Numerical Well Test Interpretation of Massive Multistage Fractured Horizontal Wells in Tight Oil Reservoirs and Effect of Permeability of Exterior Region on Well Test Curves
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摘要: 多段压裂水平井试井解释能对压裂规模、主裂缝半长等参数进行有效评价，为产能评价等提供基础参数.然而当前缺少针对实际井例数据进行的深入分析.基于PEBI（perpendicular bisector）网格对油水两相渗流方程进行数值求解，利用无限导流的主裂缝与分支缝导致的区域渗透率扩大来描述SRV（stimulated reservoir volume），建立了致密油大规模多段压裂水平井瞬态压力分析方法.基于大庆油田的实测数据进行解释并进行渗透率敏感性分析，研究了复合区域下的参数调整方法.研究表明，当外区渗透率变小时，早期的压力导数变小，后期的压力导数变大，而不是所有的压力导数值都变大.压力导数由小到大的转折点时间与渗透率大小相关.因而，当前期的压力导数曲线拟合效果好、后期的压力导数拟合效果差时，不能仅通过调整外区的渗透率来拟合，还应调整其他参数.另外，大庆致密油藏多段压裂水平井实测曲线中的启动压力梯度特征不明显.相关研究结果对致密油大规模多段压裂水平井实测数据解释具有重要的指导意义.Abstract: Numerical well test interpretation of massive multistage fractured horizontal wells can be used for the fracturing effect evaluation, which is very important for productivity evaluation. However, few field case studies have been conducted. Numerical solution of oil-water two-phase flow based on PEBI grid and description of stimulated reservoir volume (SRV) by main fractures with infinite conductivity and improved permeability of the region with minor fractures are used in combination to interpret the transient pressure of massive multistage fractured horizontal wells in tight oil reservoirs in Daqing oilfield. The interpretation and sensitivity analysis of permeability of exterior region show that the value of pressure derivative becomes smaller at early time and becomes larger at late time when the permeability of exterior region decreases, compared with pressure derivative without permeability modification, which indicates a turning point on the curves of pressure derivative. Prior to the turning point, the pressure derivative with smaller permeability in exterior region is relatively smaller, while after the point, the pressure derivative is larger. The time of appearance of the turning point is related to the magnitude of permeability between those of exterior and interior regions. Therefore, when good fitting of pressure derivative curves achieves at early time and bad fitting of pressure derivative curves at late time, adjustment of permeability of exterior region cannot wholly improve the fitting effect, and other parameters need to be adjusted to improve the fitting. This study can facilitate future transient pressure analysis for massive multistage fractured horizontal wells in tight oil reservoirs.
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图 1 等效主裂及渗透率提高的区域示意
Fig. 1. Schematic of equivalent main fracture and permeability improved region
图 4 所解释的油藏示意
a.油藏面积约为4 640 m×3 900 m；b.油藏厚度为1.7 m
Fig. 4. The sketch of the interpreted reservoir
图 6 不同K1与K2组合下的瞬态压力响应特征
a.全局图；b.压力导数曲线局部放大
Fig. 6. Characteristics of pressure transient response under different combination of K1 and K2
图 7 外区渗透率K2=4.8 mD与K2=0.8 mD的瞬态压力曲线对比
a.全局图；b.对方形框的局部放大
Fig. 7. Comparison of pressure transient curves between permeability of exterior region K2=4.8 mD and K2=0.8 mD
图 8 外区渗透率K2=0.8 mD与K2=0.1 mD的瞬态压力曲线对比
a.全局图；b.对方形框的局部放大
Fig. 8. Comparison of pressure transient curves between permeability of exterior region K2=4.8 mD and K2=0.1 mD
图 9 外区渗透率K2=0.01 mD与K2=0.1 mD的瞬态压力曲线对比
a.外区渗透率K2对瞬态压力响应的影响；b.局部放大
Fig. 9. Comparison of pressure transient curves between permeability of exterior region K2=0.01 mD and K2=0.1 mD
图 10 可通过调整外区渗透率来拟合的情形
Fig. 10. Enable to fit by adjusting permeability of exterior region
表 1 所解释油藏的相关参数
Table 1. The related parameters
名称 数值 气藏大小(m×m) 4 640×3 900 初始压力(MPa) 13.15 初始水饱和度 0.633 气藏厚度(m) 1.7 岩石压缩性(1/MPa) 0.000 58 油相粘度(mPa·s) 0.6 油相体积系数 1 油相粘度(mPa·s) 1.45 油相体积系数 1.23 孔隙度 0.139 SRV面积(m2) 115 716 水平井表皮因子 0 水平井井储(m3/MPa) 25 
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表 2 每种情形的裂缝半长
Table 2. Fracture half-length of each case
算例 裂缝周围区域的渗透率
K1(mD)其他区域的渗透率
K2(mD)解释的结果 4.8 0.8 敏感性分析算例1 4.8 0.1 敏感性分析算例2 4.8 0.01 敏感性分析算例3 4.8 4.8
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