Polylactic Acid Improves the Rheological Properties, and Promotes the Degradation of Sodium Carboxymethyl Cellulose-Modified Alkali-Activated Cement

Abstract

Abstract:In consideration of the insolubility in water, sensitivity to heat and wide application in the oil and gas industry as a degradable additive, this paper introduces polylactic acid (PLA) to a self-degradable temporary sealing material (SDTSM) to investigate its effect on the SDTSM performance and evaluate its potential to improve the rheological properties and further promote the self-degradation of the material. The thermal degradation of PLA, the rheological properties, compressive strength, hydrated products and water absorption of SDTSMs with different PLA dosages were tested. The analysis showed that the addition of 2% PLA increased the fluidity by 13.18% and reduced the plastic viscosity by 38.04%, when compared to those of the SDTSM without PLA. PLA increased the water absorption of 200 • C-heated SDTSM and had small effect on the types but decreased the hydrate products of 85 • C-cured SDTSM, and created plenty of pores in 200 • C-heated SDTSM. PLA enhanced the self-degradation level of SDTSM by generating a large amount of pores in cement. These pores worked in two ways: one was such a large amount of pores led to a looser microstructure; the other was these pores made the water impregnate the cement more easily, and then made the dissolution of substances in the 200 • C-heated SDTSM progress faster to generate heat and to destruct the microstructure.

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

“…Besides that, after heating and immersion in water, the pores formed in the 300 • C-heated material were broken. The dissolution, leaching behavior, and high in-situ exothermic energy also contributed to this self-degradation process, and those processes have been discussed in our previous studies [2,6].…”

“…In our previous studies [2,6,30,31], the self-degradation mechanism of the TSM has been much discussed. It was considered that the heat shock on the hot binders when exposed to water, the dissolution of the solid substance in the dry hot samples, the leaching behavior of soluble ions, and the high heat generated in exothermic reactions all contributed to the self-degradation.…”

“…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.…”

Using Fumed Silica to Develop Thermal Insulation Cement for Medium–Low Temperature Geothermal Wells

“…The cement slurry density was measured using a digital density meter (YMS 0.01–7.0, Qingdao Tongchun Petroleum Instrument Co., Ltd., Qingdao, China) at ambient temperature. The fluidity was measured at ambient temperature, according to the Chinese National Standard GB/T 8077-2012 [ 38 ], and the test procedure was described in a previous study [ 39 ]. The shear stress ( τ ) of the slurries at different shear rates ( γ ) (5.11, 10.21, 170, 340, 511, and 1021 s −1 ) were tested by a six-speed rotating viscometer according to API Recommended Practice 10B-2 [ 40 ].…”