Preparation And Performance Of Fracturing Thickening Agent For Reservoir Stimulation Of Shale Gas

There are abundant shale gas resource in our country.However,exploration and development of shale gas is difficult because shale gas reservoir has the characteristics of low porosity and low permeability.Volume fracturing is needed for most of the shale gas reservoir to meet the requirements of industrial production.It is more difficult in our country because almost the formations are deep.Learning the successful experience from North America,mixed fracturing fluid was widely used in volume fracturing,which was composed of slick water,linear gel and gel fracturing fluid.Linear gel and gel fracturing fluid were used to carry a certain particle size of proppant into crack to guarantee the fracturing effect.However,the conventional linear gel and gel fracturing fluid don't meet the requirement of carrying performance,causing low carrying capacity.Furthermore,there are high residue content for the conventional linear gel and gel fracturing fluid.In this work,we focus on the problem of poor carrying performance and high residue content of the conventional linear gel and gel fracturing fluid.The main contents are as follows.(1)To the problem of poor carrying performance of linear gel,we suggest a new kind of linear gel base on hydrophobic associating polymers and then two kinds of hydrophobic associating polymers were prepared.? A hydrophobic associating polymer,HAP AM,was prepared via aqueous dispersion polymerization in the ammonium sulfate solution,which provides a new method to prepared hydrophobic associating polymers.The polymer could be dissolved quickly in 20s after adding into water.It is found that the viscosity of the polymer increases with the addition of salt within a certain range,and the polymer exhibits well salt resistance.Therefore,we could used flowback water with high salt concentration to prepare the polymer solution.The addition of surfactant causes viscosity increase dramtically,which can be used to regulate the viscosity of the system.In the performance evaluation experiments,the linear gel prepared with HAP AM demonstrates superior properties compared to the conventional linear gel on aspects of shear resistance,viscoelastic,and proppant carrying capability.Besides,the linear gel is breaken easily and the residue is almost zero.? A hydrophobic monomer was synthesised with long carbon chain and two head groups to improve the association property of the polymer.And then hydrophobic associating polymers,PDH,was also prepared with aqueous dispersion polymerization.The PDH exhibits better thickening performance and salt resisitance than HAPAM.The linear gel of PDH also demonstrates superior properties on aspects of shear resistance,viscoelastic,proppant carrying capability and gel breaking.(2)To the problem of high residue content,a stimu-responsive linear gel and a nano gel breaker were prepared,respectively.? A stimuli-responsive linear gel was prepared with an anionic hydrophobic association polymer and a temperature and pH responsive surfactant,which endow the linear gel stimuli responsive property.The temperature and pH responsive linear gel is gel like in the pipeline,which is used for carrying proppant.However,the linear gel could be broken automatically under the action of formation temperature or addition of NaOH.The linear gel also shows superior properties on aspect of viscoelastic and gel breaking performance.? For reducing the formation damage of polymer and residue in microfractures,we prepared a nano gel breaker to control release base on mesoporous silica,which has excellent mechanical and chemical stability.The effective content of the nano gel breaker was about 5.24%and the embedding rate was above 90%.In the performance evaluation experiments,the nano gel breaker exhibits superior control release and gel break properties.The mechanism of release was also investigated and we found that the breaker was released through desorption and diffusion in the regular channels,which is different from the encapsulated gel breaker and is a new kind of breaker for control release.(3)To the problems of poor temperature resistance and high residue content of conventional gel fraturing fluids,two kinds of gel fracturing fluids base on hydrophobic associating polymer and hyperbranchde polymer were prepred,respectively.? A hydrophobic associating polymer HPDM with high content of hydrophobic monomer was prepared with aqueous dispersion polymerization.The polymer could be dissolved quickly in three minutes after adding in to water.HPDM has good association properties with the critical associating concentration only about 2000 In the performance evaluation experiments,the HPDM demonstrates superior properties on the aspects of salt tolerance,temperature resistance,shear resistance,surfactant compatibility,carrier performance,and gel breaking performance.The temperature resistance of HPDM reached 120?.These features indicate that gel fracturing fluids have a great potential application for fracturing,especially in high-temperature and high-mineralization oil fields.? A hyperbranched polymer was also prepared with aqueous dispersion polymerization.The BPAM gel fracturing fluid also demonstrates superior properties on the aspects of temperature resistance,shear resistance,carrier performance,and gel breaking performance compared with conventional gel fracturing fluid.The temperature resistance of BPAM was above 146?.In this work,the linear gel and the prepared gel fracturing fluid could combine with slickwater to form a series of mixed fracturing fluid.These fluids enrich the fracturing fluid types and provide the necessary theoretical basis and experimental basis for shale gas efficient development in our country.