Last week, our forum discussions covered a diverse range of operational and safety topics. Members shared insights on optimizing brittleness calibration for the Wolfcamp A formation, reflecting a keen interest in improving extraction efficiency. There was also an engaging debate around the effectiveness of NMR cutoffs versus core analysis in tight sands, which sparked numerous technical exchanges. Additionally, participants explored strategies for enhancing incident response through targeted training programs and shared resources for continuing education focused on groundwater protection at frac sites.
This Week’s Hot Topics
Brittleness calibration resource for Wolfcamp A
This discussion is unraveling the complexities of brittleness calibration in Wolfcamp A, crucial for ensuring effective fracture propagation. It’s a must-read for those working in this formation.
NMR cutoffs vs core in tight sands
There’s a lively exchange happening about the pros and cons of using NMR cutoffs as opposed to traditional core analysis in tight sands. This is a key topic for anyone focused on reservoir evaluation.
Effective training that tightens incident response
Members are sharing practical tips on how to implement training programs that significantly improve incident response times. This thread is packed with actionable advice.
Best CE on groundwater protection at frac sites
If you’re looking for the top continuing education resources focused on groundwater protection at frac sites, this conversation is a great starting point.
On our last Wolfcamp A pad, we set the NMR T2 cutoff at 3.5 ms after matching to Dean–Stark on eight plugs, which pulled movable porosity within about 2 p.u. of core and shaved a week off lab time. If clays jump or oil dips below about 25° API, I bump the cutoff 0.5–1 ms and sanity-check with a single centrifuge Pc run, per @J.Nygaard’s approach. Core still wins when invasion is messy, but this hybrid has been solid in our tighter sands.
We’ve seen the ‘T2cut’ drift in tight sands when echo spacing (TE) or filtrate salinity/temperature changes, so we apply a temp–salinity correction on the log and re-tune per zone using a couple sidewall plugs instead of one blanket cutoff. Building on @rpeters45, a quick sanity check is plotting T1/T2 against clay volume — if T1/T2 jumps, nudge the cutoff down to keep CBW out of movables. It’s like adjusting sunglasses in a tunnel — small tweak, clearer picture.
Switched to setting the T2 cutoff from the Pc curve (Swi via MICP) per zone and confirming with a quick mini-DST; in Wolfcamp A that lined up deliverability better than a core-only fit. Before logging we warm a pit-filtrate jug to bottomhole temp and run a truck-side check; it takes about 15–20 minutes and saves re-tuning. If the mud’s oil‑based, watch for microemulsion signal below about 2 ms or you’ll inflate bound-water volumes, as @dana_r2050 noted.
One thing that helped us in Wolfcamp A: we “recompress plugs to in‑situ stress before lab NMR,” which cut the apparent movables in the sub‑micron pores and made the log cutoff line up with what the wells delivered. If you can’t do that, at least adjust the hydrogen index for condensate‑rich layers or you’ll overcall free fluid.
What finally helped us in Wolfcamp A was running a single “long TW” NMR pass (TW≈6–8 s) at BH temperature to pull in the slow pores we’d been missing. That nudged our T2 cutoff about 1–2 ms higher and lined up with deliverability a lot better; if tool time’s tight, @nmr_gal’s shortcut of correcting lab spectra to in‑situ T gets you most of the way.
Quick datapoint from Wolfcamp A: we started pairing a 2–3 minute ‘short TW’ NMR pilot strip with a full-TW pass at BH temp and using the difference to estimate the movable fraction before trusting core, which only added about 20 minutes to the run and made the cutoff more defensible… It tracks well unless fresh OBM filtrate is in the zone — then I lean on core first. @Riley, if you try it, give the tool a minute to thermally stabilize.