Diagenesis and Fluid Flow Variability of Structural Heterogeneity Units in Tight Sandstone Carrier Beds of Dibei, Eastern Kuqa Depression

H Shi,Y H Lei,X R Luo,G L Lei,L K Zhang,L Q Zhang

doi:10.1155/2017/6593913

Abstract

Tight sand gas plays an important role in the supply of natural gas production. It has significance for predicting sweet spots to recognize the characteristics and forming of heterogeneity in tight sandstone carrier beds. Heterogeneity responsible for spatial structure, such as the combination and distribution of relatively homogeneous rock layers, is basically established by deposition and eodiagenesis that collectively affect the mesogenesis. We have investigated the structural heterogeneity units by petrofacies in tight sandstone carrier beds of Dibei, eastern Kuqa Depression, according to core, logging, and micropetrology. There are four types of main petrofacies, that is, tight compacted, tight carbonate-cemented, gas-bearing, and water-bearing sandstones. The brine-rock-hydrocarbon diagenesis changes of different heterogeneity structural units have been determined according to the pore bitumen, hydrocarbon inclusions, and quantitative grain fluorescence. Ductile grains or eogenetic calcite cements destroy the reservoir quality of tight compacted or tight carbonate-cemented sandstones. Rigid grains can resist mechanical compaction and oil emplacement before gas charging can inhibit diagenesis to preserve reservoir property of other sandstones. We propose that there is an inheritance relationship between the late gas and early oil migration pathways, which implies that the sweet spots develop in the reservoirs that experienced early oil emplacement.

Highlights

Tight gas sandstone is similar to conventional sandstone gas reservoirs, but with lower permeability, generally less than 0.1 mD, and lower effective porosity, which is historically not economically producible unless the well is stimulated by a large hydraulic fracture treatment or produced by use of horizontal or multilateral wells [1]
Shale gas exploration and development have witnessed a revolutionary breakthrough in the USA recently, more than 50% of natural gas production is from tight sand reservoirs [3]
We have investigated the heterogeneity characteristics in those two types of layers and clarified the reasons for reservoir quality changes according to core, logging, mercury intrusion capillary pressure (MICP), and thin section

Summary

Introduction

Tight gas sandstone is similar to conventional sandstone gas reservoirs, but with lower permeability, generally less than 0.1 mD, and lower effective porosity, which is historically not economically producible unless the well is stimulated by a large hydraulic fracture treatment or produced by use of horizontal or multilateral wells [1]. Tight sandstones can be developed more than shale reservoirs as the rocks generally have more brittle behavior and are easier to complete for production [2]. Shale gas exploration and development have witnessed a revolutionary breakthrough in the USA recently, more than 50% of natural gas production is from tight sand reservoirs [3]. The difference and diversity from rock grain component and spatial fabric of sediments or fractures were proposed to result in reservoir heterogeneity [9, 10].

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