Study On The Construction And Rheological Properties Of Alcohol-containing Fracturing Fluid System

With the depletion of conventional oil and gas resources,the status of low-permeability and ultra-low-permeability tight sandstone reservoirs is becoming more and more important.As an effective artificial modification measure for industrial production of low-permeability reservoirs,hydraulic fracturing technology can greatly enhance oil recovery.As a very important viscoelastic fluid,fracturing fluid is the core of fracturing technology and is known as the “blood” of fracturing.Low-permeability reservoirs have deep burial,high formation temperature,high pressure,and poor reservoir conditions(low porosity,low permeability),Ordinary water-based fracturing fluids are likely to cause "water lock" damage,and some formations will also suffer from additional damage such as "water sensitivity",which is difficult to recover after injury,seriously affecting the fracturing effect.Alcohols have low surface tension,low boiling point,low density and anti-clay expansion properties,Alcohol-containing fracturing fluid can increase the discharge volume of the return fluid,shorten the return flow time,reduce the fluid loss of the fracturing fluid,and greatly reduce the damage caused by the external liquid water lock to the reservoir pore throat.Particularly suitable for unconventional reservoir retrofits with water sensitivity,low pressure and low permeability.As the most commonly used thickener for fracturing,guar gum limits its application in alcohol-containing fracturing fluids due to its low alcohol resistance and high residue content.In this paper,ethanol and ethylene glycol were used for experiments.The concentration was changed to investigate the different effects of monohydric alcohols and glycols on viscoelastic fluids.Hydroxypropyl guar gum(HPG)and carboxymethyl hydroxypropyl guar gum(CMHPG)were selected as thickening agents which can be fully dissolved under high alcohol content.as well as a reasonable concentration of cross-linking agent,gel breaker,etc.,the cross-linking,temperature resistance and breaking performance were systematically evaluated under different alcohol content conditions.The results show that the addition of ethanol and ethylene glycol can improve the performance of the fracturing fluid.The addition of ethanol can improve the cross-linking performance,viscosity,temperature resistance,sand-carrying performance and gel breaking performance of the fracturing fluid;The ethylene glycol solution can dissolve the guar gum molecule better.With the increase of the concentration of ethylene glycol,the crosslinking time of the fracturing fluid is prolonged,the interfacial tension of the gel-breaking liquid is lowered,The viscosity reduction,the decrease in temperature resistance,the deterioration of the sandcarrying property,the increase in the viscosity of the breaker and the high content of the residue caused by the addition of ethylene glycol are eliminated by adding an appropriate amount of ethanol.