RE: Fingers Crossed29 Nov 2022 20:45
To understand the unpredictability of the proppant sand cleanout timeline, it is also necessary to understand the constraints it operates with, and the challenge it faces.
The cased horizontal 5300 ft is 5.5 “ OD pipe, approx. 4.9” ID ( 18.9 inches²)
The production tubing that attaches to the end of this is of an unstated diameter, but in the range of a 3.5” OD/ 2.9” ID (6.6 in²)
Inside that will be the coiled tubing unit tubing which is also an unknown diameter but likely 1.5” OD (1.8 in²)
What matters is the flow path dimension in the restricted zone where the coil tube is run inside the production tubing, in the example 6.6-1.8 = 4.8 in² of available flow cross section. PANR highlighted this as a constraint, it is the pinch point. Additionally this pinch point will not want very high velocity through it, high velocity and sand becomes a sand blaster. So this velocity will be carefully controlled to minimize damage whilst still carrying the heavier SG sands (2.6 X heavier than water) up and away out of the well.
Now to the challenge, 4.9” ID capacity is 2.32 barrels/100 ft, so the 5300ft horizontal has capacity to hold 123 barrels of sand. It would not be jam packed full but this gives the upper limit.
Visualizing what is happening down hole. A 1.5in pipe with a jet nozzle is travelling down a 4.9” tube, the return flow containing mobilized sand moves gently back down the 4.9” tube (18.9”²), before accelerating into the available space between the production tubing and coil tubing, a mere 4.8”², an approx. 4 times smaller space.
So there is a problem, the flow/velocity here is limited to protect the metal from abrasion, because of this bottleneck the velocity in the 4.9” pipe will be low, sand can drop out prior to reaching the pinch point at the production tubing.
It is not a deal breaker, but it will require pull back of the coil tubing to remobilize and flush out the proppant sand that demobilizes, a bed of sand at the bottom of the pipe is OK, a potential wedge that blocks flow and packs around and traps the coil tube is not, time, time, time.
Now assume the max 123 barrels of sand have been flushed, as each perforation is cleared at the fracture stages, a new potential for sand entry has also been introduced. At some point the perforations will be stimulated to flow by dropping wellbore pressure below reservoir pressure.
Depending on if or how freely this sand flows a repeat of the entire process may be required, and so it will continue until sand flow from the reservoir is manageable eg sand does not accumulate so quickly at the production tubing step down that it obstructs flow into the production tubing.
This has been a long winded way of saying the sand flushing rate is limited and the amount of sand to flush is an unknown.
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