启动压力梯度确定井距和判断油井压裂的新方法

A New Method of Determining Well Spacing and Fracture by Using Starting Pressure Gradient

低渗透油藏最大的特征是存在启动压力梯度,其流动为非线性渗流.在一定的井距、生产压差情况下,启动压力梯度决定油藏多大范围内原油可参与流动,这直接影响油田的采收率.根据弹性渗流理论,以油井最大产量生产时产生的压力波传到油藏内某处,其压力梯度正好等于启动压力梯度时离油井的距离作为最大泄油半径,从而建立了计算最大井距的数学模型.根据压力在压裂裂缝中的传导特征,提出了判断油井是否需要压裂和计算最小压裂缝长的方法.对2个油区6个油田的41口油井计算表明,最大井距为（4 ～449）m,约68％的油井需要压裂,最小压裂缝长为（2～73）m.结果与实际情况的一致性较好,表明该方法具有较高的可靠性和实用性.

A central feature for low-permeability reservoir is the presence of starting pressure gradient and its flow is nonlinear.Under a certain well spacing and producing pressure difference,the starting pressure gradient determines the scope of reservoir in which the crude oil can participate in the flow.Thus it directly affects the oil recovery of oilfield.Based on the theory of elastic flow in oil reservoir,a new model has been proposed to determinemaximum well spacing.In this model,the distance between some point where the pressure gradient is equal to the starting pressure gradient and the oil wellbore is used as the maximum drainage radius.According to the conduction characteristics of pressure in fracture,a method has also been proposed to estimate whether the oil well needs fracturing and to calculate the minimum fracture length.The calculation results in 41 oil wells of six oilfields show that the maximum well spacing is from 4 m to 449 m,about 65％ of these oil wells need fracturing and the minimum fracture length is from 2 m to 73 m.These results are well consistent with the real situation,indicating this new method has higher reliability and practicability.