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Petrophysical Interpretation Report — 15-135-21365


Well (UWI)	15-135-21365
Log date	19-SEPTEMBER-77
Acquisition date (header)	19-SEPTEMBER-77
BHT (measured)	124 DEGF
Mud resistivity (RM)	0.2 OHMM
Mud filtrate (RMF)	0.15 OHMM
Larionov variant	old_rocks (degraded)
Convergence status	DID_NOT_CONVERGE
Confidence tier	○ BRACKETED
Engine versions	calc_vsh 0.1.0 · calc_phie 0.1.0 · calc_sw 0.1.0 · formula_registry 0.1.0
Config hash (SHA-256)	`2a9cb78728e386ab…`
Git SHA	`bd23bea18153`
Generated	autonomously, no human in the per-report loop

Confidence legend. Each result is tagged by parameter provenance: ● FIRM (core-calibrated) · ◐ QUALIFIED (offset-derived) · ○ BRACKETED (regional/global default — read as a range, dominant uncertainty stated). The system does not claim *always correct*; it states how well-supported each number is.

1. Executive summary

The vintage log covers only the deep consolidated section, so the full logged interval is evaluated — there is no overburden on record to exclude. Within that interval the net pay is 14.9 m with average effective porosity 0.182 and average water saturation 0.353. Monte-Carlo places the P50 net pay at 44.3 m within a P10-P90 range of 21.0 to 69.4 m. CLASS-B VINTAGE WELL: porosity comes from a count-rate neutron transform (engine-anchored, validated against sonic on offset wells; structural approximation) — every number is bracketed and must be read as a range. Parameters carry regional-default provenance, so the estimate remains a bracketed range with declared uncertainty, not a certainty.

Net pay P10 / P50 / P90 = 21.0 / 44.3 / 69.4 m.
Net pay is dominated by 'Rw', which is a regional DEFAULT (uncalibrated). This is the single largest uncertainty — the result is bracketed, not a confident point estimate.

2. Data inventory (from LAS)

Curves present (canonical ← raw): DT←DT, GR←GR, NEUT←NEUT, RT←LL
Logged interval: 1142.39–1428.14 m
Log date: 19-SEPTEMBER-77
Service company: — · Company: THE MAVRRCE L. BROWN CO.
Field: SHABEN EAST
Not provided by LAS (out of scope): core, mud logs, pressure tests, production, completion, formation tops.

3. LAS quality control

Edit type	Curve	Detail
spike_removal	—	2 edits
degradation	—	—

4. Standardization

Raw mnemonics mapped to canonical curve names:

Canonical	Raw mnemonic
DT	DT
GR	GR
NEUT	NEUT
RT	LL

5. Per-curve log QC

GR baseline: gr_p5=28.7, gr_p95=113.0
Bad-hole: GOOD=0.819, DEGRADED=0.004, EXCLUDED=0.177
Low-resistivity: rt_threshold=4.28, n_flagged=155, intervals=[[1145.3, 1145.6], [1146.0, 1146.0], [1146.8, 1149.9], [1152.3, 1152.4], [1154.4, 1154.4], [1154.7, 1156.1], [1156.7, 1157.5], [1162.7, 1165.6], [1170.7, 1170.7], [1171.5, 1172.1]]

6. Data preparation

Edits applied before compute (by type): degradation: 1, spike_removal: 2.

7. Interval definition

Logged interval: 1142.39–1428.14 m
Gross evaluated interval: 285.8 m
Computed net-pay runs (pre-merge): 31
Zonation is computed by depth (no formation tops in LAS).

8. Methodology

All numbers are produced by the deterministic, golden-tested engine. The LLM only selects methods/parameters and writes prose — it never computes a number. Figures are deterministic renderings of these computed numbers for the human reader; the agent reasons over the numeric EDA digest, not images (the models have no vision).

Step	Method (frozen)	Version
Vsh	Larionov 1969 (old rocks)	`vsh_larionov_old 0.1.0`
PHIE	Vintage count-rate neutron, two-point semilog (class-B, engine-anchored)	`phi_neutron_countrate 0.1.0`
Sw	Archie 1942	`sw_archie 0.1.0`
Net pay	Vsh/PHIE/Sw cutoffs → net sand → net reservoir → net pay	`netpay 0.1.0`
Uncertainty	Monte Carlo P10/P50/P90 + parameter sensitivity	`mc 0.1.0`

9. Gamma-ray analysis

Clean baseline gr_min = 20.0 API · shale gr_max = 120.0 API
Shale index IGR = (GR − gr_min)/(gr_max − gr_min), the basis for Vsh.
GR baseline check: gr_p5=28.7, gr_p95=113.0

10. Resistivity analysis

Low-resistivity scan: rt_threshold=4.28, n_flagged=155, intervals=[[1145.3, 1145.6], [1146.0, 1146.0], [1146.8, 1149.9], [1152.3, 1152.4], [1154.4, 1154.4], [1154.7, 1156.1], [1156.7, 1157.5], [1162.7, 1165.6], [1170.7, 1170.7], [1171.5, 1172.1]].

