OXFORD, UN EJEMPLO DE PARK &RIDE

• Technique 2B

LCM pill

As above but using larger concentrations of coarse materials eg coarse mica, wood, walnut or cellophane.

• Technique 3A

High filter loss slurry squeeze (Diearth, Diaseal M etc) 100 bbl water

15 lb/bbl bentonite or 1.0 lb/bbl Drispac (or 1.0 lb/bbl XC Polymer) 0.5 lb/bbl lime

50 lb/bbl Diearth, Diaseal M

15 – 20 lb/bbl fine mica, walnut, cellophane or similar material as can be mixed and remain pumpable.

LOST CIRCULATION REMEDIES

SEVERITY OF EFFECTIVE IN

TYPE OF LOSS LOSS, bbl/hr LOSS ZONE GEOMETRY LOST CIRCULATION REMEDIAL TECHNIQUE WBM OBM*

Seeping 1 – 10 to horizontal loss zones** Technique 2A – Plug of fine bridging agents in mud yes yes to induced vert fractures Technique 3A – High-filter-loss slurry squeeze with yes yes

fine bridging agents

Partial 10 – 500 to horizontal loss zones** Technique 1 – Pull up and wait (primarily for induced yes partial vertical fracture)

to induced vert fractures Technique 2B – Plug of medium bridging agents in yes yes mud

Technique 3A – High-filter-loss slurry squeeze with yes yes coarse bridging agents

Complete 500 – complete to horizontal loss zones** Technique 3B or 3C – High-filter-loss slurry squeeze yes yes with coarse bridging agents

Technique 4B – Thixotropic cement or other cements yes no (4A, 4C, 4D)

Technique 5B – Mud + diesel-oil-bentonite plus yes no cement

Technique 5A – Downhole-mixed soft plug yes yes (mud-diesel oil-bentonite)

Technique 7B – Downhole-mixed hard plug (sodium yes yes silicate, calcium chloride, cement squeeze

Flo-Check)

Long Complete to horizontal loss zones** Technique 3A, 3B or 3C – High-filter-loss slurry yes no honeycomb or squeeze with 25 – 35 lb/bbl or coarse bridging agents

caverns (only Technique 5B – Downhole-mixed soft/hard plug in limestones) continuously mixed in large amounts

Deep induced Complete Vertical in WBM or OBM Technique 1 – Pull up and wait yes partial fractures in WBM Technique 5B – Downhole-mixed soft/hard plug yes no

in WBM Technique 5A – Downhole-mixed soft plug yes no in WBM Technique 7B – Downhole-mixed hard plug yes yes

(sodium, silicate, calcium chloride, cement squeeze, Flo-Check)

in OBM Technique 3B or 3C – High-filter-loss slurry squeeze yes yes with coarse bridging agents

in OBM Technique 4A – Neat portland cement yes yes in OBM Technique 7B – Downhole-mixed plug yes yes

(sodium, silicate, calcium chloride, cement squeeze, Flo-Check)

* Usually not in use where loss zones are WBM – water-base mud horizontal. They consist of porous sands OBM – oil-base mud and gravels, natural fractures, and

2-25

March 1995

• Technique 3B

High filter loss slurry squeeze

As Technique 3A but include the following: 15 – 30 lb/bbl medium and coarse LCM

• Technique 3C

High filter loss slurry squeeze

As Technique 3A but include the following: Reduce Diearth concentration to 10 – 25 lb/bbl Use barytes as inert filler at 300 lb/bbl

Add cement at 70 lb/bbl

Place in 30 bbl slugs into loss zone with 200 psi squeeze pressure.

Note: Wherever possible, slurry formulations should be tested prior to spotting to eliminate possible premature setting. When this is the case, always be aware of the thickening time and avoid leaving cement in or opposite the pipe beyond this time.

• Technique 4A

Neat cement slurry

Neat cement slurries give high compressive strength plugs. Mix Class G cement at 1.90 SG in water

• Technique 4B

Extended cement slurry (using bentonite)

Prehydrated bentonite slurry gives a degree of fluid loss control and ‘plating effect’ to help stop lost circulation. Coupled with this, a lightweight slurry can be formulated (1.58 SG) which helps in areas of serious lost circulation. A further benefit is that reasonable compressive strength characteristics are found with slurries of this type. Add 10 lb/bbl bentonite to pre-treated fresh water (with 0.25 lb/bbl caustic and 0.25/lb/ bbl soda ash). Mix cement up to 1.58 SG.

