两步相控反演在塔里木盆地顺北8井区碳酸盐岩断控储集体预测中的应用

Two-step facies-constrained inversion in prediction of carbonate rock fault-controlled reservoirs with post stack seismic in No.8 structure of Shunbei block,Tarim Basin

断控储集体是多期活动的走滑断裂破碎带经深部酸性流体溶蚀改造形成的多重孔隙介质特殊储层。断控储集体内部结构极其复杂,储集空间纵横向非均质性极强,缝洞结构纵横向分隔性明显,常规储层预测方法在储集体内部结构及物性变化表征上,存在分辨率低、细节缺失等问题。研究提出了一种基于两步相控反演碳酸盐岩断控储集体预测技术。第一步,计算地震数据体结构张量属性,将结构张量属性体包络作为空间约束相,建立地震相约束低频趋势模型,使用该低频模型约束进行确定性反演,能够有效降低水平层状地震反射对确定性反演造成的干扰,准确刻画地震分辨率下储层顶、底位置及储集体内部非均质性横向变化特征;第二步,基于确定性反演波阻抗及测井主要岩相概率密度函数(洞穴相、孔洞相、裂缝相和非储层相),计算得到不同岩相的贝叶斯后验概率体,将该贝叶斯推论概率体作为反演相控体约束模型,进行三级相控地质统计学反演(即,第一级为结构张量属性体约束;第二级为确定性反演岩相体约束;第三级为测井一维岩相比例空间约束),能够进一步提升断控储集体内部储层横向非均质性及纵向分辨率预测精度。应用效果显示,“两步串联,三级相控”的相控反演方法,即常规地震分辨率叠后确定性波阻抗反演与高分辨率叠后地质统计学反演两步串联,地质统计学反演内部实现过程做三级相控,将地震的预测性与测井及地质信息的描述性有机结合,突破了对地震分辨率的传统认知,刻画断控储集体内部细节精度及横向非均质性变化能力提升,能够发现更多储集体内部形态变化及物性变化特征。两步相控反演方法在类似地质及储层条件研究区具有推广应用价值。

Fault controlled reservoir is a special multiple porous media reservoir which was formed by deep acid fluid dissolution and transformation of multi-stage active strike slip fault fracture zone.The internal structure of fault controlled reservoir is extremely complex,and with strong vertical and horizontal heterogeneity of reservoir space,which has obvious separation tunnel structure in vertical and horizontal.Conventional seismic inversion methods have problems such as low resolution,missing details in characterizing the internal structure and physical properties.In this paper,a fault-controlled carbonate reservoir prediction technique based on two-step facies constrained inversion is proposed,and this is a case study in No.8 structure of Shunbei block,Tarim Basin.First step,using the envelope of the structure tensor attribute volume as the space constraint face to create the seismic facies constrained low frequency trend model,it has the benefit to reduce the interference of horizontal layered seismic reflection on the deterministic inversion effectively,getting an accurate characteristics of the top and bottom positions of the reservoir and the internal heterogeneity on the lateral variation of the reservoir under seismic resolution.Second step,based on deterministic inversion acoustic impedance and probability density function from logging lithofacies(cave facies,vug facies,fracture facies and non reservoir facies),a geosta-tistical inversion facies-constrained body model is established using Bayesian inference,and three-level facies control geostatistical inversion is carried out to improve the fault-controlled reservoir’s accuracy on lateral and the prediction resolution of reservoirs in vertical.The inversion results show that the two-step series workflow of seismic facies constrained deterministic inversion and three-level facies-controlled geostatistics inversion established in this study is both predictive and descriptive.It has broken through the limitation of seismic resolution,having the capability of describing fault-controlled reservoir’s internal details.More internal morphology and physical property characteristics of reservoir were found.The workflow of this case study has extendable and utility value to similar data and geological conditions oil field.