Method and Process for Plugging Orphaned and Abandoned Wells

Description

PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Patent Application No. 63/614,592, filed on Dec. 24, 2023, entitled ‘Method and Process for Plugging Wells,’ the entire contents of which are incorporated herein by reference.

BACKGROUND

Field of Use

This novel process aims to be the preeminent standard for plugging orphaned and abandoned wells. Well structure and design differ due to many variables. It is critical for the health and safety of our communities, our country, and our planet that a thorough analysis and customized plugging of each well be applied. With this novel process there will be responsible completion of the oil and gas well lifecycle.

Background of Prior Art

On Aug. 27, 1859, the first successful oil well was completed in Titusville, Pennsylvania. Since then, there have been millions of wells drilled across the United States of America and beyond. Many of these have ended their productive lifecycle and are now scattered across the landscape silently leaking greenhouses gasses such as methane into the atmosphere and surrounding environment. In 2022 the EPA estimated there to be 3.5 million abandoned wells and only roughly a third of those are plugged. Even more concerning according to the Department of Interior, fugitive U.S. methane emissions from abandoned wells had an estimated thermal energy value of 284 kilotons—equivalent to 7.1 million metric tons (MMT) of CO₂ (DOI 2022). As wells become older, the structure and piping in the wells degrades and thus allows stray hydrocarbons such as methane to be emitted and escape to the atmosphere, flow to another hydrocarbon zone, or to an aquifer. These leaking stray hydrocarbons are a large contributor to climate change, and methane gas is more potent than carbon dioxide emissions in the ‘warming’ of the planet during the first 20 years of its release into the atmosphere.

Not only do these un-plugged leaking, orphaned (an unplugged non-producing well with no solvent owner) or non-producing wells awaiting permanent abandonment pose an environmental threat, they also pose a potential health hazard through verifiable water contamination, air contamination, and even direct contact of humans and animals living in proximity to the wells not to mention the potential for combustion.

Identifying these orphaned or non-producing wellbores with Fugitive Methane Emissions (FME) and properly plugging them is already a big problem in the US and one that will continue to grow with time. These wells are a growing safety and environmental issue that needs to be addressed.

Orphaned or non-producing wellbores that leak greenhouse gases such as methane present a special challenge to permanently and effectively plug and abandon. There are numerous variables and circumstances that complicate and necessitate a rigorous methodology that ensures proper plugging and sealing of an orphaned well. These include but are not limited to wellbore damage and wear, undocumented wellbore composition and construction, and unique geophysical circumstances. Limited well construction and operations data from State Regulators; lack of well head; corroded casing presents difficulty in holding pressure; gas pressure buildup in casing and casing by open-hole annulus; difficulty entering well bore due to casing damage or well head damage; wellbore fill due to scale and/or sand; diminished integrity of depleted producing formation at perforations that allows loss of well abandonment fluids into formation; and multiple undocumented well structures, depths, and conditions; multiple gas zones that can leak; supercharged formations resulting from adjacent injection wells.

The current standards and methods for plugging wells are inadequate and likely allowing harm to the environment. A higher standard for plugging wells is vitally important and needed.

DESCRIPTION

Disclosed herein is a novel invention that effectively and thoroughly plugs wells that are orphaned and/or abandoned and have some measure of gas pressure on them. The presence of gas pressure being normative, the details about the gas pressure in the well structure in combination with methane pressure buildup can be consequential. Several factors are significant when considering each individual well to be plugged. These factors include: a) how is the gas pressure manifested; b) what and where is the origin of the gas; c) what is the path of the gas to the surface; d) is the gas from a production zone leaking gas to the surface or from a formation charged with gas that is leaking up through the annulus; e) is there gas in the annuli and/or in the casing; f) does the gas pressure build up over time; g) what are the fluctuations in gas pressure over time; h) what is the pressure of the well at the time of plugging; i) and any other factors deemed relevant to an effective and safer plugging.

Orphaned and nonproducing wells will be identified, monitored, evaluated, and adequately plugged when fugitive methane emissions (FME) are present.

It is an object of the present invention to plug and abandon wells so that the leaking of hydrocarbons to the surface is mitigated as well as hydrocarbon communicating to other zones in the well.

It is an object of the present invention to plug and abandon wells so that the leaking of hydrocarbons to the water aquifers is mitigated.

It is an object of the present invention to more thoroughly plug each individual well to mitigate fugitive methane emissions for a period of 1000 years. This timeframe is the ideal barrier performance target emerging within the petroleum industry. This relatively new engineering industry once aimed for well integrity over a 100 year period. However, consideration of the effects of FME from abandoned wells drives an expanded integrity target for abandonment barriers.

