碳酸盐岩岩溶储层多井评价方法及地质应用

多井评价是建立在单井精细解释对比分析基础上的预测储层及含油气性平面分布规律的技术方法,而常规测井资料无法区分碳酸盐岩岩溶储层,因而利用多井评价结果确定岩溶发育程度在平面上的分布规律就显得十分重要。为此,在岩心标定成像测井的基础上,对四川盆地高石梯—磨溪地区15口井的成像测井岩溶发育特征进行分析,建立了中二叠统茅口组岩溶发育各分带的标准成像图版,利用交会图及直方图分析各分带的常规测井响应特征,在此基础上形成了电成像测井刻度常规测井识别岩溶发育带的新方法。研究结果表明:①高石梯—磨溪地区茅口组岩溶带自上而下可划分为风化壳残积带、垂直渗流岩溶带、水平潜流岩溶带以及受岩溶作用较弱的基岩;②风化壳残积带在成像测井图像显示为"暗—亮—暗"条带状模式,垂直渗流岩溶带为垂直线状与暗色斑状组合模式,水平潜流岩溶带为水平线状—层状与斑状组合模式,基岩整体显示为亮色块状模式偶见线状或斑状特征;③有效储层主要发育在垂直渗流带和水平潜流带的顶部;④该区茅口组岩溶发育主要受裂缝发育控制,而裂缝发育又与断层关系密切。结论认为,该新方法对碳酸盐岩岩溶储层的多井评价具有普遍适用性,为四川盆地中二叠统风险探井的部署提供了技术支撑。

A multi-well evaluation method for carbonate karst reservoirs and its geological application

Multi-well evaluation is a technology for predicting a reservoir and the plane distribution laws of its oil/gas bearing property based on single-well fine interpretation, comparison and analysis, but the conventional logging data cannot be used to distinguish carbonate karst reservoirs, so it is quite important to determine how to clarify the plane distribution laws of karst development degree by using the multi-well evaluation results. In this paper, the karst development characteristics were analyzed reflected by the imaging logging calibrated based on core samples from 15 wells in the Gaoshiti–Moxi area of the Sichuan Basin. Then, the standard imaging chart for each karst development zone in the Middle Permian Maokou Formation was established, and the response characteristics of the conventional logging in each zone were analyzed by using cross-plot and histogram. Finally, on this basis, a new method for identifying karst development zones by using the electrical imaging logging to calibrate the conventional logging was developed. And the following research results were obtained. First, the karst zone of Maokou Formation in the Gaoshiti–Moxi area is divided into weathering crust residue, vertical seepage karst zone, horizontal underflow karst zone and weakly karstified basement from the top to the bottom. Second, in the imaging logging image, the weathering crust residue is displayed in a banded mode of "dark-bright-dark", the vertical seepage karst zone is in a combined mode of vertical line and dark phyre, the horizontal underflow karst zone is in a combined mode of horizontal line-layer and phyre, and the weakly karstified basement is in a mode of bright block, occasionally with linear or phyric characteristics. Third, the effective reservoirs are mainly developed in the vertical seepage zone and the top of horizontal underflow zone. Fourth, the development of Maokou Formation karst is mainly controlled by fracture development, which is in close relation with faults. In conclusion, this newly developed technology is generally applicable to the multi-well evaluation of carbonate karst reservoirs, and its interpretation results provide the key technical support for the deployment of Middle Permian wildcat wells in the Sichuan Basin.