Synthesis and characterization of polyvalent high-performance synthetic base oil for drilling operations in recalcitrant and unconventional oil and gas reservoirs

Abstract

Synthetic ester fluid is one of the most widely recommended drilling fluids for unconventional and recalcitrant reservoirs owing to its numerous technical advantages, high sustainability, non-toxic and inherently biodegradable. However, there are serious concerns about its thermal and hydrolytic stability at high temperatures and pressures (HTHP) as well as its viscosity and flow characteristics in low temperature climates such as deep-water wells. Hence, its inability to maintain stable borehole and flat rheology characteristics may invariably threaten its application under these aforementioned scenarios.In this study, a high-performance ternary mixture of synthetic ethyl esters of plants oil (SEEP mixture) fluid was synthesized by a non-catalyzed supercritical ethanol transesterification process using coconut, castor seed and linseed oil as starting materials. The nature, chemistry and fluid particle interactions of the individual components that make up the synthetic ester fluid were critically studied. The process equipment consists of a continuous flow reactor equipped with a PID controlled furnace as heat source to the reactor and a high- pressure transducer. The conversion efficiency was monitored by an Agilent 5500a FTIR machine with attenuated total reflectance (ATR) system while a GC-EIMSD system was used for fatty acid ester compositional analysis. The oil was extracted by a Soxhlet apparatus mechanism. The extracted Plant oil and the synthetic esters were characterized under standard recommended laboratory procedures by API, ASTM and the European Union (EN) standard protocols. Also, fluid's toxicity and biodegradability tests were conducted according to OECD recommended practices. The results were compared with existing synthetic hydrocarbon fluids (SHFs) for HTHP and deep-water wells.The conversion efficiency of the non-catalyzed transesterification process was 96.50%. The amount of oil yield from the plant oil after Soxhlet extraction is commendable. Hence, synthetic ester fluid raw materials are readily available in large quantities and in a sustainable manner. The GC-MS analysis shows that the coconut oil contains 92% saturated fatty acid. Whereas, the castor seed oil contains 98.31% unsaturated fatty acid with 89.75% of mono-unsaturated ricin-oleic acid (D-12-hydroxyoctadec-cis-9-enoic acid). The linseed oil has high content of linolenic acid with 89.60% unsaturated fatty acid. The designed fluid has excellent lubricity characteristics, extremely low cloud and pour point temperatures, higher oxidative stability, low peroxide value, lower copper strip corrosion value and lower kinematic viscosity and density variations with temperatures which signals flat rheology when used to form a synthetic based mud. Also, its flash point and auto-ignition temperatures are high and thus forestall possible fire hazard in high temperature zones. Finally, the fluid is non-toxic and inherently biodegradable.