Study On Low Molecular Weight Alkane Anhydrous Fracturing Fluid Of Shale

The prospect of developing shale gas is extremely attractive due to its great potential in shale gas resource. Fracturing is the most important engineering technologies to realize the effective development and ensure the long-term stable production of shale reservoir. The current exploitation of shale gas mainly employs large slick water fracturing, and it consumes a large amount of water and pollutes the environment. While most of shale gas exploration favorable area in our country is in the mountains and hills, and other important water shortage area or the adjacent area. Base on the water resource restriction and environmental protection, it is necessary to research waterless fracturing technology to lay the foundation for shale gas efficient large-scale development in the future. So the explorative study of low molecular alkane waterless fracturing fluid is conducted, the completed works are as follows:(1) The gelling agent phosphate ester is synthesized by the raw material of phosphorus pentoxide, triethyl phosphate and etc. In order to obtain the optimal synthetic condition of gelling agent phosphate ester, the evaluation of potentiometric titration and apparent viscosity test is carried out. The structure of phosphate ester is characterized by infrared spectrum and nuclear magnetic resonance spectrum under the optimal synthetic conditions, which confirms the main component in samples consistent with the experiments.(2) Screen out main agent Fe2(SO4)3, crosslinking accelerant J1and complexing agent L1. The compound crosslinking agent is formed by optimizing the quantity of three additives, and the optimal preparation conditions are acquired.(3) After the formula of low molecular alkane base fracturing fluid system is optimized, the best crosslinking ratio and the best concentration of gelling agent are obtained. The related properties of low molecular alkane base fracturing fluid are tested, and it shows that, the viscosity of the crosslinked n-hexane gel fracturing fluid is retained at100mPa·s above after it is sheared at170s-1for1.5h at90℃, the viscosity is retained at80mPa·s above after the crosslinked n-pentane gel fracturing fluid is sheared at170s-1for1.5h at60℃.(4) The rheological properties of crosslinked gel are respectively tested and analyzed in different gelling agent concentration and different base fluids, the result shows that all of the crosslinked gel fracturing fluids have obvious viscoelasticity, thixotropy and shear thinning property. Finally non-linear co-rotational Jeffreys model is used to describe the flow curves of every system.The research on waterless fracturing fluid is innovative and difficult. These works promote the development of waterless fracturing fluid, and lay a foundation for perfecting and achieving industrial application value.