Wolfcamp A · 155 °F · JPSE 2021

How does gas composition change miscibility pressure?

On Wolfcamp A sidewall cores at 155 °F and 5,000 psi, one huff-n-puff cycle recovered 23% OOIP with enriched gas (50% CH₄–50% C₂H₆) against 13% for 85/15, 9.7% for methane, and 9% for CO₂ — whose 5,000-psi performance fell below its own lower-pressure results. Ethane enrichment cut the CH₄ MMP from 5,715 to 2,853 psi. Foam co-injection with 50/50 gas recovered 19.2% in one cycle with the smallest CT disturbance of the series.

4

gas MMPs measured

23%

OOIP, one 50/50 cycle

36%

OOIP 50/50 ultimate

−2,862 psi

MMP shift, CH₄ to 50/50

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

Definition. Enriched gas denotes produced gas whose ethane fraction is raised to lower the minimum miscibility pressure of the injection gas-oil system (JPSE 2021, 202: 108472).

Record status6 records · 1 live model · 1 schematic

Fig. 5

MMP vs composition

Four measured minimum miscibility pressures.

Table 4

Single-cycle results

Recovery and average CT change, six fluids.

Table 4

Foam experiments

Two co-injection records and screening results.

Live

Composition planner

Bounded interpolation over the measured axis.

S6

Enrichment ternary

Compositions are schematic; the readout is the measured minimum miscibility pressure.

Schematic

Measured recordLive calculationReference material

Report record

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

What's in this report

Publications

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 10.1016/j.petrol.2021.108472

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 10.2118/196019-MS

Measured basis · JPSE 2021 Fig. 5

MMP vs composition

Minimum miscibility pressure was measured for four injection fluids with Wolfcamp A oil at 155 °F.

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

Fig. 1 · MMP ladderWolfcamp A · 155 °F

Fig. 1 — Minimum miscibility pressure by injection fluid. Red markers are the three methane–ethane measurements; the blue marker is CO₂, a separate fluid system. The dashed silver line is the 5,000 psi operating pressure of the huff-n-puff experiments; the shaded band marks pressures at or below the CO₂ minimum miscibility pressure, the lowest of the four fluids. All four values are from JPSE 2021 Fig. 5.

Complete figure data

Minimum miscibility pressure measurements at 155 °F.
Fluid	MMP (psi)	Source

CO₂ at 5,000 psi reached 21% ultimate — lower than its lower-pressure CO₂ experiments. Gas blockage of pore space was discussed as the cause. The low CO₂ MMP did not yield the highest recovery at 5,000 psi.

Single-cycle response · JPSE 2021 Table 4

Single-cycle huff-n-puff results

Recovery factor and average CT change were recorded after one cycle at 5,000 psi and 155 °F.

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

Fig. 2 · Recovery and CT responseone cycle · 5,000 psi

Fig. 2 — One-cycle recovery factor is shown by red bars; average CT change is shown by grey markers on the second axis. Source: JPSE 2021 Table 4.

Complete figure data

One-cycle Wolfcamp A results at 5,000 psi and 155 °F.
Fluid	RF (% OOIP)	Avg CT change (HU)	Source

Highlighted row = highest one-cycle recovery of the series.

For the CH₄ enrichment series, recovery and average CT change increase from CH₄ through 85/15 to 50/50. CO₂ does not follow the trend (17 HU at 9% one-cycle RF). Foam rows are plug-referenced values; see Foam experiments.

Foam records · Wolfcamp A · JPSE 2021

Foam experiments

Foam was co-injected at 5,000 psi and 155 °F after surfactant screening at 3 gpt.

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

Foam-1 · surfactant + 85/15

Pressure: 5,000 psi
Temperature: 155 °F
Gas rate: 13.9 ml/min
Solution rate: 5.9 ml/min
Gas fraction: 70%
RF, one cycle: 12.8% OOIP
Foam collapse (normalized CT to zero): about 48 h

Foam-2 · surfactant + 50/50

Pressure: 5,000 psi
Temperature: 155 °F
Gas rate: 13.9 ml/min
Solution rate: 5.9 ml/min
Gas fraction: 70%
RF, one cycle: 19.2% OOIP
Foam collapse (normalized CT to zero): about 24 h

Surfactant screening · 3 gpt

Contact angle

84.4° to 42.9°

screening result

IFT

18.1 to 1.1

mN/m

Lifetime observations

Reported foam half-life at 5,000 psi: over 24 h (foam-2).

Normalized CT reached zero at about 48 h (foam-1) and 24 h (foam-2).

Foam-1 recovered 12.8% against 13% for its pure-gas pair. Residual oil remained in the glass-beads pack, so the plug-referenced recovery factor understates foam performance.

Evidence matrix · JPSE 2021

Cross-comparison

The matrix keeps one-cycle and ultimate recovery in separate columns.

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

Gas and foam comparison

Measured and reported outcomes for the six Table 4 fluids.
Fluid	MMP (psi)	RF, one cycle (%)	Avg CT change (HU)	RF, ultimate (%)	Cycles to ultimate	Source

Highlighted row = highest one-cycle recovery of the series.

Em dash = not reported. Foam-system MMP not measured; the carrier gas MMP appears in its own row.

