Viscosity Model of Waxy Crude Oil Based on the Physico-Chemical Properties

Abstract

Temperature-dependent viscosity is one of critical properties in designing facilities for waxy crude oil production. Several viscosity models have been developed and available in literature. Nevertheless, those models are still insufficient to cover all waxy crude oil produced from various regions. Therefore, this work aims to develop a general viscosity model for Malaysian waxy crude oils. Extensive rheological study was conducted and showed that viscosity behavior below WAT can be best described using Herschel-Buckley model. Multiple correlation and regression analysis were also performed to identify critical physico-chemical properties dictating the viscosity behavior. Based on the finding, a general viscosity model was developed by modifying Herschel-Buckley model and incorporate the critical physico-chemical properties. The general model was compared with widely used viscosity model and other models available in literatures to assess its performance on describing the viscosity behavior. The comparison showed that the general model has lowest average absolute percentage error and hence, it is more superior than the other models. Nevertheless, the model still has limitation in describing viscosity at the transition regime which is between WAT and 5°C below WAT.

Non-Newtonian Viscosity Behaviour Investigation for Malaysian Waxy Crude Oils and Impact to Wax Deposition Modelling

“…2 to demonstrate the viscosity trends based on current and previous works. [13] that gives the same trend of instantaneous steep change of viscosity trends below WAT and PPT. Additionally, Petrus and Azuraien [9] observed similar trend when conducting rheological measurement for a waxy crude oil from the South East Asia region, as presented in Fig.…”

“…9, Malaysian waxy crude oils of higher WAT and PPT tend to exhibit an instantaneous steep change of viscosity trends below WAT and PPT which does not follow the general relationship as described by the Pedersen and Ronningsen model. One hypothesis that can be acknowledged from previous study is that rheological data from Malaysian waxy crude oils were well-described using HB model [12], hence viscosity prediction using the present model could potentially suffer from inaccuracy mainly due to incorporation of the Casson rheological model instead of the HB model. To test this hypothesis, the HB model is fitted into the present model and its performance is further evaluated as below:…”

“…Bhaskoro [12] in his work, reviewed the applications of these rheological models for four Malaysian waxy crude oils and concluded that both the Casson model and the HB model can be used to describe the rheological behaviors below WAT of all the crude samples with the latter model generally providing a better fit with R 2 =0.9998.The general viscosity model was then developed based on Malaysian crude oil's rheological and wax data based on the HB model and the results presented showcased better performance when compared with viscosity models previously available, as presented in Bhaskoro et al [13]. However, the model requires additional fluid information i.e., activation energy, which is not readily available from standard testing and applied using current engineering software.…”

“…The viscosity measurement procedures to ensure accuracy and repeatability in this paper is as per described in Petrus and Azuraien [9]. To address the viscosity measurement reproducibility, the same sample from previous work by Bhaskoro et al, [13] using one of the Malaysian crude oils, Fluid S06 (which is represented as Crude oil A in his paper) was used for the current study. Temperature dependent-viscosity measurements for crude oil A were conducted using a controlled stress rheometer AR-G2 and DHR-1 from TA instrument while the current study uses other equipment which is an AntonPaar MCR-302 rheometer in a different laboratory.…”

“…As a way forward, a more reliable model such as that proposed by Bhaskoro et al, [13] that were developed based on Malaysian waxy crude oil should be used in engineering applications. As described in his paper, above WAT, viscosity of waxy crude oil follows Arrhenius Law, while below WAT, the viscosity deviates from Arrhenius behavior up to several orders of magnitude due to the precipitated wax crystals.…”