Development Of Alkyl Phosphate / Complex Iron Oily Gelling Fracturing Fluid

In view of fracturing oil and gas reservoirs with strong water sensitivity such as shale gas reservoir, after wide investigation for research and application of oil base fracturing fluid thickener system at home and abroad at present,"alkyl phosphate/complex iron ion solution" is put forward as thickener system. It has the advantages of short gelling time and good performance to gel to prepare oil base fracturing fluid.The alkyl phosphate containing different alkyl group is synthesized by "two step methods". The reaction time, temperature and molar ratio are discussed; the results show that the temperature is the largest influence on the reaction. The optimum conditions for preparing the intermediate are reaction time5h, reaction temperature85℃and the best mole ratio of C6H15O4P and P2O53.4:1at the first step. The second step, the alkyl phosphate is synthesized under the optimum conditions of80℃,4h reaction time, and the mole ratio of intermediate and mixed alcohol is1:1.4. The crosslinking agents PE-17～PE-25are synthesized. The content of two alkyl phosphate ester is58.5～71.3%by the double indicator method. The chemical structure of product is characterized by FT-IR. A series of FC-3cheated iron solution as the activator is prepared and the activator formula which is20.0wt%ferric sulphate+16.0wt%trisodium citrate+10.0wt%ethanediol+54.0wt%deionized has been screened by the length of the gel time and gel state.The similar carbon chain length of alkyl phosphate ester is selected as the thickener for the different oil base according to the principle of similar compatible. Respectively, for kerosene, diesel oil, n-hexane and n-heptane, different base oil base fracturing fluid is prepared. The best crosslinking ratio has been Studied which is that1:1.5for n-hexane and n-heptane,1:1.75for kerosene and diesel oil.The performance of the n-hexane fracturing fluid is tested using in the normal temperature and high temperature by CVOR200and HAAK rheometer. The viscoelasticity and thixotropy of different base gel are studied and the results show that thixotropic loop area of the hexyl alkyl fracturing fluid is largest.The area of thixotropic loop decrease gradually as the carbon chain growth of base fluid. The viscosity-temperature resistance of the hexyl alkyl gel fracturing fluid is discussed, the viscosity is over450mPa-s under68℃and remained in100mPa·s in80℃.It still can satisfy the viscosity.requirement of the oil base fracturing fluid. With the increase of the temperature, the gel breaking liquid viscosity decreases for hexyl alkyl fracturing fluid.Under the same temperature conditions, with the increase of dosage of breaker, gel breaking liquid viscosity decreases. When the dosage of sodium acetate is0.40wt%, the gel breaking liquid viscosity is1.32mPa·s under70℃,that’s almost entirely gel breaking. The influence of crosslinking agent and activator on the suspended sand performance is discussed for the diesel oil base fracturing fluid. The results show that when the crosslinking agent is2.5wt%,, the settlement of hexyl alkyl fracturing fluid rate is the maximum which is0.013mm/s compare to other base fracturing fluids.The damage to the core is low.The damage rate to the core permeability of hexyl alkyl, kerosene and diesel oil base fracturing fluid gel breaking liquid is2.45%,3.11%and6.42%respectively, it’s far less than water-based fracturing fluid. It could satisfy the general technical standard of oil base fracturing fluid.