TSO effect
Brief
TSO effect - tip-screen-out is a situation when proppant bridges in the fracture prematurely during pumping and the trading pressure rises rapidly to the technical limit of the equipment.
TSO fracture designs are specifically intended to screen-out. In this case, it is often possible to continue pumping and inflate the fracture width without exceeding the pressure limits of the equipment. Very high pressures and very high proppant loadings are applied near the end of a fracture treatment where the tip of the fracture has stopped growing due to bridging of proppant at the fracture dip because frac fluid leakoff.
TSO fracture designs are mainly done in high permeable and soft formations where high fracture flow conductivity is needed.
Then dry-to-wet ratio is becoming larger then some critical value tip-screen out occurs. In this case fracture length stop to grow. And width became a function of injected proppant. If TSO design option is not chosen by the user, then we stop addition of proppant at this place. And show the warning message:” Tip screen-out occurs. Not all the proppant is placed. Try TSO design.”
Also if concentration of injected slurry became larger then defined by user maximum concentration we stop addition of proppant and show the warning message:” Maximum concentration reached. Not all the proppant is placed. Try TSO design”
There is important phenomena – tip screen-out effect, greatly influencing resulting geometry. It occurs then dry-to-wet fracture width ratio reaches specified value. This parameter called TSO ratio is specified by user in Fracture tuning input section. The value near 0.7 is recommended in Economides, Oligney, Valko (2002). If tip screen-out occurs fracture half-length stop to grow. Later pumping will force fracture width to grow with fixed half-length.
This effect is taken into account with TSO design option. If this option is selected and during conventional design critical dry-to-wet width ratio was reached we stop conventional design at this moment. As a result we reach target Xf by means of common algorithm described at step 3. Then we add additional step with injected concentration equivalent to critical dry-to-wet width ratio. Duration of this step is calculated in order to place all the proppant.