Ultimate recovery records

Enriched 50/50 gas reached 36% OOIP after 5 cycles; more than 60% of the ultimate recovery was produced in the first cycle.

Related modeling work · SPE-196019

CT-derived core-scale model; primary mechanisms multi-contact miscibility and vaporizing gas drive; diffusion minor; ternary-diagram analysis; upscaled dual-porosity compositional field model.

SPE-196019-MS · DOI 10.2118/196019-MS

Interactive model · measured compositions only

Composition planner

MMP is interpolated piecewise between the measured methane–ethane compositions. CO₂ remains a separate reference. The source reports one minimum miscibility pressure per fluid, so the planner resolves two regimes; the near-miscible band used elsewhere in the GEOR set is not defined for this fluid system.

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

HOW TO USE

Set composition: Choose an ethane fraction from 0% to 50%.
Set pressure: Choose the operating pressure and compare it with the interpolated MMP.
Save a case: Export a scenario, or import a prior text file to restore both controls.

Reading the chart: the open red marker is the composition you selected, placed on the interpolation line; the dashed silver line is the operating pressure you selected. The marker sitting on or below that line is the miscible condition.

Scenario controls

C₂H₆ fraction (%)15

Pressure (psi)5000

Live outputsinterpolated between measured compositions

Interpolated MMP

4,452.0 psi

piecewise linear

Regime

Miscible — multi-contact

regime code 1 = miscible · 0 = immiscible

CO₂ reference MMP

2,016 psi

separate fluid system

Fig. 3 · Composition planner15% C₂H₆ · 5,000 psi

Fig. 3 — Piecewise-linear MMP interpolation across the measured methane–ethane compositions. The open red marker is the selected composition; the dashed silver line is the selected operating pressure. CO₂ is excluded from this axis.

Complete figure data

Measured methane–ethane points and separate CO₂ reference.
Fluid basis	C₂H₆ (%)	MMP (psi)	Role
CH₄	0	5,715	measured axis point
85% CH₄–15% C₂H₆	15	4,452	measured axis point
50% CH₄–50% C₂H₆	50	2,853	measured axis point
CO₂	—	2,016	separate reference row

Model basis · equations and bounds

Model & equations

The planner contains one bounded interpolation. The CT equation is reproduced for interpretation of the reported CT response.

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

Numbered equations

Equation 1 · normalized CT

Normalized CT = (avg CT current − avg CT end) / (avg CT change)

JPSE Eq. 1.

Equation 2 · MMP interpolation

MMP(x) = MMP_i + (MMP_i+1 − MMP_i) × (x − x_i) / (x_i+1 − x_i)

Applied piecewise to measured x = 0%, 15%, and 50% C₂H₆. The bound is x from 0% to 50%; no extrapolation is performed.

Assumptions and limits

Composition is expressed as the C₂H₆ volume fraction x on the measured CH₄–C₂H₆ axis.
Piecewise-linear interpolation is restricted to the measured compositions; CO₂ is a separate fluid system.
Regime is classified as immiscible below the interpolated MMP and miscible at or above it. The dataset reports one MMP per fluid, so no near-miscible band is resolved.
The composition and pressure control bounds, steps, and opening values are interface ranges, not data.
Gauge/absolute distinction (15 psi or less) is below the resolution of the reported values and is not reconciled.

Figures · JPSE 2021 Table 4

Foam vs pure gas in the fracture

The schematic contrasts the two fracture-filling behaviours behind the Table 4 CT record: foam holds the fracture volume, pure gas channels through it. Geometry is illustrative; the CT and recovery values driving the readout are measured.

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

CT disturbance and one-cycle recovery from JPSE Table 4 at 5,000 psi: pure 50/50 gas 22 HU · foam-2 3 HU. Foam fills the fracture uniformly; pure gas channels through it.

Injection progress

Ethane enrichment on the pseudo-ternary

Composition schematic accompanying the 5,000 psi huff-n-puff experiments. Ethane enrichment moves the injection-gas marker toward the intermediates apex. The envelope and contact path are illustrative; they do not predict phase equilibrium or miscibility. The MMP readout uses the JPSE 2021 Fig. 5 measurements.

Fig. 4 — Ethane enrichment moves the injection-gas marker toward the intermediates apex. The fixed envelope and contact path are schematic constructions, not measured compositions or phase-equilibrium results. The MMP readout is measured.

Reference · symbols and abbreviations

Nomenclature

Symbols and abbreviations used in the report.

Prepared by Imad A. Adel · Senior Petroleum Research Engineer, Chemical & Petroleum Engineering

Symbols

Symbols used in the equations.
Symbol	Definition	Unit
x	Ethane fraction in the methane–ethane mixture	%
MMP	Minimum miscibility pressure	psi
CT	Computed-tomography attenuation	HU
RF	Recovery factor	% OOIP

Abbreviations

Abbreviations used in the report.
Abbreviation	Meaning
CH₄	Methane
C₂H₆	Ethane
CO₂	Carbon dioxide
HU	Hounsfield unit
OOIP	Original oil in place
gpt	Gallons per thousand (gallons of surfactant per 1,000 gallons of solution)
NGL	Natural gas liquids