轮古奥陶潜山油水界面识别方法及油气分布特征评价——以轮古LG7井区为例

Identification of oil-water interface and evaluation of oil and gas distribution in Ordovician buried hill reservoir in Lungu:A case in Lungu-well block 7

为保证油气勘探取得成效,本文以轮南奥陶系古潜山LG7井区为例,探讨油水界面的分析识别方法.轮古7井区位于轮古西部,岩溶储层主要为奥陶系中下统鹰山组泥晶、亮晶砂屑灰岩,灰岩原生孔隙较低,平均孔隙度仅为1.2％,但岩溶构造缝洞相当发育,平均孔隙度可达3.4％,且裂缝和溶蚀孔洞相互沟通,形成了以缝洞系统为主要储集空间的碳酸盐岩储集体.通过钻录井、测井、试油、试采等资料对比,并结合古岩溶地貌分析,认为控制岩溶残丘发育的岩溶沟谷底基本可以指示岩溶残丘的油水界面位置.在此基础上,结合完钻井生产情况,对油水界面之上的有利岩溶残丘油气储量进行了初步评价.结果表明油井产能与油水界面埋深关系密切,残丘厚度＞90 m的Ⅰ类区,其分布面积为13.86 km2,油气资源量为693×101 t；残丘厚度50～90 m的Ⅱ类区,面积为27.13 km2,资源量为1 085×104 t；残丘厚度＜50 m的Ⅲ类区,面积为20.21 km2,资源量为404×104t.

Ordovician buried hill reservoir in Lunnan is located in the Lunnan ancient uplift in Tarim basin and the geological reserves of petroleum there are more than 6 × 108 t.Ordovician buried hill in Lunnan experienced Caledonian and other period multiphase tectonic movement,karst buried hill reservoir is mainly dis tributed between 0-200 m under the ancient weathering crust,solution pore,large water-eroded cave and fracture are major effective reservoir space.The 7 well block is located in the west Lungu,karst reservoir are mainly composed of micritic,sparry calcarenite in the middle and lower Yingshan group of the Ordovician system.The primary porosity in the limestone,only average in 1.2 ％,is low.But karst structural seam hole is significant developed with the average porosity being 3.4 ％.Fractures and solution pores communi cate with each other forming seam hole system,which is the main reservoir space of the carbonate reservoir.Identifying the location of oil-water interface in the buried hill is directly related to the exploitation effec tiveness of oil.If the exploration well passes through the oil-water interface,large quantity of water yielding will take place; if the exploration well is far away from oil-water interface,oil and gas is likely to be missed.To find the suitable depth of exploration well,the position of oil-water interface should be fully understood at first.In order to provide scientific basis for exploration and exploitation of oil and gas,taking LG7 well block in Lungu buried hill as an example,the method to identify the position of oil-water interface is discussed in the paper.Through comparing the data of drilling,logging,testing and pre-production and analyzing the ancient karst landform,the paper conclude that the bottom of the karst valleys can indicate the oil-water interface position of the karst monadnock.Based on this,in combination with the production situation of completed wells,oil and gas reserves above the oil-water interface in karst monadnock are evaluated preliminarily.The results show that the well production capacity is closely related to the oil-water interface depth.ClassⅠarea （monadnock thickness ＞90 m） covers 13.86 km2,and oil and gas resource is 693 × 101 t; class Ⅱ area （monadnock thickness：50～90 m） covers 27.13 km2,and oil and gas resource is 1 085× 104 t; classⅢ area （monadnock thickness＜50 m） covers 20.21 km2,and oil and gas resource is 404× 104 t.