塔北哈拉哈塘奥陶系碳酸盐岩岩溶储层发育特征及主要岩溶期次

Characteristics and karstification of the Ordovician carbonate reservoir,Halahatang area,northern Tarim Basin

位于塔北隆起中部的哈拉哈塘地区,具有良好的油气成藏条件,是近期塔北油气勘探的突破新区,勘探的主要目标是奥陶系碳酸盐岩岩溶储层。本文通过对区域沉积、构造演化背景的分析,利用钻井、岩芯、地震等资料,对本区岩溶型储层的沉积和成岩作用特征进行了研究,探讨了储层发育的主要岩溶阶段、岩溶模式及主控因素。结果表明哈拉哈塘地区奥陶系碳酸盐岩岩溶储层的主体在一间房组和鹰山组一段,储集空间主要为近层状分布的溶蚀孔洞/洞穴和裂缝,岩溶储层的发育主要受控于一间房组沉积末期的准同生期岩溶和志留系沉积之前的表生期(潜山+顺层)岩溶。前一期岩溶具有区域分布较均匀、规模较小的特点;后一期岩溶在前期岩溶的基础上发育,并根据古地貌的差异在平面上分为4个区:北部Ⅰ区一间房组直接暴露,发育古潜山岩溶;Ⅱ区一间房组之上覆盖了厚度不等的吐木休克组、良里塔格组和桑塔木组,岩溶主要受控于河流和断裂的下切及由北部Ⅰ区地表水补给的地下水顺层岩溶;南部的Ⅲ区和Ⅳ区发育顺层及沿断裂的岩溶和淡水与南部海水的混合水岩溶。在以上两期主要岩溶作用的影响下,哈拉哈塘一间房组和鹰山组一段地层发育近层状岩溶洞穴、孔洞、角砾孔和裂缝,形态多变,具有极强的非均质性。

Favorable conditions for hydrocarbon accumulation existed in Halahatang area of central Tabei,which recently made it a breakthrough area for hydrocarbon exploration in northern Tarim Basin.The main targets explored are karstified Ordovician carbonate reservoirs.Based on the sedimentary and tectonic evolution of this area,integrated data of drilling wells,boreholes and seismic analysis are used to determine the sedimentary and diagenetic characteristics of the reservoir sections.The main stages and the corresponding models of karstification,and the controlling factors of each model,are proposed.The results show that the major reservoir sections are the Middle Ordovician Yijianfang Formation and the first member of the Lower-Middle Ordovician Yingshan Formation.Nearly layered cave or caverns and fractures are main reserving spaces.These spaces were formed mainly by karstification after the deposition of the Yijianfang Formation and by the burial hill karstification and bedded karstification during the hypergenesis before the Silurian sedimentation.The first stage of karstification was generally developed with a relatively small scale.However,the formed vugs,caverns and fractures are the passageway of water,which is the basis of the later karstification.The second stage of karstification（pre-Silurian） was largely controlled by the palaeogeomorphology and could be separated into four regions：region-I to region-IV from north to south.The region-I in the north was characterized by the direct exposure of the Yijianfang Formation and the development of the burial hill karstification.The Yijianfang Formation was covered by the Upper Ordovician Tumxuk,Lianglitag and Sangtamu formations with different thicknesses in the region-II.And the karstification was controlled by the down-cutting rivers and fractures and the subsurface water fed through the exposed Yijianfang Formation from region-I.In the region-III and region-IV of southern Halahatang,bedded karstification,karstification along fractures and by mixed water of meteric from north and marine from south were developed.After these two major stages of karstification,nearly layered karstic caverns,vugs,breccias and fractures were formed with different shapes and strong heterogeneity in the Yijianfang Formation and the first member of the Yingshan Formation.