油藏模拟的新方法——改进的快速自适应组合网格

改进的快速自适应组合网格方法(Flexible Fast Adaptive Composite Grid简称FFAC方法)实质上是利用了多重网格方法原理,用非正常连接法进行处理的区域分解方法.首先FFAC方法由于其网格的加密是在每个网格块内剖分产生的,应用非正常连接的技术来处理相邻网格步长不一致的问题,克服了FAC各子域之间不能相互接触的难题.从而也就可以比较容易地对各种驱替前缘用动态加密网格方式进行模拟.其次,FFAC方法则能够根据实际情况而灵活地采用迭代法和直接解法.第三,FAC各加密网格层和未加密的网格层是重叠的,这样就增加了网格总数,运行时需要更多的内存.FFAC则用嵌套的方法来处理,可以大大节约内存.第四,FFAC方法中各级网格之间边界值的转换通过在组合网格上求余量来实现而取代了FAC方法利用多重网格方法中插值、限制转移的方式,避免了插值、限制转移公式不易确定的难题,大大简化了计算过程.FFAC方法克服了FAC方法的不足之处,使得它的实用性更为广泛.这种算法也可用于并行计算.文中阐述了FFAC法的原理和方法,并提供了算例.

A METHOD OF FLEXIBLE FAST ADAPTIVE COMPOSITE GRID FOR RESERVOIR SIMULATION

As an update computation method, Fast Adaptive Composite Grid has brought to the field of reservoir numerical simulation more and more attention.In fact, the method which based on multigrid principal, is a kind of domain decomposition method.Many problems will be caused when FAC was used in reservoir simulation, this paper raised a Flexible Fast Adaptive Composite Grid to improve FAC. First, the grid refinement is based on every grid block in FFAC and abnormal linking skills are used to deal with the joined grids with different size, so FFAC can simulate any shape subdomain; in addition, it break down the barrier which every subdomain can`t touch each other.Then it can simulate the frontier of flooding with the dynamic grid refinements easily. Second, FFAC can alternatively use direct solver or relaxation solver according to the practical situation.Third,FFAC sets the refinement cells and coarse cells through the inlaying way, which can decrease the number of grids greatly and need less memory.Fourth, FFAC can set integrid value by attaining the residues of the composite grid instead of FAC way that uses interpolation and local restriction operators as multigrid techniques when dealing with such questions as interface interpolation and conservation objectives.FFAC overcomes the shortcomings of FAC and provides a flexible ides for reservoir numerical simulation technology.