Simulation of crude oil cracking and gas generation with semi-open condition, Baiyun Sag, Pearl River Mouth Basin
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摘要: 为深入研究珠江口盆地白云凹陷原油裂解机制及产物变化特征,选取了白云凹陷渐新统珠海组原油样品,利用高温高压模拟实验,模拟了地下压力、地下流体介质及半开放条件下、不同升温速率的原油裂解过程,分析了气产率和气体组分特征。研究表明,原油样品在365℃开始裂解,裂解产率随温度增加而增加,在20℃/h的升温速率下,最终(550℃)裂解气体产率、烃气产率和非烃气体产率分别为580.13,394.25,185.88 mg/g;而在60℃/h的升温速率下,最终(550℃)裂解气体产率、烃气产率和非烃气体产率分别为707.68,485.77,221.91 mg/g。不同升温速率下最终产率的差异和烃气的组分差异均与不同温度下原油裂解机制差异有关。从原油裂解成气模拟实验的组分特征来看,大部分原油裂解气具有较高的重烃气含量,而较高重烃含量可作为判识原油裂解气和干酪根裂解气的辅助指标。Abstract: In order to study the mechanism and product compositions of oil cracking, crude oil samples from the Zhuhai Formation of the Baiyun Sag of Pearl River Mouth Basin were carried out for the high-temperature, high-pressure pyrolysis with different heating rates with the pressure close to the conditions of underground. The underground fluid was also considered to be included with a semi-open condition for the pyrolysis, the gas yields and gas composition characteristics were then analyzed. Results showed that crude oils start to crack at 365 ℃, and the cracking yield increases with the increase of temperature. At a heating rate of 20 ℃/h, the final yields (at 550 ℃) of pyrolysis gas, hydrocarbon gas and non-hydrocarbon gas were 580.13, 394.25, and 185.88 mg/g, while at a heating rate of 60 ℃/h, these values increased to 707.68, 485.77, 221.91 mg/g, respectively. The composition of hydrocarbon gases at different heating rates also varied, and these variations were assumed to be related to the difference of cracking mechanisms of crude oils at different temperatures of pyrolysis. According to the composition characteristics of pyrolytic gas products, most of the gases from crude oil cracking has a relative higher content of high molecular weight hydrocarbon gas, thus these compounds can be used as an auxiliary index to distinguish crude oil cracked gas from kerogen cracked gas.
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表 1 原油高温高压裂解模拟实验条件
Table 1. Conditions for simulation experiments of crude oil high temperature and high pressure cracking
实验步骤 温度/℃ 流体压力/MPa 静岩压力/MPa 模拟点1 250 25 60 模拟点2 300 30 72 模拟点3 335 33 79 模拟点4 365 35 84 模拟点5 400 38 91 模拟点6 450 40 96 模拟点7 500 43 103 模拟点8 550 45 108 表 2 珠江口盆地白云凹陷LH16井原油裂解气体产率数据
Table 2. Cracked gas yields of crude oil samples from well LH16, Baiyun Sag, Pearl River Mouth Basin
升温速率/(℃·h-1) 温度/℃ 总气体产率/(mg·g-1) 烃气产率(mg·g-1) 非烃气产率/(mg·g-1) 非烃气占比/% C1 C2 C3 C1-C5 C2-C5 C3-C5 20 335 - - - - - - - - - 365 12.09 0.10 0.08 0.14 0.44 0.34 0.26 11.65 96.36 400 169.21 13.53 30.43 45.96 144.09 130.56 100.13 25.12 14.85 450 358.71 53.30 82.64 98.85 291.28 237.98 155.34 67.43 18.80 500 571.15 114.60 163.50 90.65 460.50 345.90 182.40 110.65 19.37 550 580.13 120.51 166.75 49.33 394.25 273.74 106.99 185.88 32.04 60 335 - - - - - - - - - 365 26.73 3.43 3.71 5.39 16.70 13.27 9.56 10.03 37.52 400 159.60 24.00 11.74 22.96 84.70 60.70 48.96 74.90 46.93 450 213.36 31.11 46.03 53.36 154.15 123.04 77.01 59.21 27.75 500 483.63 86.34 124.49 70.31 344.17 257.83 133.34 139.46 28.84 550 707.68 164.84 198.20 60.28 485.77 320.93 122.73 221.91 31.36 -
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