Nozzle & Choke Comparison

Nozzle & ChokeComparisonQuick Calculation MethodDouglas Cearleywww.oilfieldbooksoilfieldbooks.com

Total Flow Area•The amount of flow through the bit isdependant on the total flow area (TFA)•The TFA is the sum of the individualcross-sectional sectional areas of the bit nozzles•The TFA isr 2 ) 1 +(r 2 ) 2 …+( +(r 2 ) n wherer is the radius of each nozzle and n is thetotal number of nozzles

Nozzle & ChokeMeasurement•Bit Nozzles are measured in 1/32 of aninch, i.e. a 20 nozzle is 20/32 inch indiameter•Chokes are measured in 1/64 of an inch,i.e. a 32 choke is 32/64 inch in diameter•The same flow comparison calculationsapply to both

Derivation•Flow is directly proportional to total flowarea•The flow area of Nozzle A compared toNozzle B is expressed as:•(. (.5D A ) 2 /(. (.5D B ) 2•Simplifying yields D A2 / D2 B•Since the denominators for both nozzles arethe same, they cancel out

Conclusion•The square of the nominal diameter of asingle nozzle is proportional to thesquare of the nominal diameter of asecond nozzle•Comparison of predicated flow change isgood only for the case of all nozzles ofthe same nominal diameter, otherwiseTFA must be figured in the normalmanner

Example•AA bit dressed with three 22 jets replacesa bit with three 20 jets. How much moreflow can be expected?•222 /20 2 =1.21•21%more flow can be expected from the22 jets with the same standpipe pressure•Of course, pump SPM must be raisedaccordingly

Example 2•AA bit dressed with six 12 jets is replacedby a bit with six 10 jets•102 /12 2 =.69•The TFA of the second bit is 69% that ofthe first bit

Example 3•The same comparison is true for positivechokes•AA well is flowing through a 32/64 choke. Whatchoke should be used to cut the flow down byabout half?•x 2 /32 2 =.50•So x=√(. x (.50*322 )• And x=22.6x• Use a 22/64 choke