It is an object of the present invention to mitigate the risk to the living from seeping hydrocarbons being leaked from orphaned and abandoned wells.

The life of a plugged and abandoned well is hypothesized to be one thousand years. This method hypothesizes that the wells plugged and abandoned by this method will remain effectively plugged for the life of the well.

The types of wells this method will be applied to include but may not be limited to the following: a) orphaned wells; b) all types of well geometries; c) vertical to highly deviated wells; d) all types of well structures; e) gas pressure build-up, observed as Sustained Casing Pressure (SCP); f) all types of formations; g) wells with depth ranging from shallow to deep; and h) wells with monitored methane pressure buildup.

This novel method for plugging orphaned or nonproducing wells comprises an at least a majority of the following steps: 1) well identification and assessment; 2) plugging method/specification; 3) customized well proposal; 4) initial professional engineering assessment; 5) documentation of procedure performance on site along with recorded results and quality control; 6) post-performance report; 7) post professional engineering assessment; 8) data from performance and assessments is archived; 9) and wells are monitored for any leakages. Many of the operations in each step are normal techniques employed during well construction and remediation operations but not used in a Plug and Abandon process (P & A). Diligent adherence to each operation in each step is required to optimize complete, durable flow barrier application.

In step 1, well identification and assessment, the data necessary to design a plug and abandon (P&A) program is collected for the well in question. The information begins with the location and identification of the well, and the collection of known information regarding the well. In many cases, documentation of the history of the well has been lost over time. The surface condition of the well is determined. Then the well is monitored for some length of time to establish the pressure buildup on the well, where the buildup is occurring, and rate of FME if any.

In step 2, plugging method/specification, a specific type of plugging specification for each well will be created based on the data collected regarding each well.

In step 3, well proposal, a detailed well proposal will be developed based upon the well geometries and well information. This will develop into a working document that will be taken to the well and used as the guidelines for the specific well. The well information collected, as well as the pre-job testing data, including laboratory cement design data, will be inputs for the well proposal.

In step 4, initial professional engineering assessment, Professional Engineer (PE) certification based upon the proposal developed in step 3 will confirm proper procedures, as well as proper methods and materials will be used on the well. This will ensure the P&A plan is optimal to create durable flow barriers to prevent leakage for the estimated 1000 years and beyond.

In step 5, performance on site, the P&A work on the well is executed and documented. This step includes but may not be limited to the proposal generated, preparation of the wellbore for abandonment, placement of at least two mechanical or pumpable well sealant barriers across the entire well cross section, barrier placement confirmation, training of the operational staff on site, a decision tree that provides contingencies depending on how the actual work happens, onsite calculations, and on-site data collection. Any deviations from the proposed procedure will be documented to analyzed to confirm the revised procedure conformed to the plugging method.

In step 6, post-performance report, a detailed report will be generated with all the data from the job and be compared to what was proposed. This will be a deliverable documenting of what transpired on the performance of the plugging. Deviations from proposed procedure will be analyzed to ensure procedure revisions still deliver desired performance outcomes. Any process improvements developed in the deviation analysis will be considered for process revision.

In step 7, post-performance professional engineering assessment, PE certification will be generated based upon the actual performance of the P&A operation and its relation to this standard novel method. This review would assess if what happened on the well was in line with the novel method and standards developed. Many times, the actual procedures and methods will be modified on the well site due to unforeseen circumstances while performing the work.

In step 8, data from performance and assessments is archived, all the data developed and acquired will be archived into a searchable database to allow retrieval and will be available for future reference and study. Detailed information from Step 1 through Step 7 will be documented and placed into the database.

In step 9, ongoing monitoring of leakage, wells plugged by this method will be monitored for years after P&A completion. The data taken in this process will include detection of methane escaping from each individual well abandoned according to the subject method. Periodic analysis of this data will allow an assessment of the durability of the flow barriers established by the plugging process.

Regarding a detailed description of step 1. It is necessary to do a thorough evaluation of the well prior to performing any operations to identify the issues and roadblocks that will complicate the plug and abandonment process. A document is kept that summarizes the important parameters for this evaluation. The issues that need to be determined for step 1 are as follows but may include other issues to be later determined: a) the casing sizes and location; b) the condition of the casing in the well as to the corrosion and the ability to withstand pressure; c) the surface for well access; d) casing weights and types; e) access down through the well with tubing and or wire line; f) fish in the hole; g) magnitude of pressure build up during the plugging process; h) height of cement fill in each annulus; i) pressure on the well in the casing and the annulus; j) and the fluid level and fluid type in the well.

