准噶尔盆地砂质碎屑流砂体新发现及其油气勘探意义

New discovery of sandy debris flow sandbody and its implications for oil and gas exploration in the Junggar Basin

为了弄清准噶尔盆地凹陷区是否发育有效砂体、岩性圈闭是否落实,基于岩心观察、重矿物分析、储层表征和地震反射特征分析等方法,分析了该盆地盆1井西凹陷下侏罗统三工河组二段(以下简称三二段)古地貌、沉积微相、储层性质和含油气性,评价了砂质碎屑流砂体的岩性圈闭条件,明确了准噶尔盆地三工河组下一步天然气勘探的方向。研究结果表明:①盆1井西凹陷周缘三二段发育坡折带,坡折带之上三角洲前缘砂体发育,在燕山期构造活动的触发下,滑塌至坡折带之下的半深湖形成砂质碎屑流砂体;②砂质碎屑流砂体厚度大,垂向上具有“泥包砂”结构,侧向与前缘相砂体之间存在泥质分隔带,封堵条件较好,岩性圈闭条件优越;③砂质碎屑流砂体储层物性好,属于中等—较好的储集层,砂质碎屑流砂体整体含油气性较好。结论认为:①准噶尔盆地三工河组发育砂质碎屑流砂体,岩性圈闭条件优越,具有重要的油气勘探意义;②基于该研究成果,通过新钻井已取得了油气勘探重大突破,证实坡折带之下砂质碎屑流砂体岩性油气藏成藏条件优越,是该区下一步最有利的天然气勘探新领域。

In order to find out whether effective sand bodies are developed and lithologic traps are ascertained in the sag areas of the Junggar Basin,this paper analyzes the paleogeomorphology,sedimentary microfacies,reservoir property and petroliferous property of the second Member of Lower Jurassic Sangonghe Formation in the western Well Pen-1 sag of the Junggar Basin by means of core observation,heavy mineral analysis,reservoir characterization and seismic reflection characteristics analysis.Then,the lithologic trap conditions of sandy debris flow sandbody are evaluated.Finally,the direction of next natural gas exploration in the Sangonghe Formation of the Junggar Basin is pointed out.And the following research results were obtained.First,in the second Member of Sangonghe Formation around the western Well Pen-1 sag develops a slope break belt,above which a delta front sandbody is developed.Under the trigger of Yanshanian tectonic activity,the semi-deep lake slumping below the slope break belt develops into a sandy debris flow sandbody.Second,the sandy debris flow sandbody is thick.It vertically has a structure of"sandstone in mudstone"and laterally is separated from the sandbody of front facies through a muddy belt.Therefore,its sealing conditions are better and lithologic trap conditions are favorable.Third,the sandy debris flow sandbody has good reservoir physical properties and is classified into the category of moderate-better reservoir.And its petroliferous property is overall better.In conclusion,a sandy debris flow sandbody is developed in the Sangonghe Formation of the Junggar Basin.It has favorable lithologic trap conditions and is of great significance to oil and gas exploration.In addition,a great breakthrough of oil and gas exploration is realized by drilling new wells,on the basis of the research results.It is confirmed that the sandy debris flow sandbody below the slope break belt has favorable conditions for the formation of lithologic oil and gas reservoirs and it is the most favorable new field of next natural gas exploration in this area.