Lithologic Reservoirs ›› 2026, Vol. 38 ›› Issue (3): 182-189.doi: 10.12108/yxyqc.20260316

• PETROLEUM ENGINEERING AND OIL & GAS FIELD DEVELOPMENT • Previous Articles     Next Articles

Simulation experiment on phase behavior variation in multi-cycle injection and production of oil-ring type condensate gas reservoirs

ZHANG Xiaoyan1(), LIU Sihong1, CAO Qingbin1, LEI Tian1, WANG Yue1, TANG Lei1, XIE Yuxin1, YAN Jian2   

  1. 1 No. 2 Gas Production Plant, PetroChina Changqing Oilfield Company, Yulin 719000, Shaanxi, China
    2 College of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China
  • Received:2025-10-06 Revised:2025-11-15 Online:2026-05-01 Published:2026-01-22

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Abstract:

Based on the principle of conventional PVT phase behavior testing, a high-temperature and high-pressure formation fluid phase behavior apparatus was used to simulate the oil-ring type condensate gas reservoir. Take multiple samples from the top condensate gas and the bottom oil-ring by conducting constant-volume depletion experiments and multi-cycle injection and production experiments, and analyses were carried out on their phase behavior changes during depletion and multi-cycle injection and production process, as well as their impact on recovery rate. The results show that: （1） After natural depletion of the oil-ring type condensate gas reservoir, the oil-ring saturation increased from 3.4% to 13.2%. The presence of the oil-ring results in more condensate oil remaining in the reservoir, and the condensate oil recovery rate under natural depletion is only 24.3%. (2) After 5 cycles injection and production, the recovery rate of condensate oil increased by 25.3%, and the saturation of the bottom oil-ring decreased from 13.2% to 2.9%. The first 2 cycles of injection and production showed significant effects, and the injected gas could effectively extract and vaporize the bottom oil-ring into gas phase, mainly extracting the intermediate hydrocarbons of C3-C10 in the oil-ring. （3） With the number of injection and production cycles increases, the composition of the top condensate gas and the injected gas tends to be consistent, and their phase diagrams continuously shrink to the lower left, resulting in an increasing difference from the oil-ring composition. That weakens the evaporation effect of the injected gas on the oil-ring, and the ability of the oil-ring to dissolve gas gradually decreases.

Key words: oil-ring type condensate gas reservoir, condensate oil, recovery rate, phase simulation experiment, gas injection and production, natural depletion development

CLC Number: 

  • TE319

Table 1

Statistics of the molar content of condensate oil, oil-ring, produced natural gas and reconstituted condensate gas composition %"

组分 x（凝析油
组分）		 x（油环
组分）		 x（产出天然气
组分）		 x（复配凝析气
组分）
CO2 — 0.02 0.08 0.09
N2 — 0.11 0.36 0.71
C1 — 42.23 89.09 72.63
C2 — 2.27 6.86 11.25
C3 0.48 0.51 2.31 5.62
iC4 0.67 0.15 0.56 0.87
nC4 3.19 0.21 0.47 1.32
iC5 4.61 0.21 0.19 0.67
nC5 8.36 0.30 0.08 0.82
C6 15.95 2.17 — 0.27
C7 15.94 5.46 — 0.36
C8 13.38 8.32 — 0.30
C9 10.06 8.11 — 0.11
C10 7.59 6.56 — 0.13
C11+ 19.79 23.39 — 4.85

Fig. 1

Experimental setup for multi-cycle injection and production simulation of oil-ring type condensate gas reservoirs"

Fig. 2

Flowchart of CVD and multi-cycle injection and production phase behavior simulation experiment for oil-ring type condensate gas reservoirs"

Table 2

Phase parameters of CVD experiment simulation of the bottom oil-ring and the top condensate gas before and after CVD in oil-ring type condensate gas reservoirs"