There are a variety of tools and techniques available to address and resolve the issues identified in the plugging and abandonment process. These include diagnostic tools for assessing well conditions and operational tools for implementing necessary interventions. Some important tools are discussed including but are not limited to: a gauge ring and collar locator; bond logs; casing collar locator log or free point log; casing severing tool; cast iron bridge plug; chemically-triggered gelled or set cement plug base such as sodium silicate.

A gauge ring and collar locator is typically run to determine any obstructions in the well and any places that the casing could be thin or have holes. In addition, these can also show any perforations that may have been added that are not in the API data on the well.

While not always required, bond logs can be useful diagnosing the situation for a well that is going to be plugged. Both acoustic and ultrasonic bond logs can be used; however ultrasonic logs are much more expensive and may not be cost effective when plugging and abandoning wells. Acoustic Bond logs can provide the following information if run and evaluated properly: location of cement in contact with the casing; completeness or incompleteness of the cement bond to the pipes; qualitative measure of the cement to pipe bond; and qualitative measure of the cement to formation bond. Performance and interpretation of bond log can determine if and where the Perf and Seal method of barrier placement is performed. The Perf and Seal method is designed to inject cement slurry through perforations shot through the casing into the annulus behind the casing and into the formation adjacent to the wellbore. This method entails perforating the casing at depth chosen to place a complete flow barrier in the well, injecting well fluid into the perforations at a pressure sufficient to establish an injection rate into the formation, injecting a settable sealant fluid using the Hesitation Squeeze Technique.

The following is a general procedure for Hesitation Squeeze Technique: a) clean the perforations by pumping water through a sized orifice to obtain clean perforations b) pump water to the perforations, shut in annulus, and pump water to determine pump-in or injection pressure and rate with water; c) mix required cement slurry volume (including volume for plug left inside casing and volume of slurry to be injected through perforations) and displace the cement down to the perforation location; d) shut in annulus and pump to increase pressure to achieve the injection pressure; e) pump at least 2 bbls of cement slurry into the annulus and formation; f) stop pumping and shut in well with elevated injection pressure trapped in the well, g) monitor pressure for 15 minutes without injection (hesitation), h) resume injection monitoring pressure, i) if injection can be established, pump approximately 1 additional barrel of slurry through the perforations, j) hesitate one more time for 15 mins static and monitor pressure, and k) leave the remainder of the cement inside the casing. Injection pressure should increase with each hesitation. If injection pressure reaches maximum wellhead pressure, stop injection and shut in well.

Usually a Portland cement slurry with special additives is injected through the perforations and into the annulus and formation while leaving a portion of the sealant fluid inside the casing, and waiting on the sealant to harden to form a continuous solid seal. This seal completely fills the wellbore cross section and extends into the formation. If poor bond to surface casing below lowest usable water zone is indicated by bond log, section below water zone is perforated. Then fluid pressure is applied to break down the formation allowing fluid injection. Cement slurry is injected into the formation and allowed to set forming a complete seal across the entire wellbore and into the formation thus protecting the water zone from contamination. Perf and Seal method can also be applied to place an extra flow barrier in other well locations in which barriers of questionable integrity exist or in which well conditions prevented barrier placement exactly as designed.

The next diagnostics tool that can be useful in looking at a potential P&A well is a Casing Collar Locator/Free Point Log. This log can help identify potential problem areas with the casing in the well as well as locating potential areas of pipe that are not cemented. This log can help assist in determining the competency of the casing and the location of perforations and production zones. Many of the wells that will be plugged have uncemented upper portions of casings in them. These wells have one or more casings that the upper portion of the casing string is not cemented in the well and can be cut and removed. Removal of this uncemented casing is important when plugging to abandon a well because it allows unobstructed access to a large cross section of the well bore; in some cases to the entire cross section. This log can be helpful in determining the following issues: areas where the casing has significant corrosion; casing splits or holes; major areas of buildup of materials inside casing; potential perforations that were not documented; and indication of the free point of the casing to allow parting and pulling of said casing.

A casing severing tool will be used to separate the lower portion of casing that will remain in the well from the upper casing portion that is free. The free casing will be pulled from the well for salvage. The severing tool will be used to sever the pipe diametrically at any location deemed reasonable by the free point measurements.

A cast iron bridge plug may be used to provide a pressure resistant mechanical base where cement is needed to stay at any location in the wellbore.

A special wiper dart known as a pump-down separation tool can also be used to provide a mechanical base for a sealant. These can be pumped down tubing and placed inside casing and provide a physical base for sealant fluid to be placed on the top. This base would hold sealant fluid in place to set at the specific location needed in the well.

