100 10


0.10 1


0.01 0 3 2 1 0 0 3 2 1 0 0 0.5 1.0 Radius, m 1.5 2.0 0.5 1.0 Radius, m


Amorphous silica Borosilicate


1.5 2.0 0.5 1.0 Radius, m


Phase 1– before flowback Phase 1– after flowback Phase 2– before shut-in Phase 2– after shut-in


1.5 2.0


Initial Phase 1– before flowback Phase 1– after flowback Phase 2– before shut-in Phase 2– after shut-in


Treatment phase 1 Volume, m Rate, L/min Reservoir gas


NH4CI HCI– acetic acid 9/1 mud acid HCI– acetic acid NH4CI


Diesel oil


200 5


15 30 5 5


12 Flowback stage


Treatment phase 2 Volume, m Rate, L/min Reservoir gas


NH4CI HCI– acetic acid Fluoboric acid NH4CI


Diesel oil


200 5


14 34 5


70


Well shut-in for six hours Flowback stage


< Matrix acid-treatment model results. The two-phase Heidrun  eld treatment started with a mud-acid treatment, then a  ow- back stage, followed by a ClayACID


 uoboric phase (table). The geochemical model predicted that the treatment would improve near-well permeability (top). The total silica mineral precipitation was low, less than 2.5% of the formation volume (middle). Borosilicate precipitation, useful for stabilizing clays, peaks near the well- bore, while amorphous silica peaks farther away (bottom).


1,200 1,200 1,200 1,200 1,200 1,200


1,200 1,200 1,200 1,200 1,200 1,200 1,200


5,000 6,000


4,000 3,000 2,000 1,000 0 7/1/99 1/17/00 8/4/00


2/20/01 Date


9/8/01 3/27/02


Injection-water breakthrough


Scale-inhibitor squeeze


Acid-stimulation treatment


Oil rate PI Water cut


125 150


100 75 50 25 0 10/13/02


> Production data for Heidrun  eld Well A-48. Productivity declined when water broke through, and further productivity was lost after a scale-inhibitor squeeze treatment. The acid-stimulation treatment in September 2001 restored productivity without signi cantly increasing the amount of produced water.


Spring 2004


65


Silica volume, % Oil rate, m3/d Wellbore


Silica volume, % Wellbore


k/k0 Wellbore


Productivity index (PI), m3/bar-d Water cut, %


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