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Effects of pore fluid flow and chemistry on compaction creep of calcite by pressure solution at 150u0002C

机译:150u0002C压力溶液的孔隙流和化学性质对方解石压实蠕变的影响

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Uni-axial compaction creep experiments were performed on crushed limestone and analytical grade calcite pow-nders at 150u0002C, a pore fluid pressure of 20 MPa, and effective axial stresses of 30 and 40 MPa. Previous experi-nments have shown that compaction under these conditions is dominated by intergranular pressure solution (IPS).nThe aim of the present tests was to determine the inter-relationship between pore fluid chemistry, compactionnrate and the rate-controlling process of IPS. Intermittent flow-through runs conducted using CaCO3 solutionnshowed no effect on creep rate at low strains (<4–5%) but a major acceleration at high strains (5–10%). Mea-nsurements of the Ca concentration present in fluid samples revealed the build-up of a high super-saturation ofnCaCO3 during compaction under zero flow conditions, especially at high strains. Active flow-through led to androp in Ca concentration, which corresponded with creep acceleration. Addition of NaCl to the pore fluid, at anconcentration of 0.5 M, increased the creep rate of the analytical grade calcite samples roughly in proportion tonthe enhancement of calcite solubility. Addition of Mg2+nand HPO2u0002n4 to the pore fluid, in concentrations of 0.05nand 0.001 M, respectively, caused major retardation of compaction creep. Integrating our mechanical, flow-nthrough and chemical data points strongly to diffusion-controlled IPS being the dominant deformation mechanismnin the calcite-water system under closed-system (zero flow) conditions at low strains (<4–5%), giving way to pre-ncipitation control at higher strains. Our fluid composition data suggest that this transition is because of accumula-ntion of impurities in the pore fluid. As Mg2+nand phosphate ions are common in natural pore fluids, it is likelynthat retarded precipitation will be the rate-limiting step of IPS in carbonates in nature. To quantify diageneticncompaction and porosity-permeability reduction rates by IPS in carbonates needs to account for this.
机译:在150u0002℃,破碎流体压力为20 MPa,有效轴向应力分别为30和40 MPa的情况下,对碎石灰石和分析级方解石粉进行了单轴压实蠕变实验。先前的实验表明,在这些条件下的压实作用主要由晶间压力溶液(IPS)来控制。n本实验的目的是确定孔隙流体化学性质,压实率与IPS的速率控制过程之间的相互关系。使用CaCO3溶液进行的间歇通流试验表明,在低应变(<4–5%)下对蠕变速率没有影响,而在高应变下(5-10%)则有较大的加速度。流体样品中Ca浓度的测量表明,在零流量条件下,特别是在高应变下,压实过程中nCaCO3的过饱和度很高。主动流过导致Ca浓度升高,这与蠕变加速度相对应。在浓度为0.5 M的溶液中添加氯化钠到孔隙流体中,方解石方解石样品的蠕变速率大致按比例增加,方解石溶解度提高。 Mg2 + n和HPO2u0002n4分别以0.05n和0.001M的浓度添加到孔隙流体中,导致压实蠕变的主要延迟。将我们的机械数据,通量数据和化学数据进行了强有力的整合,发现扩散控制的IPS是方解石-水系统在低应变(<4–5%)的封闭系统(零​​流量)条件下的主要变形机制,较高菌株的预沉淀控制。我们的流体成分数据表明,这种转变是由于孔隙流体中杂质的积累所致。由于Mg2 + nand磷酸根离子在天然孔隙流体中很常见,因此延迟沉淀可能是自然界碳酸盐中IPS的限速步骤。为了量化碳酸盐中IPS的成岩作用致密性和孔隙度降低率,需要考虑到这一点。

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