参数 底部油环 顶部凝析气
CVD前 CVD后 CVD前 CVD后
GOR/（m3·m-3） 195 74 2 284 21 105
饱和压力/MPa 25.7 5.0 25.7 5.0
密度/（g·cm-3） 0.708 0.714 0.402 0.234
黏度/（mPa·s） 3.8 4.3 — —
分子量/（g·mol-1） 94.6 116.5 34.7 26.1

Fig. 3

Phase variation features of CVD experiment simulation of the top condensate gas and the bottom oil-ring before and after CVD in oil-ring type condensate gas reservoirs"

Fig. 4

CVD experiment simulated relationship of condensate oil recovery rate and saturation with pressure during the depletion process of oil-ring type condensate gas reservoirs"

Fig. 5

Multi-cycle injection and production phase experiment simulation of variations of the recovery rate of each round and the cumulative recovery rate when the depletion pressure drops to 5.0 MPa after multi-cycle gas production in oil-ring type condensate gas reservoirs"

Fig. 6

Multi-cycle injection and production phase experiment simulation of the changes of the molar content of multi-cycle produced gas composition in oil-ring type condensate gas reservoirs"

Fig. 7

Multi-cycle injection and production phase behavior experiment simulation of changes of oil-ring saturation when the pressure drops to 5.0 MPa after multi-cycle gas production in oil-ring type condensate gas reservoirs"

Table 3

Multi-cycle injection and production phase behavior experiment simulation of phase parameters of top condensate gas after multi-cycle gas injection to 25.0 MPa in oil-ring type condensate gas reservoirs"

注气轮次 GOR/
（m3·m-3）		 饱和压力/MPa 密度/
（g·cm-3）		 分子量/
（g·mol-1）
原始状态（CVD前） 2 284 25.7 0.402 34.7
第1轮注气后 3 073 24.1 0.384 32.2
第2轮注气后 4 308 23.2 0.366 30.5
第3轮注气后 6 825 21.9 0.334 27.3
第4轮注气后 9 717 18.5 0.297 26.6
第5轮注气后 13 882 14.4 0.265 24.8

Fig. 8

Multi-cycle injection and production phase behavior experiment simulation of the variation of GOR after multi-cycle gas injection to 25.0 MPa and gas production to 5.0 MPa of the top condensate gas in oil-ring type condensate gas reservoirs"

Fig. 9

Multi-cycle injection and production phase experiment simulation of multi-cycle injection and production phase of top condensate gas in oil-ring type condensate gas reservoirs"

Table 4

Experiment simulation of phase behavior of multi-cycle injection and production in oil-ring type condensate gas reservoirs: Phase parameter and components of the bottom oil-ring after multi-cycle gas production"

采气轮次 GOR/
（m3·m-3）		 泡点压力/MPa 密度/
（g·cm-3）		 黏度/
（mPa·s）		 分子量/
（g·mol-1）		 x（C1）/% x（C2）/% x（C3—C10）/% x（C11+）/%
CVD后 74 5.0 0.713 3.9 146.5 12.38 1.83 33.96 51.40
第1轮采气后 72 5.0 0.745 5.9 169.2 12.41 2.09 13.00 72.06
第2轮采气后 68 5.0 0.791 8.6 207.5 12.17 2.11 4.11 81.17
第3轮采气后 65 5.0 0.824 12.5 253.1 12.09 2.23 1.19 84.13
第4轮采气后 61 5.0 0.857 15.2 282.2 11.81 2.04 0.43 85.34
第5轮采气后 59 5.0 0.865 16.1 303.4 11.63 1.82 0.31 86.02

Fig. 10

Multi-cycle injection and production phase behavior experiment simulation of the variation of oil-ring GOR with pressure under different gas injection rounds in oil-ring type condensate gas reservoirs"

Fig. 11

Multi-cycle injection and production phase experiment simulation of multi-cycle injection and production phases of bottom oil-ring in oil-ring type condensate gas reservoirs"

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