鄂尔多斯盆地靖边气田南部古风化壳岩溶储层有效性评价

鄂尔多斯盆地靖边气田南部奥陶系马家沟组马五_(1-2)亚段白云岩储层由于风化岩溶作用形成了复杂的孔隙系统,孔隙结构的复杂性增强了储层的非均质性和各向异性,也增加了储层有效性评价的难度。通过钻井取心和录井资料标定常规测井曲线,结合压汞、铸体薄片、成像测井、核磁共振测井及试气资料,分别从影响储层孔隙结构的岩性、缝洞、物性、平面分布等方面对该层段进行了储层有效性综合评价,形成了一套适合该地区储层的测井有效性评价标准,并建立了具有不同孔隙结构储层的测井识别模式。研究结果表明:岩性较纯的细粉晶云岩孔隙结构较好、缝洞配置良好、基质物性好,因而储层有效性好,产能相对较高;向东和东北倾斜的古地貌对储层的分布具有明显的控制作用.由西向东及由西南向东北方向的储层,其有效性逐渐变差,产能逐渐降低。所得到的储层有效性评价指标在相同岩溶机理形成的其他地区也具有一定的适用性.只需根据具体储层特征和试气结果进行标定,适当调整标准即可使用。

Effectiveness evaluation of palaeo-weathering crust-type karst reservoirs in the southern Jingbian Gasfield,Ordos Basin

Dolomite reservoirs in M₅¹⁺² of Ordovician Majiagou Fm in the southern Jingbian Gasfield, Ordos Basin, contain complex pore structures due to the karst weathering process. Such complexity strengthens the heterogeneity and anisotropy of these reservoirs, and also brings a challenge to effectiveness evaluation. Through well logging calibration of drilling, coring and mud logging data, and based on mercury penetration, thin slices of cast bodies, micro-resistivity imaging logging, nuclear magnetic resonance logging (NMR) and testing data, the effectiveness of reservoirs was evaluated in respect of lithology, pore and fracture systems, physical properties and plane distribution which affect the pore structure. Standards for effectiveness evaluation of logging data in reservoirs of the area were developed. In addition, a logging data identification model for reservoirs with various pore structures was established. Research results show that fine-crystal dolomite has favorable pore structures, good combination of pores and fractures and better matrix properties, which means better reservoir properties and relatively higher productivity. The eastward and northeast-inclined palaeo-geomorphology has an obvious control effect on the effectiveness of a reservoir. From west to east and from southwest to northeast, the effectiveness and reservoir productivity gradually decreases. Reservoir effectiveness evaluation criteria obtained in this study may be also applicable in other areas with similar karst-forming mechanism. To apply the criteria, it is only necessary to calibrate the data and make suitable adjustments in accordance with the specific reservoir features and trial production data.