压汞—恒速压汞在致密储层微观孔喉结构定量表征中的应用——以鄂尔多斯盆地华池—合水地区长7储层为例

鄂尔多斯盆地华池—合水地区是典型的致密油气富集区,储层物性差,微观孔喉结构特征复杂,孔喉结构对油气的富集和后期开采有较大影响。利用压汞—恒速压汞法探讨华池—合水地区延长组长7致密砂岩储层纳米孔喉定量表征及孔喉体系中流体渗流特征。研究表明:研究区储层排替压力较高,平均喉道半径较小,孔喉体积比及孔喉比较大,渗流能力差;不同物性岩样的孔隙半径分布范围一致,喉道分布差异明显,进汞饱和度随孔隙个数的增多而增大;SHg—ΔSHg/ΔPc曲线能较好地反映进汞速率及孔喉结构,致密储层中纳米级孔喉发育,且对储层储集及渗流能力有较大的贡献;流体在注入过程中,首先进入孔隙主控区,紧接着进入孔喉共控区,最后进入喉道主控区;恒速压汞在研究致密储层孔喉结构时不能反映纳米孔喉特征,评价物性较好的储层效果较好。

Application of mercury injection and rate-controlled mercury penetration in quantitative characterization of microscopic pore structure of tight reservoirs:A case study of the Chang7 reservoir in Huachi-Heshui area,the Ordos Basin

Huachi-Heshui area in the Ordos Basin is a typical enrichment region for tight reservoirs. It has poor physical properties and complicated characteristics of microscopic pore throat structure, which has a great effect on oil and gas accumulation and exploitation.Mercury injection and rate-controlled mercury penetration were used to quantitatively characterize nanometer pore throats and to study fluid mobility characteristics in tight sandstone reservoirs in the seventh member of the Yanchang Formation (Chang7). The reservoir in the study area has high displacement pressure, low average throat radius, large pore/throat volume ratio, big pore throat and poor permeability. The distribution range of pore radius of rock samples with different properties is consistent, while the distribution of throat geometry among them is obviously different. Mercury injection saturation increases with the increase of pore numbers. The curve of S_Hg-ΔS_Hg/ΔP_c can preferably reflect mercury injection velocity and pore throat structure. Nanometer throat pore sare well developed in tight reservoirs, which make a great contribution to reservoir capacity and permeability. In the course of injection, fluid first enters the main controlling area of the pore, then the common control area of pore and throat, and finally the main control area of the throat.Rate-controlled mercury penetration is useful for the reservoirs with good physical properties, but it can not reflect the characteristics of nanometer pore throats in studying the pore throat structure of tight reservoirs.