应用测井储层品质综合评价指数来判别储层的有效性——以四川盆地西部地区二叠系栖霞组为例

四川盆地西部地区二叠系栖霞组颗粒白云岩储层目前已成为该区天然气勘探开发的新热点。由于栖霞组具有溶蚀孔洞和裂缝均较发育、基质孔隙度低、非均质性强的特点,采用传统的孔隙度评价方法来评价储层的有效性容易出现失误,导致对气井产能的预测值与实际测试结果偏差较大。为此,从分析该区栖霞组的储层特征入手,通过数值模拟研究和对特殊测井资料的精细处理,建立了川西地区栖霞组储层有效性的评价方法和评价标准。研究结果表明:(1)常规测井+电成像测井特殊处理计算基质孔、次生溶蚀孔洞面洞率,可用于评价储层的储集性;(2)深浅双侧向测井+电成像测井+斯通利波能量资料,可用于评价储层的渗滤能力;(3)所建立的栖霞组有效储层标准为:储能系数大于等于0.6、深侧向电阻率小于5 000Ω·m、面洞率大于0.6%、斯通利波衰减大于等于10%、储层综合评价指数大于等于0.25,该评价标准能较好地表征储层的品质和气井产能。该套评价方法及标准在现场应用的效果表明:储层有效性符合率由70%提升到90%以上,基本解决了该非均质碳酸盐岩储层有效性评价的技术难题,为试油选层、完井工程和开发方案的确定提供了依据,降低了天然气勘探开发成本。

Reservoir effectiveness evaluation based on comprehensive reservoir quality evaluation indexes: A case study on the Permian Qixia Fm in the western Sichuan Basin

In the western Sichuan Basin, the Permain Qixia Fm grained dolomite reservoirs are currently the new focus of natural gas exploration and development. The Qixia Fm is characterized by developed dissolved vugs and fractures, low matrix porosity and strong heterogeneity, so evaluation faults tend to occur if reservoir effectiveness is evaluated by means of the traditional porosity evaluation, and consequently the predicted gas well productivity is more deviated from the actual measurement. In this paper, the characteristics of Qixia Fm reservoirs in this area were firstly analyzed. Then, the method and criterion of the effectiveness evaluation of Qixia Fm reservoirs in the western Sichuan Basin were established by means of numerical simulation and special logging data processing. And the following research results were obtained. First, surface porosity of matrix pores and secondary dissolved vugs calculated based on the special processing of conventional logging and electric imaging logging can be used to evaluate the reservoir properties of reservoirs. Second, deep and shallow dual lateral logging in combination with electric imaging logging and Stoneley wave energy data can be used to evaluate the filtration capacity of reservoirs. Third, the criterion of effective Qixia Fm reservoirs is established, including storage coefficient≥0.6, deep lateral resistivity＜5 000 Ω·m, surface porosity＞0.6%, Stoneley wave attenuation≥10% and comprehensive reservoir evaluation index≥0.25, and this evaluation criterion can well characterize reservoir quality and gas well productivity. The field application results of this evaluation method and evaluation criterion indicate that the coincidence rate of reservoir effectiveness has increased from 70% to over 90%. Thus, the technical difficulties related to heterogeneous carbonate reservoir effectiveness evaluation are basically solved. Besides, they provide a basis for the determination of production test layer selection, completion engineering and development scheme so as to cut down the natural gas exploration and development cost.