Study On The Development Of The Nanocomposite Gel Of High-Strength And Degradability For Temporary Plugging

In the late stage of the development of the low pressure oil and gas well,workover is quite often.Owing to the depletion of the formation pressure,the loss of workover fluid happens a lot,which not only pollutes the reservoir,but also makes a negative effect on the production.For the low pressure carbonate reservoir,because of the fracture,the fluid loss is more serious.This paper is based on the Changqing gas field,whose formation temperature is about 95?,formation pressure coefficient is within 0.3 to 0.8,thus the temporary plugging layer is required to possess excellent performance in bearing pressure larger than 20 Mpa with low fluid loss,and easy to be pumped out in the late stage of the operation.To solve this problem,different kinds of temporary plugging techniques for the fractured reservoir are developed.Currently,the polymer gel is mostly applied.However,the strength of the polymer gel gelated in a short time cannot meet the filed requirement,and it usually has high viscosity that could harm the formation.Thus,through adding the nano-silica into the gel,the viscosity of the new system decreased and it can reach a high strength very fast and also has favorable elasticity and resistance to compression.Aimed at solving the problems in the fracture developed reservoir,this essay developed a novel nanocomposite gel which has high-strength and can be broken and degraded by using the gel breaker chemicals.This paper evaluated its compression resistant ability,thermal stability,mechanism and application properties.Main results are concluded as below:(1)The nanocomposite gel of high-strength and degradability is developed and it is made up of 18%Acrylamide+0.05?0.15%Crosslinker 1+0.20?0.25%Initiator YF+1.0?5.0%Nanosilica 4+0.02%Thiourea.The gelation time can be adjusted within 0.3 to 2 hours.(2)The nano-silica has little influence on the rheological property.The nanocomposite gel system performs a good fluidity and is easy to be pumped.(3)The nanocomposite gel system can be stable for 12 days with no dehydration within the temperature ranging from 75? to 105?.By adding the nano-silica,the thermal stability of the nanocomposite gel system is enhanced.Because of the connection between the hydroxyl in the nano-silica and the water molecule hydrogen bond and that the nano-silica performs negative charge in the gel liquid which can adsorb the hydronium ion,therefore,more water can be trapped in the system to resist the high temperature.(4)Nano-silica improves the mechanical performance and reduces the viscosity.As the concentration of the nano-silica increases,the microstructure of the nano-composite gel becomes more compact,thus the system's mechanical strength is well improved.Under the compressive strain of 50%,the stress increased from 8.7KPa to 21KPa.Besides,the viscosity of the nano-composite gel shows a decreasing trend.(5)As with the increase of the fracture width,the breaking-through pressure of the nanocomposite gel system decreases.When the fracture width is respectively 0.170cm and 0.398cm,the breaking-through pressures are respectively up to 20.5MPa and 13MPa,the fluid loss are respectively 2.5ml/5min and 7.5ml/5min at 25MPa.These results indicate that this nanocomposite gel has a good performance of bearing high pressure and low fluid loss.(6)Results of the permeability recovery test show that for the cores with fracture width within 0.170 to 0.398 cm,the permeability recovery rate can be higher than 83%.The research results of this essay offered the theoretical and technical reference for the temporary plugging of the fracture-developed reservoir,which has a certain guiding value.