北京德美高科科技有限责任公司

DM-09 enhanced heavy crude oil recovery with steam

一、Briefly introduction
A lot of researches have been carried out to improve the effect of steam injection development both at home and abroad. For instance, some chemical agents were added at purpose during the steam injection process to improve the effect of thermal recovery; oil displacement agents was put in to modify the wettability and interfacial tension of the rocks and reduce residual oil saturation. Viscosity reductant was injected to reduce the viscosity and flow resistance of crude oil, thereby to achieve better oil production effect.
During the steam simulation of heavy oil production, displacement efficiency of steam will directly influence the recovery ratio and production per well , so how to exert the displacement efficiency on steam wave and steam surface needs to be studied for the technology. However, in terms of the oil displacement agents and viscosity reductant that used today, they still have lots of flaws and are too difficult to exert applicable efficiency. Under this circumstances, DM-09 high temperature washing agent is used to enhance steam displacement efficiency and improve heavy oil liquidity. The product's can resist heat up to 400℃ and can be associated with steam injection (or slug). The agent can meet the requirement of steam simulation and widely improve the well production. The performance indicators of DM-09 high temperature washing agent are showed in table 1-1.

Tab Technical performance index

Item	Index
Appearance	Light yellow liquid
Density at 25℃(g/mol)	0.90
PH value	7
Flashing point	≥35℃
Boiling point(℃)	130
Flow point(℃)	-17
Temperature tolerance(℃)	400

    The main composition of this product is a zwitterion surfactant that belongs to amide class, and it is a combined solution that combines surfactant with solvent oil. The formula can be written as R₃C₁₈(O)--N(R1)(R2).
    The mechanism of this high temperature washing agent is as followed. On one hand, it reduces oil/water interfacial tension so as to enhance the displacement efficiency. On the other hand, the agent can reduce the viscosity and improve liquidity of crude oil.
    (1) Reduce oil/water interfacial tension
    The main composition of high temperature washing agent is ampholytic surface active agent. It has a long alkyl chain which can reduce the oil/water interfacial tension. According to the adhesive work formula W=σ（1+cosθ）, the lower oil/water interfacial tension, the stronger the ability of oil displacement system to peel oil droplets off from the rocks.
According to the relationship between interfacial tension and remaining oil saturation, when interfacial tension is less than 0.01mN/m, remaining oil saturation will reduce substantially. The relationship is shown in figure.

Fig The relationship of oil/water interfacial tension, capillary number,

oil displacement efficiency and remaining oil saturation

(2) Reduce the viscosity of heavy oil
It is asphaltene which exit in heavy oil contributs to high viscosity of the oil. The colloid and asphaltene could be seen as heteroatomic aroma chips, as shown in the figure.

Colloid and asphaltene of heavy oil can form supermolecular structure by electrostatic interaction, hydrogen-bond interaction, polar effect and π-π stack effect, as shown in the figure 1-3.

Heavy-oil micelle structures is in a loose state at high temperatures. Washing agent molecule can disperse into the flaky colloid and asphaltene, then bonds stronger with hydrogen.As a consequence overlapping flat packing of aggregates is broken up. At last, the supramolecular structure of heavy oil converts into a low level.

1. Application result assessment
Out of the completed 15 wells, the main production lines are Ⅲ and Ⅳ oil group, whose fill depth is at 250~450 meter, the average thickness is 1.7 meter, the combined thickness is 4.88 meter, viscosity of crude oil under reservoir conditions is 5000mPa·s to 30000mPa·s, belonging to ordinary crude oil class Ⅱ and extra thick heavy crude oil.
(1) Analysis of the steam stimulation effect before and after operation
The improved well has acquired favorable effect such as increasing daily average oil production, oil steam ratio,etc(Table 2-1).

