Surface Production Equipment
– Well head
– X-mass tree
Subsurface Production Equipment
– Tubing
– Packer
– Bridge Plug
– Safety Valve
Production Wellheads
The surface termination of a wellbore that incorporates facilities for installing casing hangers during the well construction phase. The wellhead also incorporates a means of hanging the production tubing and installing the Christmas tree and surface flow-control facilities in preparation for the production phase of the well.
– A wellbore tubular used to produce reservoir fluids. Production tubing is assembled with other completion components to make up the production string. The production tubing selected for any completion should be compatible with the wellbore geometry, reservoir production characteristics and the reservoir fluids.
X-mass tree
An assembly of valves, spools, pressure gauges and chokes fitted to the wellhead of a completed well to control production. Christmas trees are available in a wide range of sizes and configurations, such as low- or high-pressure capacity and single- or multiple-completion capacity. as shown in picture
Production and test manifolds
An arrangement of piping or valves designed to control, distribute and often monitor fluid flow. Manifolds are often configured for specific functions, such as a choke manifold used in well-control operations and a squeeze manifold used in squeeze-cementing work. In each case, the functional requirements of the operation have been addressed in the configuration of the manifold and the degree of control and instrumentation required.
Gas Compressors
A device that raises the pressure of air or natural gas. A compressor normally uses positive displacement to compress the gas to higher pressures so that the gas can flow into pipelines and other facilities
Production Separators
A cylindrical or spherical vessel used to separate oil, gas and water from the total fluid stream produced by a well. Separators can be either horizontal or vertical.
Separators can be classified into two-phase separators and three-phase separators (commonly called free-water knockout). The two-phase type deals only with oil and gas, while the three-phase type handles oil, water and gas. Additionally, separators can be categorized according to their operating pressure. Low-pressure units handle pressures of 10 to 180 psi [69 to 1241 kPa]. Medium-pressure separators operate from 230 to 700 psi [1586 to 4826 kPa]. High-pressure units handle pressures of 975 to 1500 psi [6722 to 10,342 kPa].
Gravity segregation is the main force that accomplishes the separation, which means the heaviest fluid settles to the bottom and the lightest fluid rises to the top.
Additionally, inside the vessel, the degree of separation between gas and liquid will depend on the separator operating pressure, the residence time of the fluid mixture and the type of flow of the fluid. Turbulent flow allows more bubbles to escape than laminar flow.
Packer
A packer is defined as any device that seals or “packs off” the wellbore to redirect the flow path of fluids in the well.
The packer consists of pipe which fluids flow, gripping elements called “slips” that grip the wall of the casing to anchor the packer, and a sealing element that can be all rubber, all metal or some combination of the two.
There are two type of packers :
1) Retrievable packers – can be retrieved on the production tubing or on a work string.
2) Permanent packers – the tubing and work string can detach from the packer after it is set.
Setting configuration:
1) Compression – the weight of the tubing string is set down on the packer after is set. Used in deeper wells and when the pressure below the packer will be less than the pressure in the annulus.
2) Tension – the tubing is pulled in tension when the packer is set. Used in shallower wells when the weight of the tubing is not sufficient to set the packer in tension. Also for treating wells where the pressure below the packer well be greater than the pressure in the annulus.
3) Neutral – common in the permanent packers, it is the only way when using the wireline method of setting the packer. Primarily these are used in production packer systems.
Bridge Plugs
Used to seal the wellbore, like packers but without the pipe that allows flow. Two main types, the retrievable and permanent. The retrievable can be set several times and is used in isolating zones for testing and treating in conjunction with a packer. The permanent plugs (known as cast iron plugs) are used to shut off zones permanently and can only be removed by drilling them out.
Both types of bridge plugs can be set by mechanical or wireline methods.
Safety Valve
The purpose of the Safety valves is to protect people, environment and property from uncontrolled production.
Type of Safety Valve
SSV: Surface Safety Valves: an automatic fail-safe closed valve fitted at the wellhead.
SSSV: Subsurface Safety Valve: a valve installed in the tubing down the well to prevent uncontrolled flow in case of an emergency through the tubing when actuated. These valves can be installed by wireline or as an integral part of the tubing.
