沾化凹陷沙四上亚段湖相碳酸盐岩储层岩石物理特征与模型

Petrophysical Characteristics and Model of Lacustrine Carbonate Reservoir in the Upper Fourth Member of Shahejie Formation in the Zhanhua Sag

沾化凹陷是渤海湾盆地济阳坳陷重要的油气勘探区,其中沙四上亚段湖相碳酸盐岩油藏是凹陷内关键的勘探目标。为进一步认识湖相碳酸盐岩储层岩性、沉积微相与岩石物理参数之间的关系,本文以沾化凹陷沙四上亚段湖相碳酸盐岩储层为目标,综合利用岩石学、物性表征、岩石物理测试等多种分析测试资料,系统表征湖相碳酸盐岩储层的岩石学特征、沉积微相、岩石物理参数及参数敏感性特征,并开展储层岩石物理建模。结果表明:沾化凹陷沙四上亚段湖相碳酸盐岩以灰岩为主,次为混积岩,白云岩发育较少。主要发育灰礁、灰滩、灰泥亚相,包括礁核、礁前、礁间水道、礁后、礁缘、滩核、滩缘、滩间水道微相。在样品干燥和饱水情况下,滩核微相纵波速度、横波速度、体积模量、剪切模量、杨氏模量、泊松比中相较于滩缘微相较高;生物灰岩纵、横波速度、体积模量较高,砂屑灰岩纵、横波速度、体积模量变化范围较大,灰质白云岩、砂屑灰岩、砂质灰岩及泥晶灰岩的泊松比偏低。密度、纵横波速度比和λ常数交汇,作为岩性敏感性参数反映流体对储层岩性无影响;纵、横波速度比值与λ常数在不同流体情况下对区分沉积微相的敏感性特征不同。碳酸盐岩储层整体符合Gassmann岩石物理模型预测,但局部符合DEM岩石物理模型预测;DEM岩石物理模型作为微裂缝发育的非均质储层的岩石物理模型较Gassmann模型预测结果更准确。

The Zhanhua Sag is a significant oil and gas exploration area in Jiyang Depression, Bohai Bay Basin. Lacustrine carbonate reservoirs of the upper fourth member of Shahejie Formation are the key exploration target in this sag. To further reveal the relationship between lithology, sedimentary microfacies and petrophysical parameters of lacustrine carbonate reservoir, in this paper, the upper fourth member of Shahejie Formation in Zhanhua Sag was taken as the target. The petrological characteristics, sedimentary microfsacies, petrophysical parameters and parameter sensitivity characteristics of lacustrine carbonate reservoirs are systematically characterized by comprehensive use of petrological, physical characterization and petrophysical testing data, and reservoir petrophysical modeling is carried out. The results show that the lacustrine carbonate rocks in the upper fourth member of Shahejie Formation in the Zhanhua Sag are mainly limestone, the secondary is mixed rock, and the dolomite is less developed. It mainly develops lime-reef, lime-beach and lime-mud, including microfacies of reef core, reef front, channel among reefs, reef back, reef margin, beach core, beach margin and channel among beaches. In the case of dry and saturated samples, the velocity of P-wave, S-wave, bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio of the beach core microfacies are higher than those of the beach margin microfacies. The velocity of P-wave, S-wave and volume modulus of biogenic limestone is higher, the velocity of P-wave, S-wave and volume modulus of calcarenite is larger, and the Poisson’s ratio of limy dolomite, calcarenite, sandy limestone and micrite is lower. The intersection of the density, the ratio of P-wave velocity to S-wavevelocity and λ shows that fluid has no influence on the reservoir lithology. The ratio of P-wave velocity to S-wave velocity and shear waves and λ has different sensitivity characteristics to distinguish sedimentary microfacies under different fluid conditions. The carbonate reservoir is predicted by Gassmann petrophysical model as a whole, but locally by DEM petrophysical model. The DEM petrophysical model is more accurate than the Gassmann model as a petrophysical model of heterogeneous reservoir with micro-fracture development.