Wellhead Controls (Oil and Gas Well Controls)

Instrumentation and Control Learn Oil and Gas Oil and Gas Equipments

Table of Contents                                                                            

 Introduction        

 Glossary of Terms

 General Description

Wellhead Control Sketch

 Operating Sequence – Opening                         

Panel Shut-Down Sequence   

 Operating Sequence Charts

 Routine Maintenance

  

OTIS PANEL & Well Head Controls

 INTRODUCTION

The Otis control panel is connected to monitor a number of conditions at the well site and shut the safety system if the appropriate monitors detect an abnormal condition.

The design function of the well control system is to provide an immediate shut-in of the surface and subsurface safety valves in the event of maintenance or an emergency at the well site.  A panel mounted pneumatic relay valve works in conjunction with other manual / automatic hydraulic control valves to put the safety system in operation (open the well).

Abnormally high or low pressure in the well flow line, a loss of hydraulic pressure or input pneumatic supply, or the operation of a fusible plug in the ESD pilot line, the flow line pilot will cause the system to block and bleed safety valve control line pressure and the normally closed safety valves to shut in the well flow.

 

The well safety system incorporates a special feature that (when properly adjusted for the well conditions) equalizes the well pressure on both sides of the subsurface safety valve before allowing it to open completely.  This prevents the damages to the ball and seat of the safety valve.

It must be remembered that the control panel is the central controller for the entire well safety system installed at the well site.  Incorrect operation or adjustments could render the entire system inoperable and create a dangerous situation for personnel and the possible blowout of the well in an emergency.

 

  1. GLOSSARY OF TERMS

The following list of definitions is to assist in the understanding of this manual:

Actuator                   Hydraulic (or pneumatic) cylinder which is mounted on the Christmas tree valve to provide remote opening and closing.  Can be installed on any reverse acting, gate valve and is operated from the control panel SSV system.

Air Latch                  A piston attached to pneumatic valves (e.g. PR-1 on panel) which uses air pressure to hold the valve open.  Any reduction of air pressure (such as tripping ESD) causes valve to close.

 

Ball Valve                 Downhole safety valve installed in the safety valve nipple by wire line.  Also known as SCSSV, All wire line retrievable valves presently used have ball type closures.  However, newer completions may have tubing retrievable valves installed in the completion which usually have flapper type closures and may or may not have an equalizing feature depending upon the valve design.  These tubing retrievable valves may still some times be referred to as “ball valves”.

 

Check Valve             To permit flow in one direction only.  Available for pneumatic and hydraulic circuits.

Differential Pressure The difference in pressure across the ball valve (or any barrier).

 

Downhole Valve       See ball valve and SCSSV.

Downstream             Refers to a position furthers away from the formation. Same term as for “further down a river”, as opposed to upstream, e.g. Flow line sensing point is downstream of the wellhead.

 

ESD                           Emergency Shut Down.  A means of rapidly bleeding off the 30 psi pilot pressure to cause the panel to bleed the hydraulic pressure and shut in the well.

Equalization             The slow flow of pressure through a small orifice from a high to low pressure area. Usually used to describe the balancing of pressure (equalization) across a downhole safety valve.

 

Flow line                   The main outlet pipeline from the wellhead to the gathering facility.

Fusible plug              Attached to the ESD pilot line, this device is designed to melt in a fire hazard situation and vent the 30 psi pilot line pressure so that the control panel closes in the safety valves.  Fusible plugs can a lead filled elbow or a piece of plastic tubing.

 

Interlock                     No. 2 pump “Interlock” 2NC-1: a device between supply pressure and the pump which blocks or shuts off the supply pressure from the pump until all the circuit pressures are correct.

Manifold                    or “header” is a series of connections onto one piece of tubing, e.g. to vent H2S exhaust gas from the panel; all valve exhaust outlets are connected to a manifold, which vents outside the panel cabinet.

 

Monitor                      Used to constantly check on a particular condition on or near the wellhead, e.g. erosion monitor which detects presence of abrasive sand in production and will trip ESD before critical weaknesses are created in the flowline.

Pilot                            Used to continually measure the well pressure at a particular point (e.g. flowline) until pressure exceeds preset limits (high or low).  Pilot then vents the 30-psi pilot pressure and causes panel to close the safety valve.

 

Pilot pressure             Set at 30 psi (regulator R-2) to energize the pilot system.

Pneumatic                  Air or gas (as opposed to hydraulic which refers to liquid).

 

Relay                          A device for converting a signal from one system to a signal in a system containing a different pressure or fluid.

Relief Valve               Pneumatic or hydraulic over pressure protection.  Set to vent pressure above normal working pressure but below test pressure of circuit.

 

Reverse acting           A common design of gate valve used on wellheads and flowlines.  Inward movement of the stem and gate opens the valve and outward movement of the stem and gate close the valve.  This is in contrast to a normal acting gate which closes when the gate moves inward in the valve body and opens when the gate is moved outward in the valve body.

SCSSV                       Surface Controlled Subsurface Safety Valve.  Two types are in use, the wireline retrievable (WR) and the tubing retrievable (TRSCSSV).  This valve is installed downhole in the well and may either be equalizing or non-eqlializing and may have either a ball type closure or a flapper type closure.  Presently, all WRSCSSV’s used are ball type closure valves that have the equalizing feature.  Both types of valves may be referred to as “ball valves”.

 

SSV                             Surface Safety Valve.  Refers to the wellhead valve, which has the actuator to enable remote opening and closing.  Actuator may be either hydraulic operated or pneumatic operated.  The hydraulic type is commonly used

SCFM                         Standard cubic feet per minute.  It is a unit to define volume of as flow.

