Investigation of pore structure and permeability estimation models of Kongdian Formation glutenites in the Bozhong 19-6 Gasfield
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摘要:
渤中19-6砂砾岩孔隙结构复杂,为提高渗透率的估算精度,需要从孔隙结构入手,找到与渗透率相关性最好的孔隙结构因素。以43块孔店组砂砾岩的孔隙结构和渗透率为研究对象,利用岩石铸体薄片确定发育的孔隙类型,通过高压压汞获取孔喉分布特征和孔隙结构参数。结合孔隙类型和孔隙结构参数分析孔隙结构和渗透率的关系,建立了基于孔隙结构参数的渗透率评价模型。研究表明,不同类型溶蚀孔隙的孔隙结构存在差异,粒内溶孔的孔隙结构最好,胶结物溶孔的孔隙结构最差。溶蚀孔隙类型发育不同,物性差异较大,以粒内溶孔为主且不发育胶结物溶孔的岩样物性最好。不同孔隙结构因素对渗透率控制程度不一致,其中基于孔喉大小、连通、配比和几何形状这4种因素建立的渗透率模型精度最高。渤中19-6气田孔店组砂砾岩粒内溶孔具有较大的孔喉半径和较好的连通性是促使该类岩石储集和渗流能力均较好的主要原因。平均孔喉半径、退汞效率、平均孔喉体积比和分形维数适用于估算孔隙结构复杂且(特)低孔渗的砂砾岩储层渗透率,以期为渤海湾盆地渤中凹陷砂砾岩储层的渗透率评价提供技术支持。
Abstract:The pore structure of glutenite in Bozhong 19-6 Gasfield is complicated. In order to improve the estimation accuracy of permeability, it is necessary to start with the pore structure and find the pore structure factor with the best correlation with permeability. Taking the pore structure and permeability of 43 Kongdian Formation glutenites as the research object, using rock casting thin slices to determine the pore types, and obtaining pore-throat size distribution characteristics and pore structure parameters through high-pressure mercury intrusion. Combining pore types and pore structure parameters to analyze the relationship between pore structure and permeability, a permeability evaluation model based on pore structure parameters was established. Studies have shown that there are differences in the pore structure between different types of dissolved pores. The pore structure of dissolved pores in the grain is the best, and the pore structure of dissolved pores in the cement is the worst. The physical properties of glutenite with different types of dissolution pores vary greatly. The rock samples with intragranular dissolution pores and no cement dissolution pores have the best physical properties. Different pore structure factors have inconsistent degrees of permeability control. Among them, the permeability model which based on pore throat size, connectivity, ratio and shape has the highest accuracy. The large pore throat radius and good connectivity of the dissolved pores in the glutenite grains of the Kongdian Formation of BZ19-6 Gasfield are the main reasons for the good reservoir and seepage capacity of this kind of rocks. The average pore throat radius, mercury removal efficiency, average pore throat volume ratio and fractal dimension are suitable for estimating the permeability of glutenite reservoirs with complex pore structures and (extremely) low porosity and permeability, in order to provide technical support for the permeability evaluation of glutenite reservoirs inBozhong Depression, Bohai Bay Basin.
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图 1 渤中19-6构造带位置[26]及砂砾岩储层岩性
Figure 1. Location of Bozhong 19-6 structural belt and lithology of glutenite reservoirs
表 1 孔隙结构参数意义和分类
Table 1. Pore structure parameters and its physical meaning
