古岩溶盆地岩溶作用模式及古地貌精细刻画——以鄂尔多斯盆地东部奥陶系风化壳为例
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摘要
鄂尔多斯盆地东部奥陶系风化壳天然气勘探的核心问题是寻找储层 ,关键技术是对古沟槽、古台地的识别。该区风化壳储层不发育有两方面的原因 :一是沉积相带不利 ;二是风化壳岩溶部位不利 ,属于岩溶洼地 ,溶蚀作用较弱 ,充填作用较强。鄂尔多斯盆地东部奥陶系风化壳古岩溶地貌为地势平坦、向东开口的半封闭岩溶盆地 ,这就为该区古风化壳岩溶的发育创造了相对于其他全封闭盆地更好的条件。将岩溶盆地划分为谷地、台地、残丘、沟槽、浅洼 5种三级地貌单元类型 ,东部发育 3个水平岩溶带 ,第三水平岩溶带距夷平面 70～ 85m。根据观察结果及地下水的渗流规律 ,提出深潜流溶蚀带—深泉排水模式 ,为岩溶盆地风化壳储集体的发育提供了另一种可能的溶蚀作用方式。岩溶盆地在中深埋藏期压释岩溶作用较强 ,有利于储集体孔渗的改善、上古生界烃类的带入、古台地边缘致密带的产生及圈闭的形成。综合利用地质、钻井、地震及测井手段精细刻画了神木—榆林地区奥陶系风化壳古地貌 ,结果表明该地区古台地规模适中、古沟槽较多 ,认为东部是较有利的勘探区带
The key problem in the natural gas exploration of Ordovician in the Ordos Basin is to look for the reservoirs.The key techniques are to identify the ancient groove and ancient mesa.There are two reasons that lead this area′s karst reservoirs seldom:one reason is the sedimentary faces which are in disadvantage;the other is the place which is palaeokarst basin,so the leather are weak but the filling and precipitation are very strong.The palaeokarst physiognomy characteristics of Ordovician in eastern Ordos Basin are flat and open to the east, which means it is a half closed karst basin.This is an advantage for the palaeokarst over other whole closed karst basin.This karst basin is divided into 5 types of palaeogeography units:mesa,remnant hillock,karren, groove and shallow depression.Three level leached zones are found, and the third zone is 70-85 m below the karst base level.According to the observed results and the seeping regulation of groundwater,a mode of deep underground current zone and drainage of deep spring is put forward.This new mode provides another kind of possible method about eclipse function for the generation of reservoirs in the karst basin.At the middle deep buried karst period,the eclipse function of compaction related released water is very strong, which improved the porosity and permeability of the reservoirs,and benefited the taking of the upper Palaeozoic hydrocarbon into the formation and the generation of the traps.By using geological, well,seismic and log data,the fine palaeophysiognomys in Shenmu to Yulin area are reconstructed.The results indicate that the sizes of the ancient mesas are moderate and the grooves are developed in this area.The area from Shenmu to Yulin is the prospective exploration area in eastern Ordos Basin.
The key problem in the natural gas exploration of Ordovician in the Ordos Basin is to look for the reservoirs.The key techniques are to identify the ancient groove and ancient mesa.There are two reasons that lead this area′s karst reservoirs seldom:one reason is the sedimentary faces which are in disadvantage;the other is the place which is palaeokarst basin,so the leather are weak but the filling and precipitation are very strong.The palaeokarst physiognomy characteristics of Ordovician in eastern Ordos Basin are flat and open to the east, which means it is a half closed karst basin.This is an advantage for the palaeokarst over other whole closed karst basin.This karst basin is divided into 5 types of palaeogeography units:mesa,remnant hillock,karren, groove and shallow depression.Three level leached zones are found, and the third zone is 70-85 m below the karst base level.According to the observed results and the seeping regulation of groundwater,a mode of deep underground current zone and drainage of deep spring is put forward.This new mode provides another kind of possible method about eclipse function for the generation of reservoirs in the karst basin.At the middle deep buried karst period,the eclipse function of compaction related released water is very strong, which improved the porosity and permeability of the reservoirs,and benefited the taking of the upper Palaeozoic hydrocarbon into the formation and the generation of the traps.By using geological, well,seismic and log data,the fine palaeophysiognomys in Shenmu to Yulin area are reconstructed.The results indicate that the sizes of the ancient mesas are moderate and the grooves are developed in this area.The area from Shenmu to Yulin is the prospective exploration area in eastern Ordos Basin.
引文
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[2] 郑聪斌,吕强.鄂尔多斯盆地长庆气田成藏条件及气藏分布规律[J].低渗透油气田,1998,3(1):1—7.
[3] 夏日元,唐建生,关碧珠,等.鄂尔多斯盆地奥陶系古岩溶地貌及天然气富集特征[J].石油与天然气地质,1999,20(2):133—136.
[4] 何自新,郑聪斌,陈安宁,等.长庆气田奥陶系古沟槽展布及其对气藏的控制[J].石油学报,2001,22(4):35—38.
[5] 覃建雄,刘岫峰,曾允孚.鄂尔多斯盆地东部下奥陶统碳酸盐岩储层含油气差异性的成因探讨[J].石油实验地质,1994,16(3):256—265.
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