Accurate assessment of drill cuttings’ depth plays a very important role during mud logging because it determines the true location of hydrocarbons and affects proper mapping of the formation’s petrophysical properties and lithology. Using small molecular or polymeric tags to label the cuttings when they are formed at the drill bit is a promising technology for accurate determination of the depth origin of the drilled cuttings. However, in long drilling operations employing recycled drilling mud, these tags accumulate in the drilling mud over time, causing ambiguity in detection. The accrued tags create background signals when detecting the tags via pyrolysis-GCMS during depth assessment. To overcome this challenge, we have developed a family of degradable tags that maintain their structural integrity while cuttings are generated and collected, and degrade over time in the hot, basic drilling mud. These new tags were synthesized via esterification of cost-effective polysaccharides (ie, starch, dextran) with aromatic acid chlorides. NMR, FTIR, and pyrolysis-GCMS confirm the formation of the modified polysaccharides. We have also studied their hydrolytic degradation in drilling fluids over time at varying pHs and temperatures. Finally, we optimized the workflow for unambiguous detection of the tags on the cuttings in the drilling mud. This chemistry promises a new materials platform for generating a series of degradable tags for labelling drill cuttings, which can be used in wells where conventional mud logging is not accessible.

Development of degradable polysaccharide tags for cuttings’ depth assessment

ACS Fall 2021

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