Sabei blocks are currently in the third development stage with ultra-high water-cut. The remaining oil distributes scatteredly and quite a part scattered in the third type reservoirs where exists some problems such as poor producing capacity and water injection capacity, low productivity, fast rising rate of 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, with the original working system of the water injection wells, the bio-enzyme was flooded by the continuous injection method. Firstly, 0.03PV of water was injected; then 0.5PV of the bio-enzyme solution was injected subsurface to displace oil with the concentration of 0.8%.Till the February 2008, the all the injection work has been finished. The cumulative injection of the bio-enzyme was 120.4t.
Evaluation of the Field Test
1.Improvement of the injection effect at water wells After the injection of bio-enzyme, Water could be injected in 2 water wells that had never absorbed water originally; the injection pressure of 4 injection wells decreased at the same time; the injection volume increased; and the injection profile has become better somewhat. The results show that a favorable injection-production driven system has been established. The average injection pressure of individual injection well
decreased from 12.8MPa to 12.1MPa after injection of the bioenzyme and the average injection volume of individual well increased by 16m3. The average scale of water absorbing capacity for every injection well increased by 14.18 from 19.15% to 33.33%. Good effect has been achieved.
Obvious Increment of Oil Production
The average daily oil production of individual oil well increased from 2.1t to the peak value of 3.6t while the watercut decreased by 0.8 percent. The daily oil production of the central wells increased by 1.0t at the best stage while the watercut decreased by 6.1. The cumulative oil increment by now achieved 2796t.
Improvement of Pressure Level
The average flow pressure is 3.7MPa originally while it became 4.7MPa after the field test. It can be seen from the well testing data of central oil well N-2-351-30 that the reservoir pressure resumed from 8.04MPa to 10.92MPa, which means the recovery of the formation pressure. The flow coefficient increased from 0.015μm2•m/mPa•s to 0.078μm2•m/mPa•s.
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 is 1.75t. Then this value became 1.2t after the bio-enzyme flooding. So the composite declining rate slowed down by 2.23%.
Improvement of the Physical Properties of the Crude Oil
As can be seen from complete analysis with the oil samples underground, the bio-enzyme flooding test improved the physical properties of crude oil that the viscosity, the paraffin content and the gel content all decreased somewhat (see in
table 6).
Source:
Experimental Study of Oil Displacement by the Bio-enzyme at the Third Type Reservoirs of Sabei Blocks, 2010
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