Abstract

Romashkino is a giant oil field in Russia. Flooding is a long-term oil recovery technology applied at the field. A large amount of water with different physico-chemical and biological characteristics has been injected in the formations there. That caused deep alterations in the composition of crude oil which have the significant effect on oil recovery

.

A study has been performed to investigate rheology of a series of crude oils. Crude oils were produced from the different horizons, oil wells with different period of exploitation (from 3 to 43 years). The study showed that all crude oils are currently non-Newtonian liquids and have the abnormal viscosity. The structural-group, hydrocarbon, fraction and component compositions were examined. The relationship between the dynamic viscosity of destroyed and non-destroyed structures and some parameters of dispersed composition of crude oil was established. As a result, four types of structures in crude oil with the different degree of association of tar-asphaltene components and crystallization of high-molecular paraffins, are established. For a few types of structures, the activation energy of viscous flow and the radius of a particles of dispersed phase are determined.

The viscosity of dispersed oil systems and the stability of oil-water emulsions are known to depend mostly on the degree of asphlatene aggregation but not asphaltene concentration. For asphaltenes from crude oils related to different horizons, structural-group composition and paramagnetic properties are investigated. The relationship between the parameters of asphaltene composition and the characteristics of dispersed structure and physico-chemical properties of crude oils is established. The models describing geochemical conditions of the formation of crude oil deposits are developed.

Introduction

At the late stage of exploitation of oil fields, flooding causes many negative secondary processes in a reservoir which make oil recovery more complicated. Results of the long-term studies of the Laboratory of Chemistry and Geochemistry of the Institute of Organic and Physical Chemistry are presented in the paper. The destructive role of various processes (adsorption-chromatography, sulphurisation, oxidation, biodegradation, and deposition of solid paraffins and asphaltenes in a formation) is evaluated [1–4]. Several models are proposed to describe the formation of composition of residual oil at the different areas of oil fields in Tatarstan. That is done taking into account the geological conditions and the presence of the products of non-reversible physicalchemical processes (formation of carbene-carboid compounds and pyrite). The models describe such processes as oxidation (chemical and biochemical, natural and technological), asphaltene deposition and concentration of tar-asphaltene components caused by the multi-stage filling of a deposit with crude oil or by changes of the thermobaric conditions in the deposit [5–9]. These processes are the most intense at the interface of oil-water-rock. Thus they were studied by using mainly crude oil extracted from cores. Chemical composition of crude oil from producing wells is leveled during crude filtration through the formation and its changes becomes less visible.

For produced crude oil, the alterations in its chemical composition affect the physical-chemical and rheological characteristics of the crude oil.

This content is only available via PDF.
You can access this article if you purchase or spend a download.