Civil Engineering ETDs

Publication Date

Fall 12-14-2018

Abstract

Seal integrity of wellbores has become of significant interest due to repeated leakage and spill incidents occurring worldwide that jeopardize both human health and the environment in addition to causing significant economic burden. This is attributed to the fact that wellbores intersecting geographical formations contain potential leakage pathways. The cement-steel and cement-rock formation interfaces are recognized as two critical leakage pathways.

A seal repair material that has good bond strength with both steel and rock formations in addition to the ability to completely fill thin microcracks is needed to restore the seal integrity of wellbores. In this research, engineered polymer nanocomposites are proposed for use as seal repair materials for wellbores. Novolac epoxy polymer nanocomposites (PNCs) show more than 200% and 250% higher bond strength with steel and shale, respectively, when compared with microfine cement. In addition, it was found that Novolac epoxy PNCs have up to 545% and 761% higher displacement at peak load and toughness than microfine cement respectively. Moreover, Novolac epoxy PNCs was able to completely fill 800 mm microcracks that microfine cement were not able to completely fill. Microstructural investigations using Fourier-Transform Infrared spectroscopy (FTIR) and Dynamic Mechanical Analysis (DMA) showed that incorporating aluminum nanoparticles (ANPs) in Novolac epoxy PNCs interrupted the polymerization process, which allowed free epoxy groups to improve the bond strength of PNCs with both shale and steel surfaces.

On the other hand, penetrability calculations based on contact angle and surface tension of seal repair materials showed that nanomodified methyl methacrylate (NM-MMA) incorporating 0.5 wt.% ANPs has higher potential to penetrate thin microannuli than microfine cement and Novolac epoxy PNCs. NM-MMA was able to seal thin microcracks as small as 30 mm while microfine cement has very limited penetration in such small microcracks. Furthermore, NM-MMA showed more than 1000%, 460%, and 8000% higher apparent bond strength, displacement at failure, and toughness than microfine cement respectively. Microstructural investigation using XRD analysis showed that incorporating ANPs in MMA increased the degree of polymer crystallization enabling significant improvement in polymer ductility, toughness, and reduced creep compliance.

A performance study of seal repair materials was evaluated based on their efficiency to seal the cement-steel interface, their ability to withstand cyclic casing pressure, and their ability to withstand harsh environmental conditions. The results showed that microfine cement efficiency was limited to 24%. On the other hand, NM-MMA was able to achieve seal efficiency as high as 103%. Moreover, NM-MMA was able to withstand casing pressure cycles two orders of magnitude higher than microfine cement. Finally, a durability investigation using a weight loss study showed that all PNC seal repair materials have higher resistance to harsh environmental conditions than microfine cement.

Keywords

Microannuli, MMA, Nanocomposite, Nanoalumina, Seal, Wellbore Integrity

Document Type

Dissertation

Language

English

Degree Name

Civil Engineering

Level of Degree

Doctoral

Department Name

Civil Engineering

First Committee Member (Chair)

Mahmoud Reda Taha

Second Committee Member

John Stormont

Third Committee Member

Edward Matteo

Fourth Committee Member

Yu-Lin Shen

Fifth Committee Member

Harvey Goodman

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