大巴山前构造带经历了多期构造运动,油气的保存条件复杂。通过对川东北大巴山地区构造形态和断裂特征、地层出露情况及盖层发育特征等进行综合分析,结合已有地层水矿化度数据和油气显示情况为约束,综合分析大巴山地区油气保存条件。研究结果表明：①大巴山地区保存条件整体较差,由于北大巴山地区构造带断裂破碎作用强烈,断裂分布密集,大气水下渗作用强烈,水型以NaHCO3,Na2SO4型为主,出露地层以震旦系—志留系为主,油气藏保存条件受到严重影响,为油气保存不利区域;②但因受到不同断裂带的强烈破碎作用和抬升剥蚀作用,大巴山地区油气保存条件有明显的分带性和分段性,往盆地内方向过渡区域构造变形强度逐渐减弱,断裂数量减少,水型以MgCl2,Na2SO4型为主,出露地层以泥盆系—二叠系为主,油气保存条件整体逐渐变好;③南大巴山前陆冲断带铁溪—巫溪隐伏断裂盆地方向受到中下三叠统的膏盐岩和侏罗系泥质岩盖层的封盖作用,大气水下渗被阻挡,出露地层多为三叠系以上地层,断裂分布较少,水型以CaCl2为主,为油气保存有利区域。
The Dabashan piedmont structural belt has undergone multi-stage tectonic movements, giving rise to complex conditions for oil and gas preservation. The conditions were comprehensively analyzed based on the study of the structural morphology and fault characteristics, outcrops, and development characteristics of caprocks, with the combination of available data on formation water salinity and oil/gas show in the Dabashan area, northeastern Sichuan Basin. It is found that the overall preservation conditions of the area are poor. In the northern area, the strong faulting activity of structural belt led to densely-distributed faults, atmospheric water (dominated by water types of NaHCO3 and Na2SO4) infiltrates severely, and the outcrops are mainly Cambrian-Ordovician strata. Those seriously affect the oil and gas preservation, recording an unfavorable preservation zone. Moreover, due to the strong faulting and uplift-erosion effects of different fault zones, the preservation conditions are evidently zonal and segmented. In the basinward transition zone, the structural deformation strength gradually weakens, the number of faults reduces, water types of MgCl2and Na2SO4 are dominant, and the outcrops are mainly Devonian-Permian strata, suggesting the improving preservation conditions. In southern Dabashan piedmont thrust belt, the basinward Tiexi-Wuxi concealed fault is sealed by the Middle-Lower Triassic gypsum-salt rocks and Jurassic muddy rocks, blocking the infiltration of atmospheric water, the strata outcropped are mostly the Triassic and above, few faults are distributed, and the main water type of CaCl2 is observed, suggesting a favorable preservation area.
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