Co-evolution characteristics of organic matter and reservoir in continental shale: a case study of Shahezi Formation in Changling Faulted Depression, Songliao Basin
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摘要: 松辽盆地松南断陷群陆相页岩气具有较大的勘探潜力,但对于该区Ⅲ型干酪根富有机质泥页岩的有机地球化学和孔隙特征及演化规律尚不清楚。通过对长岭断陷下白垩统沙河子组Ⅲ型干酪根富有机质泥页岩样品开展生排烃热演化模拟实验和系列储层特征测试分析,发现该泥页岩存在2个关键的热演化节点,等效镜质体反射率(等效Ro)分别是1.5%和2.0%。等效Ro从0.7%至1.5%阶段,为快速生排油阶段,孔隙形态主要为墨水瓶状孔和部分板状孔,有机质逐渐发育少量孔洞,矿物溶蚀孔出现;等效Ro从1.5%至2.0%阶段,为快速生气阶段,有机质分解使得有机孔和矿物间孔洞大量发育,孔径逐渐增大,孔隙主要为板状孔或楔形孔和少部分墨水瓶状孔;等效Ro大于2.0%阶段,孔隙几乎只发育板状孔或楔形孔,孔径进一步增大。Ro大于1.5%为松南断陷群页岩气富集的有利源储耦合阶段。Abstract: In the Songnan Faulted Depression Group of the Songliao Basin, continental shale gas has huge exploration potential. However, evolution regularities of both organic geochemistry and pore characteristics in organic shale containing type Ⅲ kerogen in this area are not made clear. According to thermal evolution simulation experiments on hydrocarbon generation and expulsion and the tests and analysis on a series of reservoir characteristics in organic shale samples containing type Ⅲ kerogen from the Lower Cretaceous Shahezi Formation, Changling Faulted Depression, it was found that there were two key nodes of thermal evolution in the shale, namely, equivalent vitrinite reflectance (Ro) of 1.5% and 2.0%, respectively. In the stage of equivalent Ro from 0.7% to 1.5%, it was the stage of fast oil generation and expulsion, in which pore shapes were mainly ink bottle and partially plate, few pores and caverns were developed gradually in organic matters, and mineral dissolution pores occurred. In the stage of equivalent Ro from 1.5% to 2.0%, it was the stage of rapid gas generation, in which a large amount of organic pores and inter-mineral pores were developed with gradually increasing pore size by organic matter decomposition, and the pores were mainly platy or wedge-like and a few pores were ink bottle shaped. In the stage of equivalent Ro higher than 2.0%, only platy or wedge-like pores were developed with further increasing size. The stage with Ro higher than 1.5% is favorable for co-evolution of source rocks and reservoir of shale gas accumulation in the Songnan Faulted Depression Group.
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图 5 氮气吸脱附滞后回线分类及对应孔隙形态[24]
Figure 5. Hysteresis loop classification of nitrogen adsorption and desorption, and corresponding pore shape
表 1 松辽盆地南部长岭断陷B1井烃源岩地层孔隙热压模拟实验方案
Table 1. Pore thermal-pressure simulation experiment scheme of source rocks from well B1, Changling Faulted Depression, southern Songliao Basin
序号 模拟温度/℃ 排烃温度/℃ 预期等效Ro/% 模拟埋深/m 静岩压力/MPa 正常地层压力/MPa 生烃釜压力/MPa 排烃釜压力/MPa 排烃压差/MPa 恒温时间/d 模拟实验时间/d 0 25 95 0.64 1 860 45 19 28 23 5 3 5 1 275 100 0.66 1 970 47 20 30 25 5 3 5 2 300 115 0.75 2 200 53 22 33 28 6 3 5 3 325 130 0.92 2 350 59 24 35 29 6 3 5 4 350 145 1.05 2 480 62 25 37 31 6 3 5 5 375 160 1.30 2 820 71 28 42 35 7 3 5 6 400 180 1.50 3 200 80 32 48 40 8 5 7 7 425 185 1.65 3 350 84 34 50 42 8 5 7 8 450 190 1.80 3 480 87 35 52 44 9 3 5 9 475 195 2.05 3 600 90 36 54 45 9 3 5 10 500 210 2.30 3 800 95 38 57 48 10 3 5 11 550 225 2.85 4 300 108 43 65 54 12 3 5 -
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