符号 孔隙结构参数 物理意义 表示信息 参数计算方法 Rave 平均孔喉半径/μm[6] 衡量岩石的平均孔喉大小,反映物性好坏。其越大,储层物性越好 孔喉大小 $\sqrt{\left(\sum\limits_1^n r_i^{\prime 2} \cdot S_{\mathrm{hg}}\right) / \sum\limits_1^n \Delta S_{\mathrm{hg}}}$ Rapex Swanson半径/μm[7, 18] 岩石内部无效孔隙向有效连通的孔隙系统过渡时的孔喉半径大小,反映对流体流动作出贡献的有效孔隙空间的体积 孔喉大小 Shg/Pc的最大值所对应的孔喉半径 Sp 分选系数[8] 反映孔喉分布的分选性(集中程度),表示以Rave为中心的散布程度。高渗储层分选越好,渗流能力越强。低渗储层分选越差,渗流能力越强 孔喉分布 $\sqrt{\left[\sum\limits_1^n\left(r^{\prime}{ }_i-R_{\mathrm{ave}}\right)^2 \cdot \Delta S_{\mathrm{hg}}\right] / \sum\limits_1^n \Delta S_{\mathrm{hg}}}$ We 退汞效率/%[9] 反映孔隙通过喉道相连接的墨水瓶现象。其越低,喉道对孔隙的控制作用越强,首先退出汞的喉道对孔隙空间连通性造成的破坏越大,渗流能力越差 孔喉连通 $\frac{S_{\max }-S_{\mathrm{r}}}{S_{\max }}$ Rpt 平均孔喉体积比[10] 反映储集空间中孔隙和喉道的平均体积比。其越大,与孔隙相连的喉道半径越小,流体在孔隙空间中流动越容易发生卡断,不能形成连续相,渗流能力越差 孔喉配比 $\frac{{{S_{\rm{r}}}}}{{{S_{\max }} - {S_{\rm{r}}}}}$ Df 分形维数[5] 刻画孔喉几何形体复杂程度的定量参数。分形维数越大,孔隙和喉道的非均质性越强,渗流能力越差 孔喉几何 ${S_{{\rm{hg}}}} \propto P_{\rm{c}}^{ - \left( {2 - {D_{\rm{f}}}} \right)}$ 注:r′i为某一进汞区间孔喉半径中值(μm);ΔShg为ri对应区间进汞饱和度增量(%);Sr为残余汞饱和度(%);Smax为最大汞饱和度(%) 表 2 6块样品的孔渗和孔隙结构参数
Table 2. Porosity, permeability and pore structure parameters of the 6 samples
样品 深度/m 孔隙度/% 渗透率/10-3 μm2 孔隙结构参数 Rave/μm Rapex/μm Sp We/% Rpt Df 1# 3 850.84 9.80 0.05 0.373 0.720 0.641 19.610 4.099 2.276 2# 4 050.49 9.50 1.89 1.022 1.572 0.777 34.600 1.890 2.109 3# 3 856.16 9.90 2.41 1.288 2.237 1.203 35.808 1.793 2.104 4# 3 850.45 10.50 0.54 0.922 1.101 0.684 25.221 2.965 2.157 5# 4 047.65 10.60 1.74 0.825 1.564 0.745 36.966 1.705 2.124 6# 3 856.85 10.70 2.57 1.308 2.216 1.110 35.970 1.780 2.096 表 3 考虑不同个数因素回归的渗透率模型以及相关性、均方根误差
Table 3. Permeability model considering the different factors, correlation coefficient and RMSE
模型编号 考虑因素 R2 均方根误差 回归模型 1 Df 0.627 6 0.876 1 lgK=15.457-46.765·lgDf 2 Df, We 0.626 1 0.873 0 lgK=14.071-45.121·lgDf+0.556·lgWe 3 Df, We, Rpt 0.633 8 0.865 6 lgK=17.860-1.401·lgRpt-45.856·lgDf-1.503·lgWe 4 Df, We, Rpt , Rave 0.894 2 0.507 7 lgK=-11.595+1.809·lgRave+4.942·lgRpt-9.174·lgDf+8.720·lgWe 5 Df, We, Rpt, Rapex 0.845 5 0.613 7 lgK=3.142+1.110·lgRapex+1.919·lgRpt-28.473·lgDf+3.618·lgWe 6 Df, We, Rpt, Rave, Sp 0.889 1 0.527 0 lgK=-8.273+0.944·lgRave+4.770·lgRpt-17.596·lgDf+8.397·lgWe+0.667·lgSp 7 Df, We, Rpt, Rave, Sp, φ 0.830 7 0.649 1 lgK=-6.527+0.631·lgRave+4.266·lgRpt-21.573·lgDf+7.655·lgWe+0.574·lgSp+0.828·lgφ 表 4 几种常用的压汞孔隙结构参数渗透率模型
Table 4. Several common permeability models built by pore structure parameters
常用回归模型 模型关键参数 岩性 渤中19-6回归公式 R2 均方根误差 Winland[22] φ,R35 碎屑砂岩 lgK=-0.662+0.988·lgφ+0.646·lgR35 0.742 8 0.755 7 Swanson[18] Shg/Pc 砂岩,碳酸盐岩 lgK=-2.767+1.767·lg(Shg/Pc)max 0.777 6 0.864 4 Pittman[20] φ,R25 砂岩 lgK=-0.577+0.621·lgφ+1.128·lgR25 0.792 9 0.703 9 Capillary-Parachor[19] Shg/Pc2 砂岩 lgK=-1.795+0.896·lg(Shg/Pc2)max 0.757 7 0.775 8 Rezaee[35] φ,R50 碳酸盐岩 lgK=-2.236+2.611·lgφ+0.151·lgR50 0.709 5 0.806 5 Rezaee[21] φ,R10 致密砂岩 lgK=0.825-1.888·lgφ+2.768·lgR10 0.781 3 0.929 4 Gao and Hu[36] R50 砂岩、页岩 lgK=0.552+0.297·lgR50 0.414 7 1.060 6 Liu[37] φ,Shg/Pc2 砂岩 lgK=-2.025+0.431·lgφ+0.806lg(Shg/Pc2)max 0.768 7 0.752 9 本文 Rave,Rpt,Df,We 砂砾岩 lgK=-11.595+1.809·lgRave+4.942·lgRpt-9.174·lgDf+8.720·lgWe 0.894 2 0.507 7 注:R10为进汞饱和度为10%时对应的孔喉半径;R50为进汞饱和度为50%时对应的孔喉半径;R25为进汞饱和度为25%时对应的孔喉半径;Φ为孔隙度 -
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