The goal of this study was to provide in-sight regarding use of laboratory asphaltene inhibitor testing to help guide expectations for inhibitor field performance. Specifically, this paper compares results from asphaltene inhibitor testing using two laboratory methods: (1) dead-oil analytical centrifuge stability analysis for asphaltenes method and (2) high-pressure live-fluid test that includes deposition evaluation. The analytical centrifuge method was developed as a simple laboratory test with test conditions pushed closer to field conditions than previous stability methods. As live-fluids are often not available, if data from the analytical centrifuge method can be used to help form better, more reliable field expectations, it would benefit operators in making field development plans and optimizing field operations.
The high-pressure testing in this study was performed with a Solids Detection System (SDS) apparatus designed to measure asphaltene onset pressures (AOPs) of live-crude oils through monitoring near infrared laser transmittance but also run with an augmented procedure to quantify the amount of asphaltenes deposited during depressurization. Although not replicating the exact higher shear flow environment in many wells, the live-fluid SDS testing represented the closest test possible to field conditions available with our current laboratory capabilities. As such, in the absence of complete field data, it represented our next best alternative to mimic field data for use in comparison against the analytical centrifuge method.
Included in this paper are results with four different asphaltene inhibitors. The high-pressure test results show the inhibitors shifting measured AOPs and reducing asphaltene deposit weights. The analytical centrifuge test results are shown over a range of crude oil to destabilizing solvent ratios at different temperatures. One example comparing analytical centrifuge testing to a field data set is also presented. Results from the study indicated that the dead-oil analytical centrifuge stability testing should be performed at equivalent temperatures and with relatively high crude oil to destabilizing solvent ratios (~30 % crude oil or greater) to achieve similar results to high-pressure live-fluid testing. When performing dead-oil testing at lower temperatures and lower crude oil to destabilizing solvent ratios, the ability of the inhibitors to increase asphaltene stability were generally significantly greater than that achieved for reducing asphaltene deposition within the SDS apparatus. Testing at lower temperatures and lower crude oil to destabilizing solvent ratios, however, did indicate trends for determining relative asphaltene inhibitor performance.