Formulation and Evaluation of Novel Fully Bio-Based Drilling Fluid with Strong Inhibition and Temperature-Enhanced Plugging Properties

Abstract

Abstract The increasingly severe wellbore instability problem of unconventional hydrocarbon resources (such as tight oil/gas and shale oil/gas) and the intensified environmental requirements necessitate the development of environmentally friendly drilling fluids with strong anti-collapse performance. Herein, a fully bio-based drilling fluid (Pure-Bio system) was formulated from self-developed chitosan-derived shale inhibitor (CMCS), carboxymethyl chitosan-derived thermal-responsive plugging agent (GCOA), rosin-derived nanocomposite plugging agent (PDSA) and optimized thickener of scleroglucan (SCG) and filtrate loss reducer of low-viscosity polyanionic cellulose (PAC-LV). The environmental performance of the Pure-Bio system was determined by biotoxicity and biodegradability evaluations. The engineering performance, including the rheological, filtration, lubrication, and particularly the inhibition and microporous plugging properties, was comprehensively investigated, and the synergistic effects among different additives were analyzed. The results showed that the Pure-Bio system is non-toxic and readily biodegradable with an acute toxicity index of median effective concentration (EC50) for photobacteria above 4 × (105 mg/L and a biodegradability index of the ratio between biological oxygen demand (BOD5) and chemical oxygen demand (COD) over 0.26. Additionally, the Pure-Bio system possesses the rheological characteristics of low plastic viscosity while a high yield point and the effective filtration control ability at both API and HTHP conditions, which can withstand a high temperature over 140°C and contamination by NaCl (10%) and CaCl2 (0.5%). Meanwhile, Pure-Bio shows a significantly reduced extreme pressure lubrication coefficient below 0.1. More importantly, Pure-Bio has strong inhibition performance, reflecting a low clay linear swelling rate and a high shale hot-rolling recovery rate. Also, Pure-Bio exhibits a temperature-enhanced plugging property owing to the synergy of thermal-responsive GCOA and temperature-sensitive deformable PDSA, significantly enhancing the adaptive nano-microporous plugging performance for filter membranes and natural cores at elevated temperatures. Taking advantage of its features, the environmentally acceptable Pure-Bio system has the potential to serve as a promising and innovative anti-collapse drilling fluid with strong inhibition and temperature-sensitive intelligent plugging characteristics for practical drilling applications in unconventional oil/gas fields.