Subsurface Safety Valve
SSV are usually divided into the following categories.
– SCSSV: Surface-Controlled Subsurface Safety Valves: SSSV which is controlled from the surface and installed by wireline or as an integral part of the tubing.
– SSCSV (storm choke): Subsurface-Controlled Subsurface Safety Valve: SSSV which is actuated by the flow characteristics of the well, and is wireline retrievable.
– ASV: Annulus Safety Valve: a valve installed in the well to prevent uncontrolled flow in the casing-tubing annulus when actuated. It consists of an annular safety valve packer with a by-pass. The opening in the by-pass is controlled by a safety valve, which can be an integral part of the packer on a wireline retrievable valve.
Subsurface safety valve classification
tubing versus annulus safety valve;
tubing versus wireline, through flowline, or coiled tubing retrievable valve;
subsurface versus surface controlled valve;
excess flow controlled versus ambient well pressure controlled valve;
hydraulically controlled versus electrically, or mechanically controlled valve;
non-hydraulically balanced versus hydraulically balanced valve;
electric cable controlled versus wireless controlled valve;
non-equalizing versus equalizing valve;
ball valve versus flapper, or poppet valve.
Safety Valves Categories
Safety valves are divided in two distinct categories: the tubing and the annulus safety valves
Tubing safety Valve
The tubing safety valve is installed to provide a flow barrier in the production tubing string, between the tail pipe and the surface or mudline.
Annulus safety Valve
The annulus safety valve (ASV) provides a flow barrier in the casing-tubing annulus. It consists of an annular safety valve packer with a by-pass.
Tubing valve types
Tubing valve types are referred to as:
- Tubing retrievable subsurface safety valves (TR SCSSV);
- Wireline retrievable subsurface safety valves (WR SCSSV);
- Excess flow valve (SSCSV).
SSV functions and requirements
flow barrier in the tubing;
fail safe closing;
hold the maximum reservoir pressure in closed position;
compatible with all well fluids (completion and well-treatment);
minimum pressure drop;
with the valve closed, downwards pump-through of kill fluid must be possible.
Annulus safety valves
The ASV is normally located at a shallow depth to reduce the volume of the gas stored in the annulus between the ASV and the wellhead.
ASV functions & requirements:
provides a flow barrier in the annulus with fail safe closing controlled from surface preferably operated separately from the tubing SSSV; hold the maximum reservoir and/or the maximum gas injection pressure in closed position; allow downwards pump-through of kill fluid when closed-in; minimum pressure drop across the gas injection path.
Installation and retrieval methods
The tubing safety valves can be divided into two main groups:
- valves threaded into the tubing string;
- temporary installed valves that can be retrieved by wireline, or coiled tubing.
Tubing retrievable valve
The valve body and connections should be at least as strong as the tubing. It should provide leak resistance to internal and external pressures and be compatible with the fluids.
A workover rig is required to retrieve the production string. Reliability and the longevity of components is vital.
During the installation of the tubing string, it is necessary to keep the valve open. This can be done by inserting a retrievable lock-open tool in the valve, without or in combination with the control signal from surface.
Completion fluids should not enter the TR SCSSV internals, in particular the spring chamber, as this can adversely affect its operation (some manufacturers recommend to use a temporary isolation sleeve).
Tubing retrievable SSSVs are well suited for:
Subsea completions, where wireline operations are costly and where valve reliability and longevity are of utmost importance.
– Wells that have high volume oil production, because a TR-SSSV has a larger bore then a WR-SSSV (Compressibility of gas allows high rates through relative small bores without appreciable pressure drop).
– Multiple zone completions, where wireline jobs are frequent on equipment installed beneath the safety valve. The larger bore of a TR-SSSV facilitates the operations, where a WR-SSSV normally has to be retrieved.
– Retrieval and installation of a WR-SSSV are difficult, because of wax or scale deposition in the landing nipple.
References:
1. Petroleum & Gas Field Processing, H K. Abdel-Alal and Mohamed Aggour, King Fahd University of Petroleum & Minerals
2. Petroleum Engineering Handbook, L.W.Lake, Vol.1 “General Engineering”
