Studies On Low Carbon Hydrocarbon-based Fracturing Fluid Systems And Their Rheological Properties

In order to obtain the fracturing fluid system suitable for the unconventional oil and gas reservoirs, environmental gelling agent was synthesised and complexing iron crosslinking agent was prepared in this paper, and the low carbon hydrocarbons (such as liquefied petroleum gas(LPG), n-hexane, octane) were used as base fluid instead of water. The fracturing fluid systems based on low carbon hydrocarbon as base fluid were developed and the related properties of the fracturing fluid systems were investigated. The rapid crosslinking processes for the fracturing fluids were realized. The rheological properties (viscoelasticity, thixotropy, shear thinning) of the systems based on the different hydrocarbons (n-hexane, octane, kerosene, diesel) as base fluid were researched and the crosslinking rheological dynamics models of kerosene-based fracturing fluid and diesel-based fracturing fluid were established. Main conclusions were obtained as follows:1) The gelling agent was synthesised by a two-step method, using triethyl phosphate, phosphorus pentoxide, and three alcohols as basic materials. The factors such as reaction temperature, reaction time, reactant ratio, and others on the yield of dialkyl phosphate ester were illustrated. The optimum synthetic condition was obtained.2) The new complexing iron crosslinking agent that could crosslink rapidly with dialkyl phosphate ester was prepared with ferric sulfate as basic material. The factors such as type and content of crosslinking accelerant, type and content of complexing agent and others on the performance of crosslinking agent were illustrated. The optimum preparation condition was obtained.3) The low carbon hydrocarbon-based fracturing fluid systems (represented by LPG-based) were developed with LPG, n-hexane and octane as base fluid respectively, dialkyl phosphate ester as gelling agent, and complexing iron as crosslinking agent.4) For the fracturing fluid systems with different hydrocarbon (n-hexane, octane, kerosene, diesel) as base fluid, the rheological properties (viscoelasticity, thixotropy and shear thinning property) changed with the length of carbon chain were found. Non-linear co-rotational Jeffreys model could be applied to describe the flow curve of every system correctly and the calculated values were in good agreement with the experimental data.5) The rheological dynamics models which were respectively suited to describe the crosslinking process of kerosene-based and diesel-based fracturing fluids were established. The meanings of the model parameters were reasonable and the calculated values were in good agreement with the experimental data.