空间几何与油气饱和度的理论研究

Principle of a Generalized Space Geometry Method to Measure and Calculate Saturation of Natural Gas Hydrate

以往计算原始地层中的油气饱和度时是通过大量岩心实验或用已知大量样品回归后计算未知样品实现的。天然气水合物的性质决定了在实验室中测量含有天然气水合物时几乎不可能满足测量其阿尔奇公式中m、n、a、b的测量条件,用快速直观法也不能实现。通过引用双源距碳氧比测井原理和方法进行测井解释方法研究,用多向量在岩心样品较少且实验室条件较难满足对饱和度值求取时计算天然气水合物的饱和度的方法和途径;分别介绍了投影法和两次坐标旋转法求解饱和度。利用二维直角坐标旋转的理论对三维直角坐标进行了2次旋转,通过2次旋转将储层中含的有天然气水合物、水和岩石骨架在3种测井方法中的测井数据点构成1个三角形平面,这个三角形平面与特定的1个坐标轴垂直,可将三维求解饱和度的问题转成二维求解的问题,最终解决天然气水合物的饱和度问题。

For calculating hydrocarbon saturation of unknown core sample with both Archie formula or visualized express method, it is necessary to regress a great deal of measured data of samples to obtain empirical formula. However, this kind of measurements can almost not be fully completed in lab limited by the character of the natural gas hydrate. Enlightened by interpretation method of 2-spacing C/O ratio logging, suggested is a new method to extract the saturation of natural gas hydrate with space geometry, which avoids the difficult in measuring the saturation of natural gas hydrate with Archie formula, needs less samples, and its lab conditions are easer to be satisfied. In the method, 3 kinds of logs with obvious discrepancy in responses for natural gas hydrate, water and matrix of mud/sand deposition, such as compensated neutron, dielectric constant, acoustic slowness or compensated density, are selected as the coordinate axes to construct a 3-dimensional generalized space coordinate system; in the coordinate system, a plane triangle is constructed with 3 vertexes whose 3 coordinate components are respectively the 3 logging values at pure natural gas hydrate, water and matrix. Utilizing the triangle, the formula for calculating the natural gas saturation can be solved through the 3 logging values of unknown sample with methods of projection or twice coordinate axes rotation.