Low-Toxicity Polymer Fluid Developed for Environmentally Sensitive Offshore Drilling
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.
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 outstanding 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.
Drilling-Fluid-System Development and Evaluation
The paper describes and explains the development and evaluation of the fluid system. Discussion topics include main treatment agents, including amount and function of each agent; formula optimization experiment and results; and evaluation of the following:
- Thermal stability time
- Performance after hot rolling for 16 hours and 72 hours at high temperature
- High temperature resistance
- Salt and calcium resistance
- Anticollapse performance
- Biological toxicity
A comparison of drilling-cuttings dispersion in water and drilling fluid showed that drilling cuttings in water were quickly hydrated and dispersed after high agitation, while the drilling cuttings in the polymer drilling fluid remained unchanged. The base liquid was still clear and transparent and had a good suspension effect, indicating that the polymer drilling fluid has strong inhibition on the hydration and dispersion of drilling cuttings.
Fig. 1 illustrates that, after 30 minutes, the water had permeated the bottom of the core cup and the polymer drilling fluid had formed a thin layer of mud cake on the surface of the drilling-powder core, which can effectively reduce the penetration depth and penetration rate of the filtrate in the core.
The extreme pressure lubrication coefficient of drilling fluid was tested for oil-based drilling fluid, the high-temperature polymer drilling fluid, and polysulfonic drilling fluid, which were prepared densities of 1.08, 1.25, and 1.60 g/cm3, respectively. The result was that the lubrication performance of the high-temperature polymer drilling fluid was better than that of the polysulfonyl drilling fluid and approached that of the oil-based drilling fluid.
From 2015 to 2017, the high-temperature polymer seawater-based drilling-fluid system was applied in more than 20 wells, with good results. The deepest test well was 6066 m, and the highest bottomhole temperature was 204°C.
High-temperature polymer drilling fluid showed good performance and better environmentally friendly characteristics than polysulfonate drilling fluid, oil-based drilling fluid, and the conventional polymer drilling fluid XC/CMC/PAC/PHPA. Its temperature resistance can be effectively increased from 12 to 200°C.
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.