小尺度断层定量预测及对注水开发的影响——以渤中34油田为例

大尺度断层往往控制了沉积盆地的形成和油气成藏,而小尺度断层则影响着注水开发效果和剩余油分布.大尺度断层可以通过二维或三维地震资料识别,而小尺度断层的识别则特别困难.本文提出了一种基于断层分形生长模式和三维地质力学模拟相结合来确定小尺度断层的数量、发育位置和方位的方法,并根据油田开发动态资料来确定小尺度断层对注水开发和剩余油分布的影响.将地震上识别的大尺度断层引入到三维数值力学模型中,模拟大尺度断层形成时期断裂带附近的应力扰动作用,然后结合破裂准则来建立最易发生破裂的方位和最大库伦剪切应力网格,以这两套网格和断层尺度的幂律分布确定的小尺度断层数量为约束条件来确定随机模型,对小尺度断层的密度、产状和发育位置进行定量预测.研究表明:利用分形理论和三维地质力学模拟可以对大尺度断层伴生小尺度断层进行有效预测;小尺度断层对注水开发效果和剩余油分布的影响取决于小尺度断层的规模(断距)以及小尺度断层方位和注采方向的关系.

Quantitative prediction of small-scale faults and its effect on water flood development: A case study of Bozhong 34 oilfield

Small-scale fault is the key factor in controlling the formation of effective reservoir, hydrocarbon accumulation and water flood development. A method based on fractal geometry and 3D geomechanical modeling is described here to constrain the positions and orientations of small-scale faults. And then, according to the dynamic data of oilfield development, the effects of small-scale faults on water flood development and remaining oil distribution. The large, seismically resolvable faults are brought into a three-dimensional（3D）numerical mechanical model to determine the stress conditions near these faults at the time of faulting. The stress field is then combined with a Coulomb failure criterion to predict the orientations and densities of the fractures. This information is represented on a pair of grids（i.e., a density and strike grid）. The grids are then used to condition stochastic models of faulting, which use a power-law distribution and/or stochastic growth processes to simulate small-scale faults. Research shows that the small-scale faults associated with large-scale faults can be predicted effectively using fractal geometry and 3D geomechanical modeling; the effects of small-scale fault on water flood development and remaining oil distribution depend on the throw of small-scale fault and the relationship between orientation of small-scale fault and injection-production direction.