不同规模辫状河三角洲前缘砂岩储层特征及差异研究——以惠州凹陷HZ25与XJ30转换带文昌组为例

Study of characteristics and differences of sandstone reservoirs in the front of braided river delta of different scales: An example from Wenchang Formation of HZ25 and XJ30 transfer zones in Huizhou sag

古近系文昌组已成为惠州凹陷近期勘探的重点层系,但储层差异性大、优质储层成因机理不清等问题严重限制了勘探工作。本文以惠州凹陷HZ25与XJ30转换带文昌组为例,充分利用各种岩矿测试手段对储层差异性进行分析。结果发现,HZ25转换带发育近源、小规模辫状河三角洲,储层表现为“高长石、高杂基、粒度粗、分选差”的特征,初始孔隙度仅为30.91%,其相对缓慢和较浅的埋藏特征导致压实减孔量较低,现今孔隙度为12.97%;XJ30转换带发育长源、大规模辫状河三角洲,储层表现为“低长石、低杂基、粒度细、分选好”的特征,初始孔隙度高达35.54%,而相对快速和较深的埋藏特征使得压实作用对孔隙破坏极其严重,现今孔隙度仅为10.41%。分析表明,搬运距离与埋藏过程决定了两个转换带的储层特征差异。该结论为惠州凹陷乃至珠江口盆地类似地区深层储层预测提供了理论支撑。

Paleogene Wenchang Formation has become the key hydrocarbon target of Huizhou sag in recent exploration. However, such problems as large reservoir diversity and unclear formation mechanism of high-quality reservoir seriously restrict the exploration work. Taking Wenchang Formation of HZ25 and XJ30 transfer zones in Huizhou sag as an example, this paper analyzes the reservoir difference according to various of mineral analytical techniques. The results show that in the HZ25 transfer zone, proximal and small-scale braided river delta is developed, which is characterized by “high content of feldspar, high content of matrix, coarse-grained size and poor sorting”. The primary porosity was only 30.91%. The relatively slow and shallow burial characteristics resulted in low compactional porosity loss, with a current porosity of 12.97%. In the XJ30 transfer zone, distal and large-scale braided river delta is developed, which is characterized by “low content of feldspar, low content of matrix, fine-grained size and well sorting”. The primary porosity was as high as 35.54%. Due to the relatively fast and deep burial characteristics, the porosity was severely damaged by compaction, and the current porosity is only 10.41%. The analysis shows that the transport distance and burial process determine the difference of reservoir characteristics between the two transfer zones. This conclusion provides theoretical foundation for deep reservoir prediction in Huizhou sag and similar areas in Pearl River estuary basin.