Abstract
Abstract
Cyclic steam injection is one of the most effective EOR technologies for Bohai off-shore heavy oil field. Production capacity of thermal recovery has reached 1.9 times of cold production in the same period. However, with the increase of huff and puff cycles, large amount of water-in-oil emulsion is produced with water cut increasing gradually, especially in the range of 30-50%, which leads to poor oil-water separation effect on the platform's heating dehydration equipment, and even causes the working current of the electric dehydration equipment to be too high, resulting in the increase of water cut of the exported crude oil. At the same time, oil-water emulsification may block the formation pore roar, affecting the oil flow channel, resulting in the reduction of thermal production.
Our work is mainly focused on the emulsification characteristics and Anti-emulsification of the emulsions from thermal well production fluids. Based on the characteristics of the produced liquid during thermal recovery and injection, a high-speed disperser is used for preparing water-in-oil emulsion. Effects of water cut on emulsion viscosity, crude oil and emulsion are carried out by using remoter, one-dimensional core displacement device as well as microscope. Meanwhile, microscopic characteristics of emulsions, and phase state of cores and dynamic anti-emulsification of cores are also studied.
The results show that with the increase of water cut, viscosity of the emulsion increases greatly, which is risen to 5.9 times more than that of crude oil when the oil-water ratio is 5: 5. At the same flow velocity, the pressure gradient of the emulsion in the low-permeability core tube of 1000 μm3 is significantly higher than that of crude oil. In the hypertonic tube of 3000 μm3, the difference between the pressure gradient of the emulsion and the crude oil is not obvious at the same percolation velocity. Testing results show that the emulsion increased the maximum steam injection pressure to 3.15 MPa. After adding the anti-emulsion demulsified solution to the emulsion, the number of water drops was extremely reduced. The demulsifier has dual functions of anti-emulsification and reducing steam injection pressure in rock core.
Anti-emulsification can effectively reduce the emulsification degree of the produced liquid in thermal recovery of offshore steam huff and puff, so as to improve the thermal recovery effect.