钻井泥浆对储层损害的理论预测模型

Theoretical Models Forecasting the Formation Impairment Induced from Drilling Fluid

考虑钻开储层时粘土水化膨胀、微粒沉积与释放、微粒运移堵塞等对井壁周围储层渗透率的影响,建立了一套与钻井泥浆有关的储层损害程度数学预测模型。包括:①渗透率与孔隙度联立方程;②连续性方程;③微粒运移方程;④粘土水化膨胀速率方程;⑤侵入液微粒沉积速率方程;⑥岩石微粒释放速率方程;⑦微粒运移喉道堵塞模式。运用有限差分近似方法求解模型参数和测量可测参数,并将此过程编成计算机程序,可计算出钻开储层时钻井泥浆对储层的损害程度(损害渗透率和损害表皮因子),室内模拟试验表明,建立的模型是有效的。

A series of mathematical models predicting the degree of formation impairment related to drilling fluid are presented, in which the known dominant damage mechanisms including clay swelling, fines depositing and fines migrating to plug the throat pores have been considered. These models are: ①the simultaneous equations about permeability and porosity: ②a equation of continuity; ③a equation of fines migration: ④a equation of swelling rate for clay hydration: ⑤a equation of fines depositing rate in the borehore wail: ⑥a equation of fines releasing rate: ⑦model of plugging throat by fines migration. The degree of formation damage, the damage permeability and the damage skin factor induced from drilling fluid when a reservoir has been penetrated can be calculated, by solving the modl parameters from an implict finite diffenence solution and by measuring the measurable parameters. This process has been programmed. The simulatingtest in a laboratory demonstrates the efficiency of the models.