11. Water resistivity (Rw)

Rw = 0.0400 ohm-m · provenance: default
Sourced by the engine (Pickett / SP / default); never authored by the LLM.
Net-pay sensitivity to Rw: 37.5 m swing.
Formation-temperature correction (Arps, gradient from the MEASURED header BHT): Rw ≈ 0.0710 ohm-m at 48.4 °C (evidence only — Sw uses the calibrated Rw).

12. Figures

Composite log

Composite log

Pickett plot

Pickett plot

Buckles plot

Buckles plot

Hingle plot

Hingle plot

Distributions

Distributions

Sensitivity tornado

Sensitivity tornado

Net-pay Monte-Carlo distribution

Net-pay Monte-Carlo distribution

13. Shale volume (Vsh)

Mean Vsh by method (selection is the agent's; the LLM authors no number):

Method	Mean Vsh	Selected
vsh_larionov_old	0.249	✓
vsh_larionov_tertiary	0.183
vsh_linear	0.358
vsh_clavier	0.236
vsh_steiber	0.204

14. Porosity

_Not computed — no RHOB/NPHI curve for the comparison._

15. Water saturation

Mean Sw (Archie 1942) = 0.756 (a=1.00, m=2.00, n=2.00, Rw=0.1081 ohm-m). Electrical parameters are engine-sourced; alternative Sw models are optional sections.

Mean Sw by method (engine-computed comparison; the LLM authors no number):

Method	Mean Sw	Selected
sw_archie	0.756	✓
sw_simandoux	0.399
sw_indonesia	0.529

16. Zonation (net-pay intervals)

Raw net-pay runs merged into 19 intervals (gap tolerance 1.5 m); showing the 15 thickest, depth-ordered. Full set traces in the ledger.

Interval	Top (m)	Base (m)	Net pay (m)	Avg PHIE	Avg Sw	Avg Vsh
Z1	1172.9	1174.9	1.4	0.161	0.387	0.062
Z2	1189.9	1191.5	0.6	0.181	0.440	0.278
Z3	1198.8	1198.9	0.3	0.133	0.346	0.245
Z4	1214.5	1214.6	0.3	0.153	0.287	0.284
Z5	1230.2	1231.2	0.6	0.160	0.417	0.215
Z6	1233.5	1236.7	3.4	0.211	0.202	0.093
Z7	1266.6	1266.7	0.3	0.130	0.375	0.265
Z8	1270.6	1271.0	0.6	0.177	0.430	0.232
Z9	1278.0	1278.3	0.5	0.201	0.351	0.179
Z10	1284.6	1285.8	0.5	0.244	0.468	0.212
Z11	1330.8	1331.4	0.5	0.161	0.209	0.279
Z12	1335.0	1335.2	0.3	0.130	0.437	0.252
Z13	1342.0	1348.0	3.5	0.187	0.409	0.214
Z14	1349.7	1350.6	0.3	0.188	0.496	0.118
Z15	1355.3	1356.8	1.4	0.168	0.420	0.076

17. Results

Quantity	Value
Gross interval	285.8 m
Net pay (P10/P50/P90)	21.0 / 44.3 / 69.4 m
Net-to-gross	0.052
Avg PHIE (net pay)	0.182
Avg Sw (net pay)	0.353
Avg Vsh (net pay)	0.170

18. Uncertainty and sensitivity

Monte Carlo, 500 realizations (seed 42). Net pay swing per parameter (one-at-a-time):

Parameter	Net-pay swing (m)
Rw	37.5
m	21.5
a	15.4
n	5.8

Dominant uncertainty: Rw (swing 37.5 m).

Multi-seed robustness: P50 UNSTABLE across seeds (spread 5.4 m across 4 seeds).

Net pay is dominated by 'Rw', which is a regional DEFAULT (uncalibrated). This is the single largest uncertainty — the result is bracketed, not a confident point estimate.

