Impact of Waxy Crude Oil on Appropriate Crude Conditioning Techniques and Core Flood Testing for the Maari Oilfield

Abstract

Abstract The Maari Field is located 50 miles off the coast of South Taranaki, New Zealand. In this paper, we will present details of a laboratory test programme which was conducted to assist in the design of removal and mitigation treatments for flow assurance in the Maari oilfield. Main operating partner OMV initiated laboratory testing of a series of carbonate and sulphate scale dissolver and inhibitor treatments for use in the field, examining formation damage aspects potentially associated with the use of such fluids in the field. The waxy nature of the reservoir crude oil presented challenges for core flood testing, in particular the design of appropriate crude oil conditioning techniques to provide representative samples and core flood protocols to omit potential laboratory artefacts. The Maari crude oil contains heavy oil fractions, high wax content and a high wax appearance temperature. Standard field sampling, laboratory conditioning and sub-sampling methods can result in loss of light fractions through evaporation and thus a crude oil sample weighted towards the heavier molecular weight oil fractions. Also there is potential for heavy end losses due to insufficient conditioning temperature, filtering and sub-sampling. Appropriate protocols were therefore required to condition the crude oil to a field representative state for use. Heavy oil fractions within the crude oil presented challenges for conducting effective core flood tests. Oil particulates and heavy fractions can induce wax deposits and fines mobilisation effects that can be considered test artefacts obscuring formation damage test results. Alternative test methods were therefore designed to ensure the crude conditioning methods and core flood tests are as representative as possible of the oilfield whilst also providing clear and accurate formation damage assessment. This paper therefore presents a laboratory strategy designed to account for the aforementioned challenges alongside laboratory test results and subsequent recommendations for crude and core conditioning and core test protocols under similar conditions.