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Decommissioning oil field facilities
Module 7a

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Oil recovery mechanisms

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Field production life

The production life of oil and gas fields depends on many factors: Size of reserves Field daily production rate relative to reserves Application of various production mechanisms; primary, secondary, and tertiary Economic limit of the field, which depends on: Operating costs Commodity prices Remaining reserves Well/field decommissioning

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Why abandon a well?

They are no longer needed to support oil and gas development or because an operator’s mineral lease has expired. As of June 2013, approximately 151,000 abandoned wells exist in Alberta, representing 35% of all wells in the province. Before a well is abandoned, the licensee must inform all affected landowners of the proposed abandonment. Licensees are also required to test the well to ensure that it will not pose any risk to the environment or the public. The operator must design an abandonment program that identifies any wellbore integrity issues, all oil or gas formations, and all groundwater zones. They must also evaluate the cement present in the well.

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When to abandon a well?

Check the expected remaining reserves Identify production problems and remedial solutions The economic feasibility of working over the well or applying new technology to increase productivity Can the wellbore be used for water injection or as an observation well?

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Typical performance of waterflood projects

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What are orphan wells?

In the upstream oil and gas industry, an orphan is a well, pipeline, facility or associated site which has been investigated and confirmed as not having any legally responsible or financially able party to deal with its abandonment and reclamation. There are 1,590 orphan wells in Alberta awaiting abandonment and clean-up. Costs onshore are anywhere between $60,000 to $300,000, depends on depth, location and geological formations. Because of low oil price, 20 oil and gas companies went into receivership in 2015. Over the past 25 years, the industry spent over. $MM200 on well abandonment and clean-up. Inactive wells pose a variety of environmental and financial risks to the public. Most inactive well sites leak methane and can contaminate soil and groundwater and support invasive weed growth. They also fragment ecosystems, devalue property and prevent farmers making full use of their land.

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Inactive well in Alberta (1993-2015)

There are over 57,000 orphan wells in USA, mostly drilled before 1980 when rules were not firm about well abandonment.

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Abandonment procedures

Removing downhole equipment This can be done using an existing drilling or conventional workover rig with the capacity to pull out of hole all downhole equipment, such as production tubing, downhole pumps and packers. If tool removal is not possible due to stuck or lost equipment, well abandonment strategies must be revised and approved by concerned authorities. Wellbore cleanout After the removal operation, the wellbore needs to be cleaned from fill, scale and other debris. To this purpose the wellbore is flushed by a circulation fluid with sufficient density to control pressure and with the physical properties that enable the removal of debris. Plugging The principal technique applied to prevent cross flow between permeable formations is plugging of the well, creating an impermeable barrier between two zones.

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API classifications of oil well cement
Depths cement classifications are used at
Class A: Surface to 6,000 feet (1830 m) depth when special properties are not required. Available only in ordinary type (similar to ASTM C 150, Type I) Class B: Surface to 6,000 feet (1830 m) depth, when conditions require moderate to high sulfate-resistance. Available in both moderate (similar to ASTM C 150, Type II) and high sulfate-resistant types. Class C: Surface to 6,000 feet (1830 m) depth, when conditions require high early strength. Available in ordinary and moderate (similar to ASTM C 150, Type III) and high sulfate-resistant types. Class D: 6,000 feet to 10,000 feet (1830 m to 3050 m) depth, under conditions of moderately high temperatures and pressures. Available in both moderate and high sulfate-resistant types. Class E: 10,000 feet to 14,000 feet (3050 m to 4270 m) depth, under conditions of high temperatures and pressures. Available in both moderate and high sulfate-resistant types. Class F: 10,000 feet to 16,000 feet (3050 m to 4880 m) depth, under conditions of extremely high temperatures and pressures. Available in both moderate and high sulfate-resistant types. Class G&H: Used as basic well cement from surface to 8,000 feet (2440 m) depth as manufactured or can be used with accelerators and retarders to cover a wide range of well depths and temperatures. No additions other than calcium sulfate or water or both, shall be blended with the clinker during manufacture of Class G or H well cement. Available in moderate and high sulfate-resistant types.

