The Effect of Fracturing Fluid Saturation on Natural Gas Flow Behavior in Tight Reservoirs

Abstract

Hydraulic fracturing becomes an essential method to develop tight gas. Under high injection pressure, fracturing fluid entering into the formation will reduce the flow channel. To investigate the influence of water saturation on gas flow behavior, this study conducted the gas relative permeability with water saturation and the flow rate with the pressure gradient at different water saturations. As the two dominant tight gas-bearing intervals, the Upper Paleozoic Taiyuan and Shihezi Formations deposited in Ordos Basin were selected because they are the target layers for holding vast tight gas. Median pore radius in the Taiyuan Formation is higher than the one in the Shihezi Formation, while the most probable seepage pore radius in the Taiyuan Formation is lower than the one in the Shihezi Formation. The average irreducible water saturation is 54.4% in the Taiyuan Formation and 61.6% in the Shihezi Formation, which indicates that the Taiyuan Formation has more movable water. The average critical gas saturation is 80.4% and 69.9% in these two formations, respectively, which indicates that the Shihezi Formation has more movable gas. Both critical gas saturation and irreducible water saturation have a negative relationship with porosity as well as permeability. At the same water saturation, the threshold gradient pressure of the Taiyuan Formation is higher than the one in the Shihezi Formation, which means that water saturation has a great influence on the Taiyuan Formation. Overall, compared with the Shihezi Formation, the Taiyuan Formation has a higher median pore size and movable water saturation, but water saturation has more influence on its gas flow capacity. Our research is conducive to understanding the effect of fracturing fluid filtration on the production of natural gas from tight reservoirs.

Rock Fabric of Tight Sandstone and Its Influence on Irreducible Water Saturation in Eastern Ordos Basin

“…After soaking, the weight of the saturated sample was measured. Permeability was tested by a piece of conventional permeability equipment, and the detailed schematic diagram can be found in Meng et al 45 The measurement principle of permeability was based on measuring the gas flow volume per minute. The confining pressure was 5 MPa, imposed by water, and the pore pressure was 0.25 MPa, imposed by nitrogen.…”

Research on Transformation of Connate Water to Movable Water in Water-Bearing Tight Gas Reservoirs

“…The movable water saturation in tight reservoirs is a vital parameter that signifies water production capacity and is intricately linked to gas well water production characteristics [12,25,26]. In experimental research on formation water mobility, scholars often employ methods such as X-ray diffraction, scanning electron microscopy, and centrifugation combined with nuclear magnetic resonance [27][28][29].…”