纵横波联合反演在苏里格含气性检测中的应用

苏里格气田目的层属于辫状河和曲流河沉积环境下的多种砂体组合，而且含气层速度值与泥岩的速度值有较大的重叠。因此，单纯纵波反演在该地区不能有效地剔除低速泥岩，区分致密砂岩与有效砂岩。AVO理论和实践证明，含气砂岩随饱和度的下降，纵波速度明显变化，而横波速度变化较小。纵横波联合反演可得到纵波阻抗和横波阻抗，进而可有效区分岩性。纵波阻抗和横波阻抗的比值，可消除密度项得到纵横波速度比。根据Aki Richards公式可知，在纵横波速度比为1.5左右时，可确定砂岩含气。据此，在推导纵横波联合反演公式和确定反演过程的基础上，对苏里格气田某测线进行纵横波联合反演，得到纵波阻抗、横波阻抗和纵横波速度比，从而确定了低速泥岩、致密砂岩与有效砂岩的分布范围。

APPLICATION OF P AND S WAVE INVERSION TO DETECTING GAS POTENTIAL IN THE SULIGE GAS FIELD

The target horizons of the Sulige gas field are combination of some sand bodies of braided stream and meandering stream under the sedimentary circumstances and have large overlapping of the velocity value of gas bearing zone and mudstone. So simplex P wave inversion can neither effectively eliminate low speed mudstone nor distinguish between tight sandstone and effective sandstone. AVO theory and practices have proved when gas bearing sandstone Saturation decreases, p wave velocity has apparently change and s wave velocity has little change. P and S wave joint inversion can obtain the impedance of P wave and S wave and effectively tell the differences of lithology from various rocks. The ratio of P/S wave can eliminate density item and get the VP/VS. Depending on Aki Richards formula, it proves the sandstone bears gas when the VP/VS is 1.5. Based on conducting P/S wave joint inversion formula and ascertaining the inversion process, we make the P/S wave inversion of some seismic line of Sulige gas field, obtain the P wave impedance, S wave impedance and the VP/VS and limit distribution range of low speed mudstone, tight sandstone and effective sandstone respectively.