroleum Engineers
General
Well integrity begins with well planning Successful and safe well execution is the end result of good
4.1.1 and early multi-disciplinary planning by drilling engineers, geologists, geophysicists, regulatory personnel, completion engineers, and production engineers amongst others
The fracture stimulation load can be the highest load the well may experience Therefore, the well
4.1.2 design process for wells to be fracture stimulated should begin with the completion engineer providing the drilling engineer with a high level fracture design This design should include
— estimated stimulation loads (treatment and flowback),
— fluid information (including any corrosion issues), and
Determining rock properties essential for fracture design can be achieved through seismic and log data prior to drilling, or by utilizing logs, cores, and fracture monitoring from initial wells in a new area A collaborative approach involving geology, geophysics, drilling, completion, and production disciplines is crucial for a solid design foundation Input from specialists like metallurgists and directional planners can further enhance well design Many operators and service companies employ fracture design and rock mechanics experts who collaborate on these designs.
A drilling engineer must gather essential subsurface information, including the depth of usable quality groundwater protection from local regulatory agencies, formation tops, pore pressure and fracture gradient plots, and current or potential problem zones like injection, loss, corrosion, and flow, along with other area-specific data.
The information listed in 4.1.2 is used to determine the number and location of casing seats/barriers
A comprehensive drilling program and preliminary completion design are crucial before commencing a well The meticulous planning of wells significantly enhances the likelihood of achieving project objectives safely and successfully A multi-disciplinary team must acknowledge the unique characteristics of each well and tailor the well plan accordingly The drilling program should include essential data to meet geological and completion goals in the safest and most cost-effective way Each operational phase must be evaluated for potential issues, risks, and mitigation strategies developed by the team to ensure optimal design.
The plan should highlight any potential hazards along with appropriate contingency plans The
4.1.4 program must be planned to comply with applicable regulations as well as the operator’s policies and practices
When executed properly, the well will provide the necessary containment for fracture stimulation
Additionally, internal and external stakeholder involvement early in the planning phase can result in
Improved overall project performance is achieved through advanced planning, which is essential for meeting regulatory and legal notification requirements specific to local conditions during various operational phases These considerations should be integrated into the project scheduling timeline.
After the well is drilled and prior to fracture stimulation, a review and confirmation of the actual well
4.1.6 construction including barriers should be undertaken to confirm that the well integrity and fracture containment are within specifications for the actual planned fracture stimulation.
Groundwater Sampling
Before drilling a well, it is essential to identify groundwater sources, as well as nearby rivers, creeks, lakes, ponds, and existing water wells If the operator chooses to perform baseline groundwater sampling, this should be done before starting fracturing operations For more detailed information on groundwater sampling, refer to API 100-2.
Offset Well Data
Offset information should be gathered and reviewed Proximity of offset wells, offset water wells, and other potential hazards need to be identified and the risks evaluated
Wells that are currently in operation or abandoned, including orphaned wells, present potential risks to the containment of fracturing and well fluids when located near active drilling and hydraulic fracturing operations This section does not cover well collision, which refers to the unintended intersection of two wellbores To assess and mitigate these risks, operators should define an area of investigation (AOI) around each well undergoing drilling and hydraulic fracturing.
4.3.2.1 An AOI is a three-dimensional area of the subsurface where there is the potential for unintended fluid migration associated with the fracturing process Generally, the AOI is determined by
— geological heterogeneity (layers, permeability, stress, natural fractures, non-sealing faults, etc.);
— direction of hydraulic fracture growth; and
— fracture height and half-length (design and observed)
The Area of Influence (AOI) height is determined by confining layers that prevent fracture growth above them For horizontal wells, the AOI length is primarily dictated by the well's length, with little extension beyond the well's toe The AOI width, which indicates the direction of fracture propagation, carries the greatest uncertainty and necessitates a larger safety factor This width consideration is applicable to both vertical and horizontal wells, and in the case of vertical wells with uncertain propagation direction, the AOI length and width are equivalent.
In the Area of Interest (AOI), operators must identify well penetrations and potential non-sealing faults before drilling While new exploration areas may lack existing wells, many regions contain numerous wells, making it challenging to ascertain their locations and conditions To locate wells within an AOI, operators can utilize various methods, including company records, offset operator records, public databases, regulatory agency records, maps, aerial or satellite photographs, landowner interviews, field reconnaissance, magnetometer surveys for hidden metal casing detection, and satellite radar for monitoring injection pressures and creating 2D maps.
Operators must perform a risk assessment for wells within the Area of Interest (AOI) to evaluate potential impacts on other wells This assessment should examine the location of each well in relation to the drilling and fracturing activities, as well as the estimated fracture growth Additionally, it is crucial to assess the construction integrity of each well, including the status of any plugs, and to identify any faults or geological heterogeneities that may connect the wells.
To safeguard against loss of containment, operators must implement risk mitigation strategies for each identified risk These strategies may involve redesigning the well to circumvent hazards, adjusting the completion parameters, intervening in the well to ensure integrity, monitoring the well during drilling or fracturing operations for signs of communication, or opting not to drill the well at all.