 

System pressure        is 80 psi in the control panel and is set by regulator R-3.  The 80-psi pressure is used to control the Sigma 3-way hydraulic block and bleed valve.

Trips point                 The adjustable pressure point at which the pilot will vent the pilot pressure.

 

Upstream                   Refers to the point closer to the formation, i.e. against the flow of the well.

WHSIP                       Wellhead shut in pressure. Also known as THP (tubing head pressure), CITP (Closed in tubing pressure) or SITP (Shut in tubing pressure).

  

Well-Head:

 

Wellhead Control Sketch:

  

  1. GENERAL DESCRIPTION

 

OTIS CONTROL PANEL FEATURES:

 

 

  1. Built-in flowline pilot with direct high-low monitoring facility.
  2. Equalizing circuit which (when properly adjusted to the well conditions) allows the SCSSV to equalize any differential pressure before the pressure is increased to the hold open pressure.
  3. To protect the subsurface safety valve from damage when closing, a time delay circuit prevents SCSSV from closing until after the SSV is closed.
  4. The ESD circuit is separate from the pilot line circuit. It allows the SSV to close due to fluctuations in the flowing pressure in the pipeline without closing the SCSSV.
  5. The internal components of the panel are H2S rated so that the panel may be operated with an H2S supply gas.
  6. All components in the panel exhaust into a manifold, which discharges any H2S gas at ground level outside the cabinet of the panel.

 

OTIS CONTROL PANNEL

 

 

Pilot on Flow Line

 

                                                            Pilot Valve

 

 

 

4.0.      OPERATING SEQUENCE:

 

Detailed Control Schematic

 

 

 

To flow the well the following sequence is to be followed:

 

  1. Check that all ESD valves and / or pilots are closed.
  2. Check the input gas supply to the panel (100 – 140 psi).
  3. Check the 30-psi pilot system (regulator-2) and the 80-psi system pressure (regulator 3).
  4. Insure that the flow line pressure on the DS dial pilot (P-1) is between the high and low tripping points as indicated by the red needles on the pilot gauge face.

Note:   If the flow line pressure is below the low setting of the pilot, read just the needle to below the indicated flow line pressure.

 

  1. Check that the ball valves to the SSV and the SCSSV are open on the panel outlet and the needle valve for the SCSSV is open at the wellhead.
  2. Pull the handle of the ESD relay valve (PR-1) located in the top right corner of the control panel. The locking button should be depressed while pulling out the handle until the valve is locked in the “in-service” position.  The locking pin will automatically unlock and release when the air-latch on PR-1 is energized.  This will not occur until the ESD line is fully pressurized through the fixed orifice in the line downstream of PR-1.
  3. Pump No. 2 will now pressurize the control line to the SCSSV. Provided the Pilot-2 (located in the rear lower left hand side of the panel) has been adjusted correctly and the equalizing delay circuit in the panel is adjusted correctly, pump No. 2 will be stopped with the SCSSV (ball valve) in the equalizing in position.
  4. Once the equalizing delay circuit has been pressurized through the orifice, the air supply is restored to pump No. 2 and the proper hold open pressure will be applied to fully open the SCSSV.
  5. The SSV can now be opened by pressing PB- I (located on the front of the panel to the right of flow line pilot P-1). This will activate pump No. 1 which opens the SSV.

 

Note:   If PB-1 is pressed prior to SCSSV opening fully, pump No. 1 will not operate.  However, the circuit will remain activated and will automatically open the SSV once the SCSSV has opened.

 

5.0.      PANEL SHUTDOWN SEQUENCE

 

Panel will shutdown as per the following conditions:

 

  1. SSV will close when:
  2. PB-2 is pressed manually.
  3. The flow line pressure exceeds the high or low limits as set on P-1.
  4. The SSV and then (after a delay time) the SCSSV will close when:
  5. The pressure in the ESD line is bleed off either by a remote sensing pilot or by opening a remote valve.
  6. PR-1 on panel is manually pressed.
  7. The input gas supply is lost.

 

6.0.    Operating sequence Charts

 

The final operating sequence should be as shown on the following charts.

 

OPENING SEQUENCE:

 

 

Shutdown Sequence Charts:

   

7.0     Routine Maintenance

 

  1. Check the hydraulic fluid level regularly.

Caution:

The hydraulic reservoir cannot be filled full while the safety valves are open. If the reservoir should be filled while the valves are open, when the valves are closed at a later time, the reservoir will not be able to contain the returned fluid and the reservoir tank will over-flow onto the location.  It is for this reason that reservoir tanks must be fitted with pressure relief caps so that the returned fluid or any well pressure can be relieved to prevent the tank from rupturing.

 

  1. Check for hydraulic and pneumatic leaks in panel. Vibration can cause fittings to loosen and can cause leaks to occur.  Re-tightening all fittings in the panel periodically is recommended.  However, care should be exercised not to over-tighten these fittings as this may also cause leaks, especially in the hydraulic lines, which must contain much higher pressures.
  2. Hydraulic filter strainers – clean and replace every six months.
  3. H2S filter cartridges – replace every 4 months. This time will vary according to service conditions and it is suggested that the service interval be adjusted to suit local conditions when necessary.

 

Note:

If supply gas is taken from scrubber on location and the scrubber is not efficient, condensate will saturate these filters and reduce the flow of gas to the panel.  Fluid will also accumulate in the various components of the panel.

 

  1. Remove the spool piece from the top of each Haskel pump and coat the o-rings with Haskel grease. Failure to keep these components greased will lead to pump cycling slowly and possibly stopping.