IBAMA recently proposed in its Technical Note of 2014 that organic base stocks used for offshore drilling fluids in Brasil must meet performance standards as measured by 10-day sediment toxicity and 275-day closed bottle anaerobic biodegradation tests. A series of organic bases and organic base blends were tested to measure the link between organic base chemical structure and performance in these tests.

All fluids chosen for the study are materials currently in use for drilling offshore Brasil or available for use. The components include linear olefins, internal olefins, low toxicity mineral oils, linear paraffins, branched paraffins and oleo based ester. All materials were evaluated independently and as mixtures in the 10-day ASTM E1367-99 sediment toxicity test with Leptocheirus plumulosus and the 275-day modified ISO 11734:1995 anaerobic closed bottle test using estuarine marine sediment. As the proposed Technical Note requires, the performance of all materials were measured against that of a C1618 internal olefin standard.

The results show that the sediment toxicity of organic base stock is connected primarily with molecular weight or carbon number of the hydrocarbon backbone. Materials with a carbon backbone greater than C15 had lower sediment toxicity than those with carbon numbers C14 or lower as measured against the standard. Performance of base stock in the anaerobic biodegradation test was dependent on the chemical structure. Products containing a more chemically reactive olefin or ester group degraded more than the C1618 IO standard. The relative anaerobic biodegradation performance of the organic bases was ester, olefin > paraffin. The linearity of the carbon backbone of an organic base also played a role in anaerobic biodegradation with linear materials degrading faster than branched materials. The sediment toxicity and anaerobic biodegradation performance of a blend was influenced by the proportion of the constituents present and their individual sediment toxicity and anaerobic biodegradation properties.

This testing demonstrates the ability of the proposed sediment toxicity and anaerobic biodegradation tests to differentiate the performance of organic bases depending on their chemical and structural characteristics.

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