As I've said before fracture treatments are simple hydraulics. But I hate them; I get all worked just thinking about the myriad of ways I tend to get them wrong. The Guidebook has a single frac page, 7 PRD 2 in a desperate attempt to keep it simple. But not too simple!
Getting an initial shut-in pressure (ISIP, or just the wellhead pressure) is a common calculation. In this problem ISIP calculates to 1,600 psi (depth 10,000 ft TVD, MW = 8.46 ppg, reservoir pressure 2,800). But ISIP already given, anyway.
All the problem wants? Required (or theoretical) hydraulic pump power (in HP) to frac the reservoir. This is just [ISIP*Qbpm]/40.8 (equation conveniently shown the bottom of the GB frac page). Don't use the starting wellhead pressure. Since the frac is pumped at 50 bbl/min: (1,600)50(1/40.8) = 1,961 hp or (C).
I think we should take into consideration the pressure loss in tubing ( assuming the fracking fluid is being pump trough tubing) to calculate the pump pressure, because the pumps will fist overcome friction (600 psi) before applying 1600 psi to the reservoir. if we were calculating the frac gradient 1600 psi + hydro-static will work.
ReplyDeleteI'm plundering my memory so I'm prob wrong but doesn't ISIP naturally include tbg loss since it's PP the instant of frac...I can't remember offhand...let me know...
DeleteThe question asks for the hhp which can only work when pumping, so I believe that, yes tubing friction should be taken into account.
DeleteIt doesn't need it. Check out the 2004 practice exam, which has a problem just like this using ISIP.
DeleteIt says in the problem to ignore those
ReplyDeleteThanks Unk. Problem 39 says: A frac used 8.46 lb/gal fluid pumped at 50 bbl/min. Tubing pressure loss was 600 psia. The pressure loss through the perforations, at centered at 10,000 TVD feet, was negligible. The maximum and average treating pressure was 3,303 and 3,000 psig, respectively. Prior to treatment, the well was at 50 psig at the wellhead and the reservoir pressure was estimated to be 2,800 psig. When the treatment ended, the initial shut-in pressure was 1,600 psig. The hydraulic hp required to fracture the formation is: (A) 1,760 (B) 1,860 (C) 1,960 hp (D) 2,060
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