异常高压对储层溶蚀及成岩阶段的影响机理——以渤中凹陷西北次凹为例

Influence mechanism of abnormal high pressure on reservoir dissolution and diagenetic stage:an example from northwestern Bozhong sag

综合运用薄片、岩心、粒度、SEM等分析方法,研究了渤中地区异常高压对溶蚀作用和成岩阶段的影响机理,发现了一种新溶蚀机制：不同地层压力条件下,颗粒溶蚀会优先发育于特定粒级的砂岩.揭示了异常高压会促进其界面内外储层的溶蚀作用,提供了其抑制有机质成熟和黏土矿物转化的有力证据.异常高压区→常压区,溶蚀强度变化不大,其包络线呈缓坡状.研究表明：异常高压区,颗粒溶蚀优先发育于粗粒级砂岩,平均溶蚀增孔率为32.0％,3 200～3 400 m段平均Ro值为0.56％,混层中蒙脱石质量分数为20.0％;2 950 m深度以下常压区,颗粒溶蚀优先发育于细粒级砂岩,平均溶蚀增孔率为34.2％,平均Ro值为0.58％,混层中蒙脱石质量分数为14.6％;2 950 m深度以上常压区,溶蚀与粒级无相关性,平均溶蚀增孔率为26.5％.紧邻异常高压的常压区,溶孔发育的深度段大于430 m.总结异常高压对溶蚀作用的影响模式,结合新溶蚀机制,为寻找次生溶孔有利区提供理论依据.

Based on data from thin section analysis, core analysis, particle analysis, and SEM, this paper studies the influence mechanism of abnormal high pressure on dissolution and diage- netic stage in northwestern Bozhong sag. A new mechanism of reservoir dissolution was found. The particles dissolution was prior to occur in the specific grain size of sandstone under differ- ent reservoir pressures. The new mechanism reveals that reservoir dissolution will be promoted by abnormal high pressure. The dissolution strength changes very little and the envelope curve represents the gentle slope shape as depth decreases from abnormal pressure regions to the nor- mal pressure regions. The new mechanism provides compelling evidence for inhibition of organ- ic maturation and clay mineral transformation due to abnormal high pressure. The results show that particles dissolution is prior to develop in sandstone with coarser grain size in abnormal high pressure regions, where average added rate of secondary pore is about 32.0%, R_0 is near 0.56% in the depth from 3 200 m to 3 300 m and the mass fraction of montmorillonite in mixed- layer is 20%. The sandstone with finer grain size has priority to form particle dissolution in normal pressure regions deeper than 2 950 m. The average added rate of secondary pore is ap- proximate 34. 2%, Ro is about 0. 58% and the mass fraction of montmorillonite is about 14.6%. However, the particle dissolution has no obvious correlation with particle grain size in the normal pressure regions below 2 950 m. And the average added rate of secondary pore is a- bout 26.5%. The developing depth of reservoir dissolution is over 430 m in normal pressure re- gions next to the abnormal high pressure regions. The influence model of abnormal high pres- sure on reservoir dissolution is summarized. Combined with the newly found dissolution mech- anism, the hydrocarbon exploration in search of secondary pore zone can be guided.