Low Temperature Demulsifier, its Application & Results

Size: px

Start display at page:

Download "Low Temperature Demulsifier, its Application & Results"

Lesley McCarthy
5 years ago
Views:

1 Low Temperature Demulsifier, its Application & Results S. P. Garg, Dr. A. K. Gupta & Dr. N. K. Kapoor Chemistry Section, Neelam & Heera Asset, ONGC, Mumbai ABSTRACT Breaking oil emulsion in areas where sufficient temperature is not available at process end has been a challenge to offshore oil installations. To solve this problem in Heera field a dual approach has been suggested. A silicone based low temperature Demulsifier, apart from regular one was field tested and very encouraging results have been obtained. Mixing of silicone demulsifier with regular demulsifier has further improved the results. As a second option injecting the regular Demulsifier through gas injection line is field tested. This is a very effective and innovative option for utilizing the well temperature to break the emulsion. This technique has also provided excellent result not only by breaking emulsion but also by increasing productivity. Ultimately combination of both the approach has been selected for effective demulsification. PREAMBLE: The crude oil is always produced along with water. The presence of water in crude oils is caused by: Natural mixing with oils during their migration Injection in secondary recovery operations to maintain pressure Leaking from formation above the producing one Water causes problems downstream of the production. It increases cost of transportation and corrosion problems in pipelines and vessels. Since water is almost always salted, it may lead to fouling of heat exchanger and corrosion of distillation equipment in refining. Both water and salt content are regulated. Thus, it is economically important to separate brine from crude oil directly at the production site. Water mixed in the crude oil can be "free" or as an "emulsion". Free water is separated by simple settling. Emulsions form and stabilize at many areas where there is turbulence at locations such as tubing, pump, valves etc and require adequate treatment. The formation of emulsion poses many problems. Emulsion formation not only affects the quality of crude but also

2 the quality of effluent discharged. There are natural emulsifier present in crude such as polar compounds like resins, asphaltenes, organic acids and fine solids like crystallized wax, clays and scales etc which help in formation of protective interfacial film. Some of these components are polar and stabilize emulsions with their polar properties and their lack of symmetrical structure favors their concentration at the interface. One part of the molecule, the hydrocarbon part for example has affinity for oil while the other polar part of the molecule has an affinity for the aqueous phase. The demulsification of crude requires the demulsifier molecule to reach the interface and destabilize the emulsion. This requires availability of adequate temperature in the system. Demulsifiers are being used effectively since long to break oil emulsion. These conventional Demulsifiers require high temperature (60 70 C) to effectively break the emulsion. However in field, where the temperature is low, the conventional demulsifiers are not very effective. In view of this, Demulsifier suitable for low temperature range is required to break the emulsion. The problem of high water cut in dispatched crude from Heera field has been long standing issue. The reasons for high water content are mainly attributed to low temperature available at separators and the nature of emulsion which is toughest in Mumbai offshore. The conventional demulsifier presently in use is not very effective below 60 C even at present level of dosing i.e ppm. With maximum temperature achievable at separators of Heera Process Platform i.e. 57 C, a water cut of 3-4 % could be achieved. This has led to search for suitable demulsifier which can reduce the water cut to < 1.0 % even at low temperature. APPLICATION OF TECHNOLOGY: The approach for tackling the problem of demulsification of Heera Emulsion is divided under following heads: 1. Evaluation of suitable low temperature Demulsifier. 2. Injection of Demulsifier in gas injection grid.

3 RESULT AND DISCUSSION: (A) Application of Low Temperature Demulsifier: A number of products were screened to find suitable candidate for low temperature application. During the search it was found that silicone based demulsifier could be useful to achieve this goal. The main advantages of silicone based Demulsifier over conventional demulsifier are: (i) Low temperature application (ii) Highly surface active and can efficiently orient at surface. (iii) Can move to surface very quickly. (iv) Sharp oil / water separation (v) Enhanced water drop rate (vi) Better effluent water quality (vii) Can act as defoamer and enhance the separator efficiency. A commercially available Silicone Based Demulsifier was tried at Heera platform. It was found to be very effective at temperature as low as 45 C with a dosing rate of 6-7 ppm. Comparative results are shown below: CONVENTIONAL ν DOSE : PPM ν W/C IN TREATED CRUDE : 3 TO 5 % ν OIL PPM IN EFFLUENT WATER AT SEP. OUTLET : >100 PPM SILICONE BASED ν DOSE : 6 7 PPM ν W/C IN TREATED CRUDE : <1 % ν OIL PPM IN EFFLUENT WATER AT SEP. OUTLET : 46 PPM In spite of very good result obtained during the field trial the main constraint for using this demulsifier has been its exorbitant cost. In view of this it was decided to study the effect of mixing silicone based low temperature Demulsifier with conventional Demulsifier. Very encouraging results were obtained when Heera emulsion was subjected to different dosage of combined demulsifier during laboratory studies. The result is tabulated in Table-1. A combination of 2-3 ppm silicone demusifier with ppm regular demulsifier gave best results. It is interesting to note that the consumption of silicone based demulsifier can be reduced to 1/3 rd of its requirement when dosed along with conventional Demulsifier.

