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 A wellhead is 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. The primary purpose of a wellhead is to provide the suspension point and ...

Background

Preserving

well integrity Well integrity, in regard to oil wells, is defined bNORSOK D-010as the "“Application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well”. There ...

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

. 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 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 or bubble pumps use the artificial lift technique of raising a fluid such as water or oil by introducing bubbles of compressed air, water vapor or other vaporous bubbles into the outlet tube. This has the effect of reducing the hydrostati ...

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 ⁻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 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 hydrostatic head ...

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

can reach 2904 psi before 5020 psi is reached at the bottom. Therefore, the MAASP for casing burst is 2904 psi.

Collapse of inside casing

The inside casing is 9⅝" L80 {{convert, 47, lbft, Nm, 0, abbr=on⁻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

Wellhead A wellhead is 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. The primary purpose of a wellhead is to provide the suspension point and ...

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.

Published MAASP

Collapse of the 9⅝" casing is clearly the limiting factor so the MAASP will be published as 2634 psi.