Stable Foam

Description

foam_unit_947_1

 

Mike’s Oilfield Services Ltd. has foamed wells since1992

  • 6 Stable Foam Units
  • Newest unit is 1350 C.F.M.  Output To 2500 P.S.I. used for horizontal cleanouts.
  • Foams low density and high viscosity at low shear rates makes it extremely useful as a circulating medium in low pressure reservoirs.  These properties minimize fluid loss to the formation and reduce needed annular velocities yet provide high lifting capability at minimum circulating pressure.
  • Stable foam circulating has proven an efficient method of removing sand, cement, pyrite balls, coal and rubber from PC pump.

Preformed Process
The preforming of foam on the surface is of critical importance.  It has been found experimentally that preformed foams can withstand much more contamination from crude oil, salt water and formation debris than those foams generated down the hole.

Foam can be generated very easily.  A surfactant is mixed with fresh or brine water and stored in a tank on the unit.  Through a system of piping, the mixture is added to an air stream in the “foam generator” and introduced to the well as foam.

Foam Generator
The foam generator is designed to produce a small bubble foam for  maximum stability.  The controlled variables are the liquid rate and the air rate in the proper variables to maintain a stable foam.

Stable foam has 2 to 8 times the lifting ability than water.  This superior lifting ability is due to it’s high viscosity, linear viscosity and expansion as it moves up the annulus.

Foam Applications

Foam is used in oil well servicing in connection with drilling or production rigs, snubbing units or any pipe handling equipment.  Foam clean-out has a wide range of applications.

Stable foam circulation has proven an efficient method of removing sand from producing wells, replacing bailing.

Many completion and removal jobs are difficult under low pressured reservoirs where conventional fluid circulation results in severe loss of fluids to the producing zone.

With stable foam most of these jobs can be accomplished such as:

  • Milling
  • Fishing
  • Drilling  plugs and cement
  • Liner running and recovery
  • Gravel packing
  • Well stimulation
  • Lifting fluid off gas wells
  • Application for cleanouts on horizontal wells

Stable foam is superior coring fluid in under pressured reservoirs for several reasons:

  • Less loss circulation
  • Less core invasion
  • Bottom hole circulation pressure can be controlled and cores have no mud coating.

Foam also has many drilling applications:

  • Deepening surface hole drilling in perma-frost
  • Removal of debris
  • Running and pulling liners
  • Foaming horizontal wells with 2″ Endless Tubing Unit ( ETU )

3 Methods of monitoring sand, drilling mud & clays & debris:

  1. 5 gallon pail sample
  2. Centrifuge

Safety

Stable foam has an excellent safety record with no incidence of down hole or surface fire reported.  This record could probably be attributed to:

  • Very little foam (air) enters the hydrocarbon bearing zones because of the low pressure gradients and viscosity exhibited by foam.
  • Accelerated clean – out and drilling rates minimize the time that foam (air) is in contact with hydrocarbon bearing formations.
  • The gaseous phase in a foam is encapsulated in a film of liquid and any reasonable amount of formation gas is absorbed into the bubble.
  • With the use of foam, nominal hydrogen sulfide gas can be neutralized by the addition of chemicals, such as, ammonia in the foam.  The gas is trapped in the foam and then slowly released and safely dispersed as the foam breaks in the return tank.
  • At higher pressures, nitrogen or other non gas can be used for greater safety if crude oil or flammable solvents are present as in the well.

Foam Method Procedures

In foam clean out, foam replaces mud, oil or other fluids as the circulating medium in drilling, well completion or remedial operation.

Foam is made as needed.  Foam quality is maintained and adjusted by varying the gas and liquid rates, foam injection pressure and back pressure.  Simple procedures on each unit will accomplish this.  When properly controlled, the foam is stable until it leaves the well then breaks rapidly in the air.

In the first foam clean-outs, the foam quality and procedures were carried out strictly by trial and error.  Adjustments were made depending on hole depth, fluid type and level, temperatures, pipe sizes, pressure changes and characteristics of the well itself.

Using this criteria from laboratory and pilot tests, a computer model was developed which simulates the circulation of stable foam in a well bore.  By making a series of computer runs at various rates and conditions, a family of bottom hole circulating curves were plotted.

