三项式产能方程中启动压力梯度影响因素分析

Influencing factors of threshold pressure gradient on trinomial deliverability equation

在计算低渗透气藏的产能时,如果不考虑启动压力梯度将导致计算结果偏差较大。启动压力梯度受众多因素的影响,为了明确影响因素的主次关系并据此得到较为准确的产能计算结果,特进行三项式产能方程中启动压力梯度影响因素分析。通过正交实验,分析了地层孔隙度、渗透率、地层岩石黏土含量、地层岩石天然裂缝发育程度及气体黏度等因素对三项式产能方程中启动压力梯度的影响。结果表明:随着天然裂缝密度的增加启动压力梯度呈降低趋势;启动压力梯度随着地层黏土含量的增加呈迅速上升趋势;启动压力梯度随着地层孔隙度的增加呈递减趋势;气体黏度对启动压力梯度的影响不具有规律性;启动压力梯度随储层渗透率增加呈递减的趋势。以长岭气田下白垩统登娄库组致密砂岩气藏为例,其启动压力梯度影响因素顺序为:黏土含量、孔隙度、渗透率、天然裂缝密度、气体黏度。该结果为分析低渗透气藏启动压力提供了一种有效手段。

There will be relatively large deviation in the calculated results of production capacity of low-permeability gas reservoirs if the threshold pressure gradient is not taken into account.Threshold pressure gradient,however,is affected by many factors.In order to clarify primary and secondary relations of these influencing factors and to accordingly obtain more accurate capacity calculations,we thereby analyze the threshold pressure gradient influencing factors in trinomial capacity equation.Through orthogonal experiments,we also discuss the impact of the following factors on the threshold pressure gradient in trinomial capacity equation: the formation porosity,permeability,clay content of formation rocks,natural fracture development degree of formation rocks,and gas viscosity.The results show that the threshold pressure gradient decreases with the increasing of natural fracture intensity,the formation porosity,and the reservoir permeability respectively,but rapidly increases with the increasing clay content of formation rocks;however,there is irregular impact of gas viscosity found on it.Moreover,the threshold pressure gradient influencing factors from the strong to weak are as follows: clay content,porosity,permeability,natural fracture density and gas viscosity in the case study from the Lower Cretaceous Denglouku tight sandstone gas reservoirs in the Changling Gas Field.The results provide an effective approach to analyzing the threshold pressure of low-permeability gas reservoirs.