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白家海凸起深部煤储层可压性评价及压裂优化以彩煤−2−004H井为例

Evaluation and fracture optimization scheme of deep coal reservoirs in Baijiahai bulge: An example of CaiMei−2−004H Well

  • 摘要: 准噶尔盆地东缘白家海凸起彩探1H井目的层为侏罗系西山窑组煤,其产量破万昭示着该地区深部煤层气存在着巨量产气潜力。以新疆油田2023年最新施工的深部煤层气评价井彩煤−2−004H井为例,在分析白家海凸起侏罗系西山窑组煤层展布特征、深部三场特征的基础上,对该井煤储层力学性质、脆性指数、裂缝发育等特征进行了深入分析,在此基础上构建了可压性评价模型,对该地区西山窑组煤储层进行可压性评价,进一步结合Mayer数值模拟,给出了压裂优化建议。结果表明:通过地质与三场特征分析发现,研究区侏罗系西山窑组煤层埋深超过1 500 m,煤层在凸起中下部稳定分布;地温梯度分布在2.6~3.6 ℃/hm,平均3.1 ℃/hm,地温梯度分布比较平缓,等值线呈东西向展布,目标层位储层压力系数接近1或小于1,为正常—异常低地层压力,现代地应力主要为正断层型力学机制类型;通过三轴力学实验测试发现,深部高温高压与常温常压条件相比,煤储层泊松比减小,峰值强度增大,脆性指数增强。根据研究区特有储层物性构建了耦合脆性指数、天然裂缝发育程度、水平主应力差和抗压强度的可压性评价模型,提出了可压性分级评价标准。计算结果显示:上层煤可压指数16.15,模拟原始储层条件下可压性提高,可压指数为28.04;下层煤可压指数最高为28.07。下层煤可压性高于上层煤,并且下层煤含气量也高于上层煤,为优先开发段,且深部高温高压环境使目的层煤可压指数升高,更有利于压裂改造。基于Meyer数值模拟软件模拟压裂改造效果,结合经济评价优化排量、压裂液及支撑剂用量,结果确定排量在15 m3/min,压裂液用量11.5 m3/m,支撑剂用量在3 m3/m可以获得最优改造效果。研究结果对于认识深部煤储层可压性和优选压裂层段具有重要意义。

     

    Abstract: The target layer of Caitian 1H well in Baijiahai Bulge, the eastern margin of Junggar Basin, is Jurassic Xishanyao Formation coal, and its production rate exceeded 10 000, indicating that there is a huge potential for deep coalbed methane (CBM) gas production in this area. Taking Caimei−2−004H well, the latest deep CBM evaluation well constructed by Xinjiang Oilfield in 2023, as an example, on the basis of analyzing the spreading characteristics of the Jurassic Xishanyao Formation coal beds in the Baijiahai Bulge and the three field characteristics of the deep part of the well, we conducted an in-depth analysis of the mechanical properties of the coal reservoir in the well, such as brittleness index and fracture development, and constructed a fracturability evaluation model on the basis of which we made a study of fracturability evaluation of the Xishanyao Formation coal reservoirs in this area. Fracturability evaluation is studied, and further combined with Meyer numerical simulation, fracture optimization suggestions are given. The results show that: Through the geological and three-field characterization, it is found that the depth of the Jurassic Xishanyao Formation coal seam in the study area is more than 1 500 m, and the coal seam is stably distributed in the middle and lower part of the bulge; the distribution of the ground temperature gradient is in the range of 2.6−3.6 ℃/hm, with an average of 3.1 ℃/hm, and the distribution of the gradient is relatively flat, and the contour lines are spreading in an east-west direction; the pressure coefficient of the target reservoir is close to or less than 1, and it is a normal-anomalous low formation pressure, and the modern ground stress is mainly positive and low. The pressure coefficient of the reservoir in the target layer is close to 1 or less than 1, which is normal-anomalous low stratigraphic pressure, and the modern geostress is mainly of positive fault-type mechanical mechanism type; the triaxial mechanical experimental tests revealed that the Poisson's ratio of the coal reservoir decreases, the peak strength increases, and the brittleness index enhances when the deep high temperature and high pressure is compared with the normal temperature and normal pressure conditions. A fracturability evaluation model coupled with the brittleness index, the degree of natural fracture development, the horizontal principal stress difference and the fracturability strength was constructed, and the fracturability grading evaluation standard was proposed. Calculation results show that the fracturability index of the upper coal is 16.15, and the fracturability index is 28.04 under the simulated original reservoir conditions; the fracturability index of the lower coal is 28.07, which is higher than that of the upper coal, and the gas content of the lower coal is higher than that of the upper coal, so it is a preferred section to be developed, and the high-temperature and high-pressure environment in the deeper part of the reservoir makes the fracturability index of the coal of the target layer increase, which is more conducive to the fracturing and reforming. Based on the Meyer numerical simulation software to simulate the fracturing modification effect and optimize the displacement, fracturing fluid and proppant dosage in combination with the economic evaluation, it was determined that the optimal modification effect can be obtained with a displacement of 15 m3/min, a fracturing fluid dosage of 11.5 m3/m, and a proppant dosage of 3 m3/m. The results are of great significance for recognizing the fracturability of deep coal reservoirs and selecting the optimal fracturing section.

     

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