Tab The contrast between before well operation and after operation

After operation, daily average oil production has increased from 1.2t/d to 1.44t/d and average oil steam ratio has increased from 0.13 to 0.37. Out of 15 wells12 has increased oil production, and the average oil production per well is 122 tons, in total having increased 1473.2 tons of oil.
(2) Effect analysis of steam channeling well
During the heavy oil thermal recovery process, steam channeling between wells is severe. Steam channeling phenomenon leads to the rising temperatures of steam channeling well, increasing water content, making wells shut in and steam sweep volume decreasing . In the steam injection process, due to the adding of high temperature wash agent, displacement efficiency increases, at the same time, some of steam channeling wells’ production situation are improved, in total increasing 806.4 tons of oil.

Typical case, Lou 3033
    Well Lou 3033 is a production well located in northern area of Jingyou oil field, which began operation on August 14, 2003. It went back to IV1-3 layer for production on April 29, 2008. Its sand thickness is 3.9 meter, net pay thickness 3.2 meter.
    The oil of IV1-3 layer of Jingyou oil field is extra-heavy oil, whose high viscosity led to a bad stimulation effect. By the end of operation, the well in total had stimulated for one cycle, having injected steam 868 tons, producing liquid 373 tons, oil 97 tons, whose production-injection ratio was 0.43, oil steam ratio 0.11, recovery percent of reserves 2%. Before operation, liquid production was 4.3 tons, daily oil production was 0 tons, water percentage was 99%. In order to improve the well development effect and the efficiency of steam flooding, pilot experiment of high temperature washing agent was carried out on July 12 to 16, 2008.
    The production effect improved a lot after operation. The drainage period had decreased from 7 days to 3 days, while at peak daily oil production had increased from 3.6 tons to 4.6 tons.Average daily oil production had increased from 1.46 tons to 2.52 tons.Cumulative oil production had increased from 85 tons to 289.3 tons. Oil steam ratio had increased from 0.1 to 0.35.Good results were achieved.

2.Application assessmentStatistical comparisons were made, by the end of September 24, 2011, 10 wells had finished producing. Production results were showed in table2-4.
The improved wells acquired favorable effect such as increasing daily average oil production, oil steam ratio. The average oil steam ratio increased from 0.16 to 0.24, and the average single well increased was 82 tons, in total increasing 665 tons of oil.

（二）Test applications of Lean oil field
In 2012, field trail with high temperature washing agent for Guang 9 block had put into practice for 4 times. Totally increased 1389 tons of oil and the average single well increased was 800 tons, oil steam ratio had increased by 0.2. At present there are still 3 wells which can normally operate.

Typical case, Caogu 101-ping 15 well
Caogu 101 ping 15 well’s production layer is located in Ordovician, the depth of which is 530-650 meter, formation pressure is 6.28 MPa, porosity is 0.3-29%, permeability is 0.004-162×10^-3um², viscosity is 35229-69439 mPa·s.

50 m³ DM-9 high temperature agent was injected before steam injection, and also with 10 m³ hot water above 70℃. By the end of February 18, 2013, it has produced for 224 days and totally increased 663 tons of oil. Compared with Caogu 101 ping 15 well, oil production increased 663 tons for less 79 days. Compared with the same period, oil production increased 987 tons, currently liquid production was 15.6 tons, daily oil production was 8.6 tons, water ratio was 44.3%. Obvious effect was achieved.

Typical case: caonan ping 31 well
It locates in Guantao formation.The main reservoir lithology was conglomerate, sandy conglomerate with thin layer, and pebbly sandstone coarse clastic reservoir layer. Initial formation pressure is 8.2～9.3MPa, pressure factor is 1.0, saturation pressure is 1.78MPa, reservoir temperature is 50℃~ 54℃, geothermal gradient is 4.2℃/100m. Ground oil viscosity was generally 55714.9mPa·s at 50℃. The edge water was active and oil-water interface was -960m. Reservoir type belonged to hypertonic conglomerate structure stratigraphic with strong edge water super heavy oil reservoirs.
50 m³ DM-9 high temperature agent was injected before steam injection, and also with 10 m³ hot water above 70℃.By the end of February 18, 2013, it has been producing for 98 days and totally increased 648 tons of oil. Compared with last period, oil production increased 180 tons for less than 29 days. Compared With the same period, oil production increased 266 tons.Currently liquid production is 30.3 tons, daily oil production is 4.3 tons, water ratio is 85.6%, and obvious effect achieved.