Identification of Crude Oil Components Responsible for Foaming

Abstract

Abstract The foaming characteristics of a number of crude oils from a variety of sources were determined by Bikerman's pneumatic method. Extraction of these crudes with both pneumatic method. Extraction of these crudes with both alkali and acid indicated that the crude oil components responsible for the foam stability were removed by the alkali extraction. Further examination of the alkali extract revealed that after neutralization it was the chloroform soluble part of this extract (0.02% wt% of the whole crude) that was responsible for the foaming properties of the crudes investigated. This latter point was confirmed by demonstrating that the surface rheological properties of one of the extracted crudes could be restored by adding back the chloroform-soluble portion of the neutralized alkali extract. Analysis of this extract indicated that the foam-stabilizing materials were short-chain carboxylic acids and phenols of molecular weight -400. In principle, such analytical information could be used to identify principle, such analytical information could be used to identify crude oils likely to present severe foaming problems in the field. Such information could enable the process engineer to take appropriate corrective measures early in the life of a new field, thus avoiding the need for high capital expenditure at a later stage. Introduction Crude oil foams can pose major problems for operators of gas/oil separation plants, causing a loss of crude in the separated gas stream and consequent loss of revenue and possible damage to downstream compressors. Thus, an possible damage to downstream compressors. Thus, an understanding of the factors controlling crude oil foam stability is highly desirable, since it should lead to better methods of foam prediction and control. With this end in mind, we have attempted to identify those crude oil components responsible for foam stabilization. This paper outlines our findings to date and attempts to demonstrate that a similar suite of compounds is responsible for the stabilization of a wide range of crude oil foams. Experimental Materials Crude Oils. Chemical-free samples of 16 different stock-tank crude oils were obtained from a variety of sources (see Table 1). Particular care was taken to ensure that these samples were stored under nitrogen to prevent oxidation of the crudes. prevent oxidation of the crudes. Reagents used were cyclohexane, spectroscopic grade (from BDH); chloroform, general purpose reagent grade (from BDH); diethyl ether, general purpose reagent grade (from BDH); sodium hydroxide pellets, technical grade (from BDH); and SIL-PREP reagent: Applied Science Laboratories Ltd. All solvents were distilled before use, and only an 80% heart cut was taken. Techniques Foaminess Index Measurements. The foaming column used in this work consisted of a graduated glass tube approximately 30 cm [12 in.] in length with two fine sintered glass disks placed 1 cm [0.4 in.] apart, situated at the base of the tube just above the gas inlet. The gas used to create the foam is admitted to the column by way of a pressure reduction and flow meter assembly (see Ref. 1). The measurements were initiated by pipetting an aliquot of crude oil, just sufficient to cover the upper sintered disk, into the foaming column. The oil was allowed to spread over the sintered disk. Compressed air (or natural gas), flowing at a constant rate (40 cm3/sec [40 mL/min]), then was admitted to the column by way of the sintered disk and the crude oil was taken up into the froth. The bubbling was continued for 5 minutes after all the liquid had been taken up into the foam. When a homogeneous foam had been achieved, the height of the upper foam/gas interface was recorded. Three runs were performed on each crude oil studied. The foaminess index performed on each crude oil studied. The foaminess index (E) of each of the stripped and complete stock-tank crude oils then was determined by Bikerman's method. (1) where V, is the constant foam volume at time t and V is the volume of gas injected during time t. Extraction of Crude Oil Surfactants. Treatment with dilute aqueous sodium hydroxide solution was found to be the best means of extracting the acidic components in the crude oils. The oils were dissolved in cyclohexane to give 10% vol/vol solutions, thereby reducing viscosity and thus facilitating rapid phase separation. Despite this precaution some oil still was removed with the aqueous precaution some oil still was removed with the aqueous phase, which necessitated thorough back extraction with phase, which necessitated thorough back extraction with fresh solvent to ensure the selectivity of the separation. The sodium salts in the aqueous extract then were converted back to the free acids by treatment with excess mineral acid. The concentrate obtained was derived for analysis by combined gas chromatography/mass spectrometry (GC/MS). SPEJ P. 171