An important parameter to understand is where the fluid level is in the well. It is always recommended to shoot a fluid level in the well. In addition, measurement of the volume of fluid to fill the well is important and determining when the fluid level falls due to the hydrostatics in the well.

In regard to a more detailed description of step 2, this method's plugging specification, all penetrated zones with potential production that have been identified as requiring isolation should be isolated from each other and the surface by a minimum of two permanent barriers. These two permanent barriers may be combined into a single large permanent barrier provided it is as effective and reliable as the two barriers and is an appropriate method to achieve the objectives that two barriers would otherwise provide.

A specially designed sealant system, most commonly Portland cement slurry, should be used for the barriers for plugging and abandoning. Cement has been used in the industry for over 100 years and has proven itself to be durable if it is designed correctly.

A column of 200 ft of good cement will constitute a good barrier design across the “critical zone”. A range of 100 ft to 500 ft of cement could be applicable to some wells. There can be several critical zones in the well. These will be described in detail in the following sections. As a rule, the U. S. land-based P&A industry practice is normally restricted to a minimum 100 ft of good cement above the top of a critical zone. Good cement is defined as cement that is placed with proper volumes and can be tagged to be at the location where the plug was to be placed (within acceptable limits). This novel method recommends a minimum of 250 ft of cement above the top of the critical zone. A range of 100 ft to 500 ft of cement could be applicable to some wells. In addition to the primary barrier on top of the zone in question, an additional barrier needs to be placed so that every critical zone in the well has at least two barriers between it and the surface of the well. The following general guidelines are to be used for the location of the plugs in a wellbore:

The bottom production zone is the first critical zone of concern. First either a wire line or tubing will be placed in the well to determine the accessible depth of the well. If there is buildup at the bottom of the well with scale or sand from production, a decision will need to be made on where the cement plug can be and should be placed. A cleanup operation may be required prior to placement of the first plug in the well.

If the well cannot be cleared to allow access to the perforations with tubing, a volume of cement slurry sufficient to penetrate and seal the perforations, cover the perforations, and fill the casing to a level of 250 ft above the top perforation will be injected past obstructions and placed to form the initial barrier. In this instance, the exact placement of the barrier cannot be confirmed, so a Perf and Seal operation will be performed in the production casing at some depth up the hole.

Other production zones up the wellbore should be treated like the lower production zones and around 250 ft of cement should be placed above these zones.

A 200-ft barrier of cement should be placed at the top of a liner. Again, a range of 100 ft to 500 ft of cement or other material could be applicable to some wells. The liner lap is a potential area for communication of gas and thus attention must be given to ensure gas does not leak at this juncture.

Every shoe of the casing strings, except for that of the production casing, is required to have at least a 250-ft barrier to insure containment of the hydrocarbon in the well.

A cement plug must be placed inside the casing stub, which refers to the remaining section of casing left in the wellbore after the upper portion has been severed and removed, that extends to the wellbore above the stub when the casing above the stub is removed.

It is important that the freshwater aquafers be protected from the invasion of methane hydrocarbon. Once the lowest usable aquafer zone is determined, at least a 250-ft barrier plug below it must be placed. These applications will require the Perf and Seal method of perforating and placing barrier material in the annulus. Placement ideally entails breaking down the formation at the perforations, injecting cement slurry into the parted formation, and allowing it to set. If formation cannot be broken down to accept injection, squeeze placement of the cement into the perforations and any annular flow paths creates a full well bore seal.

At the surface, the final plug inside pipe must be 200 ft of barrier material. This is to ensure the well has final flow barrier at the surface to ensure any fugitive methane migrating to this point is prevented from escaping to the atmosphere.

The surface pipe open hole annulus can be source of leaking hydrocarbon, thus it is necessary that this annulus has a secure barrier material placed by the Perf and Seal method. The adequacy of the barrier may be determined from the original cement job, or a remedial job done when plugging and abandoning the well.

When the production string is severed a cement barrier must be placed inside the production string extending into the well bore above the production casing stub and in the non-cemented annulus. Both areas will have cement placed to ensure no communication of fluids up the wellbore or annulus.

It is very important that all plugs remain where they are placed in the wellbore and no movement in the wellbore occur due to density while being set or after placement i.e., that the cement solids do not settle to the bottom of the plug and release water at the top. Each of these issues will be discussed in detail.

For a cement plug to remain stable in the wellbore there must be a base for the cement plug to sit on. This could be a higher density fluid, mechanical bridge, chemical bridge, bottom of the wellbore, the top of a set cement plug below, or a high-viscosity mass created in the well bore by interaction of reactive fluid combinations. Potential devices that are allowed to establish a base are: a bridge plug, wiper balls, a pump-down separation tool; a cement plug base; a reactive, viscosifying fluid system, and/or a sand or barite plug.

