Low-Toxicity Polymer Fluid Developed for Environmentally Sensitive Offshore Drilling
Authors: Feder Judy 
Published: November 2019

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE/IADC 190967, “Development of Low-Toxicity and High-Temperature Polymer Drilling Fluid for Environmentally Sensitive Offshore Drilling,” by Xiaodong Liu, CNPC; Binqiang Xie, Yangtze University; Yonghui Gao, Huiling Gu, Yongle Ma, and Yong Zhang, CNPC; Ruxin Zhang, China University of Petroleum-Beijing; and Qingyang Li, Southwest Petroleum University, prepared for the 2018 IADC/SPE Asia Pacific Drilling Technology Conference, 27–29 August, Bangkok, Thailand. The paper has not been peer reviewed.
This paper discusses a new, environmentally safe, water-based polymer drilling fluid that has been developed for offshore drilling applications with temperature resistance to 200°C and low biological toxicity. The system comprises two basic polymeric components for high-temperature rheology and filtration control, along with a special nanoplugging agent, glycol shale inhibitor, extreme-pressure lubricant, and barite or formate weight material. The base slurry is light-colored and nontoxic to the marine environment, and so can be discharged directly into the sea. Results from field testing in a Bohai offshore oil field are presented in•the complete paper.
Introduction
Historically, significant limitations have been placed on the use of drilling fluids in high-temperature operations in environmentally sensitive areas of China. Oil-based drilling fluid is restricted in use by laws and regulations; polysulfonated, water-based drilling fluid and waste liquid are on the national hazardous waste list; and polymer drilling fluid such as XC/CMC/PAC/PHPA can only be used in temperatures lower than 150°C. Additionally, the offshore drilling-fluid discharge requires a low biological toxicity value. These harsh operation conditions and strict environmental laws and regulations pose severe challenges for high-pressure/high-temperature water-based drilling-fluid-formula design and field construction.
In recent years, international oil companies have conducted research on environmentally friendly, high-temperature, polymer water-based drilling fluids for reducing toxicity of the drilling fluid, improving the anti-temperature performance of the treatment agent, and enhancing the anticollapse performance of the drilling fluid.
To meet the requirements of high-temperature, deep-well drilling operations and environmental protection in environmentally sensitive offshore areas, a high-temperature synthetic polymer filtrate loss agent and high-temperature viscosifier have been developed, and a matching nanoplugging agent and lubricant were also studied. Then, a high-temperature polymer seawater-based drilling-fluid system was developed, based on a high-temperature synthetic polymer as the main agent, supplemented with the properties of a nanoplugging agent, shale inhibitor, and extreme-pressure lubricant. It can achieve performance comparable to oil-based drilling fluids in terms of lubricity and inhibition of shale hydration and dispersion, and the biological toxicity (LC50) value is greater than 100,000•mg/L. This system has out-standing high-temperature thermal stability and shale-inhibition performance, making it environmentally friendly and able to be discharged directly into the sea. Good results have been achieved in offshore Bohai field•applications.