考虑启动压力梯度的低渗气藏水平井产能计算

低渗透气藏的开发在石油工业中占据着重要的地位，水平井因其特有的增产优势而广泛应用于开发低渗透气藏。水平井的成本投入较高，准确预测其产能可为水平井的钻井和采油工程方案设计提供科学的依据。低渗气藏水平井的产能预测大多忽略了低渗气藏的启动压力梯度效应，使预测产能与投产后的实际产能相差很大。在Joshi水平井渗流理论基础上，以上下边界封闭的低渗透气田为例，推导了考虑启动压力梯度的低渗气藏水平井的产能计算公式，引入无因次参数s表征启动压力梯度引起的产能损失程度。矿场资料验证了产能公式的计算精度，并分析了启动压力梯度对气井产能的影响趋势，结果表明随着启动压力梯度的增加，其损失的气量呈线性增加。这为水平井开发低渗透气藏提供了理论支持。

PRODUCTIVITY CALCULATION OF HORIZONTAL WELLS IN LOW PERMEABILITY GAS RESERVOIRS CONSIDERING STARTING PRESSURE GRADIENT

The development of low permeability gas reservoir plays an important role in petroleum industry. Owing to its peculiar stimulation advantage, horizontal wells have been widely used in the development of low permeability gas reservoirs. Due to the comparatively high cost input of horizontal wells, it is necessary to forecast their productivity accurately so as to provide a scientific basis for designing the drilling and production engineering projects of horizontal wells. The productivity prediction of a horizontal well in low permeability gas reservoirs mostly neglected starting pressure gradient effect, which leads to the great difference between the predicted and the actual productivity. Based on the Joshi percolation theory of horizontal wells and taking the low permeability gas reservoirs with enclosed top and bottle boundaries as an example, the formula for productivity calculation of horizontal wells in low permeability gas reservoirs considering starting pressure gradient was deduced and the dimensionless parameter s was introduced to represent the degree of production loss caused by starting pressure gradient. The field data have verified the productivity formula's accuracy and analyzed the influence trend of starting pressure gradient to gas wells' deliverability. Results showed that with the increasing of starting pressure gradient, the loss of gas amount would increase linearly, which provides a theoretical support for the development of horizontal wells in low permeability gas reservoirs.