Bridge plugs are normally set with wireline both electric line and slick line. These typically will hold pressure by themselves and can be used to place a barrier base in casing anywhere in the wellbore necessary. Note however that for the bridge plug to set, there must be good casing at that location.

When the wellbore has some level of fluid in it, a foam wiper ball can be used as a temporary base. This ball can be pumped down tubing to any location in the well that has fluid in it. Cement can then be placed on top of the wiper ball and allowed to set.

There are available separation tools that can be deployed by wireline and/or pumping through tubing. The tool is placed with wireline, slickline or through tubing down to location in the casing or wellbore and deployed. These tools will expand to the size of the casing and create a base for a barrier material to be placed upon. There are also tools that can be deployed by pumping the tool as a collapsed diameter to be pumped into place and then once it exits the tubing will expand the diameter of the casing or hole. The sealant material can then be placed on the established base and allowed to set.

Cement can be placed in water or mud that will eventually set and provide a bottom for a competent cement plug to be placed above it. A 200′ plug placed in water or drilling mud may only have 5 to 10 ft of solid cement left at the top due to the heavier cement slurry falling through the lighter fluid. This solid cement, however, at the top may be enough to allow a competent cement plug on top of it as a bottom.

Sand can be placed into a well on top of a fish or constriction in the pipe to form a bridge of sorts. This sand pack can then be used as a bottom for the cement slurry to be placed upon it and set and form a base for a permanent barrier. Typically, sand plugs cannot support much force so they are limited to a small volume of cement. However, the sand bridge could be used to set and create a base by which larger lengths of cement can be placed up it. A precipitation/accelerated cement setting reaction can be produced upon mixing sodium silicate solution with Portland cement slurry. The two fluids form a highly viscous or solid mass on intermixing. Causing this intermixing at the point in the well targeted for the plug base can provide sufficient separation and stability to build a suitable cement plug above.

It is important that once a plug is placed, the plug material does not separate due to instability in the cement slurry in place. Prior to the job, tests need to be conducted that measure both the free fluid separation and the solids segregation of the cement slurry to be used in the well. These tests will need to be conducted at downhole well conditions, i.e., under pressure, temperature, and chemistry of the wellbore fluid.

The barrier material of choice is Portland cement. This is not the only material that can be considered (e.g. epoxy resin) but at this juncture Portland cement has a long history documenting the ability to provide integrity as it has been used for 100 years to plug wells. It is important that the cement system utilized should be optimized to insure maximum seal and long-term durability. In this document we will provide recommendations for use of Portland cement with additives to provide the desired seal. There are several parts to the Portland cement system which are significant to proper design and longevity: type of cement system; mixing water for the system; additives used in the cement system; condition of the various surfaces for cement bond; the fluid containing the cement plug; and/or specialty fluids for optimal cement bonding to casing and/or formation.

Portland cement systems are used for the barrier plugs for this novel method. A variety of cement types can be used for the plugging operation. The following table is a summary of the type of cement system used and the standard slurry properties produced by each system. All the cement systems in the following table can be used.

TABLE 1
Types of Portland Cement Acceptable

	Mix Density	Normal Water	Slurry Yield
Cement Type	(lb/gal)	Required (gal/sack)	ft3/sack
Type 1	15.6	5.2	1.18
Class A	15.6	5.2	1.18
Class C	14.8	6.3	1.32
Class H	16.4	4.3	1.06
Class G	15.8	5.0	1.15

Table 1 provides details for the various types of cement systems that can be used in the Rebellion Method for plugging wells. Of vital concern is that the slurry achieves the designed density downhole. To accomplish this, the correct cement-water ratio must be used. If a density is different than stated in Table 1, the cement will have less or more water than designed and the resulting density downhole, under temperature and pressure, will not be as calculated. It is important that the cement slurry be optimized at the correct density to achieve the set properties necessary to provide optimal sealing and durability.

It is important that the water used for mixing of the cement slurries be freshwater as contaminants in water can impact the quality of the cement. Freshwater will be defined as drinking water. Water from wells or ponds or other locations will not be acceptable for the mixing of the cement slurries due to the potential to contain contaminants that will affect the cement properties, setting time, and long-term durability. Freshwater, i.e., drinking water, will provide the best option for the cement slurries to set to full strength in order to protect and seal the well for the duration of the life of the well.

Several different material properties are required to optimize the plugging, setting, and sealing of the cement barrier. The performance of the cement slurry requires special additives that are used to achieve the necessary properties and placement of the cement.

