储层参数岩石物理反演在“甜点”储层预测中应用研究——以W17油田为例

Application of reservoir parameters rock physics inversion in the prediction of “Sweet Spot”: a case study in W17 oilfield

乌石凹陷流砂港组地层岩石粒度变化大,低孔、低渗目标占比近50%,'甜点'储层预测是实现油田经济开发的关键因素,而储层孔隙度、黏土杂积含量评价是'甜点'储层预测的核心问题.本文应用一种新的直接求解包体理论岩石物理方程的储层参数反演方法来进行'甜点'储层评价,该反演方法基于约束最小二乘与信赖域算法直接求解有效介质包体理论岩石物理方程,能够关联弹性参数与储层参数之间的高阶变化,可反演地质体孔隙度、黏土含量空间细节变化特征,通过孔隙度、黏土含量双参数约束实现'甜点'储层分布评价.本文以W17油田为例,首先通过岩石物理分析明确常规储层与'甜点'储层的岩石物理规律;然后运用相控叠前地质统计学反演技术得到高分辨率敏感弹性参数体;最后开展孔隙度、黏土含量储层参数岩石物理反演和'甜点'储层预测.通过与当前业界常用的基于统计关系的地质统计学协模拟储层参数评价方法结果进行对比得到,本次研究应用的储层参数岩石物理反演方法得到的地质体内部细节丰富,盲井预测孔隙度及黏土含量参数精度提高,具有精细刻度储层内部的参数变化,保持弹性反演的分辨精度等优势,有利于解决'甜点'储层连通性及非均质性评价等难点问题.

The main Liushagang formation rock of Wushi geology structure has the feature of wide particle size distribution,low porosity and low permeability,whereas those kind of reservoir rock is accounted nearly 50 percent in the whole.'Sweet Spot'prediction is the most important factor to realize this oilfield’s development economically.Reservoir porosity and clay volume evaluation are the key questions to establish'Sweet Spot'prediction successfully.A new rock physics inversion method was applied to'Sweet Spot'prediction in this paper.This method solves effective media inclusion model function directly by constrained least squares and trust region approach,and can link the elastic parameters with reservoir parameters’high order changers,has the ability to invert geobodies’porosity and clay volume details in 3 D space directly,and then with the constrain of those 2 parameters,'Sweet Spot'prediction was achieved.With the example of W17 oilfield,this paper clarify the difference on rock physics discipline between conventional and'Sweet Spot'type reservoirs first.Then a facies control pre-stack geostatistical inversion was carried out to get high resolution elastic parameters volume.On the basis of previous rock physics forward modeling and seismic inversion research,rock physics inversion study was applied to invert porosity and clay volume directly,and the result was compared with geostatistical co-simulation output which is used popularly in industry before.It shows that the internal details of geobodies from direct rock physics inversion are more abundant.Blind well test show that the precision of inverted porosity and clay volume is improved by comparing the pseudo logs on well point location.In the whole,reservoir parameters rock physics inversion has the benefit of describe reservoir internal properties elaborately and accurately,keeping the final resolution equivalence with the geostatistical elastic inversion solutions,but not going down straightly such as based on geostatistical co-simulation multi realization average method.Those progress has the capability to solve or in favor to evaluate'Sweet Spot'reservoir connectivity and heterogeneity such tough geology problem.