霸县凹陷西部陡坡带沙三段成岩演化及其对储层物性的影响

Diagenetic evolution and its effect on physical property of Es_3 reservoir in the western steep zone of Baxian depression

利用岩心观察、岩石薄片分析、物性资料及试油资料,结合盆地埋藏演化史,研究霸县凹陷西部陡坡带岔河集—高家堡地区沙河街组三段(沙三段)扇三角洲成岩作用特征及其对储层物性的影响。结果表明:西部陡坡带沙三段储层目前处于中成岩A期,在持续埋藏的背景下,经历碱性—酸性—碱性成岩环境的演变;成岩演化序列为压实作用/早期碳酸盐胶结—长石溶解/石英次生加大/自生高岭石胶结—灰泥杂基重结晶/晚期碳酸盐胶结/硬石膏胶结/石英弱溶解—黄铁矿胶结。不同沉积相带沉积特征不同,控制成岩演化特征的差异,决定物性演化的不同。扇三角洲平原辫状河道泥质砂岩埋藏早期压实作用较强,后期灰泥重结晶使物性急剧降低,现今主要发育干层。扇三角洲前缘水下分流河道远泥岩端储层,由于酸碱两期溶蚀作用使长石、石英和早期碳酸盐胶结物发生一定程度的溶蚀,油气充注进一步抑制晚期碳酸盐胶结作用,现今保留大量的残余原生孔隙和次生孔隙,可作为良好的油气储集层。扇三角洲前缘席状砂和水下分流河道近泥岩端砂岩早期碳酸盐胶结极为发育,在一定程度上抑制压实作用,但整体上中等的压实作用和较强的胶结作用使物性降低较快,早期碳酸盐胶结堵塞孔隙和喉道,导致酸性流体难以产生大范围的溶蚀,晚期碳酸盐、硬石膏胶结使孔隙度进一步降低,现今物性中等。

The diagenetic process and porosity evolution history of Es_3 reservoir in the western steep zone of Baxian depression are studied based on core observation,analysis of thin section,physical property/oil test data and burial history of the western steep zone of Baxian depression.The results indicate that sandstone reservoir is currently at the stage A of middle diagenesis.Under the background of continuous bury,the diagenetic environment of the western steep zone of Baxian depression underwent an evolution of alkalescence-acid-alkalescence process,and the corresponding diagenetic evolution sequence is compaction/early carbonate cementation-feldspar dissolution/quartz overgrowth/authigenic kaolinite-limemud matrix recrystallization/late carbonate cementation/anhydrite cementation/quartz dissolution-pyrite cementation.Different sedimentary characteristics of each sub/micro-facies of delta fan cause different diagenetic process,which leads to varied porosity evolution history.The shaly sand in the braided channel of fan delta plain experienced strong compaction in the early time and lime-mud matrix recrystallization in the late time caused physical property to a rapid reduction.The present physical property of the the braided channel of fan delta plain reservoir becomes extremely poor and mainly consists of dry layer.Because of alkalescence and acid dissolution,feldspar,quartz and early carbonate cement of reservoir far from mudstone layer in the underwater distributary channel of the fan delta front had been dissolved,and the hydrocarbon filling inhibited late cementation,thus reservoir far from mudstone layer in the braided channel of the middle fan remains lots of residual primary pore and secondary pore and can be effective reservoir of hydrocarbon.Though early carbonate cementation of the sheet sand and reservoir adjacent to mudstone layer in the underwater distributary channel of the fan delta front inhibited compaction in the early period,the combination of moderate compaction and cementation reduced the physical property rapidly;early carbonate cement had plugged pore and throat of the reservoir,thus the extent of acid dissolution had been limited;late carbonate and anhydrite cementation reduced porosity further,therefore the reservoir has moderate physical property at present.