Zwitterionic Polymer P(AM-DMC-AMPS) as a Low-Molecular-Weight Encapsulator in Deepwater Drilling Fluid

Xin Zhao,Weian Huang,Hanyi Zhong,Zhengsong Qiu,Yongjun Zhang,Zhichuan Tang

doi:10.3390/app7060594

Abstract

In deepwater oil and gas drilling, the high-molecular-weight encapsulator aggravates the thickening of the drilling fluid at low temperatures. Therefore, it is hard to manage the downhole pressure, and drilling fluid loss occurs. In this paper, a zwitterionic polymer P(AM-DMC-AMPS) which was the terpolymer of acrylamide, methacrylatoethyl trimethyl ammonium chloride, and 2-acrylamido-2-methylpropane sulfonic acid, was developed as a low-molecular-weight encapsulator. It was characterized by Fourier transform infrared spectrum analysis, nuclear magnetic resonance, and gel permeation chromatography. Moreover, the low-temperature rheology, shale inhibition and filtration properties of water-based drilling fluids (WBDFs) containing different encapsulators were experimentally investigated and compared. The results showed that the molecular weight of P(AM-DMC-AMPS) was about 260,000, much lower than that of the conventional encapsulators. In the deepwater drilling temperature range 4–75 °C, WBDF containing P(AM-DMC-AMPS) had lower and more stable rheological property because of its short molecular chains. The high shale recovery rate and low swelling rate indicated its strong shale inhibition performance, owing to its adsorption on the clay surface and the wrapping effect through both hydrogen bonding and electrostatic interaction. It also improved the filtration property of WBDF, and was compatible with other WBDF components. This product is expected to simultaneously realize the good encapsulation performance and low-temperature rheological property for deepwater drilling fluid.

Highlights

Offshore deepwater regions are rich in oil, natural gas and gas hydrate resources
All the drilling fluid additives used for preparing the testing water-based drilling fluids (WBDFs) were provided by China Oilfield Services (Sanhe, China) and Shida Chuangxin technology Co., Ltd. (Dongying, China); sodium bentonite with a cation exchange capacity of 74 mmol/g was purchased from Boyou
For the shale recovery rate tests, the shale sample #1 was obtained from the deepwater wells in the South China Sea, and it consisted of 23% clay, 45% quartz, 13% calcite, 10% anorthose, 4% dolomite, 4% halite, and 1% gypsum; the shale sample #2 was obtained from wells in Bohai Bay, and it consisted of 25% clay, 43% quartz, 20% anorthose, 9% potassium feldspar, 2%

Summary

Introduction

Offshore deepwater regions are rich in oil, natural gas and gas hydrate resources. The drilling fluid is called the blood of drilling engineering [1], and it is extremely important for deepwater drilling operations. Shale in deepwater is water sensitive, so it is prone to hydration on exposure to filtrates of. Sci. 2017, 7, 594 water-based drilling fluid (WBDF), causing wellbore instability [2,3,4,5]. Serious thickening of the drilling fluid occurs in deepwater drilling when it is cooled down by the low-temperature environment (approximately 4 ◦ C) [6,7,8], leading to operation troubles

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