天然气水合物储层导电特性模拟与饱和度计算

由于天然气水合物只能在低温高压环境下保持稳定，导致以原状天然气水合物岩石样品进行岩石岩电测试较为困难，用阿尔奇公式计算的饱和度误差会比较大。为了提高天然气水合物饱和度的计算精度，建立了反映天然气水合物储层结构特征的逾渗网络模型。根据Kirchhoff连续性方程和各节点、线的电导率，通过Cholesky分解算法计算网络模型中的电流参数。通过数值模拟研究了水合物饱和度、地层水矿化度和黏土矿物含量对天然气水合物储层数字岩心的影响，并根据模拟结果建立了修正的阿尔奇公式。模拟结果表明，数字岩心的电阻率随水合物饱和度的增加呈指数增长。随着地层水电导率的增大，天然气水合物数字岩心的电阻率呈线性减小。随着黏土矿物含量增加，岩心电阻率呈负指数下降趋势，当孔隙度、黏土矿物含量较低时，天然气水合物饱和度对数字岩心电阻率的影响较大。利用修正前后的Archie公式，对南海神狐地区W18井的测井资料进行了水合物饱和度估算。修正前的计算结果相对误差为33.2%，修正后为22.5%，说明修正后的饱和度公式精度有明显提高。

Simulation of conductivity characteristics of gas hydrate reservoirs and its saturation calculation

Because natural gas hydrate can only keep stable in low temperature and high pressure environment， it is difficult to conduct rock electrical test with undisturbed natural gas hydrate rock samples， and the saturation error calculated by Archie formula is relatively large. In order to improve the calculation accuracy of gas hydrate saturation， a percolation network model reflecting the structural characteristics of gas hydrate reservoir is established. According to the Kirchhoff continuity equation and the conductivity of each node and line， the current parameters in the network model are calculated by Cholesky decomposition algorithm. The effects of hydrate saturation， formation water salinity and clay mineral content on the digital core of gas hydrate reservoir are studied by numerical simulation， and the modified Archie formula is established according to the simulation results. The simulation results show that the resistivity of digital core increases exponentially with the increase of hydrate saturation. With the increase of formation water conductivity， the resistivity of gas hydrate digital core decreases linearly. With the increase of clay mineral content， the core resistivity shows a negative downward trend. When the porosity and clay mineral content are low， the gas hydrate saturation has a greater impact on the digital core resistivity. Using the modified Archie formula， the hydrate saturation of Well W18 in Shenhu area of South China Sea is estimated. The relative error is 33.2% before the correction and 22.5% after the correction， which shows that the accuracy of the modified saturation formula has been significantly improved.