China's Sabei Blocks: Bio-Enzyme Oil Displacement Study
Updated: Aug 18
Editorial note: This case study documents laboratory and field work conducted in China from December 2007 to February 2008 (see source citation below). It is republished here for technical reference. The date shown at the top of this post reflects when it was added to this site, not when the original field work took place.
Sabei blocks are currently in a later development stage marked by ultra-high water-cut. The remaining oil is scattered, much of it in the third-type reservoirs, which suffer from poor producing capacity, poor water-injection capacity, low productivity, and a fast-rising water-cut.
The Bio-enzyme is a kind of agent produced by microbial technology. It has the high capability of releasing hydrocarbon from the surface of reservoir rock particles, and can change the wettability of reservoir rocks and reduce the interfacial tension, thereby to reduce the flow resistance of oil in the reservoir pores and release the crude oil from the surface of the rock particles.
The lab experiments in cores by bio-enzyme solution show that this agent can increase the recovery rate by 5.0% and reduce the injection pressure by 40%. The field test results showed that the bio-enzyme can improve the physical properties of underground oil, decrease the injection pressure of water wells, increase the injection volume, improve the injection profile and establish a good injection production drive system. The oil well production increased significantly and the composite declining rate slows down at the same time.
Implementation of the Testing Programs
In December 2007, using the original working system of the water-injection wells, the bio-enzyme was introduced by continuous injection. First, 0.03 PV of water was injected, followed by 0.5 PV of a 0.8% bio-enzyme solution injected downhole to displace oil. By February 2008, all injection work had been completed, with a cumulative bio-enzyme injection of 120.4 t.
Evaluation of the Field Test
1. Improvement of the injection effect at water wells
After the injection of bio-enzyme, two water wells that had never previously absorbed water were able to take injection; the injection pressure of four injection wells decreased; injection volume increased; and the injection profile improved. This shows that a favorable injection-production drive system was established. The average injection pressure per well dropped from 12.8 MPa to 12.1 MPa, and the average injection volume per well increased by 16 m³. The average water-absorbing capacity per injection well rose by 14.18 percentage points, from 19.15% to 33.33%. A good effect was achieved.
2. Obvious Increment of Oil Production
The average daily oil production of individual oil wells increased from 2.1t to a peak value of 3.6t while the water-cut decreased by 0.8 percent. The daily oil production of the central wells increased by 1.0t at the best stage while the water-cut decreased by 6.1 percent. The cumulative oil increment achieved was 2,796t.
3. Improvement of Pressure Level
The average flow pressure was originally 3.7 MPa and became 4.7 MPa after the field test. Well-testing data from central oil well N-2-351-30 shows the reservoir pressure recovered from 8.04 MPa to 10.92 MPa, indicating recovery of formation pressure. The flow coefficient increased from 0.015μm2•m/mPa•s to 0.078μm2•m/mPa•s.
4. The Composite Declining Rate Slows Down
Before the bio-enzyme flooding test, the average monthly composite decline of the 8 oil wells in the testing block was 1.75t. This value became 1.2t after the bio-enzyme flooding. So the composite declining rate slowed down by 2.23%.
5. Improvement of the Physical Properties of the Crude Oil
Complete analysis of the underground oil samples showed that the bio-enzyme flooding test improved the physical properties of the crude oil — viscosity, paraffin content, and gel content all decreased somewhat (see Table 6).
6. Wettability and Salinity Response
Separate lab measurements in the same study showed the mechanism behind these field results. Contact-angle tests on quartz chips found the rock surface becoming markedly more water-wet after bio-enzyme exposure, with the angle dropping from 94.35° to near 0° within 30 hours. Interfacial tension tests also showed a consistent salinity trend: as brine salinity rose from 200 to 8,000 mg/L, oil-brine IFT dropped from 1.28 mN/m to 0.39 mN/m — indicating the bio-enzyme's effectiveness held up, and even improved, in higher-salinity water.
Sources & Credits
"Experimental Study of Oil Displacement by the Bio-enzyme at the Third Type Reservoirs of Sabei Blocks." 2010 Asia-Pacific Power and Energy Engineering Conference (APPEEC), Chengdu, China. doi:10.1109/APPEEC.2010.5448872
