沁水南部柿庄南区块3号煤层现今地应力特征及其与渗透率的关系研究

Characteristic of in-situ stress in No.3 coal seam of southern Shizhuang block,southern Qinshui basin,and its influence on the permeability

为了研究沁水盆地柿庄南区块3号煤层地应力特征,揭示地应力对渗透率的影响规律,根据研究区3号煤层形成后的古构造应力场特征,划分出煤层褶皱不同部位叠加区,采用水压致裂法和声波测井互相印证法计算出煤储层地应力,应用实测和地质强度指标(geological strength index,GSI)相结合的方法得出煤储层渗透率,对煤层现今地应力与埋深的关系进行回归分析,查明了地应力随埋深的变化特征,在此基础上总结了地应力对煤储层渗透率的影响规律。结果表明:研究区煤层地应力随埋深增加呈线性增大;在700 m以浅地区,σV>σH>σh,现今地应力状态为大地静力场; 700～900 m,σH≈σV≈σh,为准静水压力场; 900 m以深,σH>σV>σh,最大水平主应力起主导作用,具有大地动力场特征。对于同一构造部位,煤储层地应力与埋深相关性较好,呈负指数关系;不考虑多期构造叠加时,应力差与渗透率关系不明显,考虑构造分期后,同一叠加区其应力差与渗透率符合指数关系。

In order to investigate distributions of in-situ stress in No. 3 coal seam of southern Shizhuang block, southern Qinshui basin and determine influences of the stress on permeability, the superposition area of the coal seam folds was divided based on characters of paleo tectonic stress field of No. 3 coal seam. Hydraulic fractu- ring method and acoustic logging were adopted to obtain the stress data. Coal reservoir permeability was ob- tained by using the measured and geological strength index （GSI）. The regression analysis was carried out to find out relations between the present stress and depth of coal seam. The ettect of the present stress on the per-meability of coal reservoir was summarized. The results showed that the principal stress linearly increased with depth. When the burial depth of coal reservoir was lower than 700 m, the present stress state showed σv 〉 σH 〉 σh. The stress state was the static field. When the burial depth was between 700 and 900 m, the present stress showed σH≈σv≈σb and the stress state was quasi-hydrostatic. When the depth is more than 900 m, the pres- ent stress showed σH 〉 σv 〉 σb. The stress state was the static field and the maximum horizontal principal stress was dominant. For the same tectonic site,the coal present stress and buried depth had a good negative exponential relations. When there was no muhi period structural superposition, the relations between present stress and permeability was not significant. While structural stage was considered, the relations between the stress ditterence and the permeability in the same superimposed area was exponential relation.