A fluid loss additive is required for all the primary cement barriers used in the well. Fluid loss additives prevent the premature dehydration of the cement while it is setting across permeable formations and or small casing holes. It is recommended that an API Fluid Loss Test be conducted with the cement materials from the wellsite to produce an API fluid loss of less than 300 mL/30 min at the downhole temperature and pressure of the well. Any type of fluid loss additive can be used, but the result much limit the API fluid loss to acceptable values.

It is recommended that a post-set expansion material be used in the primary cement barriers. This material will promote linear expansion after the cement has set. It is recommended that the loading of expansion material be at least 0.5 to 1.0% loading by weight of cement. It is also recommended that a Liner Expansion Test measures the expansion of the cement system using field materials be at least 0.1%.

If the temperature of well is high enough, set retarders may be included in the slurry design to ensure the fluid time of the cement slurry is long enough to be placed safely at the proper depth in the well. A Thickening Time Test (TTT) should be conducted on the cement barrier material from the wellsite prior to any pumping operation. There should be a safety factor of at least 2 hours above the time necessary to place the cement plugs in place.

If the temperature of the well is in excess of 230° F., then a strength stabilizing additive should be used in the cement. Normally this is crystalline silica at a 100-mesh or 200-mesh particle size. The amount recommended is 35% by weight of cement.

Hydrocarbon products may create films of hydrocarbon on the casings. Cements do not bond very well to hydrocarbons. Therefore, special cement flushes may be employed to remove the oil film from the casing to ensure proper bonding of the cement with the pipe.

The fluid that the cement barriers are exposed to is very important. It is vital that freshwater or water-based drilling mud be used in the well and no salt or brine are allowed to encounter the cement. Cements exposed to brine can deteriorate with time.

When hydrocarbon films are present in the wellbore. Pre-cement flushes may be used before the cement slurry to remove films and promote a water-wet surface. The volume of the fluid is recommended to be at least 5 bbl or 50% of the cement volume, whichever is greater.

In regard to pre-performance testing, Table 2 summarizes the performance properties that are required for the cement barrier to optimally seal the well. These are testing prior to the job with materials that will be used for the job. This is done to ensure that the cement system meets the criteria set forth in the Standard Recommendation.

TABLE 2
Performance Properties for Optimal Well Sealing

	Test	Requirement		Additive
	Thickening	Plus 2		Concentration
Property	Time	hours of	Additives	0.1 to 0.5%
Thickening	Test/HTHP	longest	Type	By Weight
Time	consistometer	placement	Retarders	of Cement
Fluid	API Fluid Loss	<300 mL API	Polymeric	0.4% BWC
Loss	Test at Well		Materials
	Temperature
Slurry	Free Fluid	Trace	Gelling	NA
Stability	Test at Well	or less	Materials,
	Conditions		Water
			Requirement
Set	WOC Time	<8 hours	None	NA
Time	at Well
	Temperature
Unconfined	Compressive	>1000 psi in 24	None	NA
Strength	Strength	hours at well
	at Well	conditions,
	Temperature	>3000 psi
		ultimate
		at well
		conditions
Expansion	Expansion	<0.1% liner	Reactive	1.0% BWC
	Molds at Well	expansion	Post Set
	Temperature	at well	Expansion
		conditions	Material
Set	Water	<0.1	NA	NA
Permeability	Permeability	millidarcies

During the plug and abandoning operations there is one test that is performed on cement slurry taken from the mixing operation: Waiting on Cement Penetrometer (WOCP).

A sample of the cement slurry is taken from the mixed slurry that is pumped into the well, and the density is measured. That sample of cement is subjected to a WOCP test is at the well site. A heated water bath is used to bring slurry temperature to the well temperature in the well at the plug location. The sample is penetrated periodically via a handheld penetrometer. This is performed every 2 hours until the cement slurry achieves 50 psi or greater. This then provides the time that the well operations can continue.

Samples of materials are obtained from the well site to allow quality assurance testing of the cement slurries pumped into the well. This testing is performed in a cement testing laboratory after P&A completion. The following samples are to be obtained: sample of the neat cement (at least 3 gallons); sample of the mix water used (at least 3 gallons); and four cube samples of slurry mixed for each of the cement barriers (placed into water in a bucket).

The following tests may be conducted after the job:

	Property	Test	Requirement	Time
	Unconfined	Compressive	>1000 psi in 24	One month,
	Penetrometer	Strength	hours at well	6-month,
	Strength	at Well	conditions,	one year
		Temperature	>3000 psi
			ultimate
			at well
			conditions
	Density	Archimedes	+ or −1.0 ppg
			of mix density
	Set	Water	<0.1	One month,
	Permeability	Permeability	millidarcies	6-month,
				one year

The mixing of the cement barrier slurries, details regarding pumping of the slurries, and the placement of the barrier are important criteria to the success of the well plugging operations.

