Abstract

A low temperature curable resin gelling system was developed to meet the requirements of deep water shallow hydrate layer cementing. The test shows that the system has obvious characteristics of right-angle thickening at 20°C ~ 40°C, and the compressive strength at low temperature is greater than 20 MPa, which can achieve effective sealing of the hydrate layer, prevent hydrate from decomposing and escaping. Compared with Portland cement at low temperature, it has a fast strength development, better durability and excellent long-term sealing.

Introduction

With the increasing demand for energy source, deep-water drilling has gradually become an attractive exploration area. Among the large oil and gas fields discovered in the 21st century, 56 are located in deep water areas and 12 are located in ultra-deep water areas. With the rapid growth in their outputs, deep-water oil and gas fields have gradually become the research focus in marine oil and gas industry (Liu et al., 2018; Liu et al., 2019., Zhang et al.,2017).

There are tremendous risks and challenges in the exploration and extraction of deep-water oil and gas assets. When the water depth exceeds 610 m, natural gas hydrate is a major problem in the deep-water drilling and exploitation (Bai et al., 2009; Nimblett J N et al., 2005). Natural gas hydrate, also referred to as hydrate and "flammable ice", is an icy, crystalline clathrate compound formed by water and natural gas under high-pressure and low-temperature environment. Natural gas hydrate-bearing sedimentary layers are generally unconsolidated stratum. Hydrates fill the pores and spaces of unconsolidated formation like fluids (Sloan et al., 2008; Wu et al., 2014). Cementing of the hydrate layer primarily faces following problems (Ravi et al., 2009; Wang et al., 2009; Sairam et al., 2012; Zhang et al., 2020): (1) The hydrate-bearing stratum has higher mud content and is relatively loosely packed; hence, it is difficult to ensure the interfacial cementing effect. (2) Due to changes in temperature and pressure of the cementing process, the decomposition of hydrates is easy, which causes gas channeling in the cementing process and formation of micro-annular gaps between the cement ring and stratum. (3) Ordinary Portland cement has longer solidification time at low temperatures, and then, its strength increases slowly. Accordingly, owing to low strength, it is difficult for the formed cement ring to ensure an effective isolation of stratum. The decomposition of natural gas hydrate can produce a volume variation of over 170 times (Xu et al., 2014). The presence of the above-mentioned potential risks in the cementing process provides a large amount of released gas through the migration channels to the wellhead, which increases the risk of serious accidents.

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