conference paper · SPE Nigeria Annual International Conference and Exhibition
Disposal of synthetic-based drill cuttings during deep-water offshore operations poses environmental concerns because fluids can aggregate into hydrophobic solids that settle and bioaccumulate in seabed sediments. To examine this issue, the bioaccumulation potential of synthetic hydrocarbon-based and ester-based drilling fluids was assessed by measuring their octanol-water partition coefficients. Chemical functional groups were identified using Fourier transform infrared spectroscopy, and partition coefficients were derived using reversed-phase high-performance liquid chromatography. Spectroscopic analysis identified aromatic structures in the hydrocarbon fluids and ester functional groups without aromatic bonds in the ester fluid. The hydrocarbon-based fluids recorded logarithmic partition coefficient values between 4.0 and 5.5, indicating a strong tendency to bioaccumulate in benthic sediments. Conversely, the synthetic ester fluid recorded a value of 1.75, demonstrating low bioaccumulation potential and higher suitability for offshore drilling. Theoretical models underestimated the coefficients for hydrocarbon fluids and overestimated the coefficient for the ester fluid.
Discharging drill cuttings into deep-water environments can cause synthetic fluids to accumulate in seabed sediments, creating ecological imbalances across marine ecosystems. Establishing the octanol-water partition coefficients of different formulations clarifies their environmental persistence. Demonstrating that ester-based drilling fluids have a markedly lower bioaccumulation potential than hydrocarbon-based alternatives provides environmental assessors and offshore operators with clear data to select less damaging materials for marine drilling.
This work can inform fluid selection and chemical procurement for offshore oil and gas drilling operators, as well as synthetic mud manufacturers aiming to meet environmental standards. The evidence directly points to synthetic ester fluids as safer substitutes for hydrocarbon-based formulations in deep-water drilling. Because the findings are based on laboratory characterisation and comparative modelling of existing fluid classes, the work represents applied testing rather than a finished commercial product.
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Abstract A major environmental concern associated with the offshore disposal of synthetic-based drill cuttings during deep-water drilling operations in offshore environments is the propensity of some synthetic fluids to speedily aggregate into clumps of hydrophobic solid particles that settle through the water column (pelagic ecosystem) and subsequently bioaccumulate in seabed sediments (benthic ecosystem) at an appreciable rate. This process can result in significant ecological imbalances within marine and freshwater ecological systems. In this technical paper, the bioaccumulation potential of synthetic hydrocarbon- and ester–based drilling fluids in marine environment was evaluated through the determination of their octanol–water partition coefficients (Pow). Functional groups present in the fluid samples were identified using an Agilent 5500a Fourier transform infrared (FTIR) spectrometer. The n-octanol/water partition coefficients were determined from the retention times that were obtained by using an Agilent 1200 series reversed-phase high-performance liquid chromatography (RP-HPLC) system equipped with an ultraviolet (UV) detector. The stationary phase was made up of Octadecylsilyl (ODS) (C18H37Si) and bonded to the hydroxyl group (-OH) of the silica gel to form a highly hydrophobic (non-polar) ODS stationary column with analytical-grade methanol-water mobile phase. The FTIR spectra of the synthetic hydrocarbon fluids exhibited several in-plane and out-of-plane bending vibrations that are characteristic of aromatic C–H bonded compounds. In contrast, the FTIR spectrum of the synthetic ester fluid showed prominent C=O ester stretching vibrations in the range of 1750–1725cm−1, confirming the presence of ester functional groups, with no evidence of aromatic ring stretching or aromatic C–C and C–H bonds. The synthetic hydrocarbon-based fluids recorded logarithmic octanol–water partition coefficient (log Pow) values ranging from 4.0 to 5.5, indicating a strong tendency for bioaccumulation in seafloor sediments. Conversely, the synthetic ester fluid exhibited a log Pow value of 1.75, suggesting low bioaccumulation potential and, therefore, greater suitability for deep-water drilling applications. Finally, the predicted log Pow values were lower than the experimentally observed values for the synthetic hydrocarbon fluids, whereas a higher partition coefficient was predicted for the synthetic ester fluid compared to its experimentally determined value.
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DOI: 10.2118/234839-ms
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