准东地区云质岩储层叠前反演及脆性预测

Prestack inversion and brittleness prediction of dolomitic reservoir in eastern Junggar area

脆性是一种评价致密储层可压裂性的重要指标,对油气勘探与开发有着重要的意义。准东地区勘探程度低、探井少,二叠系中下部云质岩致密储层的精细描述和脆性的准确预测均有着很大的难度。为此,根据岩石物理实验结果,利用叠前地震角度域数据体,开展储层叠前反演及脆性预测。通过AVO反演,获取P(截距)+G(梯度)和P×G属性;通过Y(杨氏模量,E)P(泊松比,σ)D(密度,ρ)和L(拉梅常数,λ)M(μ)R(ρ)反演,获取弹性参数的变化率(反射系数);通过测井约束反演,获取弹性参数的实际值,并用多种表征公式计算脆性,分析其物理含义及应用效果。研究结果表明:①研究区横波速度与纵波速度有较好的拟合关系,杨氏模量、泊松比和密度对泥岩、非泥岩区分度明显;②云质岩具有高速特征,研究区储层呈双“甜点”结构;③用三个小角度数据体直接反演弹性参数反射系数,YPD反演方法相较LMR的储层识别效果更好、分辨率更高,密度反射系数数据体可见比较明显的扇体及河道冲积特征;④脆性表征结果与弹性参数特征有一定的区别,脆性表征的云质岩有利区呈条带状分布,而弹性参数预测的云质岩有利区基本呈连续、成片分布;⑤ρE/σ为研究区最佳的脆性表征公式,可为类似油田云质岩储层脆性预测提供借鉴。

Brittleness is an important index to evaluate the fracturing ability of tight reservoir and is of great significance to oil and gas exploration and development.Due to the low exploration degree,large area and few exploration wells,it is difficult to describe and predict the brittleness of the dolomitic tight reservoir in the middle and lower part of Permian in the eastern Junggar basin.This paper carries out the prestack inversion and brittleness prediction of the reservoir by using the angle domain data,according to the petrophysics experiment.Prestack inversion includes the following methods.AVO inversion is applied to obtain the P+G and P×G attributes.Y(Young’s modulus,E)P(Poisson’s ratio,σ)D(density,ρ)and(L(λ)M(μ)R(ρ)inversions are applied to obtain the reflection coefficient of elastic parameters logging constrained inversion is utilized to get the actual value of multiple elastic parameters.Then,the brittleness is calculated with various characterization formulas,and its physical meaning and application effects are analyzed.The practical application shows that:①There is a good fitting relationship between shear wave velocity and P‑wave velocity in the study area,and Young’s modulus and Poisson’s ratio are distinguished from mudstone and non‑mudstone.②The dolomitic rock has the characteristic of high velocity,and the reservoir shows a double sweet spot structure.③Using three small‑angle data bodies to directly invert the reflection coefficient of elastic parameters,the YPD inversion method has a better reservoir identification effect and high resolution than LMR inversion.Especially in the density reflection coefficient data,obvious fan and channel alluvial features can be seen.④There is a certain difference between the brittleness characterization results and the characteristics of elastic parameters.The favorable areas of the dolomitic rock characterized by brittleness are distributed in bands,while the elastic parameters basically distributed in continuous patches.⑤ρE/σis the best brittleness characterization formula in the study area,which can provide a reference for the prediction of brittleness in dolomitic tight reservoirs.