深部煤系气合采压裂裂缝扩展规律及其主控因素

Fracture propagation law and main controlling factors of fracturing in deep coal measure gas mining

  • 摘要: 【目的】 煤系气合采是提高我国非常规天然气单井产量的重要开发方式。然而,煤系气储层物质组成截然不同、物理性质差异巨大,导致煤系气合采储层在压裂过程中裂缝在不同储层内的扩展方式和发育程度存在不确定性。如何协调好多储层改造实现多气共采对于降低煤系气开发成本、提高产能至关重要。【方法】 以鄂尔多斯盆地东北缘临兴区块为例,剖析影响煤系气储层合层压裂效果的地质因素、工程因素,利用数值模拟方法,研究不同储层内压裂裂缝的扩展规律,并对合层压裂提出针对性建议。【结果】 结果表明,储隔层最小水平地应力差值、抗拉强度差值、泵注排量和黏度的增大有利于缝高和缝宽的扩展,其值越高,裂缝的穿层能力越强。岩层的最小水平地应力和压裂液黏度主要影响储层中裂缝宽度,具体表现为,岩层相对最小水平地应力越大或压裂液的黏度越小,裂缝宽度越小。储隔层弹性模量差值和泊松比差值的变化对整体压裂效果的影响较小,但弹性模量差值增大会减少裂缝穿层时间,使裂缝更快到达极限高度。【结论】 基于上述研究,提出了临兴地区煤系气合采储层优选方案及排采建议,即应优先选取储隔层最小水平地应力差在0~4MPa、抗拉强度差值大于4.5 MPa 的储层进行合采压裂,并以6~9 m3/min 的泵注排量进行开采,从而能实现更高效的资源开发。

     

    Abstract: Coal-measure gas co-production represents a pivotal approach to enhancing unconventional natural gas production in China. However, the material composition and physical characteristics of coal-measure gas reservoirs vary significantly, introducing uncertainty in the fracture propagation mode and degree of fracture development in different reservoirs during the fracturing process of coal-measure gas reservoirs. Effective coordination of multiple reservoir transformations for achieving multiple gas co-recovery is crucial for minimizing development costs and maximizing production capacity. This study focuses on the Linxing block, located on the northeastern margin of the Ordos Basin. It analyzes the geological and engineering factors influencing the fracturing effectiveness of Coal-measure gas reservoirs. Utilizing numerical simulation technology, the study simulates the propagation patterns of fractures in various reservoirs and proposes recommendations for multi-reservoir hydraulic fracturing in the Linxing block. The results show that the increase of the minimum horizontal in-situ stress difference, tensile strength difference, pumping displacement, and viscosity of the reservoir and barrier is conducive to the expansion of fracture height and width, and the higher the value, the greater the penetration capacity of the fracture. Specifically, the minimum horizontal in-situ stress and fracturing fluid viscosity of the rock layer primarily influence fracture width, where a larger relative minimum horizontal in-situ stress or lower fracturing fluid viscosity results in narrower fractures. Additionally, variations in the difference between the elastic modulus and Poisson's ratio of the reservoir have minimal impact on the overall fracturing effect, although an increase in the elastic modulus difference reduces the time required for fractures to penetrate through the bed, enabling faster attainment of ultimate height fracture. Based on these insights, the study proposes an optimal scheme and drainage recommendations for coal-measure gas co-production reservoirs in the Linxing area. Specifically, reservoirs with a minimum horizontal in-situ stress difference of 0~4 MPa and a tensile strength difference exceeding 4.5 MPa should be prioritized for co-production fracturing, utilizing larger pumping displacements to achieve more efficient resource development.

     

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