Research And Application Of Scale Inhibition And Low Damage Fracturing Fluid System

Hydraulic fracturing technology is currently the most widely used method of stimulation in oilfields.However,the formation water and fracturing fluid configuration water in the Western China Oilfield（Mahu）have high salinity,and serious scaling problems in pores and support zones after fracturing.It is of great significance to clarify the type and source of formation scaling,and to identify the scaling mechanism in the support zone and pores after fracturing,and finally to form a fracturing fluid system for scale inhibition and scale removal.In this thesis,by means of numerical scaling simulation（Scale Chem）,ion chromatography,mineral analysis and water-rock reaction methods,the scale source,scale type and scaling conditions of the reservoir have been identified.At the same time,the scaling mechanism and damage characteristics of the support zone and the core after the water-rock reaction are clarified from the perspective of the pore throat with the nuclear magnetic resonance instrument;The scale inhibitors and descaling agents suitable for fracturing fluids are optimized,and the action mechanism of the agents is clarified by Mapping scanning;Finally,a fracturing fluid system with scale inhibition and low damage is formed,and the scale inhibition,scale removal and comprehensive performance evaluation of the fracturing fluid are carried out.The conclusions are as follows:The Ca CO₃ scale in the target block accounts for more than 50%of the total scale;The sources of scale include:fluid entering the well（fracturing fluid and injection fluid,etc.）,acidification,and water-rock reaction,among which acidification produces the most scale-forming ions;After acidification,the scale-forming ions can make the flowback liquid scale under the action of the formation alkaline substances or the dilution of the injected fluid.The scaling amount is up to 731 mg/L,which is higher than the scaling amount of the flowback fluid after fracturing,which is 327.37 mg/L;A small amount of Ca²⁺ions will also be generated after the injection of fracturing water and the water-rock reaction.Among them,the water-rock reaction will dissolve plagioclase and calcite,and the dissociation of rock powder minerals will be accelerated with the increase of temperature and the decrease of pressure.In addition,the alkaline guar gum fracturing fluid easily dissolves quartz and clay minerals.After the water-rock reaction,the Ca²⁺concentration of guar gum is 68.846 mg/L,which is more than 6times higher than that of slick water.In the proppant scaling model experiment,it is found that in order to reduce the surface energy,more scaling crystals would gather on the rough support zone and the surface of the main seepage channel,and the scaling amount decreased with the decrease of temperature and the increase of pressure;NMR showed that the number of large pores decreased and the number of small pores increased after the water-rock reaction.In the research of scale-inhibiting fracturing fluid,YTZY-4 scale inhibitor is preferred,which has strong temperature resistance and acid and alkali resistance,and has better scale inhibition ability of mixed scale.It can evenly act on the scale crystal to achieve the effect of crystal screw dislocation and lattice distortion;The autogenous acid SGE-C has a good descaling effect,can maintain the weakly acidic environment of the formation for more than 12 hours,and plays the role of auxiliary scale inhibition;Drag reducer DR800 has a moderate molecular weight and a drag reduction rate of over 70%.The final scale inhibition and low damage fracturing fluid system is:0.08%drag reducer DR800+0.3%scale inhibitor TYZY-4+4%autogenous acid SEG-C+0.2%clay stabilizer.The fracturing fluid has good compatibility,the scale inhibition rate is 96.29%,the core permeability is increased to 150%of the original core.It solves the scaling problem in the core and support zone,and provided theoretical support for the fracturing of unconventional scaling reservoirs in china.