四川盆地东北部飞仙关组台缘早期鲕滩带的发现及宣探1井天然气勘探突破意义

Discovery of early platform-margin oolitic shoal zone of Feixianguan Formation in the northeastern Sichuan Basin and natural gas exploration breakthrough in Well Xuantan 1

四川盆地东北部(以下简称川东北地区)下三叠统飞仙关组是四川盆地高含硫天然气勘探开发的重要层系之一,已在飞一段上部—飞二段取得了重要的勘探开发系列成果。为了进一步扩大该地区的天然气勘探开发局面,寻找新的有利勘探区带及油气富集区,通过对该区地震资料“双高”处理解释,结合490余口老井复查,开展了飞一段台缘早期鲕滩发育特征研究,预测了台缘早期鲕滩的分布规律,并结合宣探1井的钻探成果,分析了台缘早期鲕滩储层发育特征及高含硫天然气勘探潜力。研究结果表明:①研究区飞仙关组划分5个四级层序,台缘早期鲕滩发育于SSQ1—SSQ2层序,分布于渡口河—七里北地区,岩性主要为亮晶鲕粒石灰岩和残余鲕粒白云岩,具有礁滩叠置和鲕滩向台内不断迁移的特征;②台缘早期鲕滩储层分布于老君庙地区以东、渡口河地区以及渡口河—七里北之间的向斜区,储层平均厚度超过100 m;③宣探1井飞仙关组台缘早期鲕滩储层类型以Ⅱ和Ⅲ类为主,局部见Ⅰ类储层,总体为含气层和气层,为岩性气藏,试油效果良好。结论认为,宣探1井成功钻遇礁滩储层,证实飞仙关组发育台缘早期鲕滩带,这对于重新认识开江—梁平海槽两侧台缘礁滩勘探领域具有重大战略意义,开辟了川东北地区天然气勘探新领域,且预示该区仍具有非常好的天然气勘探潜力,同时也为克拉通边缘或内部海槽(台洼)两侧类似地区礁滩油气勘探开发提供了思路。

The Lower Triassic Feixianguan Formation in the northeastern Sichuan Basin is one of the importation layers of high-sulfur natural gas exploration and development in the Sichuan Basin,and a series of significant exploration and development achievements have been made from the upper part of the first Member of Feixianguan Formation(Fei 1 Member)to the second Member of Feixianguan Formation(Fei 2 Member).In order to further expand the fields of natural gas exploration and development in this area and search for new favorable exploration zones and gas-rich zones,this paper performs"double-high"processing and interpretation on the seismic data of Puguang,Laojun,and Qilibei gas fields.Then,by reviewing more than 490 old wells,the development characteristics of the early platform-margin oolitic shoal of Fei 1 Member are studied,and its distribution laws are predicted.And combined with the drilling data of Well Xuantan 1,the development characteristics and high-sulfur natural gas exploration potential of the early platform-margin oolitic shoal reservoir are analyzed.And the following research results are obtained.First,the Feixianguan Formation in the study area is divided into five fourth-order sequences.The early platform-margin oolitic shoal is developed in the SSQ1-SSQ2 sequence and is distributed in Dukouhe-Qilibei area.It is lithologically dominated by sparry oolitic limestone and residual oolitic dolomite,and characterized by reef shoal superposition and continuous migration of oolitic shoal into the platform.Second,the early platform-margin oolitic shoal reservoirs are distributed in the east of the Laojun area,the Dukouhe area,and the syncline between Dukouhe and Qilibei,and their average thickness exceeds 100 m.Third,the early platform-margin oolitic shoal reservoirs of Feixianguan Formation in Well Xuantan 1 are mainly types II and III,and locally type I.They are generally gas-bearing layers and gas layers,which are lithological gas reservoirs,exhibiting good production testing performance.In conclusion,the successful discovery of reef shoal reservoirs in Well Xuantan 1 confirms the development of the early platform-margin oolitic shoal zone in the Feixianguan Formation,which is of great strategic significance to recognizing the platform-margin reef shoal exploration along both sides of the Kaijiang-Liangping Trough,and opens up a new field of natural gas exploration in the northeastern Sichuan Basin,indicating a huge potential in natural gas exploration in this area.Furthermore,it provides an idea for the exploration and development of reef shoal reservoirs in the similar areas along the cratonic margin or both sides of the inner trough(platform depression).