• Technique 4C

Aggregated cement slurry (with sand or ground coal)

Add aggregrate to the neat cement slurry at 1.90 SG up to a maximum weight of 20 – 35 lb/sack of cement in the mix.

2-26

March 1995

• Technique 4D

Thixotropic cements

Cement of this type exhibits good flow characteristics when being pumped and a quickly developing gel strength when stationary. This thixotropic behaviour is beneficial for the following reasons:

– A plug of cement displaced past the loss zone is self supporting and does not fall back under its own weight.

– The cement will tend to remain next to the wellbore when squeezed into fractures due to their rapidly developing gel strength.

Due to the temperature and chemical formulation sensitivity of this type of slurry, it is not recommended to use this cement without rigorous quality control and testing prior to each job. Halliburton Thixset 1 or 2 are examples of this type of cement.

• Technique 5A

Downhole mixed soft plug

This type of lost circulation pill is designed to mix with a water base mud or formation water in the downhole environment and subsequently be squeezed into the formation. Mix 10.5 gal of diesel or base oil to 100 lb of bentonite.

Granular or fibrous LCM may be added to this mix if required, ie mica at 10 ppb plus walnut at 10 ppb.

This mixture must be kept away from contact with water until it is placed out of the drillpipe. To do this, a 10 bbl oil spacer is pumped ahead of a plug, followed by 10 bbl after the plug.

The principle of this plug is to form a rubbery plug whenever the mixture contacts the water base mud. Formation water will assist the hydration of the bentonite.

• Technique 5B

Downhole mixed soft/hard plug

This type of lost circulation pill is designed to mix with a water base mud or formation water in the downhole environment. It can be designed to form an initially fluid mixture of a soft or semi-hard nature depending on its composition, and can be squeezed into the formation where it will harden and develop compressive strength.

The proportion of mud to the pill in the final mix downhole will determine the strength of the plug. For example, a 1:1 mix with fresh water will result in a soft plug, whereas a 1:3 (water/mix ratio) mix will result in a hard plug. In every case however, pilot tests should be carried out at surface for various mixes, prior to spotting the pill.

Mix on surface 300 lb of G neat cement and 158 lb of bentonite to 1 bbl of diesel or base oil. All water should be excluded from the mix on surface.

2-27

March 1995

• Technique 6

Downhole mixed soft plug Oleophilic clay and water

This type of plug formulation is designed for use in an oil base mud. It works by the same principle as 5A, except that the clay disperses in water and hydrates in oil (the opposite of a bentonite squeeze).

Mix on surface 280 lb of oleophilic clay to 1 bbl of water. Add lignosulphonate at 4/lb/ bbl water.

An example of oleophilic clay is Baroid Geltone.

The spacers ahead and behind this plug must be water based.

• Technique 7A

Surface mixed soft plug (polymer type)

These formulations are mixed on surface, where polymers are blended with activators and extenders, to give a delayed thickening reaction. This allows enough time to place the plug in the loss zone before the chemical reaction takes place.

Haliburton Temblok is an example of this type of material.

This treatment is only temporary and the yield strength breaks down fairly quickly. It should be followed by a cement slurry to effect a permanent seal.

• Technique 7B

Downhole mixed hard plug

Haliburton Flocheck can be used for this.

This is a Sodium Silicate material which on contact with calcium ions forms insoluble Calcium Silicate. By pumping a CaCl2 brine to the formation, followed by the Flocheck material, plugging of the formation occurs when the two chemicals mix in the formation matrix.

Placement as follows:

Pump 50 bbl 10% (by weight) CaC12 followed by 10 bbl fresh water. Then pump 35/bbl␣of Flocheck followed by a further 10 bbl fresh water. Care must be taken to ensure that CaC12 does not come into contact with Flocheck on surface as it will go hard in the pits. This treatment, whilst permanent, may be reinforced by a cement slurry.