Cemnet: A Network For Fighting Lost Circulation

CemNET A Network For Fighting Lost Circulation

Lost Circulation • Time consuming – Lost time due to slow drilling progress – Poor cuttings removal (stuck pipe) – Additional casing strings

• Dangerous operation – Kick/Blow out due to unbalanced pressure in the well – Loss of well

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Lost Circulation • Additional remedial work – Difficult cement Squeeze after the primary cement job – Mobilization of workover rig

• Costly due to lost mud • Casing corrosion due to poor cement coverage – Cathodic protection – Cost of chrome casing (3 times more than steel) – Complete loss of well

• Environmental concerns – Aquifer contaminations with hydrocarbons 3

CemNET* • Features – Advanced fibers mixed with cement to seal lost circulation – Engineered to an optimal size – Inert • No effect on Thickening Time • No effect on compressive strength development • Compatible with all cementing additives

– Extremely effective with CemCRETE systems • Better plugging effect due to PSD • Lower rheology 4

CemNET* • Applications – – – –

Used across fractures, fissures, vugs, and permeable zones Temperature limitation up to 450 0F Used for cement plugs and primary cementing operations Not for mud applications

• Benefits – Easy to handle – No cement fall back – Cure losses during primary cementing • It is always preferred to cure losses prior to cementing

– Reduces disposal costs by reducing cement excess returns 5

Fibers in Cement Is the concept new? No but,… – Nylon and other fibers have been used with cement before – No size optimization • • • •

Difficult to handle Difficult to disperse in cement Difficult to mix with cement (fiber lumps or fur balls) Tend to plug pumping and float equipment

– Difficulty in water wetting the fibers

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Mechanism • Dry fibers are bound together

– Easy to handle and add to cement • No fiber lumps in mixing fluid • Well dispersed fibers once agitated – High plugging efficiency

• Water wetting effect by the surfactant • Fibrous network across loss zones 7

Mechanism

Circulation

Fibrous network across lost circulation zones

Losses

Losses

Losses

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Experimental Study ∆P

• • • • • •

Modified HPHT fluid loss cell Grids with 1 and 2 mm holes Grid with 46 mm slot by 1 mm width Conventional and CemCRETE systems Apply 20 bars of pressure Collect and measure the filtrate

METAL PLATE

METAL GRID WITH HOLES OR SLOT

COLLECTED SLURRY 9

Experimental Study • Results – CemNET was effective in plugging the holes and the slot – Less fibers were required when CemCRETE was used • CemCRETE is more effective than conventional systems • Lower slurry rheology

– Well dispersed fibers have higher plugging efficiency

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Field Applications 70 m

• Canada (Shallow Gas Wells) – – – – – –

Ground Water

Losses in over 90% of the wells Coal Seams Large coal seams sections Difficult to identify Losses encountered during cementing Ground water was not protected Regulations called for cement to surface 1100 m

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7” Surf. Casing

4 1/2” Production Casing

Field Applications • Alternatives – Drilled with gel mud • Higher mud cost • Longer drilling time

– Standard LCM’s and viscous pills were ineffective – RFC-HE cement systems were ineffective – Excess cement volumes • Cost increase due to cement handling and disposal • Logistical difficulties in the cementing operation 12

Field Applications Percentage

80% 60% 40% 20% 0%

Complete Losses

75%

50%

No CemNET

25%

CemNET

• CemNET used on the first 95 bbls

• Reduced costs related to remedial cementing • Cement disposal cost dropped by 46% 13

No Losses

Field Applications • Indonesia

16” @ 150’

– Losses while drilling • Range from1bbl/hr to total losses

– – – – – – 14

Mud weight 8.5-8.7 ppg 80 bbls of mud / LCM were ineffective Continue drilling blind till TD Unconsolidated Sand Log the open hole Plug back with thixotropic cement Run casing and cement with thixotropy cement

Natural Fractures

10 ¾” @ 400’- 700’

Field Applications Results – Required thixotropy level was not always achieved • Cement fall back • Increased cost due to spotting additional plugs

The Solution??

CemNET 15

Field Applications • CemNET Results – – – –

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30 bbls of 14 ppg CemNET plug cured the losses Casing cemented with 15.8 ppg CemNET 23 bbls of cement returned to surface CBL showed excellent bonding with 2 mV

CemNET A strong barrier against lost circulation across: • Highly permeable zones

• Natural fractures • Induced fractures • Vugular formations

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