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A high flowback rate of hydraulic fracturing fluid (HFF) yields a high gas production rate in a tight sand gas reservoir. This idea is well followed when it comes to the hydraulic fracturing of a s...

The wellbore stability in shale gas reservoir is the key factor for safe drilling and effective development of shale gas. However, the instability mechanism remains unclear in shale gas wells. In this work, the wellbore instability mechanism was studied by conducting experimental and field case studies in Longmaxi shale. A high-pH condition strengthened clay mineral hydration by increasing the absolute ζ-potential of the shale clay minerals. Alkali-soluble minerals (clay minerals, quartz, feldspar, etc.) were eroded greatly in a high-pH fluid, resulting in a large number of dissolution pores and weakening the microstructure of the shale. The high-pH fluid further reduced the difficulty of shale frictional sliding by lubricating the shale surface and weakening the asperity strength of the surface. Adjusting the pH value of drilling fluids and plugging lost circulation channels became key jobs to maintain the wellbore stability in shale gas wells. This study provides theoretical guidance for drilling fluid optimization used in shale gas wells.

Due to high salinity and complex components including varied inorganic salts, organic agents, released heavy metals, radioactive elements and clastic particles, environmental and economical treatme...

A large amount of fracturing fluid enters a well of a shale gas reservoir to create a fracture network, but the recovery of fracturing fluid is generally less than 30%. Fracturing fluid from the hy...

Spontaneous microfracture propagation caused by mineral crystallization or growth has been demonstrated in a variety of volume-increasing mineral replacement reactions. This brings a new look on th...

Fines migration has posed a great challenge to gas and water production in CBM reservoirs, resulting not only in dramatic permeability reduction but also in excessive wear on equipment. The objective of this study was to investigate critical flow conditions for massive fines detachment in the dewatering phase, for the purpose of yielding an improved understanding of fines detachment mechanisms and their effective control in the field. First, fines migration experiments under saturated conditions, including effluent concentration and permeability measurements, were conducted at elevated pressure gradients on fractured coal samples with various apertures. Experimental results indicate the existence of a critical pressure gradient (CPG) for massive fines detachment. Second, a mathematical model was developed to describe single particle detachment in the fracture, accounting for the coupling effects of hydrodynamic and extended-DLVO forces. Effects of fines size and fracture aperture on fines detachment were ...