A Study on the Effects of Starches on the Properties of Alkali-Activated Cement and the Potential of Starch as a Self-Degradable Additive

Abstract

An urgent problem of geothermal energy source development is how to cut down the production costs. The use of temporary sealing materials can reduce the costs associated with the circulation lost by plugging, and increase the production by self-degradation. Based on the utilization of starches as self-degradable additives in the medical field, this paper investigated the effects of three kinds of starches, namely corn starch (CS), hydroxypropyl starch (HPS) and carboxymethyl starch (CMS) on the properties of alkali-activated cement (AAC). In addition, the thermal properties of starch, the compressive strength and microstructures of the cement with starch were tested, to evaluate the potentiality of starch as self-degradable additive for geothermal cement. The analysis showed that: (1) all the starches have the effect of increasing the apparent viscosity, prolonging the setting time and reducing the static fluid loss of alkali-activated cement; (2) the addition of starch increased the number of pores in 200 • C-heated cement, facilitated the leaching process, and thus promoted the self-degradation; and (3) among the three starches, CMS has the most potential as a self-degradable additive.

The Self-Degradation Mechanism of Polyvinyl Chloride-Modified Slag/Fly Ash Binder for Geothermal Wells

“…The sources of SFB and the chemical compositions of slag and fly ash were the same as in our previous study (Table 2) [2]. The PVC was obtained from Xingwang Plastic Material Co., Ltd. (Dongguan, China).…”

“…The mix proportions of all mortars are shown in Table 1. The mixing procedure, the prepared conditions and processes, and the size of specimens, as well as the treatment of filtrate-treated PVC, are also the same as previously reported [2].…”

“…Although there have been a few cases of slag/fly ash binder (SFB) being used in geothermal wells, its characteristic of a high thermal stability [17][18][19] could meet the high-temperature resistance requirements of geothermal wells. The SFB's strength increased with the heat-curing temperature rose, when the temperature was below 90 • C [20], indicating that the binders are applicable for the 85 • C geothermal environment [2,21]. Additionally, the cement containing slag also exhibited a better compressive strength and water permeability than the Portland cement [22].…”

“…According to the development process of geothermal wells, the temporary sealing material (TSM) should provide sufficient strength to seal the fractured formations for drilling operations, but degrade later on to open the sealed fractures for hydraulic-stimulation or the production process [1,2]. In order to develop this material, sodium carboxymethyl cellulose has been introduced into sodium silicate-activated slag/fly ash cementitious materials [1,[3][4][5].…”

“…In order to develop this material, sodium carboxymethyl cellulose has been introduced into sodium silicate-activated slag/fly ash cementitious materials [1,[3][4][5]. In addition, poly-lactic acid and starch, as self-degradable additives, have been introduced into the materials to improve the rheological and degradation properties in our previous studies [2,6]. All of the developed materials can self-degrade to certain degrees.…”