These results were applied to a series of down hole field scale tests representative of field operations.  The correlation of these results with the computer curves proved very accurate.

” Foam-up ” was the name of the computer.

Stable Foam Technical Data

“Foam up” is an engineering tool.  It can be used when estimating the size of equipment required, the bottom hole circulating the pressure or lighting capability and circulating time of the foam for a proposed job.

The single most important factor in foam circulation is the “quality” of the foam, hence it’s ability to lift.  The term used to describes the consistency is the “Liquid-Volume-Fraction”.

Mike’s Oilfield Services Ltd. has a handbook which demonstrates and describes the computer “foam-up” and outlines in detail the “trends” and “changes” that effect the foam Quality (L.V.F.), hence the foam process itself.
The following is a list of those trends:

  • Liquid – Volume – Fraction
  • Pressures
  • Contamination
  • Lifting Steps

Anyone wishing to go through the book is welcome to do so and copy anything of interest in better understanding this process.

Typical Concerns

Concern
Formation Contamination
This worry is the fluid, water and foaming agent entering the production zone, swelling the formation clays or making an emulsion which blocks the pay zone.

Answer
Firstly, air foaming agents are bio-degradable.  If formation or KCL solutions are used, the formation clays should not be disturbed.  There is no doubt some foam fluid could be lost to the formation in the initial lift.  Once circulation is established and the hydrostatic head removed, formation flow back should remove these immediately.  Formation damage is minimal compared to high volume fluid pumping where up to 50% could be lost to the formation.


 

Concern
Blow-out
What happens when a well is unloaded with foam, particularly a steam well, and the formation kicks ?

Answer
The working string is always under control with a B.O.P. in addition to a hydraulic pipe pack-off is installed.  This gives the added ability to move the work string while circulating with B.O.P. open.

String check valves are installed in the work string so as circulation can be stopped and a joint added without having to bleed off the well bore.

If a kick occurred which needed control, this foam unit can immediately become a kill unit, simply by cutting off the air and increasing water input.  If necessary, a high displacement kill pump can be tied in through existing manifolds.  A controlled kick is excellent in sand clean up.

Return Foam Tank

  • We have foamed slant, horizontal and vertical wells.
  • Heavy oil wells to clean up the sand problems.
  • Water disposal’s to help injection rates and pressure.
  • Steam wells at Pikes Peak.  Mike’s has high temperature foam good for up to 205 degrees Celsius.
  • Milled casing and foamed liners into position for Mobil Celtic.
  • Perf washed with foam.
  • Foamed new wells after they have been perforated under balance.
  • Drilled out bridge plugs that had perfs open above plug.
  • Drilled out cement.
  • New method of using mud motors to drill out cement & bridge plugs.
  • Poor inflow wells injected air or foam to build up formation pressure then released pressure.  This has helped to increase the flow of heavy oil.
  • Foam is used to recover loss drilling fluid.
  • PFWUB Perf & Foam While Under-Balanced.

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5 Catch Tanks now available.  Used for catching returns from foaming operations.  As a catch tank it is used for de-watering pipelines after a hydro test.

Circulating Tubing Head

tubingheadBenefits

  • Allows a well to be circulated with a Flush-by rig rather than with a conventional service rig.
  • Fluid may be circulated down the tubing while the tubing is moved vertical or rotated in the wellbore without the use of a conventional Blow Out Preventer (BOP).
  • Foam jobs may be performed to remove sand or stimulate the formation utilizing a flush-by rig rather than a service rig.
  • The sealing assembly will maintain control of the well without the need of a BOP while circulating.
  • Tubing rotations can be performed with flush-by.
  • Foam jobs are more cost effective utilizing a flush-by unit instead of a service rig.

Directive 033

Mike’s Oilfield Services Ltd. has been granted DIRECTIVE 033 approval from the Alberta Energy Regulator (AER).

To view a copy of the Directive 033: Well Servicing and Completions Operations—Interim Requirement Regarding the Potential for Explosive Mixtures and Ignition in Wells, please click here.

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