(1) Piecewise-linear gas recovery
RFgas(P) = RFi + (P − Pi) × (RFi+1 − RFi) / (Pi+1 − Pi)
Applied between adjacent HNP_EF measurements from 1,450 to 3,500 psig inclusive. No extrapolation is performed.
Hybrid CO2 and surfactant recovery · Eagle Ford cores
What does surfactant imbibition add after CO2 huff-n-puff?
Compare the gas and surfactant-assisted spontaneous imbibition (SASI) stages across four Eagle Ford plugs. Measured, digitised and derived values are labelled by record; the planner constructs a separate scenario from the gas envelope and a selected SASI increment. Four Eagle Ford core plugs ran CO2 huff-n-puff at 1,400–3,500 psig and then surfactant-assisted spontaneous imbibition. Gas recovery reached 49% OOIP at 3,500 psig and SASI added a further 8.6%, totalling 57.6%; the plug operated below the MMP produced under 1% from gas but 8.7% from SASI. The two mechanisms act on different pore classes and their contributions are complementary, not additive constants.
4
core plugs
57.6%
OOIP maximum combined
< 1%
gas RF below MMP
41–67%
of ultimate in cycle 1
Definition. Surfactant-assisted spontaneous imbibition (SASI) recovers oil by counter-current imbibition of an aqueous surfactant solution, acting through wettability alteration and interfacial-tension reduction (SPE-191502).
Record statusprovenance by plug
Measured values are stated in the source text. Digitised values are read from the published figures. Derived values are per-plug sums of reported or digitised component values and are not reported as totals in the source.
What's in this report
Publications
- Zhang, F., Adel, I.A., Park, K.H., Saputra, I.W.R., and Schechter, D.S. 2018. Enhanced Oil Recovery in Unconventional Liquid Reservoir Using a Combination of CO2 Huff-n-Puff and Surfactant-Assisted Spontaneous Imbibition. SPE-191502-MS, SPE Annual Technical Conference and Exhibition, Dallas, Texas, 24–26 September. DOI
- Adel, I.A., Tovar, F.D., Zhang, F., and Schechter, D.S. 2018. The Impact of MMP on Recovery Factor During CO2–EOR in Unconventional Liquid Reservoirs. SPE-191752-MS, SPE Annual Technical Conference and Exhibition, Dallas, Texas, 24–26 September. DOI
- Zhang, F., Adel, I.A., Saputra, I.W.R., Chen, W., and Schechter, D.S. 2019. Numerical Investigation to Understand the Mechanisms of CO2 EOR in Unconventional Liquid Reservoirs. SPE-196019-MS, SPE Annual Technical Conference and Exhibition, Calgary, Alberta, 30 September–2 October. DOI
- Zhang, F., Adel, I.A., Saputra, I.W.R., and Schechter, D.S. 2019. Numerical Investigation of EOR Applications in Unconventional Liquid Reservoirs through Surfactant-Assisted Spontaneous Imbibition (SASI) and Gas Injection Following Primary Depletion. SPE-196055-MS, SPE Annual Technical Conference and Exhibition, Calgary, Alberta, 30 September–2 October. DOI
- Zhang, F., and Schechter, D.S. 2021. Gas and Foam Injection with CO2 and Enriched NGL's for Enhanced Oil Recovery in Unconventional Liquid Reservoirs. Journal of Petroleum Science and Engineering 202: 108472. DOI
SPE-191752 supplies the Eagle Ford huff-n-puff pressure series; the 2021 journal article supplies the Wolfcamp A ultimate point.
Core data · records
Core records
The selector isolates one plug record and its cumulative gas-recovery sequence.
Selected coreSPE-191502
Identity and recovery
Scroll across to inspect every column.
| Parameter | Value | Source status |
|---|
SPE-191752 reports 49.31% for the same 3,500-psig experiment; SPE-191502 rounds to 49%.
