川东北飞仙关组鲕滩气藏气水界面预测方法

PREDICTION METHOD OF GAS-WATER INTERFACE FOR OOLITIC BEACH RESERVOIR OF FEIXIANGUAN GROUP IN NORTHEAST SICHUAN

气水界面的预测为早期评价气藏规模提供了依据。地震及实钻资料表明 ,川东开江—梁平海槽东北侧较大范围内飞仙关组鲕滩储层连片分布 ,以裂缝—孔隙型为主的鲕滩储层内 ,其气水分布应符合物理学中“连通管”原理。文章应用实钻正常超压 (压力系数 1.0～ 1.2 5 )水井资料建立的压力—海拔关系方程 ,并与已获气井的气柱方程联立求解 ,可预测在钻获一口气井情况下的气水界面 ;在钻获一口水井情况下 ,应首先判定是否属“正常超压” ,若是 ,则可用超压等于地层条件下气水柱压力梯度差乘以气藏高度的原理 ,反求气藏高度 ,再配合精度较高的地震构造解释资料 ,就可推算出气水界面的海拔。

Prediction of gas - water interface will provide the ground to evaluate the size of the gas reservoir in early stage. Seismic and drilling data show there is large distribution of oolitic beach reservoir of Feixianguan group in the northeast region of Kaijiang - Liangping ocean trench of East Sichuan. The gas and water distribution in the oolitic beach reservoir with fracture porosity should meet the principle of 'connecting pipe'. With normal overpressure (pressure coefficient 1.0-1.25) for water well drilling, the equation of pressure vs. elevation is established, which is resolved with the equation of gas column in the existing gas well to predict the gas-water interface when a gas well is drilled. If the drilled well is a water well, it should be first judged whether or not the 'normal overpressure' exists. If yes, according to the overpressure is equal to that the difference between pressure gradients of gas and water columns multiplied by the elevation of the gas reservoir, the elevation of the gas reservoir can be calculated. Then, using the seismic data of structure interpretation with high accuracy, the elevation of the gas-water interface can be derived.