疏松砂岩储层压裂液滤失特性与压裂能效分析

Fracturing Fluid Filtration and Fracturing Energy Efficiency in Unconsolidated Sandstone Reservoirs

压裂充填是解决渤海油田防砂与增产问题的主导工艺技术,但高渗储层压裂滤失特性及其对压裂能效影响规律不明确,造成压裂选井选层和施工优化缺乏有效指导。通过对储层岩心压裂液滤失评价和疏松砂岩岩心三轴压裂模拟试验,并基于压裂液滤失和裂缝形态,构建了中高渗储层压裂模拟和能效评价指标与方法,实现了对不同储层条件和施工参数下起裂效率和裂缝延伸效率的有效评价。研究结果显示,相对于低渗透储层,非均质性明显的疏松砂岩储层裂缝不规则性更加明显,并且存在主裂缝分支多条细裂缝的情形。基于压裂机理和滤失特性的压裂能效的分析结果,得到了渤海油田典型工况下的推荐作业参数范围:压裂充填实施的储层渗透率低于2.0~4.0μm^(2);滤失系数控制在0.006 m/min^(0.5)以下;压裂排量不低于2.0~2.5 m^(3)/min;压裂液黏度保持在180~200 mPa·s以上。所得结论可为渤海油田中高渗储层压裂充填选井选层和施工参数优化提供理论支撑。

Fracturing and packing are the leading techniques used at Bohai Oilfield for sand control and production improvement.However,the fracturing fluid filtration in high-permeability reservoirs and its impact on fracturing energy efficiency are unknown,resulting in inadequate evidences for deciding candidate wells/formations to be fractured and also for operation optimization.Fracturing fluid filtration experiment with reservoir cores and triaxial fracturing simulation experiment with unconsolidated sandstone cores were conducted.Based on the fracturing fluid filtration and fracture morphology obtained,the fracturing simulation and energy efficiency evaluation indexes and methods were developed for medium and high-permeability reservoirs,and they were effectively used to evaluate the fracture initiation efficiency and fracture extension efficiency under different reservoir conditions at different operating parameters.The results show that,compared to low-permeability reservoirs,highly heterogeneous unconsolidated sandstone reservoirs generate more irregular fractures,including multiple slim branch fractures extending form the main fracture.Through fracturing energy efficiency analysis based on fracturing mechanism and fluid filtration characteristics,the recommended operating parameters at Bohai Oilfield under typical working conditions are obtained as follows:the permeability of reservoir to be fractured/packed should be lower than 2.0~4.0μm^(2);the filtration coefficient should be controlled below 0.006 m/min^(0.5);the fracturing displacement should not be less than 2.0~2.5 m^(3)/min;and the viscosity of fracturing fluid should be kept above 180~200 mPa·s.The conclusions can be good guidance for deciding the candidate wells/formations to be fractured/packed and optimizing the operation parameters in medium-to high-permeability reservoirs of Bohai Oilfield.