The exploration potential of the Upper Paleozoic tight sandstone gas reservoirs in Linxing area

Ordos Basin is huge

but the accumulation patterns and migration pathways are relatively controversial.Based on the characteristics of structure

sedimentary facies and sand-body distribution

the source-reservoir combination relationship of the Upper Paleozoic in Linxing area can be categorized into three types:in-source-

near-source- and far-source-reservoir combinations.Using the data of rock pyrolysis

thermal maturity measurement

core description

thin-section observation

scanning electron microscopy

petrophysical property analysis

seismic and well logging interpretation

we analyzed the development characteristics of the source rock

reservoir

charging dynamics and faults.The results show that there are three sets of hydrocarbon source rocks in Linxing area

including coal

carbonaceous mudstone and dark mudstone source rocks with Type Ⅲ and Ⅱ

2

kerogens.The source rocks have high abundance of organic matter and are mostly mature to highly mature

thus are large in hydrocarbon generation potential.The reservoir rocks are dominated by feldspar lithic sandstone of moderate maturity

and are characterized by high heterogeneity and multiple pore throat types

including primary intergranular pores

dissolved intergranular pores

dissolved intragranular pores

intercrystalline pores and micro-cracks.The reservoirs mostly have low porosity and low permeability

with an average porosity of 6.81% and an average permeability of 0.61×10

-3

μm

2

which reflects a typical tight reservoir.Overpressure is common and gas expansion force is the main driving force for gas accumulation of the in-source- and near-source-reservoir combinations.The well-developed faults can serve as the migration pathways for the natural gas vertically charging to the far-source-reservoir combination and can also improve the reservoir quality and strengthen the lateral migration ability of natural gas.Physical simulation experiments were carried out on the established accumulation model

and it was found that reservoir heterogeneity and faults are the main factors affecting the gas-water relationship.The in-source-reservoir combination is the favorable area for hydrocarbon accumulation

and can be selected as the focus of later exploration and development.