Effectiveness of drainage, depressurization and gas production of coalbed methane wells based on production data: A case study of the Zhijin Block in Western Guizhou
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摘要:
煤层气井排水、降压、产气是一个递进过程,可分解为排水降压与降压解吸产气2个环节,任一环节失效均会导致产气受限。通过分析排采数据剥离上述2个环节的有效性,明确解吸产气的主要制约因素,对于促进煤层气经济有效开发具有重要意义。构建了一种基于累计产水量与井底流压、累计产气量与井底流压、以及累计产水量与累计产气量3条关系曲线的排采有效性分析方法,具有水侵识别、水源劈分、气藏参数获取与关键环节剥离等功能,将其应用于黔西织金区块煤层气井排采动态分析,取得一定成效。基于累计产水量与井底流压关系曲线,上凹型代表水侵井,下凹型代表非水侵井。面向开发需求,将含气系统概念延伸为产气系统,指具有相近水文地质条件、开发动态及生产规律的含气系统及其组合,不同产气系统合采兼容性差。织金区块含煤地层可划分为上部(1~9号煤层)与下部(10~35号煤层)2套产气系统,上部产气系统水文地质开启程度高,易发生水侵,而下部产气系统水文地质条件较为封闭,无明显水侵现象,有利于高效降压与产气。气藏属性参数计算结果显示,水侵井具有启抽压力低,弹性产水指数高的特点,非水侵井与之相反。水侵井的水侵产水量大于弹性产水量,总产水量高;非水侵井主要产出弹性水,总产水量低。产水能量驱动类型的差异决定了排水降压有效性,进而影响了气井的产能潜力。限制或避免水侵、提高排水降压有效性将是织金区块老井提产改造与新井开发设计的基本思路。研究成果可为叠置煤层气系统发育背景下的煤层气井排采动态分析与产能主控因素诊断提供方法借鉴。
Abstract:The process of drainage, depressurization, and gas production in coalbed methane wells is a progressive process that can be decomposed into two steps: the effectiveness of drainage inducing depressurization, and the effectiveness of depressurization inducing gas production. Failure in either step can lead to limited gas production. Discriminating the effectiveness of the two steps based on the analysis of production data and identifying the main constraints on gas production are of great significance for promoting the economic and efficient development of CBM. An analysis method was constructed for the effectiveness of CBM recovery based on three relationship curves: cumulative water production and bottom-hole flow pressure, cumulative gas production and bottom-hole flow pressure, and cumulative water production and cumulative gas production. It has the functions of water invasion identification, water source splitting, gas reservoir parameter acquisition, and key production step distinction. It has been applied to the dynamic analysis of CBM production in the Zhijin block in western Guizhou, and has achieved certain results. Based on the relationship curve between cumulative water production and bottom-hole flow pressure, the up-concave type represents water-invaded wells, while the down-concave type represents non-water-invaded wells. Facing the development demand, the concept of gas-bearing system is extended to gas-producing system, which refers to gas-bearing system and their combinations with similar hydrogeological conditions, development dynamics, and production rules. The compatibility of different gas-producing systems is poor. The coal-bearing strata in the Zhijin block can be divided into two gas-producing systems: the upper system (Coal Seams 1-9) and the lower system (Coal Seams 10-35). The upper system has a high degree of hydrogeological opening and is prone to water intrusion, while the lower system has relatively closed hydrogeological conditions and no significant water intrusion, which is conducive to efficient pressure reduction and gas production. The calculation results of gas reservoir parameters show that water-invaded wells have characteristics of low start pumping pressure and high elastic water production index, while non-water-invaded wells have the opposite characteristics. The water-invaded wells are characterized by producing more intrusion water than elastic water, resulting in a high total water production. The non-water-invaded wells mainly produce elastic water with low total water production. The difference in the type of energy driving the water production determines the effectiveness of drainage and depressurization, which in turn determines the productivity potential of the gas well. Limiting or avoiding water intrusion and improving the effectiveness of drainage inducing depressurization will be the main ideas for the production increase of old wells and the design of new wells in the Zhijin Block. The research results can provide methodological references for the dynamic analysis of CBM production and the diagnosis of main factors controlling productivity in the context of the development of superimposed CBM systems.
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表 1 煤层气井数据信息
Table 1 CBM well data information
井号 产层组合(煤层编号) 产层埋深/
m最大跨度/
m产层厚度/
m平均日产水量 /
(m3·d−1)平均日产气量 /
(m3·d−1)峰值日产气量 /
(m3·d−1)Z−1 9、10、炭质泥岩段、23、24 214~376 162 14.1 3.81 305 428 Z−2−1 20、23 407~432 25 3.2 0.56 1650 2772 Z−2−2 6−1、7、8、10、12、14、17 240~389 149 6.8 3.51 387 770 Z−3 14、16 697~737 40 4.7 0.80 817 1137 Z−4 6、7、17、20、23、27、30 283~531 248 11.7 1.98 798 2465 Z−5 16、17、20、23、27 355~426 71 7.6 0.85 1433 2806 Z−S1 8、9、10、14、15、16、17、19、
20、21、22、23、26、27270~453 183 18.4 23.08 5 68 注:Z−2−1代表Z−2井第1生产阶段;Z−2−2代表Z−2井第2生产阶段,下同。 表 2 煤层气井不同排采阶段产水产气特征
Table 2 Characteristics of water and gas production in different production stages of CBM wells
井号 阶段划分 峰值日产气量/ (m3·d−1) 平均日产气量/(m3·d−1) 峰值日产水量/(m3·d−1) 平均日产水量/(m3·d−1) Z−1 见气前 0 0 5.60 2.83 初期产气 427.51 305.88 5.88 4.62 稳定产气 424.43 304.69 4.01 3.44 Z−2−1 见气前 0 0 4.08 1.86 初期产气 2771.84 1974.02 2.80 0.66 稳定产气 2658.10 1548.40 0.07 0.06 Z−2−2 见气前 0 0 3.34 1.12 初期产气 769.92 320.54 6.11 4.18 稳定产气 765.83 422.12 4.02 3.48 Z−3 见气前 0 0 2.03 1.70 初期产气 1137.26 412.79 1.56 0.68 稳定产气 1076.36 978.71 0.32 0.14 Z−4 见气前 0 0 21.22 5.69 初期产气 2465.41 429.59 3.47 1.52 稳定产气 2434.18 2001.89 1.42 0.76 Z−5 见气前 0 0 7.01 1.43 初期产气 2805.94 1356.00 1.90 0.78 稳定产气 2798.43 1696.79 0.16 0.13 表 3 气藏属性参数提取与产水量劈分结果
Table 3 Results of gas reservoir property parameters extraction and water production sources identification
气井 气藏参数 产水量劈分 启抽压力/MPa 弹性产水指数/(m3·MPa−1) 井控动态储量/106m3 弹性量/m3 水侵量/m3 总量/m3 Z−1 2.65 238 0.19 500 1570 2070 Z−2−1 4.47 52 0.84 147 0 147 Z−2−2 2.87 233 0.70 709 1216 1925 Z−3 7.22 36 0.44 203 0 203 Z−4 5.73 233 1.06 659 38 697 Z−5 4.13 89 0.57 265 0 265 Z−S1 2.95 1000 — — — 5978 -
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