鄂尔多斯盆地中东部盐下储层预测关键技术

Key techniques for subsalt reservoir prediction in the central and east parts of Ordos Basin

鄂尔多斯盆地中东部奥陶系膏盐岩下发育白云岩储层,由于储层薄,非均质性强,与围岩阻抗差异小,致使利用地震方法预测储层难度较大。为此,结合前人的研究成果,在奥陶系碳酸盐岩内幕高精度成像资料的基础上,形成了模型正演、岩石物理建模、基于敏感参数的叠前弹性参数反演、含气性检测等针对性储层预测关键技术,在储层预测和井位部署中获得了较好的效果,获得以下认识:①盐下有利储层的地震反射特征为弱复波反射;②选取Brie指数等于2时的Brie方程计算研究区混合流体的体积模量,能较好地表征盐下储层弹性参数与含气性的关系,可用于岩石物理建模和横波预测;③气层的泊松比小于0.27,它与纵波阻抗交会可以较好地圈定有效储层,流体活动性属性的高频"小负异常"指示含气储层。

Dolomite gas reservoirs were well developedunder gypsum and salt rocks in the Ordovician Majiagou Formation,the central andeast of Ordos Basin,However,it is very difficult to predict this kind of gas reservoirs because they are characterized by thin beds,strong heterogeneity,laterally rapid change,andlittle impedance difference with surrounding rocks.Therefore,based on high-precision internal imaging in the Ordovician carbonate rocks, a series of key techniques are used to predict dolomite gas reservoirs,such as seismic forward modeling,rock physical modeling,and prestack inversion of sensitive elastic parameters.Good results have been achieved in the reservoir prediction and the well deployment.The following understandings are obtained:①Favorable subsalt reservoirs show weak complex wave;②Brie equation(e=2)can be used to calculate the bulk modulus of mixed fluids, and can also be used for rock physical modeling and shear wave prediction because it characterizes the relationship between elastic parameters and the gas-bearing property of subsalt reservoirs;③If the Poisson ratio of gas-bearing beds is less than 0.27, gas reservoirs can be delineated by crossplots of the Poisson ratio with p-wave impedance,and "small negative anomaly"of high frequency of fluid mobility indicates gas-bearing reservoirs.