Nitrogen/Surfactant Compound Flooding Technology

1、Technology Introduction

The surfactant mainly emulsifies crude oil by reducing oil and water interfacial tension and changing wettability on the surface of oil-wet rock, so as to reduce viscous fingering phenomenon to improve the oil displacement effect.

On the basis of nitrogen stimulation, surfactant for oil displacement is added. Under the high pressure of the gas, the agent enters the further well zone, and the more crude oil in the pores is quickly removed to form a low viscosity water oil emulsion to improve the oil washing efficiency.

The application range of compound stimulation is wide and there are no strict conditions. It can be used for heavy oil or thin oil and it can be used in both high permeability reservoirs and low permeability reservoirs. It is more advantageous to the small fault blocks and small complex lithological reservoirs that can not be effective in other recovery method and whose interwell flow is poor.

2、Mechanism of oil Increment  

The technique is a combination flooding of surfactant and nitrogen. The agent is mainly composed of compound surfactant, which has good temperature resistance, salt resistance, emulsification and other properties. It has the following mechanism to improve the effect of oil well stimulation and prolong the production cycle.

（1）Under the high pressure of the gas, the agent enters the further well zone, and the more crude oil in the pores is quickly removed to form a low viscosity water oil emulsion to improve the oil washing efficiency.

（2）With the synergistic effect of gas molecules and surfactant parent molecules, the oil/water interfacial tension is greatly reduced, so it is easy to form a low viscosity oil-in-water emulsion and reduce seepage flow resistance of crude oil.

（3）The surfactant adsorbed on the surface of the rock and changed the wettability of the reservoir rock so as to facilitate the outflow of crude oil.

（4）The inorganic composition in surfactant which has a certain shrinkage effect on the rock cement can increase the seepage channel of reservoir rock and reduce the seepage resistance, so as to extend the oil well production cycle and improve the well liquid producing capacity.

（5）Compound flooding which combines the advantages of steam injection and surfactant injection, has more obvious effect of oil increase through synergism.

3、Scope of Application

Well type	Reservoir properties	Fluid properties	Ground condition	Limiting condition
1.Low permeability fracture well 2.Isolated well	1. Small interference between the well layers. 2. Good sealing of oil layer 3. Remaining oil saturation ≥35% 4. The permeability difference between layers is small. 5. The thickness of the target layer ≤20m	The divalent and trivalent cationic concentrations are small in the formation water.	1.Large well site 2.Better road	1 Complex well conditions: There are mechanical problems such as casing damage. 2. It is connected with the adjacent well. (There are high permeability layers, fractures or faults.)

4、Paired Agents

Oil Displacement Surfactant:

Items	Specifications
Appearance	Uniform liquid
pH	6~9
solubility（10%	Rapid dissolution, no precipitation
Solid content	>30%
Oil-water interfacial tension	<10-2mN/m
Interfacial tension after adsorption by oil sands	<10-2mN/m
Organochlorine	0.0%

5、Technical Application Cases

With the cooperation of Deshi group, the Nitrogen/Surfactant Compound Flooding Technology Project designed by the geology and science institute of Jiangsu oilfield, organized and constructed by first factory was successful implemented in the Zhen 175 well.

Before the measures, the well produced 6.9 cubic meters of liquid and 1.7 tons of oil per day and the water content is 75%. The measures began on December 10, 2010, was completed on January 5, 2011 and the production began on January 20, 2011. After the measures, the well produced 5.2 cubic meters of liquid and 2.4 tons of oil per day and the water content is 54%. Daily oil production is 1.4 times higher than before measures, and the water content dropped 21%.