Research On High Temperature Resistant Delayed Crosslinking Agent For Water-based Fracturing Fluid

The distribution of low permeability oil and gas resources in Chinais more oil and gas, more hydrocarbon reservoir types, wide distributionarea,etc. The reserves accounts for more than two-thirds of the provenreserves, they have great potential for exploitation. The oil and gas fieldhas dense reservoir, low permeability, larynx way subtle features,subject to have permanent jams damage effect. Therefore, lowpermeable oil and gas reservoir has higher requirements on theperformance of fracturing fluid system. Requires the discharge abilityof fracture fluid return is better and less damage to the formation.According to the above characteristics of low permeable oil andgas fields, to improve the defects that existing water-based fracturingfluid can’t gelout completely, can’t easy to backflow, and damage onreservoir permeability is big, two water-based fracturing fluidhigh-temperature delayed crosslinking agent were synthesized: boron-organic crosslinking agent BOC-1and zirconium-organic crosslinkingagent ZOC-1. Boron&zirconium-organic crosslinking agentBZC-1were blended with both BOC-1and ZOC-1. Compared to theexisting organic boron&organic zirconium crosslinking agent, we’vedone some improvement on thickener types and crosslinking system pHvalue. Using polyvinyl alcohol (PVA) respectively, carboxymethylhydroxypropyl guar gum (CMHPG) and hydroxypropyl guar gum (HPG)as thickening agent, developed organic boron/polyvinyl alcohol(BOC/PVA), organic zirconium/carboxymethyl hydroxypropyl guargum (ZOC/CMHPG), organic boron zirconium/hydroxypropyl guar gum(BZC/HPG) crosslinked fracturing fluid system. At the same time, thispaper studies the different factors on the performance of thecrosslinking frozen glue, and evaluates the fracture fluid in laboratory. The results are as follows:(1) The best synthetic process of BOC-1:20%of borax,13.5%ofmannitol,65%of water/glycerin（3:1volume ratio）,1.5%of NaOH，pH value9～10， reaction temperature80℃, reaction time4～5h.The best synthetic process of ZOC-1:8%of zirconium oxychloride,25%of mannitol/lactic acid，65%of water/glycerin（3:1volume ratio）,2%of NaOH， pH value3～4, reaction temperature85℃, reaction time4～5h.The mass ratio of BOC-1and ZOC was1:1, compound them andadd special absorption inhibitors, stir and get easy gel breaking, hightemperature resistant organic boron zirconium crosslinker BZC-1.(2) BOC-1, ZOC-1and BZC-1crosslinked gel have good delaycrosslinking properties, delay crosslinking time can be up to70～120s、85～125s、80～120s respectively. We can control crosslinking time andfrozen glue performance by adjusting the system temperature, pH valueand crosslinking ratio, etc.(3) In laboratory, we studied influence of the thickener amount,crosslinkeing ratio, pH value and temperature on crosslinking frozenglue,determined the basic formula of BOC/PVA, ZOC/CMHPG andBZC/HPG fracturing fluid system:1.5%/0.8%/0.6%thickener+1.5%/2%/1.5%crosslinking agent+1.5%/2%/2%pH regulator+1%/1%/1%gel breaking agent+1%/1%/1%clay stabilizer.(4) With reference to “the SY/T5107-2005water-based fracturingfluid performance evaluation method "and" SY/T6376-2008fracturingfluid general technology conditions”, the performance evaluationresults of the three kinds of fracturing fluid system show that:BOC/PVA, ZOC/CMHPG and BZC/HPG fracturing fluid system havegood rheological properties, the best temperature is up to95℃,115℃and130℃respectively, the apparent shear viscosity undercorresponding temperature is respectively70～80mPa·s,80～90mPa·sand80～90mPa·s, had better resistance to shear performance, goodproppant carrying capacity.(5) BOC/PVA, ZOC/CMHPG and BZC/HPG fracturing fluid system have low gel breaking liquid viscosity, the biggest viscosity isrespectively6mPa s、4.8mPa s and5.5mPa s, low resikual volume,is respectively100mg/L,321mg/L and208mg/L, low core damage, is15.02%,24.51%and20.41%respectively, lower than theindustry-standard requirements.(6) By using composite inhibitor adsorption and special gelbreaking agent,BZC/of HPG fracturing fluid system combines theadvantages of BOC/PVA and ZOC/CMHPG fracturing fluid system,suitable for low permeability of the high temperature deep wellfracturing transformation.The results show that, the newly developed fracturing fluid systemhave good resistence of heat and shear, low glue residue, and low coredamage. It’s suitable for high environmental requirements and lowpermeability of deep well of oil and gas reservoir fracturingtransformation with different well depth and well temperature.