Feasibility Experiments and Injection/Production Optimization of Associated Gas Flooding for Enhanced Oil Recovery: A Case Study of the Chang 7 Shale Oil in the West 233 Area of the Ordos Basin

doi:10.7657/XJPG20260207

Abstract

Abstract:

The Chang 7 reservoir in the West 233 area of the Ordos Basin is a typical sandwiched shale oil accumulation with low formation pressure coefficient, rapid production decline, and abundant associated gas. Associated gas flooding experiments were conducted on reservoir rock samples. Combined with NMR T₂ spectra, the results of associated gas flooding and huff-n-puff experiments were analyzed, and the huff-n-puff efficiency under varying well spacing was simulated. The results show that the presence of bound water significantly reduces the efficiency of associated gas flooding. After displacement, the signal intensity of pores with T₂>10 ms decreases significantly; the displaced oil mainly comes from large pores, while only a small part of oil in small pores is mobilized, leaving a large quantity of residual oil. Associated gas huff-n-puff can effectively improve the recovery of shale oil, with the first cycle contributing most to the recovery, the second cycle witnessing a recovery greater than 85% OOIP, the third cycle recording a recovery not exceeding 15%, and the fourth cycle remaining a recovery basically unchanged. This indicates that the oil in large pores has been mainly mobilized. With the increase of huff-n-puff cycles, the incremental oil production decreases, the oil replacement rate drops, and the increase in recovery factor slows down, gradually entering an inefficient cycle. For associated gas huff-n-puff in horizontal wells with well spacing of 200 m, the optimal associated gas injection time is 639 d, the optimal slug size is 900 m³, the optimal injection rate is 15 m³/d, the optimal shut-in time is 40 d, the optimal injection-production time per cycle is 160 d, and the optimal number of huff-n-puff cycles is 3. The optimal timing for continuous associated gas flooding is 1,200 d, and the optimal associated gas injection rate is 15 m³/d.

Key words: Ordos Basin, Chang 7 formation, shale oil reservoir, associated gas flooding, associated gas huff-n-puff, enhanced oil recovery, injection-production optimization, numerical simulation

CLC Number:

TE357

CHEN Bo, LIU Shuaishuai, WANG Yijun, LENG Xiangang, LEI Qihong, LI Desheng, WANG Ning. Feasibility Experiments and Injection/Production Optimization of Associated Gas Flooding for Enhanced Oil Recovery: A Case Study of the Chang 7 Shale Oil in the West 233 Area of the Ordos Basin[J]. Xinjiang Petroleum Geology, 2026, 47(2): 184-191.

Figures/Tables 9

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样品编号	直径/ mm	长度/ mm	密度/ （g·cm^-3）	孔隙度/ %	渗透率/ mD
S1	25.16	43.50	2.379	8.260	0.237
S2	25.16	42.57	2.417	8.802	0.086
S3	25.10	40.17	2.448	7.421	0.142
S4	25.17	40.96	2.358	9.860	0.209
S5	25.16	42.61	2.462	6.550	0.072
S6	25.11	40.18	2.436	8.485	0.175
S7	25.12	43.56	2.448	8.047	0.170
S8	25.09	41.56	2.404	9.990	0.172
S9	25.14	40.88	2.462	7.860	0.112
S10	25.12	41.08	2.457	7.676	0.112

样品编号	孔隙度/ %	渗透率/ mD	氮气驱效率/%	伴生气驱效率/%	是否含束缚水
S1	8.260	0.237	38.49	52.49	否
S2	8.802	0.086	26.90	27.79	否
S3	7.421	0.142	37.95	38.29	否
S4	9.860	0.209		39.60	是
S5	6.550	0.072		19.23	是
S6	8.485	0.175		38.75	是

样品编号	孔隙度/ %	渗透率/ mD	压力/ MPa	实验前重量/g	实验后重量/g	周期采收量/g	累计采收量/g	采收贡献率/ %
S7	8.047	0.170	19	79.36	78.69	0.521 3	0.521 3	82.75
				78.69	78.53	0.078 2	0.599 5	12.41
				78.53	78.46	0.030 5	0.630 0	4.84
				78.46	78.50	0	0.630 0	0
S8	9.990	0.172	16	51.56	51.10	0.309 6	0.309 6	80.07
				51.07	50.98	0.062 9	0.372 5	16.26
				50.97	50.94	0.014 2	0.386 7	3.67
				50.90	50.90	0	0.386 7	0
S9	7.860	0.112	16	70.75	70.10	0.393 9	0.393 9	76.18
				70.10	69.92	0.112 2	0.506 1	21.70
				69.85	69.83	0.011 0	0.517 1	2.12
				69.78	69.80	0	0.517 1	0
S10	7.676	0.112	13	71.57	70.97	0.405 6	0.405 6	82.49
				70.90	70.80	0.067 6	0.473 2	13.75
				70.76	70.73	0.018 5	0.491 7	3.77
				70.73	70.70	0	0.491 7	0