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Description:
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Success of acid fracturing treatment depends greatly on the created conductivity
under closure stress . In order to have sufficient conductivity , the fracture face must be
non -uniformly etched while the fracture strength maintained to withstand the closure
stress . While there have been several experimental studies conducted on acid fracturing ,
most of these have not scaled experiments to field conditions and did not account for the
effect of rock weakening and etching pattern . Hence , acid fracture conductivity
predictions based on the above works have not been able to match actual results .
In order to develop a more appropriate and accurate prediction of acid fracturing
treatment outcome , a laboratory facility was developed that is properly scaled to field
conditions and enables analysis of etching pattern and rock strength . A systematic
experimental study that covered a variety of formations , acid types , and acid contact
times was conducted . An acid fracture conductivity correlation was developed based on
etched volume , etched pattern , and fracture strength under closure stress .
Results suggested that there is an optimal time of acid exposure resulting in
maximum fracture conductivity . There were large differences in the conductivity created with the different acid systems tested due to different etching patterns and degree of rock
strength weakening . There was an optimal acid system depending on formation type ,
contact time and overburden stress . The acid fracture conductivities measured did not
agree with the predictions of the Nierode -Kruk correlation . The newly developed
correlation predicts conductivity much closer as it includes the effect of rock strength
and surface etching pattern on resulting conductivity . |