高温下油井固井避免抗压强度退化的替代材料

Romero Gomes da Silva Araújo, J. Freitas, Bruno Costa, Paulo Moreira, Fabrício Pereira Feitoza da Silva, Y. H. Oliveira
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引用次数: 5

摘要

当波特兰水泥环在油井条件下处于110℃以上的温度时,会出现抗压强度倒退现象。这是由于水合硅酸钙(C-S-H)转化为不稳定相,导致低抗压强度和高渗透性。为了最大限度地减少抗压强度问题,指南建议添加35-40% BWOC(按水泥重量计)的额外二氧化硅源,以平衡CaO/SiO2的关系,并将其转化为更稳定的硅酸钙相。硅粉(SF)是目前世界范围内常用的抗强度倒退剂。目前的工作提出稻壳灰(RHA)作为一个可持续的二氧化硅源,在替代SF的环境温度下,抗压强度倒退是明显的。测试了四种水泥浆组成:(i)不添加二氧化硅(SF0)的15.6 ppg水泥浆;(ii) 15.6 ppg浆料,添加35% BWOC的SF (SF35);(iii)添加35% BWOC RHA的浆料为15.0 ppg (rha1); (iv)添加35% BWOC RHA的浆料为14.5 ppg (rha2)。样品分别在60°C和110°C的常压和2,000 psi的固化压力下放置7天。通过单轴压缩试验来评价RHA作为抗强度倒退剂的作用。所有实验程序均按照API RP 10B-2进行。采用x射线衍射(XRD)、扫描电镜(SEM)和热重分析(TGA)对样品进行温度暴露后的分析。结果表明,RHA试样的抗压强度高于普通的SF试样。在110℃固化的样品中,RHA-1的抗压强度最高(44.6 MPa),其次是含有SF成分的SF35样品(40.4 MPa)。样品rha2的抗压强度为37.9 MPa,与SF35相似,而对照样品SF0的抗压强度较低,为28.3 MPa,这是由于回归现象。在60℃下固化的样品表现出与110℃相同的趋势。XRD分析表明,含RHA的水泥样品中存在典型的硅钙石、托贝莫来石等稳定晶相。SEM图像和TGA分析与XRD评价一致。结果表明,RHA在重浆(15.0 ppg)和轻浆(14.5 ppg)中均表现出抗强度倒退剂的潜力。可再生二氧化硅源的可持续性使RHA成为通常二氧化硅粉的有趣替代品。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Alternative Material to be Applied in Oil Well Cementing Subjected to High Temperatures to Avoid Compressive Strength Retrogression
When Portland cement sheath is submitted to temperatures above 110 °C in oil well wellbore conditions, the compressive strength retrogression phenomenon is observed. This occurs due to the conversion of calcium silicate hydrate (C-S-H) to unstable phases, resulting in low compressive strength and high permeability. To minimize that compressive strength issue, guidelines suggests the addition of 35-40% BWOC (By Weight Of Cement) of an extra silica source to balance the relation CaO/SiO2 and convert it into more stable calcium silicate phases. Silica flour (SF) is the silica source worldwide used as anti-strength retrogression agent in cementing operations. The present work presents rice husk ash (RHA) as a sustainable silica source, in alternative to SF, for temperature of the environments where compressive strength retrogression is pronounced. Four compositions of cement slurries were tested: (i) a 15.6 ppg slurry with no silica addition (SF0); (ii) a 15.6 ppg slurry with 35% BWOC of SF addition (SF35); (iii) a 15.0 ppg slurry with 35% BWOC RHA addition (RHA-1) and (iv) a 14.5 ppg with 35% BWOC of RHA (RHA-2). The samples were submitted to 60 °C and 110 °C at atmospheric and 2,000 psi curing pressure, respectively, during 7 days. A uniaxial compression test was performed to evaluate RHA as anti-strength retrogression agent. All experimental procedures were performed in accordance to API RP 10B-2. X-ray diffraction (XRD), scanning electronic microscopy (SEM) and thermogravimetric analyses (TGA) were carried out to analyze the samples after temperature exposure. Results have shown that RHA samples developed more compressive strength in relation to the usual SF sample. Among the samples cured at 110 °C, RHA-1 presented the higher value of compressive strength (44.6 MPa), followed by sample SF35 (40.4 MPa) containing SF in its composition. The sample RHA-2 with 37.9 MPa of compressive strength was similar to SF35 and, as expected, the compressive strength of control sample SF0 was the lower with 28.3 MPa, due to the retrogression phenomenon. The samples cured at 60 °C showed the same tendency of 110 °C samples. XRD analysis showed the presence of typical stable crystalline phases such as xonotlite and tobermorite in cement samples containing RHA. The SEM images and TGA analyses were in accordance to XRD evaluations. As observed, RHA showed great potential as anti-strength retrogression agent even in weighted (15.0 ppg) or light weight (14.5 ppg) slurries. The sustainability of a renewable silica source makes the RHA an interesting alternative to the usual silica flour.
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