Acids of crude oils from Timan-Pechora province

Abstract

Petroleum acids possess many valuable properties and are widely used in a number of fields of the Soviet economy [1]. The study of petroleum acids is of great interest from the viewpoint of petroleum geochemistry. The formation of the composition of petroleum acids in natural conditions is a complex, little studied process. It is assumed that here both the nature of the initial oil-yielding matter and the conditions of generation and occurrence of the crude oil and processes of secondary transformation of crude oils in formations have a part to play. In the very few known papers devoted to formation of the composition of petroleum acids, the variation in their composition has been studied mainly as a function of the degree of biodegradation of the crude oils [2,3]. The influence of other factors, including such an important factor as the depth of occurrence, has not previously been investigated. It is obvious that the influence of the depth of occurrence on the composition of acids can be traced on crude oils of a single genetic type and not subjected to biodegradation. A number of crude oils of Timan-Pechora Province meet these requirements (acids in crude oils of this region have hardly been studied). In the present paper a study has been made of the composition of acids in crude oils of the Pashnya (well 57.2637-2646 m), Dzh'yer (well 118.1552-1573 m), and Nibel' (well 95.911-926 m) fields. These crude oils differ considerably in depth of occurrence, are nonbiodegraded (are of type A l according to Petrov), and lie within one formation (Pashiisk level, formations la + lb). This fact, and also the almost completely identical nature of their hydrocarbon composition (according to GLC data) make it possible to classify these crude oils as a single genetic type. Furthermore, an investigation was made of the composition of the acids in Khar'yaginsk crude oil (same region, well 48.2516--2578 m). Acids were isolated from the crude oils by extraction with a 2% KOH solution in 70% aqueous ethanol by the procedure given in [4]. The acids were separated from other components of the extracts by means of liquid chromatography on L 40/100 silica gel impregnated with 10% KOH [5]. Final purification of the acids was carried out by means of liquid chromatography on L 40/100 silica gel in a 1:4 diethyl ether-hexane system [6]. As a result, 11.5 mg (Pashnya), 14.7 mg (Dzh'yer), 21.5 mg (Niber) and 319 mg (Khar'yaginsk) of acids were isolated from 200 g of each crude oil, amounting to 0-006, 0.007, 0.011 and 0.15% of the crude oil respectively. Before GLC analysis, the acids were converted into more volatile methyl esters by treatment with an ether solution of diazomethane by the procedure given in [7]. GLC analysis