MAASP
Encyclopedia
Maximum Allowable Annulus Surface Pressure is an absolute upper limit for the pressure in the annulus
of an oil and gas well
as measured at the wellhead
.
is a vital task for the operators. This includes ensuring that the annuli remain intact. One major threat to annulus integrity is overpressure within the annulus, which could lead to burst or collapse of a casing
or damage to the formation below. This will happen first at the shoe of the annulus because the pressure will naturally be higher with the weight of the column of brine. However, annuli usually only have pressure gauges at the wellhead
. Therefore, a MAASP is calculated to provide a surface pressure, which will produce the limiting pressure at the shoe.
The following example is for the 'B' annulus of a gas lift
ed well, filled with 1.2 sg brine from the shoe at 4070ftTVD (true vertical depth) to surface.
for the mathematical basics of hydrostatic heads). Therefore, the column of brine produces a pressure difference between top and bottom of 2116 psi. Therefore, the pressure at the wellhead
can reach 2903 psi before 5020 psi is reached at the bottom. Therefore, the MAASP for casing burst is 2903 psi.
s usually have a pressure rating of 5000 psi, 10,000 psi or 15,000 psi. These are far in excess of the other limits. As such, surface equipment is not usually the limiting factor.
Annulus (oil well)
The annulus of an oil well refers to any void between any piping, tubing or casing and the piping, tubing, or casing immediately surrounding it. It is named after the corresponding geometric concept...
of an oil and gas well
Oil well
An oil well is a general term for any boring through the earth's surface that is designed to find and acquire petroleum oil hydrocarbons. Usually some natural gas is produced along with the oil. A well that is designed to produce mainly or only gas may be termed a gas well.-History:The earliest...
as measured at the wellhead
Wellhead
A wellhead is a general term used to describe the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment....
.
Background
Preserving well integrityWell integrity
Well integrity, in regards to oil wells, is defined by as the "“Application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well”...
is a vital task for the operators. This includes ensuring that the annuli remain intact. One major threat to annulus integrity is overpressure within the annulus, which could lead to burst or collapse of a casing
Casing (oil well)
Casing is large diameter pipe that is assembled and inserted into a recently drilled section of a borehole and typically held into place with cement.-Purpose:Casing that is cemented in place aids the drilling process in several ways:...
or damage to the formation below. This will happen first at the shoe of the annulus because the pressure will naturally be higher with the weight of the column of brine. However, annuli usually only have pressure gauges at the wellhead
Wellhead
A wellhead is a general term used to describe the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment....
. Therefore, a MAASP is calculated to provide a surface pressure, which will produce the limiting pressure at the shoe.
Determining a MAASP
There are four different ways in an annulus may be overpressured: burst of the outside casing, collapse of the inside casing, fracturing of the formation at the shoe, overpressure of the surface equipment. Each of these produces its own limiting pressure at the shoe. The MAASP is taken as the most limiting of these.The following example is for the 'B' annulus of a gas lift
Gas lift
Gas lift is one of a number of processes used to artificially lift oil or water from wells where there is insufficient reservoir pressure to produce the well. The process involves injecting gas through the tubing-casing annulus. Injected gas aerates the fluid to reduce its density; the formation...
ed well, filled with 1.2 sg brine from the shoe at 4070ftTVD (true vertical depth) to surface.
Burst of outside casing
In this well, the outside casing of the 'B' annulus is 13⅜" N80 grade with a weight of 68 lbft-1. The burst pressure of this casing is 5020 psi. 1.2 sg brine produces a pressure gradient of 0.52 psi.ft-1 (see Well killWell kill
A well kill is the operation of placing a column of heavy fluid into a well bore in order to prevent the flow of reservoir fluids without the need for pressure control equipment at the surface. It works on the principle that the weight of the "kill fluid" or "kill mud" will be enough to suppress...
for the mathematical basics of hydrostatic heads). Therefore, the column of brine produces a pressure difference between top and bottom of 2116 psi. Therefore, the pressure at the wellhead
Wellhead
A wellhead is a general term used to describe the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment....
can reach 2903 psi before 5020 psi is reached at the bottom. Therefore, the MAASP for casing burst is 2903 psi.
Collapse of inside casing
The inside casing is 9⅝" L80 47 lbft-1. The collapse pressure of this casing is 4750 psi. Therefore, pressure at the shoe of the 'B' annulus cannot exceed this. Given a hydrostatic head of 2116 psi, the pressure at the wellhead must not exceed 2634 psi.Fracturing the formation
Geologists will have logged fracture pressures of the formation as the well was drilled. This can be used to provide a limiting pressure much as before. If the cement used to cement the casing in place is still intact, fracturing the formation is not a hazard.Surface equipment
WellheadWellhead
A wellhead is a general term used to describe the component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment....
s usually have a pressure rating of 5000 psi, 10,000 psi or 15,000 psi. These are far in excess of the other limits. As such, surface equipment is not usually the limiting factor.