Original fracs placed 2 ppg 20/40 sand. PBUs on 12 wells indicated no appreciable frac contribution. 3 wells refractured with up to 75,000 lbs 20/40 ISP at concentrations up to 5 ppg. Well #1: Refrac placed 23,000 of 75,000 lb design. Well doubled in production, eventually stabilizing at 40 bopd with 14 month payout. Well #2: Reperfed, refraced with 71,000 lb ISP, generating 8-fold increase in oil rate, with 3 month payout. Well #3 refractured with 90,000 lb ISP. This refrac undesirably communicated with Upper Devonian, but still doubled production rate, generating an 18 month payout.
Case histories of three hydraulically refractured wells are presented including selection criteria, fracture design and field execution.
The field was developed on 40-acre spacing in the 1960's. The original completions in the Devonian formation at an average depth of 9000 feet included a fracture stimulation. The stimulation consisted primarily of gelled brine water carrying a maximum of two pounds per gallon of 20/40 sand. Recent pressure buildup analysis confirmed that sustained fracture lengths were not created during these original completions.
Three wells were selected as refrac candidates using the following criteria: future field development plans, "high" bottom hole pressure, positive to slightly negative skin, and original completion design (stimulation size, type, success, and initial well potential).
The objective of refracturing designs was to create longer, more conductive fracture wings, with the ultimate goal of optimum drainage.
Problems encountered during refracturing included: 1) the presence of proppant still in place from the original proppant still in place from the original stimulation, 2) casing integrity, 3) inadequate wellbore to formation communications, 4) rate and pressure limitations, 5) open zones above the zone of interest, and 6) poor hydraulic isolation between zones.
This paper will conclude with guidelines for well selection, design techniques, and suggestions for addressing "old wellbore" problems.
Author(s): K.E. Olson, Mobil E and P U.S. Inc.
Paper Number: SPE 22834