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Well abandonment

	Well abandonment required sealing off hydrocarbon bearing zones to prevent any leakage and protect freshwater aquifers. Removal of the wellhead (Xmas tree) and all surface facilities (tanks, pumps, flowlines, etc.) Clean-up of area at surface and bring the landscape to its original condition.

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Examples of poor well abandonment

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Well abandonment

Well abandonment operations are considered routine based on the following: Type of well Well geographic location Impact of well in any oil sands zones Absence of wellbore problem

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Well abandonment

Well abandonment operations depend on: The location of the well within the province Whether the well is in the oil sand area Type of well completion; open hole and cased hole

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Unacceptable plugs

	For formations shallower than 1,500 m, the top of cement should be at least 15 m above it. For deeper formations than 1,500 m, the cement top should be at least 30 m

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Open-hole well abandonment

Well abandonment operations depend on: Cement plugs must set in sufficient length to ensure no cross-flow between porous zones occurs Plugging program must include all non-saline groundwater and must isolate all porous zones from hydrocarbon zones

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Open-hole well abandonment

Porous zones are defined as: Carbonates: Effective porosity > 1% Sandstones: Effective porosity > 3% Offset production zone with conglomerate, fractured carbonates or shales that have been produced from a well regardless of the porosity Any zone with a drill stem test formation fluid recoveries greater than 300 linear meters or gas volume greater than 300 m3

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Open-hole well abandonment

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Cased-hole well abandonment

Well abandonment operations depend on the location: Each completed zone must be abandoned and cement plugs must set in sufficient length and to ensure no cross-flow between porous zones All non-saline ground water must be isolated with cement

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Cased-hole well abandonment

Surface casing string(s) must be cut at minimum 2 m from surface (final contour elevation) if well is: Within 15 km of urban development In an area with special farming practices, such as drainage work, peat land, or deep tillage Otherwise, surface casing string(s) must be cut at minimum 1 m below surface (final contour elevation). Records of type of steel plate and welding procedures used in well abandonment must be retained for audit

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Typical cased-hole well abandonment diagram

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Leaky well

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Casing accessories

Scratchers

Centralizers

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Decommissioning offshore wells

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Permitting and regulatory compliance

	Up to three years to complete Operators often utilize local consulting firms

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Platform preparation

	To prepare a platform for decommissioning, tanks, processing equipment and piping must be flushed and cleaned and residual hydrocarbons be disposed of. Platform equipment must be removed, which includes: Cutting pipe and cables between deck modules Separating modules Installing pad eyes to lift the modules Reinforcing the structure

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Well plugging and abandonment

Well abandonment involves: Well entry preparations Use of a slick line unit Filling the well with fluid Removal of downhole equipment Cleaning out the wellbore Plugging open-hole and perforated intervals(s) at bottom of well Plugging casing stubs Plugging of annular space Placement of a surface plug Placement of fluid between plugs

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Wellbore before and after

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Mobilization/demobilization & platform removal

Pilings must be removed to at least 15 ft below the mudline. First, topsides are taken apart and lifted onto derrick barge. Topsides can be removed in one piece, in groups of modules, reverse order of installation, or in small pieces. If removing topsides in one piece, the derrick barge must have sufficient lifting capacity. This option is best used for small platforms. Also keep in mind the size and the crane capacity at the offloading site. Removing the jacket is the second step in the demolition process and the costliest. First, divers using explosives, mechanical means, torches or abrasive technology make the bottom cuts on the piles 15 ft below the mudline.

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Material disposal and site clearance

	Four-step site clearance procedure: Pre-decommissioning survey maps the location and quantity of debris, pipelines, power cables, and natural marine environment. Post-decommissioning survey identifies debris left behind during removal process and notes any environmental damage. ROVs and divers are deployed to further identify and remove debris that could interfere with other uses of the area. Test trawling verifies the area is free of potential obstructions.

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Cost of decommissioning

The main factor in decommissioning directly relates to the weight of the materials to be removed Location water depth Function (oil or gas)

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Thank you
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