Selected-core cycle plateausdigitised from Figs. 2–3
Scroll across to inspect every column.
| Cycle | Cumulative gas RF (% OOIP) | Source |
|---|
Core data · cycle dynamics
Cycle dynamics
Cumulative gas-recovery plateaus are compared at the same cycle number without extending a core beyond its last reported plateau.
CYCLE LOOKUP
16
All-core production sequencesSPE-191502 Figs. 2–3
Scroll across to inspect every column.
| Core | Cycle 1 | Cycle 2 | Cycle 3 | Cycle 4 | Cycle 5 | Cycle 6 |
|---|
Cycle lookup
| Core | Cumulative RF (% OOIP) |
|---|
CORE4 ran three cycles; oil was produced only in cycles 1 and 2. A dash is shown beyond its last reported production plateau.
Core data · aqueous stage
SASI contribution
Per-plug gas recovery and the subsequent SASI increment are kept as separate measured contributions.
Gas and SASI recovery sharesSPE-191502
Scroll across to inspect every column.
| Core | Gas RF (%) | SASI (%) | Combined (%) | Status |
|---|
How this was computed
Gas recovery and the SASI increment are the per-plug values reported in SPE-191502 or read from its figures; each carries its own provenance badge. The combined column is the arithmetic sum of those two components for the same plug. The source does not report a combined total for every plug, so a sum computed here is badged derived rather than measured.
No value on this pane is interpolated and no plug's components are combined with another plug's.
Foam appeared in the graduated cylinder early in SASI after CO2 huff-n-puff; CO2 had adsorbed or penetrated the plugs. CORE4's SASI share dominated its total. The SASI contribution was measured over approximately 240–300 h.
Core data · pressure dependence
Pressure dependence
Eagle Ford huff-n-puff recovery increased across the reported pressure series; the separate Wolfcamp A point uses a different rock and oil.
CO2 huff-n-puff recovery170 °F · Eagle Ford MMP 2,132 psig
Scroll across to inspect every column.
| Rock/oil system | Pressure | RF (% OOIP) | Source |
|---|
Eagle Ford values are as tabulated in the source figure. The Wolfcamp A result is an ultimate value for a different rock and oil.
Related modelling work
SPE-196055
SASI and gas injection sequencing after primary depletion; a core-scale history match carried into a hydraulically fractured well model with realistic fracture geometry and conductivity.
DOISPE-196019
CT-derived core-scale model; primary mechanisms multi-contact miscibility and vaporising gas drive; diffusion minor; ternary-diagram analysis; upscaled dual-porosity compositional field model.
DOIInterpretation · matrix
Cross-comparison
The measured and derived fields are aligned by plug without normalising pressure or cycle count.
Core comparison matrixSPE-191502
Scroll across to inspect every column.
| Core | Pressure (psig) | Cycles | Gas RF (%) | SASI (%) | Combined (%) | Sources |
|---|
How this was computed
Pressure, cycle count, gas recovery and the SASI increment are per-plug source values. The combined column is the per-plug sum of the gas and SASI components and is badged derived where the source reports no total.
Rows are aligned by plug. Pressure and cycle count are not normalised, so the four records are compared as they were run, not as a single series.
Interpretation · interactive planner
Hybrid planner
The gas envelope is the piecewise-linear interpolation of the Eagle Ford huff-n-puff dataset.
HOW TO USE
- Choose a pressure within the measured gas-envelope span of 1,450–3,500 psig.
- Then select a SASI increment from the stated 5.2–11.6 percentage-point range.
- Read the interpolated gas recovery and the scenario sum; the sum is not a prediction outside these bounds.
Reading the chart: the curve is the gas-recovery interpolation of the five measured Eagle Ford points. The vertical segment is the selected SASI increment. Their sum is a constructed scenario, not a new measured plug result. The dashed line at 2,132 psig is the Eagle Ford MMP and the shaded band spans the near-miscible regime up to 2,400 psig.
Scenario controls
1,4503,500 psig
5.211.6%
Import a scenario text file to restore the planner pressure and SASI increment.