Simultaneous Operations and Offset Well Considerations
In risk assessment, it is crucial to prevent communication between surrounding wellbores, including those that are drilled, produced, completed, fractured, or abandoned Drilling in areas with fractured wells can lead to issues such as lost circulation, stuck pipe, fluid kicks from charged reservoirs, and loss of well control The pressure effects from stimulated wells can extend beyond the modeled fracture length, highlighting the importance of careful planning and monitoring.
Key considerations for managing fracturing operations include establishing a clear process to assess their impact on offset activities such as drilling and production It is essential to create an internal network with stakeholders like the interventions and completions managers to facilitate efficient information exchange and scheduling Building relationships with regional operators and service companies is crucial for sharing intervention schedules and understanding the proximity of offset operations Additionally, investigating regional stress-state directions and developing seismic interpretations of faulting and fracturing regimes are important A conservative estimate of fracture half-length should be generated based on historical data, and all relevant information must be compiled from various sources into a single, easily interpretable format, such as avoidance mapping.
General
Casing design and selection are critical to well integrity The casing shall be designed to withstand the
During the drilling process, various forces such as axial, collapse, and burst are exerted on the wellbore These forces, along with the loads experienced during hydraulic fracturing and different phases of the well's life, significantly impact its integrity and performance.
Ensuring wellbore integrity is essential to maintain the isolation of usable quality groundwater and other unique formations, thus creating a vital pathway for production to reach the surface gathering system.
An operator should have documentation and guidance on casing design, based on accepted industry
Casing utilized in oil and gas wells must comply with API 5CT or equivalent industry standards mandated by regulatory authorities to ensure the protection of usable groundwater quality and maintain overall wellbore integrity It is essential that casing strings are engineered to endure the expected load cases, including drilling, workover, hydraulic fracturing, production, corrosion, and erosion The use of previously employed casing in new wells is not addressed in this document.
Well design and construction generally consists of four main components that are focused on the
This section explores the design considerations for various casing strings, including conductor casing, surface casing, intermediate casing, and production casing, which are essential for protecting usable quality groundwater and managing hydraulic fracture stimulation loads Additionally, it covers important components such as fracture/tie-back strings, casing heads, production liners, and wellheads.
Conductor Casing
The conductor casing is the first casing installed in a well, serving as its foundation Its primary function is to contain unconsolidated surface sediments and, in some cases, support the loads of the wellhead Below the conductor-drive pipe, there is typically harder, more consolidated rock, which helps maintain the stability of the surface sediments during drilling operations The requirements for the conductor hole can vary by state and region, with the typical setting depth ranging from 50 ft to 100 ft (15 m to 30 m), unless geotechnical constraints necessitate a different depth.
The conductor-drive pipe can be installed through drilling or by hammering the casing into position When drilled, the casing is secured with cement, which ensures structural integrity and prevents the downward movement of surface pollutants The drilling process utilizes air or water-based fluids, although there are situations where hammering the conductor casing is a suitable method of installation.
Surface Casing
The surface casing string primarily serves to protect usable quality groundwater by providing isolation It is engineered to comply with regulatory standards for groundwater protection and is also designed to withstand the loads encountered during drilling operations before the installation of the subsequent casing string.
Surface Casing Depth and Useable Quality Groundwater
The surface hole is drilled to a specific depth, taking into account the depth of usable quality groundwater, local geology, regulatory requirements, and pressure control for future drilling This drilling is usually performed with air, mist, water, or water-based fluids Local regulations often specify the minimum depth for setting the surface casing, which must generally be below the known usable quality groundwater In cases where regulations are not available, the surface casing should be set at a minimum depth of 50 feet.
When determining the appropriate depth for surface casing, it is essential to consider several factors: the depth of usable quality groundwater, the presence of a competent formation beneath this groundwater, the need for a sufficient shoe track to handle contaminated cement, potential flow zones, and specific considerations for permafrost in arctic environments.
Centralizing surface casing is essential for ensuring proper casing standoff, which facilitates effective mud removal and cement placement Local regulatory agencies typically outline specific centralization requirements For guidance on selecting and positioning centralizers, refer to API 10TR4 and API 10D-2.
Implementing industry best practices in cementing operations is essential for ensuring the integrity of the surface casing string It is crucial that the surface casing is fully cemented back to the surface to effectively isolate any usable quality groundwater The cement must be specifically designed for surface returns and, at the very least, should adequately cover usable groundwater zones or potential flow zones present in the open-hole section.
If cement returns are not observed at the surface corrective actions shall be taken per local regulations
Casing Testing and Casing Shoe Test
After the surface casing string cement reaches the necessary compressive strength, it is essential to conduct a casing pressure test before drilling out This test, often referred to as a casing pressure test, can be performed right after the cement plug is bumped.
(green cement pressure test) in lieu of waiting for cement to set Local or federal regulations typically dictate surface casing pressure test requirements
5.3.5.2 Immediately after drilling out of the surface casing plus a short interval of new hole, a casing shoe test
Performing a Formation Integrity Test (FIT) or Leak-Off Test (LOT) is essential to ensure that the cement surrounding the shoe has adequate strength to safeguard usable groundwater and withstand the maximum pressures required for drilling the next open-hole section If the FIT results are insufficient, remedial actions may be necessary.
5.3.5.3 In some instances it may be difficult to obtain a valid shoe test due to one or more of the following cases
— The surface casing is set shallow [