The mixing operation of the cement barrier slurry is critical. There are several important aspects of this operation. First the composite cement composition should be batch mixed. This novel method recommends a batch mixing process using a batch mixer capable of mixing at least 8 bbls of cement slurry at one time. It is critical that all the cement mix, water, and additives are to be mixed and placed into a batch tank. This is done for several reasons. First a uniformity of cement must be obtained. The slurry is mixed to a specific density. That density will dictate the volume of water, cement, and additives so that an optimal slurry is produced. A pressurized mud balance should be used to verify that the cement slurry density is within the range of acceptability. Second, all the slurry for the plug will have the same amount of shear and wetting time at the surface to ensure uniformity and optimal performance downhole. Several important aspects of the batch mixer are necessary: mixing volume of 8 to 20 bbls; overall stirring of the slurry in the batch tank with a paddle stirrer inserted into the mix fluid; recirculation of the slurry out of the batch tank back into the batch tank with recirculating pump; ability to place the dry additives into the batch tank by hand; ability to obtain slurry samples.

Once the slurry is mixed, it must be pumped into the well. In the plugging operation, the rate the slurry is pumped into the well and the displacement should not exceed one barrel per minute to ensure minimal intermixing with the well fluids and displacement fluids. A piston or plunger positive displacement pump is recommended. It is also important to monitor the volume of the slurry pumped into the well as well as the volume of the displacement fluids. This could be with a stroke counter on the pump or direct measurement with displacement tanks. It is important to keep the pump rate low to minimize the intermixing of the displacing fluid and the well fluid with the cement slurry.

Several different placement methods are acceptable for producing competent cement plugs in a well. Depending on the well conditions, one technique may be preferred over another.

The simplistic method of placement of a cement plug into a well is the Bull Head Method. This requires that the perforations at the bottom of the interval can take fluid. This method is also used when fluids can be pumped to locations in the wellbore, but workstrings cannot be placed down to those locations. In the Bull Head Method, the fluid is pumped directly into the production casing and displaced into position. A specific volume of cement slurry is pumped into the well to yield the desired fill requirements. A specific volume of displacement fluid is pumped until the slurry is at desired location.

The most desired method of placement of the cement plugs in the well is through the Balanced Plug Method. This method places the tubing or work string into the well to the depth that the bottom of the cement plug is to be. The cement slurry is then pumped into the work string down to the bottom and up the work string via the casing annulus and displaced with well fluid down the tubing until the length of the cement slurry in the annulus is the same as the length inside the pipe. At this point the cement slurry is balanced as to the location and hydrostatic pressure. The work string is then pulled slowly out of the well leaving the cement plug in the well.

The coiled tubing pump and pull method of setting a balanced plug is somewhat similar to the method described above except for the length of coiled tubing at the surface and how the plug is pumped. Once the cement slurry is pumped to the bottom of the coil the coil is removed as the slurry is pumped into the wellbore. The only displacement needed is the total displacement of the coil down to depth.

Once the cement barrier is placed into the casing and enough waiting on cement (WOC) time has passed, it is necessary to tag the top of the cement barrier. This can be done two ways, either tagging with slickline or tagging with tubing. The tag depth should be noted and recorded. It is necessary that the plug tag is approximately where it was planned. There is some variability in this depth due to the various inaccuracies with the fluid volume measurements.

Hydrocarbon flow in an orphan well can come from either inside the casing due to production zone leakage, through holes in the pipe, from the openhole sections, or flow directly up the annulus. Even cemented annuli can flow hydrocarbon due to micro-flow paths being created in the annulus. In any case, the flow of hydrocarbons that currently exists or will be created in the future needs to be addressed and stopped by the plugging of the wells. Several general guidelines will be presented below that will provide the basic procedures and methods to get cement barrier material into various annuli.

As in the casing barrier application, it is important to have two annular cement barriers to the surface to ensure long-term seal of the wellbore. Each barrier is to be 100-ft length if possible. However, it is not possible to validate or ensure that an annulus squeezed with cement will achieve this result. It is however important that the squeeze performance meets minimum requirements as to pressure and pump in.

In order to achieve a fluid flow area in the annulus it is necessary to perforate the casing and be able to establish a pump-in rate. The perforation density (number of perforations per foot of casing) should be as high as possible (this varies for the size of the casing) and have a length of at least 5 ft of perforations. The depth of the penetration should be sufficient to make sure that the entire annulus has been penetrated so that any flow channels can be sealed. Perforation and seal depth should be selected or determined. Depths shallower than 3000 ft are recommended to ensure creation of horizontal pathway for cement pumped into the perforations. With water in the hole, perf the location with high density, deep penetrating charges.

