Study On Self-aggregating Proppant In Channel Fracturing

Hydraulic fracturing techonology is the most important stimulation treatment for the development of reservoirs with low permeability.However,the conventional fracturing techonology basing on homogeneous proppant placement offen suffers from proppant crush,embedment,and flowback,causing the fracture conductivity far lower than the expected value.In order to obtain higher conductivity,a new techonolgy named Channel Fracturing has appeared in recnet years,providing a feasible technology for solving the prolems like low flowback rate of the fracturing fluid,and low conductivity of the proppant pack,which are common problems in low permeability reservoirs after hydraulic fracturing.Aiming at the key technology of channel fracturing,fracture supported by “proppant column”,the heterocyclic polymer which endows the modified proppant the property of “keeping together” was prepared,the mechanism of self-aggregating proppant was clarified,and the self-aggregating modifier used for the on-the-fly modification of self-aggregating proppant was developed.This new self-aggregating proppant provides a new idea and method for fracture supported by “proppant column”.The polymer with the aromatic heterocyclic side chains was designed and synthesized.The strength of the aggregated proppant column increased with the increase of the molecular weight of the heterocyclic polymer.However,the optimum molecular weight of the heterocyclic polymer was 5200-5500g/mol,condiering the modified proppant need to be prepared by wet coating method.The optimum reaction conditions was determined according to the conversion rate of the reaction: the reaction temperature was 57.5?,the reaction time was 5.5h,the dosage of the initiator was 1.0%,and the stirring speed was 250 r/min.The molecular weight of the polymer was 5339g/mol,and the synthesis conversion rate was 89.42%.For the novel heterocyclic polymer,the tests of the determination of the forces between modified glass balls showed that the self-aggregating force could promote the aggregation and the cohesion force inhibit the separation of the modified paricles.The essence of the water softening effect to the heterocyclic polymer was revealed by the study of the changes of the functional groups,the crystal form,and the microstructure of the heterocyclic polymer before and after the action of water: water can penetrate the heterocyclic polymer,and weaken its crystalline state,thus the interactions of the heterocyclic polymer molecules in the hydration layer makes the viscoelastic body have some bonding effect.Furthermore,the mechanism of the proppant aggregation of the heterocyclic polymer was verified: the polymer coating can reduce the Zeta potential of the proppant surface,contributing to the self-aggregation of the modified proppant;under the bonding effect of the viscoelastic body of hydration layer of the polymer coating,the modified proppants maintain the state of agglomeration.According to the requiremnts of the on-the-fly preparation of the modified proppant proposed by field application,the self-aggregating agent was constructed from the three aspects of enchancing the dispersibility of the main agent in water,strengthening the adsorbability of the main agent on the proppant surface,and improving the evenness of the polymer coating.In addition,the re-aggregating property of the self-aggregating proppant can reduce the migration of the proppant particles,inhibit the release and migration of proppant fragments,and reduce the migration of formation fines.Therefore,in channel fracturing,the fracture conductivity of the self-aggregating proppant is superior to the proppant pack treated with fiber or non-curing resin.