Mudstone compaction is widely used in the estimation of subsidence caused by sediment load, basin modeling, and overpressure genesis. The boundary for the depth at which chemical compaction in mudstones begins in the Xihu Depression is across two wells; in Well A, the depth is 2200 m, while in Well D, it is 1750 m. The porosity shows a gradual decreasing trend, followed by a sharp decrease and then an increase. Compared with Well A, the pores in Well D show a faster reduction (resulting in higher compaction) with increasing burial depth. The compaction process is controlled by clay mineral transformation and temperature increase. At a temperature range of 65–105 °C, local dissolution of quartz and pyrite, as well as precipitation of plagioclase, occur in Well D. The quartz, pyrite, and plagioclase contents in Well A do not significantly change, while K-feldspar corrosion and illitization are dominant. At a temperature range of 125–135 °C, diagenesis is reversed. The mixed layer increases across a low range, while chlorite and kaolinite contents increase; the dissolution of dolomite and the intermittent dissolution of calcite cause a local increase in pore size at 4460 m in Well A and 3300 m in Well D. The report values of geothermal gradient raise the depth limit of chemical compaction in Well D compared to that in Well A, thus accelerating the process of illitization and the cementation rate of quartz, and becoming the leading cause of the steeply decreasing trend of porosity in Well D. A compaction model for the Xihu Depression has also been established, which involves mechanical compaction, coexistence of chemical compaction and mechanical compaction, and chemical compaction. In the chemical compaction stage, the chemical/diagenetic compaction of mudstones locally increases the pore size. Moreover, abnormally enlarged pores became important reservoirs in the Xihu Depression.

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泥岩化学压实成因机制——以东海陆架盆地西湖凹陷为例

泥岩压实广泛应用于估算沉积物负荷引起的沉降、盆地建模和超压成因。西湖凹陷泥岩化学压实开始深度的边界跨过两口井； A井深度为2200 m，D井深度为1750 m。孔隙率呈现逐渐减小的趋势，然后急剧减小，然后增加。与A井相比，随着埋深的增加，D井的孔隙减少得更快（压实程度更高）。压实过程由粘土矿物转变和温度升高控制。 D 井温度范围为 65~105 ℃，局部发生石英、黄铁矿溶解，斜长石沉淀。A 井石英、黄铁矿、斜长石含量没有明显变化，而钾长石含量变化不大。腐蚀和伊利化现象占主导地位。在 125–135 °C 的温度范围内，成岩作用发生逆转。混合层在低范围内增加，绿泥石、高岭石含量增加；白云石的溶蚀和方解石的间歇溶蚀导致A井4460m和D井3300m处孔径局部增大。地温梯度报告值较D井提高了化学压实深度极限。 A 井，加速了伊利石化过程和石英胶结速度，成为导致 D 井孔隙度急剧下降的主要原因。还建立了西湖凹陷机械压实、压实作用并存的压实模型。化学压实和机械压实，以及化学压实。在化学压实阶段，泥岩的化学/成岩压实局部增加了孔隙尺寸。此外，异常增大的孔隙成为西湖凹陷重要的储层。