Utah FORGE 16A → 16B cross-well frac hits, April 2024 (measured)

The original model is unchanged above. Here each new piece of physics is switched on one at a time with textbook or published inputs only — nothing is adjusted to match the arrival times.

• FORGE core rock stiffness (applied)
  E = 56.9 GPa, ν = 0.296 (FORGE 58-32 core triaxial tests at 7,500 psi confinement (McLennan 2019), lab-measured), replacing the assumed 55 GPa / 0.26. FORGE only.
• Path along a mapped natural fracture (not blind) (applied)
  Distance = shortest path inside one fracture of the 2025 FORGE fracture map that crosses both the 16A stage and 16B (Stage 7 98 m, Stage 8 95 m, Stage 9 97 m). Stage 5 has no mapped fracture reaching 16B, so it is left blank. The map was built partly from the 16B frac hits, so this column is not a blind test.
• Rock resistance to cracking (toughness) (applied)
  K_Ic = 1.5 MPa·√m (Textbook granite K_Ic (Atkinson & Meredith 1987 lab range 1–3 MPa·√m); assumed, not fitted). Only slows growth when the toughness bound is smaller than the fluid-flow bound.
• FORGE's own measured rock toughness (applied)
  K_Ic = 1.14 MPa·√m (Utah FORGE granite, lab-measured at 179–230 °C (Dvory & McLennan 2026, GDR 1819, SCB tests); mean of the four ≥175 °C tests, fixed rule, not fitted). Replaces the textbook value for FORGE only; EGS Collab is phyllite, so it keeps the textbook figure.
• Flow-log check of the wear split (can only widen the gap — not applied)
  SLB's Aug 2024 injection-profile log in 16A does not agree with the camera wear: the cluster nearest the hit takes 2.7% of Stage 8's logged water (wear says 17%), 7.9% of Stage 9's (wear 11.8%), and Stage 7 takes none at all. The log was run four months later at circulation rates, so it is a check, not a replacement. Using it would make Stages 8 and 9 arrive later still. Wear split kept, labelled as uncertain.
• Flattened (height-limited) fracture shape (needs data)
  Needs a published stress barrier between the stage and the monitoring well. None is published for these sites; FORGE stress falls with height, which favours upward growth, so a barrier cannot be assumed.
• Uneven split between clusters (applied)
  From the 2024 downhole camera survey: each cluster's share of the stage's perforation wear (eroded hole area) is used as its share of the rate. The cluster nearest the hit took 39% (Stage 7, vs 33% equal), 17% (Stage 8, vs 12.5%) and 12% (Stage 9, vs 12.5%). Wear is an indirect sign of fluid share, labelled as such, and is a fixed input.
• Hot gel thins out (can only widen the gap — not applied)
  Lower viscosity speeds radial growth (R ∝ μ^(-1/9)), so temperature thinning can only make arrival earlier. Not applied.
• Surveyed well-to-well distance (applied)
  From the 16A and 16B well surveys: 299–326 ft from each 16B hit depth to the nearest point on 16A, so the published 300 ft was already close. With the 2024 perforation depths from the camera survey, the straight distance from the nearest cluster to the hit is 334 / 330 / 560 / 438 ft (Stages 5 / 7 / 8 / 9) — Stages 8 and 9 hit 16B well beyond the end of their own stage.

Public FORGE fiber record along 16B (strain and temperature, 12–16 August 2024 flow test). Zones are depths where the change over the test stands out more than 20× the background noise. These are our own picks, not published values, and the threshold was set after a first look at the profile.

April frac hits within 25 ft of a zone: 10 of 27 (H18, H19, H20, H21, H22, H23, H24, H25, H26, H27). Hits H1–H11 (8,776–9,267 ft) show no strong fiber change, so those connections may have closed or carried little flow in August.