API RP 65-3:2021 pdf free download.Wellbore Plugging and Abandonment
NAF non-aqueous fluid
PWC perforation, wash, and cement
psi pound-force per square inch (lbf/in. 2 )
SCP sustained casing pressure
VRP viscous reactive pill
WOC waiting-on-cement
4 Applications and Operating Environment
4.1 Formation Types
Potential Flow Zones
Potential flow zones are any formations in a well where flow is possible when the wellbore pressure is less than the pore pressure (e.g., hydrocarbon zones, shallow gas, or overpressurized water zones that may be natural or induced). Isolation of these zones shall be the primary objective of wellbore plugging and abandonment unless cross flow is deemed acceptable.
Prior to permanent abandonment operations, all potential flow zones in the wellbore shall be identified. Usable Water Sources Subsurface waters (aquifers) suitable for consumption by humans or animals with or without treatment are classified as usable water sources.
These formation types shall be protected from contamination by fluid migration or surface water runoff. Injection and Depleted Zones Injection or disposal zones are geological formations whose strata are isolated from overlying usable water sources by an impermeable layer into which fluids are injected for disposal or charging.
These formations may or may not be classified as depleted zones. Depleted zones are formations whose reservoir pressures are less than the adjacent formation pressures as a result of production operations. These zones may prevent plug stability during placement. Both injection and depleted zones shall be isolated during abandonment unless cross flow is deemed acceptable.
4.2 Positions Barrier Installation During the drilling of a well, the natural geologic seals to overpressured formations are penetrated by the wellbore. During well abandonment, the placement of a barrier prevents the flow of formation fluids to surface or seabed, cross flow between permeable formations, and contamination of usable water sources. Since the initial geologic state was a continuous seal, well abandonment is typically performed by creating a continuous barrier across the wellbore at the natural seal location. See Figure 2 for an illustration of a continuous barrier across the wellbore at the natural seal location.
Permanent annular barriers set adjacent to the natural seal during the well construction phase can increase the efficiency of the permanent abandonment operations. During the construction of the well, considering field operational life can aide in the placement of barriers (e.g., conversion of a well to an injector, disposal). During planning for permanent abandonment operations, potential flow zones identified during the well construction are reviewed and redefined if applicable. Local regulatory authorities may define zones that require permanent abandonment barriers. The inclusion of a draft well abandonment plan or schematic showing the proposed locations of permanent barriers can aide in optimizing well construction activities in preparation for well abandonment.
Formation Pressures and Strengths
The location of a permanent abandonment barrier is typically at a depth where formation integrity can withstand the pressure from the potential flow zones being isolated. A natural seal for a potential flow zone typically starts immediately above the top of the potential flow zone. An understanding of individual seals to potential flow zones, and seals, which can contain all the pressures from above and below, can help plan the placement of permanent abandonment barriers.
The fluid gradient from each potential flow zone can be used in the determination of permanent abandonment barrier locations.
See Figure 3 for an example of the location of a permanent abandonment barrier placed at a depth where formation integrity (natural seal) can withstand the pressure from the potential flow zone being isolated.
Considerations for the placement of permanent abandonment barriers can include:
— location of potential flow zones and pore pressures;
— location of usable water sources;
— formation fracture pressure of natural seals;
— cross flow potential; direction and resultant equalized pressures;
— future field plans (e.g., injection activities);
— compaction, subsidence, and recharged formations;
— corrosion risks;
— field reservoir management requirements;API RP 65-3 pdf download.API RP 65-3:2021 pdf free download
