Add optional scaling of the well bhp and rate primary variables - #7286
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Add optional scaling of the well bhp and rate primary variables#7286hnil wants to merge 2 commits into
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The bhp column of the well D block sits 6-7 decades below the others: the
conservation-equation derivatives w.r.t. bhp are ~1e-7 because bhp is in
Pascals, while the control equation contributes d(bhp)/d(bhp) = 1. Measured
cond(D) medians are 9.7e8 (SPE1CASE1) and 1.3e10 (SPE1CASE2_THERMAL), fully
removable by diagonal scaling - i.e. units, not physics.
Scale only the derivative when the well Evaluations are created:
createVariable(totalNumEq, value_[eqIdx]/s, numEq+eqIdx) * s
The stored value_ stays physical, so update(), copyToWellState(), the
absolute bhp lower limit, the convergence checks and getPrimaryVars are all
untouched; only the Newton increments convert back (they arrive in scaled
units). B, C, D and resWell_ stay mutually consistent because they are all
assembled from the same scaled Evaluations, and C D^-1 B is exactly
invariant under the column scaling - confirmed: iteration counts are
unchanged (437 -> 437, 72 -> 73).
--well-bhp-scaling=8388608 (2^23, ~84 bar) equilibrates: cond(D) median
drops to 3.8e3 / 3.7e3 and min |det| moves from 2.9e-11 to 2.4e-4, seven
decades further from matrixblock.hh's absolute 1e-40 branch. The gain is
robustness (float builds, absolute thresholds), not iterations.
--well-rate-scaling exists for symmetry; the rate column measures as
already O(1). Defaults are 1.0 and reproduce unscaled results bit for bit.
A per-well scale derived from the current bhp was tried and rejected:
better median conditioning but ~8x worse in the tail, because stopped and
zero-rate wells are not scaled by their bhp magnitude - and the tail is
what the scaling exists for.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Same design as for standard wells: the stored values stay physical and only the Evaluation derivative carries the scale, so B, C, D and the Schur complement remain mutually consistent by construction. The Newton increments for segment pressure and total rate arrive in scaled units and are converted in updateNewton(), where the physical limits (max_pressure_change, the bhp lower limit) then apply unchanged. Fractions and the temperature variable keep scale 1. One consumer needed a matching fix: the classic CPRW coarse well row builds its column entries from C's segment-pressure column, which carries the scale, while the default row-sum diagonal estimates the physical bhp derivative from unscaled B entries. Without the same factor the coarse well column and diagonal disagree by the scale, which doubled linear iterations on BASE2_MSW_HFA (30 -> 59) and SPE1CASE2_MSW_THERMAL (73 -> 139). With it, scaling is iteration-neutral (30/356/73 with and without 2^23), as the C D^-1 B invariance requires. The contracted-diagonal convention needs no fix since it inherits the scale from D itself. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Extended to multisegment wells (same derivative-only design; segment pressure and total rate). One consumer needed a matching fix: the classic CPRW row-sum well diagonal estimates the physical bhp derivative and must carry the scale, otherwise linear iterations double on MSW decks. With it, scaling is iteration-neutral also for MSW (BASE2_MSW_HFA 30/30, MSW-2D-HZ 356/356, SPE1CASE2_MSW_THERMAL 73/73 with and without 2^23). |
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August 7, 2026 15:35
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The bhp column of the well D block sits ~7 decades below the rate column because bhp is in Pascals: measured cond(D) is 1e9 (SPE1) to 1e10 (thermal). This adds --well-bhp-scaling and --well-rate-scaling, applied to the AD derivative only, so stored values stay physical and B, C, D and the Schur complement remain consistent; C D^-1 B is invariant and iteration counts are unchanged.
Defaults are 1.0 and bit-identical off. Recommended setting: --well-bhp-scaling=8388608 (2^23, ~84 bar), which brings cond(D) to ~4e3 and moves the smallest |det| from 3e-11 to 2e-4 — seven decades further from the absolute 1e-40 singularity threshold. Rate scaling measures as already O(1), hence its default. Main gain is robustness for float builds and threshold tests; open question is whether the default should become 2^23 after wider testing.
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