Run squeeze packer to 50′ above the perforation location (this is to minimize the pressure applied to pump into the formation from being transmitted to all of the casing string to the surface). Conduct Hesitation Squeeze technique as described previously.

Results of field application of this plugging method to orphaned wells are presented below.

A group of wells in Oklahoma that were plugged and abandoned with the Rebellion Method between March 2023 and June 2024. All were orphan wells with measured wellhead pressures and methane release rates of <10 to 1,800 psi and 2 to 300 mcf/d respectively prior to the start of plugging and abandonment.

A high majority of the wells showed no detectable methane emission immediately after plugging. This initial 94.6% success rate is outstanding. Few real statistics on success rates for abandonment are available, but most estimates are considerably lower-some even as low as 50%,^{1 1} Wigston, A., Wiliams, J., Davies, L., and Ryan, D. 2019. “Technology Roadmap to Improve Wellbore integrity SUMMARY REPORT. M134-59/2019E-pdf. www.doi.org/10.13140/RG.2.2.36212.30081

The two leaking wells were monitored while remediation procedures were developed. Remediation became unnecessary when emissions from both wells stopped before the remediation operations could begin. Since the emissions stopped within 90 days after P&A, the ultimate short-term success rate is 100%. Continued monitoring confirms no further fugitive methane emissions from any of the 37 wells. Monitoring which will continue over the prescribed 20-year period will complete the evaluation of the Rebellion success.

A study of these two problematic wells identified two areas for modification to improve barrier effectiveness and continued P&A success-cementing and process control. The source of those leaks for the two wells was determined (by industry experts) to likely be gas trapped in the wellbore during plug placement combined with very slight, but critical deviations from the stipulated Rebellion Methodology. The Rebellion Methodology has since been adjusted to eliminate the potential for this problem in future jobs.

In the project review, it was noted that the well plans for both wells did not take into account the impact of the cement formulation on cement shrinkage and set time or the impact of plug stability derived from a mechanical base. However, a key part of the Rebellion Method is not only specification of products and exact steps but also verifying that the wellbore has been sealed and there are no FME. The review and verification step caught the issue and at the time of this article, the methane emissions for both wells have ceased.

Essential elements of the present invention comprise the well identification, plugging method specification; tailored well proposal, initial professional engineering assessment, on-site plugging, post-plugging performance report, post professional engineering assessment, data from performance and assessment is recorded, and wells are monitored for issues and leakages.

The present invention is implemented by a particular well being identified, a plugging method specification, a tailored well proposal, initial professional engineering assessment, on-site performance of plugging, post-plugging performance report, post-professional engineering assessment, data collected from all steps is archived, and well is monitored for issues and leakages.

The present invention of plugging a well with barriers to prevent FME for estimated 1000 years is implemented by following a comprehensive method of accessing well condition, designing barriers to seal the hydrocarbon in situ thus preventing emission at the surface, contamination of water supply, or pressurizing formations up the well, and documenting performance to confirm proper barrier placement. A minimum of 2 flow barriers are established in the well. These barriers extend across the entire borehole cross section. Barrier materials comprise Portland cement or other hardenable material with sufficient durability, adhesion, and Impermeability to arrest methane migration.

The present invention is a method and process for more effectively plugging orphaned wells.

The present invention is a method and process for mitigation harmful gas emissions from orphaned or abandoned wells.

All elements of the device can be modified to accommodate updates and advancements in technology.

The invention relates generally to systems and processes for plugging orphaned or abandoned wells.

Although the invention has been described in detail with reference to several embodiments, additional variations and modifications exist within the scope of the spirit of the invention as described.

Although the disclosed invention has been described with reference to various exemplary embodiments, it is to be understood that these embodiments are merely illustrative of the principles and application of the present invention. Those having skill in the art would recognize that various modifications to the exemplary embodiments may be made, without departing from the scope of the invention.

Moreover, it should be understood that various features and/or characteristics of differing embodiments herein may be combined with one another. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the scope of the invention.

Furthermore, other embodiments of the invention will be apparent to those skilled in the art from considerations of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a scope and spirit being indicated by the claims.

Finally, it is noted that, as used in this specification and the appended claims, the singular forms “a”, “an”, and “the,” include plural referents unless expressly and unequivocally limited to one referent, and vice versa. As used herein, the term “includes” or “comprising” and its grammatical variants are intended to be non-limiting, such that recitation of an item or items is not to the exclusion of other like items that can be substituted or added to the recited item(s).

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of the novel process and method.