深层储集层长石溶蚀增孔的物理模拟与定量计算

Physical simulation and quantitative calculation of increased feldspar dissolution pores in deep reservoirs

以塔里木盆地库车坳陷克拉苏构造带白垩系巴什基奇克组深层储集层为例,开展成岩物理模拟实验研究,定量计算巴什基奇克组砂岩在早期长期浅埋—后期快速深埋地质过程下,长石骨架颗粒的溶蚀率及溶蚀增孔量。运用场发射扫描电镜大面积扫描分析技术,定量计算大北、克深地区实际岩心样品中长石骨架颗粒的溶蚀度及溶蚀增孔量值,实验数值与实际岩心数值相互校验,由此建立了陆相深层较高长石骨架颗粒含量储集层中长石溶蚀增孔量的演化过程模型。定量计算出克深地区长石在早期长期浅埋—后期快速深埋地质过程下,最大溶蚀增孔量为0.86%~2.05%,模拟的埋深超过7 000 m砂岩的长石溶蚀增孔量值稍稍偏大,校准后绝对误差值为0.23%。大北地区次生溶蚀孔隙的贡献者主要是方解石,长石次之,定量计算出该地区长石最大溶蚀增孔量为0.62%~1.48%,模拟埋深超过7 000 m砂岩中长石溶蚀增孔量值稍稍偏大,校准后绝对误差值为0.15%。造成误差的原因有二:(1)模拟实验代表了深层储集层的均一、理想状态;(2)实际地质情况下深层储集层的非均质性强,不同地区溶蚀作用强弱存在差异。

The physical simulation of diagenesis was conducted for the Cretaceous Bashijiqike Formation deep sandstone reservoir in Kelasu structural belt of Kuqa Depression, Tarim Basin, and the dissolution rate and increased dissolution pores of feldspar matrix grains in such reservoirs were quantitatively calculated in the process from long-term shallow burial in early stage to quick deep burial in late stage. Through the field emission large-area SEM analysis, the dissolution rate and increased dissolution pores of feldspar matrix grains in core samples taken from Dabei and Keshen areas were quantitatively calculated. After the experimental data and the actual core data were cross-checked, the evolution model was established for increased feldspar dissolution pores in deep continental reservoirs with high content of feldspar matrix grains. According to the calculation results, the maximum increased feldspar dissolution pores in Keshen area during the process from long-term shallow burial in early stage to quick deep burial in late stage is by 0.86%-2.05%. The simulated sandstone reservoir with burial depth of more than 7 000 m reveals a larger quantity of increased feldspar dissolution pores, with the absolute error value of 0,23% after calibration. In Dabei area, calcite is the primary contributor to secondary dissolution pores, followed by feldspar. Quantitative calculation shows the maximum increased feldspar dissolution pores in Dabei area to be by 0.62%-1.48%. Similarly, the simulated sandstone reservoir with burial depth of more than 7 000 m reveals a larger quantity of increased feldspar dissolution pores, with the absolute error value of 0.15% after calibration. There are two causes of the experiment errors： One cause is that the simulation experiment uses ideal conditions and the simulation reservoirs are homogeneous; Another one is that deep reservoirs have strong heterogeneity and there are big differences in the dissolution within different areas.