Deterioration of cement/casing adhesion in wellbore scenarios can result in unwanted and potentially harmful leakage with the potential of serious repair costs. In this work, the authors explore the use of self-healing polymers added to conventional wellbore cements as a way to bring about self-healing and readhering (to casing) properties to the composite. Self-healing capability was demonstrated by permeability analysis showing that polymer-cement composites reduce flow by 50–۷۰% at cement bulk and at the cement/steel interface. Use of atomistic simulations imply that these polymers have good wetting properties on the steel surfaces. Interactions between steel/polymer and cement/polymer are complementary, resulting in a wider range of bonding patterns. Cracks seem to expose under-coordinated sites that result in more bonding interactions, which agrees well with the permeability measurements showing high degree of healed cracks and cement-steel interfacial gaps together with an overall increased in structural integrity of these advanced polymer-cement composite materials.

Introduction

Wellbore integrity is a significant environmental consideration in industries which use deep production wells such as in geothermal energy production. During wellbore construction, cement and cement composites are injected into the annulus between the geologic formation and the wellbore casing to hydraulically isolate production zones from overlying aquifers[1]. When applied using strict industry standards, cement and cement composites can extend the life of a producing well as well as protect the near surface environment. The potential for short life of wells and expensive remediation costs can hinder the development of geothermal energy despite of the fact that a large number of reserves of this clean energy alternative exist in the United States and around the globe[2]. A study of over 380,000 wells worldwide found that nearly 7% of wells experience wellbore failure[3] with one of the main reasons being the high temperature  (up to 400 °C), thermal cycles, and chemically corrosive (typically hypersaline, CO2 and H2S rich) environments[4] typical of low and high temperature geothermal systems. Failure of the wellbore cement can be due to a combination of chemical degradation, fracturing, and deboning from the host rock or well casing. Wellbore integrity issues are most common in the form of leakage pathways allowing for unwanted fluid migration. Cement bonding to the interface of both the casing and host rock has been identified as one of the most significant wellbore integrity issues[5].