致密砂岩裂缝气藏的地震预测

Seismic prediction of tight-sandstone gas reservoirs

1. 百灵计算机应用技术研究所,北京100083;2. 新星公司西南石油局,成都610081

Beijing Lark Computer Applied Technique Institute, Beijing 100083

川西侏罗系上沙溪庙组砂岩气藏极具潜力,但砂岩致密,物性差,储层非均质性很强,常常出现干井或低产井。地震预测是提高高产稳产井命中率的重要手段。我们用百灵油气预测软件系统LarkRP2.1等对一块三维地震资料进行反演,提取了纵横波视品质因素Q_p和Q_s^*,AVO分析中的截斜积PG及视泊松比差σ,纵波阻抗、速度及密度I_p、v_p、ρ,孔隙率及孔隙压力φ和ρ_p,以及波形、相关、频谱分析各特征值;进行了关联维(D)预测及模式识别(R)预测。用一套BES评价系统,根据已知井储层评价结果对各参数(包括特征值及预测值)进行评价,选出3～5个最优参数进行各种方案的复合,以尽可能排除参数的多解性;再对各种复合方案用BES进行评价,选出一个最佳复合方案;对复合图作构造、沉积环境的叠合,选出最佳复合异常,作出高产气层的解释,钻探效果较好。我们发现横波视品质因素Q_S^*对高渗高裂缝带最敏感,是预测致密砂岩气藏最有潜力的参数。

The sandstone gas reservoir in upper Shaximiao Formati on, Jurassic Syst em, western Sichuan area has a very good prospect, but dry wells or low output w ells have been drilled frequently due to tight sandstone, bad physical property, and strong reservoir isotropism. Seismic prediction is an important means to im prove the hit ratio of high and stable output wells. The authors used the Bailin g hydrocarbon prediction software Lark RP2.1 to invert for a block of 3-D seism i c data, and extract many parameters such as compressional and shear apparent qua lity factors, interception and the contrast of apparent Poison's ratio in AVO an alysis, compressional wave impedance, velocity, and density, porosity and pore p ressure, as well as feature value of waveform, correlation, and spectrum analysi s. Correlation dimension prediction and pattern recognition prediction were also performed. A BES evaluation system was used to evaluate each parameter (includi ng feature value and prediction value) based on reservoir evaluation results of known wells, and select 3～5 optimal parameters for the composition of several sc hemes so as to possibly remove the ambiguity of parameters. These composite sche mes were then evaluated by the BES system to select out an optimal composite sch eme. By correlating composite maps to do the superposition of structural and sed imentary environment and selecting the optimal composite anomaly, the interpreta tion of high-output gas reservoir were made, which results in good drilling res u lts. It is found that the apparent shear quality factor is the most sensitive to highly permeable and highly fractured zone, and is a parameter of the most pote ntial to predict gas reservoirs in tight sandstone.