4 (B) Application of Demulsifier in gas injection grid As it known that demulsification is most effective at temperature above 60 C it was thought to be practical to utilize the temperature available in the well. To achieve this it was decided to inject the regular demulsifier in the gas lift line. This approach gave encouraging results not only by reducing water cut but also by improving well productivity due to decrease in fluid viscosity resulting in increase in draw down. The increase in free content in well fluid after dosing the conventional demulsifier in gas injection line is shown in Table II. It is evident from the results that although increase is observed in free water content for most of the well fluid lines yet in some lines this was not the case. This may be due to (a) non-transportation of demulsifier by gas lift line for all wells and/ or (b) formation of emulsion due to turbulence. In view of this a part of the demulsifier was dosed at separators. CONCLUSION 1. Silicone based demulsifier can be effectively used for low temperature demusification of crude. 2. Mixing of silicone demulsifier with organic demulsifier is economically viable and gives good result. 3. Injection of conventional demulsifier in gas lift line is an effective and efficient option. 4. Injection of regular demulsifier in gas injection lines and silicone based demulsifier in separators will give best results. ACKNOWLEDGEMENT The authors express their sincere gratitude to Shri. P.K.Verma, ED AM, N & H Asset, for his valuable guidance and encouragement before and during the course of this work. The authors would like to thank Shri. N.V.Subrahmanyam, GGM (P) SM, N & H Asset & Shri. D. D. Sathe, DGM (P) SAM-Heera for their constructive technical suggestions, guidance and personal involvement in carrying out this work. The authors acknowledge the services rendered by Multi Disciplinary Team (MDT) of Heera Platform, especially Process, Maintenance & Chemistry personnel under the guidance of OIM, Heera.

5 Table-I. Efficiency of Combined Demulsifier vis a vis Single Demulsifier (Based on Laboratory evaluation; Test Temperature 50 C) Combination Demulsifier % Efficiency Quality of sepration SD -1= 1ppm; Reg.Demul= 09ppm 35 not clear y SD -1= 2ppm; Reg.Demul= 18ppm 45 clear N SD -1= 3ppm,Reg; Demul= 27ppm 48 clear N SD -2= 1ppm; Reg.Demul= 09ppm 22 not clear y SD -2= 2ppm; Reg.Demul= 18ppm 50 clear N SD -2= 3ppm; Reg.Demul= 27ppm 52 clear N SD -3= 1ppm; Reg.Demul= 09ppm 30 not clear y SD -3= 2ppm; Reg.Demul= 18ppm 45 clear N SD -3= 3ppm; Reg.Demul= 27ppm 50 clear N SD -4= 1ppm; Reg.Demul= 09ppm 25 not clear y SD -4= 2ppm; Reg.Demul= 18ppm 40 clear N Sludge pad SD -4= 3ppm; Reg.Demul= 27ppm 53 clear N % Quality of Sludge Single Demulsifier Efficiency sepration pad SD -1 = 6 ppm 07 not clear y SD -2 = 6 ppm 10 not clear y SD -3 = 6 ppm 06 not clear y SD -4 = 6 ppm 14 not clear y Reg. Demul= 30 ppm 08 not clear y

6 Table-II DISTRIBUTION OF WATER CUT IN PRE AND POST DEMULSIFIER DOSAGE IN GAS INJECTION LINE PLATFORM PERIOD % FREE WATER % EMUL. WATER H1 PRE DOSAGE DO- POST DOSAGE H2 PRE DOSAGE DO POST DOSAGE H3 PRE DOSAGE DO- POST DOSAGE H4 PRE DOSAGE DO- POST DOSAGE H5 PRE DOSAGE DO- POST DOSAGE H6 PRE DOSAGE DO- POST DOSAGE H7 PRE DOSAGE DO- POST DOSAGE H8 PRE DOSAGE DO- POST DOSAGE NOTE: POST DOSAGE DATA HAVE BEEN OBTAINED BY TAKING AVERAGE OF LAST ONE MONTH READING

Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 06, June 2018

Aegis Tech Line Aegis Chemical Solutions Technical Newsletter Volume 06, June 2018 EMULSIONS IN OIL PRODUCTION CRUDE OIL SPECIFICATIONS Pipeline Operators and Refiners set specifications on the quantity of basic sediment and water (BS&W) in the crude oil that enters their equipment and