深层碎屑岩储层次生高孔带发育特征及成因——以吐哈盆地台北凹陷下侏罗统为例

对于吐哈盆地下侏罗统深层碎屑岩有利储层的分布规律认识不清，严重制约了该盆地油气的规模勘探与开发。为了厘清该盆地台北凹陷下侏罗统深层碎屑岩有利储层的分布规律，应用岩石实测物性、测井解释物性、铸体薄片、扫描电镜等资料，在分析储层基本特征、原生孔隙演化等的基础上，研究了下侏罗统深层高孔带发育特征，并探讨了高孔带成因。研究结果表明：①下侏罗统储层岩性主要为成分、结构成熟度中等的长石岩屑砂岩和岩屑砂岩，储层埋深与正常最大原生孔隙度呈现出较好的对数函数关系；②在下侏罗统储层整体低孔、低渗的背景下，发育正常演化高孔隙度储层和次生高孔隙度储层两类有利储层，上述两类储层在平面上主要分布于火焰山、葡北及鄯善弧形构造带；③次生高孔隙度储层孔隙度介于10%～15%，渗透率介于1.0～10.0 mD，储层中原生孔隙含量占60.5%～90.0%，平均含量可达81.5%；④次生高孔隙度储层在埋深4 000～4 300 m与4 450～4 550 m发育2个次生高孔带；⑤辫状河三角洲前缘水下分流河道和河口坝中高石英质碎屑含量、相对弱压实弱胶结的粗砂岩和砂砾岩为深层次生高孔带的形成提供了物质基础，有机酸溶蚀增孔是深层次生高孔带发育的成因机制。结论认为，4 000 m以深次生高孔隙度储层和正常演化高孔隙度储层是吐哈盆地台北凹陷深层油气勘探的新领域。

Development characteristics and genesis of secondary high porosity zones in deep clastic reservoirs: a case study of the Lower Jurassic in the Taibei sag of the Tuha Basin

The distribution laws of the favorable Lower Jurassic deep clastic reservoirs in the Tuha Basin are not understood clearly, which seriously restricts the large-scale oil & gas exploration and development in this basin. In order to clarify the distribution laws of the favorable Lower Jurassic deep clastic reservoirs in the Taibei sag of the Tuha Basin, this paper studies the development characteristics of the high porosity zones in the Lower Jurassic deep layer and discusses their genesis by using the data of measured petrophysical property, physical property by logging interpretation, casting thin section and scanning electron microscope, after analyzing the basic characteristics of the reservoirs and the evolution of primary pores. And the following research results were obtained. First, the lithology of the Lower Jurassic reservoir is mainly feldspathic litharenite and litharenite with moderate compositional maturity and textural maturity, and the burial depth is in a better logarithmic function relationship with the normal maximum primary porosity. Second, under the background of low-porosity and low-permeability of the Lower Jurassic reservoir, two kinds of favorable reservoirs are developed, i.e., normally evolving high porosity reservoir and secondary high porosity reservoir. In plane, these two types of reservoirs are mainly distributed in the Huoyanshan, Pubei and Shanshan arc structural belts. Third, the porosity and permeability of the secondary high porosity reservoir are in a range of 10–15% and 1.0–10.0 mD, respectively. The percentage of primary pores in the reservoirs is 60.5–90.0%, averaging 81.5%. Fourth, two secondary high porosity zones are developed at the depth of 4 000–4 300 m and 4 450–4 550 m in the secondary high porosity reservoir. Fifth, the weakly compacted and consolidated coarse sandstone and glutenite which have high quartzose clastic content and are developed in underwater distributary channels and mouth bars of braided river delta front provide the material base for the formation of deep secondary high porosity zones, and porosity increase due to the dissolution of organic acid is the genetic mechanism for the development of deep secondary high porosity zones. In conclusion, the secondary high porosity reservoir below 4 000 m and the normally evolving high porosity reservoir are the new fields of deep oil and gas exploration in the Taipei sag of the Tuha Basin.