油气沿断层输导的压力降模型

Pressure fall model of hydrocarbon conducted by fault

断层在地下流体运移中具有重要作用,断层活动会对地下流体的压力及流体势分布产生影响。流体在相对封闭(未喷出地表)的较宽阔的断裂系统中受超压作用上侵流动时,其性质接近于流体力学中有压管流的流动情况,其动力学特征可以用柏努利方程进行描述。为获得油气沿断层运移之后的压力,依据油气运移时的能量守恒及油气沿势能降低方向运移的原则,探索性地利用柏努利方程描述油气的流动状态,建立了油气沿断层输导时的压力降方程。根据该方程,可以计算出油气沿断层纵向运移之后进入上部侧向输导层时的剩余压力,进而求得指明油气运移方向的剩余压力系数。将压力降模型应用于埕北凹陷的周边油田,发现流体向上运移后剩余压力场的空间变化与上部油气分布格局相吻合,高剩余压力系数分布带指示了油气运移方向,说明该模型具有较高的可信性。

Fault plays an important role in fluid migration,and fault activity affects the distribution of pressure and fluid potential underground. While the fluid flows up along relative close and wider rift system (not blowout to surface) under overpressure, its nature is close to pressure conduit flow in fluid mechanics,which could be described by Bernoulli equation. In order to obtain the hydrocarbon pressure after migration,based on energy equilibrium and the principle of migration along potential energy declining direction , Bernoulli equation was introduced to describe flow condition so as to establish the pressure fall equation of the oil and gas conducted by the fault. According to this equation, the surplus pressure of hydrocarbon reaching upper conduction layer after longitudinal migration can be calculated, then the surplus pres-sure modulus pointing hydrocarbon migration direction will be calculated. This model has been applied in oilfields around Chengbei Depression. Steric alternation of the surplus pressure field after the fluid migrated upward coincides well with upper hydrocarbon distribution. High surplus pressure modulus zonation directs the hydrocarbon migration direction, which confirms the practicability of this model.