Multi-fractured horizontal well for improved coalbed methane production in eastern Ordos basin, China: Field observations and numerical simulations
Multi-fractured horizontal well for improved coalbed methane production in eastern Ordos basin, China: Field observations and numerical simulations
复制标题
中国鄂尔多斯盆地东部多段压裂水平井提高煤层气产量：现场观测和数值模拟
DOI：
10.1016/j.petrol.2020.107488
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发表时间：
2020-11-01
影响因子：
--
通讯作者：
Yan, Xia
中科院分区：
文献类型：
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作者：
Zhang, Jiyuan;Feng, Qihong;Yan, Xia
鄂尔多斯盆地东缘是中国煤层气工业活跃产区，具有煤层薄、渗透率低、瓦斯含量高的特点。水力压裂直井是该地区煤层气开采的主要手段，但通常存在产气量低、经济效益差等问题。针对多裂缝水平井在鄂尔多斯盆地东部提高煤层气采收率的现场试验情况，提出了利用多裂缝水平井开采致密油藏和页岩油藏的有效方法。一口经6级水力压裂改造的水平井在降压效率、产气量和最终采收率方面明显优于HFVW。MFHW的峰值气体速率是HFVW的五倍以上。对MFHW和具有代表性的HFVW进行了历史匹配，以获得关键的储集层属性，这些属性随后用于产量预测。数值模拟预测，在15年的生产周期内，MFHW的累积产气量是每台HFVW的3-15倍。模拟了研究区500个随机地质情景，分析了地质参数对MFHW相对于4个HFVW(相当于建井费用)在累积产气量方面的优势的影响。然后利用交替条件期望(ACE)回归方法建立了相关性，得到了在对数-对数坐标系中优势指标与渗透率和解吸压力之间的线性关系。这种相关性有可能被用作快速确定目标煤层中最佳完井方案的标准。回归结果还表明，在低透气性和低瓦斯含量的薄煤层中，MFHW比HFVW的优势尤为突出。最后，分析了模拟区域(SA)的大小和间距对MFHW产能的影响，表明在压裂作业预算有限的情况下，增加SA之间的间隔是一种经济上可行的选择。
Eastern margin of Ordos basin has been an active commercial coalbed methane (CBM) production area in China, where coal seams are typically characterized with thin layers, low permeability and high gas content. Hydraulically fractured vertical wells (HFVWs) are the primary means for recovery of CBM in this area, which however are usually subject to low gas production and unpromising economics. Although the multi-fractured horizontal well (MFHW) has proven as an effective solution for producing hydrocarbon resources from both tight and shale reservoirs, its applicability in efficient development of CBM reservoirs remains yet unclear.This paper presents a pilot field application of MFHW to improve CBM recovery in eastern Ordos basin. A horizontal well stimulated with 6 stages of hydraulic fractures was observed to significantly outperform HFVWs in terms of depressurization efficiency, gas production and ultimate recovery factor. Peak gas rate of the MFHW is more than five times higher than an HFVW. History matches of the MFHW and representative HFVWs were conducted to obtain key reservoir properties that are subsequently used for production predictions. Numerical simulation predicts that cumulative gas production for the MFHW is 3-15 times as that for each of the HFVWs during a production duration of 15 years. A total of 500 stochastic geological scenarios for the study area were simulated to analyze the effect of geological parameters on the superiority of an MFHW over a group of four HFVWs (which are at equivalent well construction outlays) in terms of cumulative gas production. A correlation was then developed using the alternating conditional expectation (ACE) regression method, resulting in a linear relationship between an indicator of the superiority with permeability and desorption pressure in a log-log coordinate system. This correlation can be potentially used as a criterion for fast determination of the optimal completion option in the target CBM seams. The regression results also show that the superiority of an MFHW over HFVWs is especially highlighted in thin coal seams with low permeability and low gas content. Finally, the effect of the size and spacing of stimulated area (SA) on MFHW producibility was analyzed, showing that increasing the spacing between SAs is an economically viable option when the budget for fracturing operations is limited.