19. Derived parameters

Bulk-volume water (BVW = PHIE*Sw): mean 0.0801 v/v
Porosity-thickness (Phi·H over net pay): 2.721 m
Hydrocarbon pore thickness (HCPV = Σ PHIE·(1−Sw)·step): 1.786 m
Buckles constant (BVW at P10 of net pay): 0.0351 → Swirr (mean) ≈ 0.192 over 98 pay samples

20. Parameters and provenance

Parameter	Value	Unit	Provenance	Source
gr_min	20.000	API	default	—
gr_max	120.000	API	default	—
rho_ma	2.710	g/cc	default	Schlumberger 1989
rho_fl	1.000	g/cc	default	—
phie_max	0.450	v/v	default	—
phi_sh_d	0.100	v/v	default	—
phi_sh_n	0.350	v/v	default	—
a	1.000	-	default	Winsauer et al. 1952
m	2.000	-	default	Archie, G.E. 1942
n	2.000	-	default	Archie, G.E. 1942
Rw	0.040	ohm-m	default	Kansas Geological Survey 2000
rt_hydrocarbon_floor	5.000	ohm-m	default	—
vsh_cutoff	0.350	v/v	default	—
phie_cutoff	0.100	v/v	default	—
sw_cutoff	0.500	v/v	default	—
bit_size_config	7.875	in	default	—
qc_abort_threshold	0.800	-	default	—
circuit_breaker_n	3.000	-	default	—

The citations table (not RAG) gives each cited parameter exactly one frozen source. Parameters tagged default are regional/global — they drive the bracketed tier.

21. Petrophysical cutoffs

Boundary-inclusive criteria applied by the engine (netpay) to flag reservoir:

Stage	Criterion	Cutoff	Provenance
Net sand	Vsh ≤ cutoff	0.350	default
Net reservoir	+ PHIE ≥ cutoff	0.100	default
Net pay	+ Sw ≤ cutoff	0.500	default

Cutoff values are engine parameters (never LLM-authored); the dominant net-pay uncertainty is Rw — see Uncertainty for the swing.

22. Data quality and validator objections

Curve provenance (canonical ← raw mnemonic): DT←DT, GR←GR, NEUT←NEUT, RT←LL.

QC edits applied before compute — degradation: 1, spike_removal: 2.

Validator	Type	Detail
vsh_phie_anticorrelation	support	Vsh-PHIE Pearson 0.99 > 0.3 (dirty rock + high porosity)

23. Methodology (decision graph)

flowchart TD
    dec_1["decision: step: compare_methods"]
    act_1["tool_call: compare_methods"]
    dec_2["decision: step: compute_vsh"]
    act_2["tool_call: compute_vsh"]
    dec_3["decision: step: compute_phie"]
    act_3["tool_call: compute_phie"]
    dec_4["decision: step: compare_methods"]
    act_4["tool_call: compare_methods"]
    dec_5["decision: step: compute_sw"]
    act_5["tool_call: compute_sw"]
    dec_6["decision: step: apply_cutoffs"]
    act_6["tool_call: apply_cutoffs"]
    dec_7["decision: step: run_uncertainty"]
    act_7["tool_call: run_uncertainty"]
    dec_8["decision: step: derived_parameters"]
    act_8["tool_call: derived_parameters"]

24. Data gaps for calibration

This is a LAS-only study. Data that would calibrate the interpretation is absent:

Core (routine + SCAL): would anchor PHIE and Archie m, n, a.
Pressure tests (RFT/MDT): would give true fluid contacts and gradients (log-based).
Production/flow data: would test the net-pay flag against deliverability.
Dominant net-pay uncertainty driver (from the sensitivity): Rw (calibrated by produced-water salinity or a Pickett/SP Rw calibration).
Standard curves absent: RHOB, NPHI, SP, PEF, CALI, DCAL.

25. Limitations

LAS-only study: no core calibration, no pressure tests (no true fluid contacts), no production, no mud logs, no formation tops (zonation computed by depth).
Standard curves absent in this well: RHOB, NPHI, SP, PEF, CALI, DCAL.
Results are uncalibrated; accuracy depends on data not provided.

26. Conclusions

Vintage class-B well: logged interval covers only the deep consolidated section (no overburden recorded), GR-only clay indicator, count-rate porosity with engine anchors, Archie saturation. Structural-uncertainty caveat applies to every number. Method choices were made against the engine's numeric comparisons, not by preference; the comparison tables show the rejected alternatives beside the selected method. All numbers in this report come from the deterministic engine; the analyst chose the interval, the methods and the analyses, and wrote this prose — nothing more. Remaining uncertainty is dominated by the uncalibrated regional parameters.

Appendix A — Ledger excerpt (traceability)

{
  "net_pay_total_m": 14.935199999994438,
  "net_pay_p10_p50_p90": [
    20.970239999992195,
    44.27219999998351,
    69.35723999997417
  ],
  "driving_params": {
    "a": 1.0,
    "m": 2.0,
    "n": 2.0,
    "Rw": 0.04
  },
  "claim_verifier": {
    "result": "PASS",
    "flags": [],
    "tone_flags": []
  }
}

Appendix B — Completeness gate

Item	Present
QC edits recorded before compute	✓
Every number ledger-traced	✓
Confidence tier on the run	✓
Parameter citations frozen	✓
Validator objections listed, not hidden	✓
Uncertainty propagated (Monte Carlo)	✓
Claim verifier run on prose	✓