Scenario outputs
Gas RF
31.03%
piecewise interpolation
SASI increment
8.6%
scenario input
Combined scenario recovery, % OOIP
39.63%
constructed scenario sum — recorded combined values ranged 9.6–57.6%
Pressure regime
Miscible
at or above 2,400 psig
Maximum measured combined recovery: 57.6% OOIP (Core 3, SPE-191502). The combined output above is a constructed scenario, not a measured plug result.
Gas envelope and scenariowithin measured span only
Scroll across to inspect every column.
| Record | Pressure (psig) | Gas RF (%) | SASI (%) | Combined (%) |
|---|
How this was computed
Gas recovery is interpolated linearly between adjacent measured Eagle Ford huff-n-puff points and only inside the measured span of 1,450 to 3,500 psig. Outside that span no value is returned.
The SASI increment is an entered value inside the 5.2 to 11.6 percentage-point range reported or digitised across the four plugs. The combined output is the sum of the interpolated gas value and the entered increment: a constructed scenario, not a measured plug result. The maximum measured combined recovery is 57.6% OOIP (Core 3, SPE-191502).
The regime line compares the selected pressure with the Eagle Ford minimum miscibility pressure of 2,132 psig and the 2,400 psig miscible threshold.
Interpretation · model
Model & equations
The planner applies a bounded interpolation and a per-plug recovery sum; it does not recompute a compositional or fracture-scale model.
Governing equations
(2) Combined-recovery definition
RFcomb = RFgas + RFSASI
A per-plug sum of reported or digitised component values, where RFSASI is the recovery increment contributed by the aqueous stage on that plug. It is not a universal additive constant.
Assumptions and bounds
- The HNP_EF pressure-response points are experiment ultimates as tabulated in SPE-191752 Fig. 9.
- Linear interpolation is restricted to adjacent measured points from 1,450 to 3,500 psig.
- Two pressure spans coexist. The four core plugs span 1,400–3,500 psig; the HNP_EF pressure-response series spans 1,450–3,500 psig. CORE4 sits at 1,400 psig, below the interpolation floor, so the planner does not reproduce that plug.
- The selected SASI increment is restricted to the measured 5.2–11.6 percentage-point range; it does not represent a pressure correlation.
- The combined result is a plug-scale scenario sum. Matrix heterogeneity, fracture geometry, soak time, and fluid-contact differences are outside this calculation.
- The slider ranges, steps, and defaults are interface ranges, not data.
- The pressure regimes are read against the Eagle Ford MMP of 2,132 psig: immiscible below 2,132 psig, near-miscible from 2,132 to 2,399 psig, miscible at or above 2,400 psig.
- The gauge/absolute distinction (at or below 15 psi) is below the resolution of the reported values and is not reconciled.
Figures · huff-n-puff cycle
Schematic
The schematic steps through the inject, soak, and produce phases of one huff-n-puff cycle on a fractured plug. It is a diagram of the reported sequence, not a simulation.
CO2 huff-n-puff cycle
Scroll across to inspect every column.
Cycle plateaus are the measured Core 3 values at 3,500 psig, digitised from SPE-191502 Fig. 3a (25.8 to 49.3% OOIP over six cycles).
Schematic pressure–time trace of one huff-n-puff cycle: injection to the working pressure, soak at constant pressure, production drawdown.
Cycle 3 of 6
Reference · nomenclature
Nomenclature
Symbols and abbreviations used in the report.
Symbols
| Symbol | Definition | Unit |
|---|---|---|
| P | Pressure | psig |
| RFgas | CO2 huff-n-puff recovery factor | % OOIP |
| RFSASI | Recovery increment contributed by the SASI stage | % OOIP |
| RFcomb | Combined gas and SASI recovery factor | % OOIP |
| RFi | Gas recovery factor at the bracketing measured pressure | % OOIP |
Abbreviations
| Term | Definition |
|---|---|
| CO2 | Carbon dioxide |
| HNP | Huff-n-puff |
| MMP | Minimum miscibility pressure |
| OOIP | Original oil in place |
| SASI | Surfactant-assisted spontaneous imbibition |