页岩气藏综合地质建模技术

Comprehensive geological modeling technology for shale gas reservoirs

目前,页岩气藏地质建模采用的技术思路和实现方式主要源于常规油气藏,对页岩气藏并不适用,而可资借鉴的国内外相关成果则鲜见。为此,首先针对页岩气藏的特殊性,确定相配套的地质建模技术流程;再结合测录井资料解释、地震叠前叠后资料解释及采样地质实验分析等结果,建立工区构造和页岩小层发育模型;并在此格架体模型下应用地质统计学建模方法建立了页岩气储层厚度、孔隙度、含气饱和度、总有机碳含量、硅质含量、脆性指数等属性模型;综合应用地震AFE属性、构造曲率、应变体积膨胀资料,结合地质认识与钻井显示,采用目标建模方法,建立天然裂缝DFN模型;在人工压裂缝展布模式判断及参数拟合分析的基础上,建立了人工压裂缝模型;最后,采取逐级叠加的方法,建立了页岩气藏综合地质模型并进行气井的生产史拟合与动态预测。研究结果表明:①与常规油气藏相比,页岩气藏地质建模更为复杂,主要表现在小层划分与对比困难、基质参数多且存在着相互约束关系、天然裂缝成因和尺度多样以及天然裂缝干扰和影响下人工压裂缝分布复杂;②天然裂缝模型实现了对裂缝系统几何形态和分布的有效细致描述,人工压裂缝模型能较好地体现人工裂缝分布状况及压裂改造体积,通过逐级融合叠加页岩气藏构造和小层发育模型、多种基质属性参数模型、多尺度天然裂缝模型及其约束下的人工压裂缝模型,可以完成页岩气藏综合地质模型的建立;③气井生产史拟合结果显示,在井底压力误差小于3.3%的情况下,所建立的页岩气藏综合地质模型是可靠的。

At present, the technical ideas and implementation modes adopted in the geological modeling of shale gas reservoirs are mainly derived from those used in conventional oil and gas reservoirs, so they are not applicable to shale gas reservoirs. Moreover, there are few reports on the results of shale gas geological modeling at home and abroad. In view of this, a technical process of geological modeling for shale gas reservoirs was firstly established according to its particularity. Secondly, a structure and shale sublayer development model for the working area was established based on logging interpretation results, pre-stack and post-stack seismic interpretation data and geological test analysis results of samples. Thirdly, property models of shale gas reservoirs, including thickness, porosity, gas saturation, TOC, silicon content and brittleness index, were established using geostatistic modeling method in the frame model. Fourthly, a natural fracture DFN model was established using the object-based modeling method, based on seismic AFE attribute, structural curvature and strain and dilatation data, combined with geological knowledge and drilling display. Fifthly, a hydraulic fracture model was established based on the estimate of hydraulic fracture distribution pattern and the parameter fitting analysis. Finally, a comprehensive geological model for shale gas reservoirs was established by virtue of step-by-step superposition. What’s more, it was applied to the production history matching and performance prediction of shale gas wells. And the following research results were obtained. First, the geological modeling of shale gas reservoirs is more complex than that of conventional oil and gas reservoirs, and the complexities are presented as difficult classification and correlation of sublayers, multiple matrix parameters restricting each other, diverse geneses and sizes of natural fractures, and complicated distribution of hydraulic fractures under the interference and influence of natural fractures. Second, the natural fracture DFN model is capable of describing the geometrical shape and distribution of fracture system effectively and finely, and the hydraulic fracture model can better embody the distribution of hydraulic fractures and the stimulated reservoir volume (SRV). The establishment of the comprehensive geological model for shale gas reservoirs can be realized by progressively integrating and superposing the structure and sublayer development model, the multi-matrix property parameter model, the multi-scale natural fracture model and the hydraulic fracture model under the constraint of multi-scale natural fracture model. Third, production history matching results of gas wells show that the error of bottomhole pressure is lower than 3.3%, which indicates that the newly established comprehensive geological model of shale gas reservoirs is reliable. In conclusion, the modeling process and method developed in this paper can be used as reference in the establishment of a comprehensive geological model for shale gas reservoirs.