Next, {HEAD ~ a second fracturing fluid} that may or may not have a second viscosity greater than that of the first fracturing fluid, is injected into {TAIL ~ the fractures} 24 to thereby propagate said fractures 
is injected into
Next , { HEAD ~ a second fracturing fluid } that may or may not have a second viscosity greater than that of the first fracturing fluid , is injected into { TAIL ~ the fractures } 24 to thereby propagate said fractures
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH