Chuikina D.I., Sherstyuk S.N., * Stakhina L.D., Serebrennikova O.V.

Institute of Petroleum Chemistry SB RAS, Tomsk, Russia

The composition of high-viscosity crude oils extracted using EOR technologies

The production of heavy-viscosity crude oils in most oil fields of Russia and other countries is carried on using water shutoff technology. It is known that the application of EOR methods, e.g. oil-water two-phase flows or oil displacement agents, is liable to cause a change in the composition and physical and chemical properties of recovered crude oil. Crude oil production results in local underbalance condition of the well; therefore, the volume of injected water would make up for that of produced crude [1].

New EOR technologies developed at the Institute of Petroleum Chemistry (Tomsk, Russia) are intended for the recovery of high-viscosity crude oils, which make up a large proportion of the total oil production. The use of technologies developed in combination with thermal-steam treatment methods permits reduction in crude oil viscosity and increase in oil displacement factor. Some of these methods employ thermotropic inorganic and polymer gels intended for the regulation of filtration flows as well as for increasing formation steam sweeping factor and decreasing water cut of wells. Other methods employ surfactant-based systems, which cause generation of carbon dioxide and ammonia, thereby creating an alkaline buffer system. The systems developed are widely used commercially not only in Russia but also in other countries, e.g. China [2].

The goal of the present work is to study the effect of physico-chemical EOR technologies on the dynamics of variation in the composition of high-viscosity crude oils produced from oil fields of Russia and Germany.

Two crude oil samples were collected from No. 1- G well (Germany) before and after treatment NINKA system. Three crude oil samples were collected from No. 3063-R (Russia) well at different time intervals after the Netrol system injection and three samples - from No. 611-R well, which had been subjected to the sequential treatment first with the Netrol system and then with the NINKA system. Two samples were obtained from No. 1073-R well, which had been subjected to thermal-steam treatment followed by the NINKA system injection. Two test samples of native oil were collected from Nos. 3000-R and 2983-R wells located in the vicinity of Nos. 3000-R and 2983-R wells, respectively, which had not been treated by any physico-chemical methods [3].

The group composition of the oil samples were determined by the method of liquid-adsorption chromatography of the deasphalted oil [4]. The data obtained is listed in the Table (here alkanes and naphthenes are designated as Sat and aromatic hydrocarbons, resins and asphaltenes as Ar, R and A, respectively).

Table. The composition of the crude oils produced from the oil fields of Russia

(R) and Germany (G)

Well No. (date of sampling)	EOR methods	Content, wt %
		Fraction Tb.p-200^îC	Sat	Ar	R	À
3000-R (02.2007)	-	22.8	24.1	38.7	7.0	7.4
3063-R (02.2007)	Netrol system	16.3	23.5	40.3	12.5	7.4
3063-R (11.2008)	Netrol system	13.3	36.4	31.4	10.0	8.9
2983-R (02.2007)	-	25.0	34.3	25.4	8.3	7.0
6111-R (02.2007)	NINKA system	22.5	33.5	28.6	7.2	8.2
6111-R (11.2008)	NINKA system	26.1	35.2	21.6	9.2	7.9
1073-R (12.2007)	Thermal-steam treatment	4.8	48.9	21.6	14.9	9.8
1073-R (11.2008)	NINKA system + thermal-steam treatment	24.2	33.7	24.3	8.4	9.4
1-G	-	25.2	36.2	21.9	12.2	0.3
1-G	NINKA system	11.8	43.9	22.5	17.8	1.6

We examined the effect of the Netrol and NINKA systems on the group composition of the studied crude oils. The data listed in the Table suggests that the studied samples of the crude oil collected from the oil fields of Komi Republic are characterized by high contents of resins+asphaltenes and those collected from the oil fields of Germany have also high paraffine contents. The resin+asphaltene contents of the native and treated oil samples are in the range of 12.0 - 16.3 % and 15.0 - 20.4 % (by mass), respectively.

The individual composition of n-alkanes of the original and treated crude oil samples was analyzed using gas chromatography technique on a unit «Chromos GC-1000» (Russia), equipped with flame-ionization detector, using helium as gas carrier; the capillary column having length of 25 m was coated with SE-54 phase. Chromatogram recording was performed using linear temperature programming from +80 °C to +280 °C at a rate of 4 °C per min (see the figure).

Figure. Molecular mass distribution of n-alkanes of the original and treated

crude oil samples

The data presented in Table 1 and Fig. 1suggests that no significant change has occurred in the molecular mass distribution and in the contents of light and heavy n-alkanes of the oils treated with the NINKA composition.

The above changes in the group composition and properties of the crude oil must be due to the application of the EOR technologies (for enhanced oil recovery). It can thus be concluded that the analyzed parameters can serve as criteria of the treatment effectiveness; besides, these might help determine the time of operation of oil displacement systems.

Conclusions

1. It is found that the NINKA and thermal-steam system injections cause an increase in the hydrocarbon content of the treated crude oil, in particular, low-boiling hydrocarbon content (oils included).

2. The resin+asphaltene contents of the crude oils treated by the NINKA system injection are found to decrease. A two-fold increase in the resin+asphaltene and saturated hydrocarbon contents as well as a decrease in the aromatic hydrocarbon content is observed for the crude oils treated by the Netrol system injection relative to the untreated native oils.

References

1. Meyer R.F., Attanasi E.D., Freeman Ph.A. Heavy Oil and Natural Bitumen Resources in Geological Basins of the World. US Geological Survey. Open-File Report. Reston, Virginia. 2007. 345 p.

2. Altunina L.K., Kuvshinov V.A. Improved oil recovery of high–viscosity oil pools with physicochemical methods at thermal–steam treatments. Oil & Gas Science and Technology. 2008. V. 63. No.1. PP 37–48.

3. Sherstyuk S.N., Serebrennikova O.V., Stakhina L.D. Organic vanadium and nickel compounds in crude oils of Usinskoye field. Regional geology and metallogeny. 2009. No. 40. PP 49-51.

4. Serebrennikova O.V., Strelnikova E.B., Stakhina L.D. Oxygen-containing compounds in oils occurring in Jurassic deposits of the South-East of West Siberia. Book of abstracts of 24^th International Meeting on Organic Geochemistry. September 6-11, 2009. Bremen. Germany. PP 175-178.