Evolution Mechanism of Differential Diagenesis Combination and Its Effect on the Reservoir Quality in the Tight Sandstone: A Case from the Lower Shihezi Formation in the Hangjinqi Area of Ordos Basin, China

Abstract

The physical property heterogeneity of tight sandstones was mainly caused by complex alteration of various diagenesis combinations during burial process. However, diagenetic evolution of different diagenesis combinations which generally result in the strong difference and heterogeneity of physical property and pore structure is rarely well understood. The Middle Permian lower Shihezi Formation is one of the most important tight gas sandstone reservoirs in the Hangjinqi area of Ordos Basin, China. The reservoir heterogeneity of lower Shihezi Formation, which was caused by the differential diagenesis combination, is crucial to efficient exploration and development. Evolution mechanism of differential diagenesis combination and its effect on the reservoir quality in the tight lower Shihezi Formation sandstone in the Hangjinqi area of Ordos Basin was investigated by means of thin-section description, cathodoluminescence (CL) imaging, X-ray diffraction (XRD), scanning electron microscopy (SEM), and homogenization temperature of fluid inclusions. The lower Shihezi Formation sandstones can be divided into four diagenesis combination types according to the reservoir characteristics and diagenetic relationship. The main diagenetic sequence was mechanical compaction-chlorite rim-early pore-filling calcite cementation-dissolution-authigenic kaolinite-quartz cementation-late calcite cementation. Differential diagenesis combination was mainly controlled by the petrological characteristics, microfacies, and fault. Low content of rock fragment and high content of detrital quartz were beneficial to the compaction resistance and cementation. The moderate content of pore-filling calcite was conducive to pore space protection and feldspar dissolution. The faults control dissolution and differential diagenesis combination by influencing the migration of acid fluids. Moderate compaction-moderate cementation-moderate dissolution type (BBB type) and weak compaction-moderate cementation-strong dissolution type (CBA type) were in favour of high-quality reservoir development.

Diagenetic–Porosity Evolution and Reservoir Evaluation in Multiprovenance Tight Sandstones: Insight from the Lower Shihezi Formation in Hangjinqi Area, Northern Ordos Basin

“…It is a typical multicycle craton basin [41][42][43] composed of six secondary structural units [44,45]: the Yimeng Uplift, Yishan Slope, Tianhuan Depression, Western Thrust Belt, Jinxi Fault-Fold Belt, and Weibei Uplift (Figure 1(b)). [11,30]); (c) generalized stratigraphy of the Permian successions in the Upper Paleozoic of the Ordos Basin, showing the stratigraphy, lithology, and facies (modified from [3,19]). 2 Lithosphere…”

“…They have developed the Upper Carboniferous Benxi Formation, Lower Permian Taiyuan and Shanxi Formations, and Middle Permian Lower and Upper Shihezi Formations, as well as Upper Permian Shiqinfeng Formation from bottom to top, covering unconformably upon early Paleozoic carbonate (Majiagou Formation) due to the lack of strata in the middle-late Paleozoic-early Carboniferous [13,19,20,31]. The exploration and development practice of the gas fields in the Ordos Basin show that tight sandstone gas reservoirs are mainly distributed in the Taiyuan, Shanxi, and Lower Shihezi Formations (Figure 1(c)), and the most favorable reservoir in Hangjinqi area is the Lower Shihezi Formation sandstone with low porosity and permeability [15,16,19,20,33,35,38,46]. The Lower Shihezi Formation, as the target layers of this study, was mainly deposited in fluvial and delta.…”

“…Previous exploration activities were mainly focused on the Sulige, Yulin, Wushenqi, Zizhou, and Daniudi gas fields within the Ordos Basin [3,9,11,12]. However, with the exploration of Dongsheng gas field in recent years, increasing attention has been paid to the Upper Paleozoic sandstone in the Hangjinqi area of northern Ordos Basin [13][14][15][16][17][18][19][20].…”

“…Despite numerous studies are available [13,[15][16][17][18][30][31][32], researches on diagenetic-porosity evolution mechanism of the Lower Shihezi Formation tight sandstone reservoirs in Hangjinqi area were mostly concentrated in the specific area (e.g., Shilijiahan zone in the south [19,20,32,33], Shiguhao and Haoraozhao zone in north [34][35][36][37], and Dongsheng gas field in the east [38]) or the comparison of different layers [36,39], and the comparative investigation on diagenetic characteristics and diagenetic-porosity evolution of sandstone reservoirs under multiprovenance systems of the whole Hangjinqi are obviously insufficient. In addition, there are also some differences in buried depth and formation temperature and pressure in different provenances of Hangjinqi [18,40].…”

“…Figure 1: Structural location of study area. (a) The location of the Ordos Basin in China; (b) the structural location of Hangjinqi area in the Ordos Basin (the basin outline modified after[11,30]); (c) generalized stratigraphy of the Permian successions in the Upper Paleozoic of the Ordos Basin, showing the stratigraphy, lithology, and facies (modified from[3,19]). …”