centralizer spacing

hello
I have problem
how can i calculator centralizer spacing for this :-
type well = vertical drilling
mud inside 12ppg
cement outside 15ppg
top of cement 1600 ft
shoe last casing 13 3/8 " = 1923 ft
Hole daimeter = 12.250 in
casing 9 5/8" & wt =43.5 ib/ft
TVD=6810 ft
Davation from 2615 to 2900 ft = 0.5 degree
Davation from 2900 to 4005 ft= 0.75degree
Davation from 4005 to 6800 ft= 0.25 degree

best regards

Hi Ammar, what you are asking is a simple exercise when using propriety software, (Opticem or similar), where you can solve for standoff. The methodology for the calcs are described in API 10D.
[url]http://www.4shared.com/office/exkEZ3jXba/10D.html[/url]