The Micropore Characteristics and Geological Significance of a Tuffaceous Tight Reservoir Formed by Burial Dissolution: A Case Study of the Carboniferous Tuff in the Santanghu Basin, NW China

Abstract

As a distinct type of reservoir, tuffaceous tight reservoirs have attracted much attention. However, previous studies on tuffaceous tight reservoirs formed in the burial diagenetic stage are few, particularly regarding the genesis of micropores, which restricts the in-depth exploration of tuffaceous tight oil. According to thin section observation, scanning electron microscopy (SEM) identification, X-ray diffraction (XRD) experiments, elemental analyses, porosity and permeability tests, and pore structure analyses, the micropore characteristics of the Carboniferous tuffaceous tight reservoir formed by burial dissolution in the Santanghu Basin, NW China, are studied. In addition, the cause of the tuff micropore formation and its geological significance are also researched in this paper. The results are as follows: (1) The tuffaceous tight reservoir formed by burial dissolution mainly consists of quartz, feldspar, dolomite, and clay minerals. The reservoir space mainly consists of intergranular pores between minerals, intragranular dissolution pores within feldspars, calcite, dolomite, clay minerals, and locally developed organic matter pores. (2) The formation of micropores in tuff reservoirs formed by burial dissolution is mainly related to the original composition of the tuff. (3) Tuffaceous reservoirs with good physical properties are usually formed at the bottom or top of a large set of source rock. The results of this investigation can provide innovative theoretical evidence for the accumulation mechanism of tuffaceous tight oil formed by burial dissolution. Meanwhile, it can be considered a reference regarding the distribution of and predictions for tuffaceous reservoirs formed by burial dissolution in similar situations in other parts of the world.