Development And Evaluation Of Anti-high Temperature Reservoir Plugging Gel System

The reservoir in Tahe Oilfield is a fracture-type carbonate rock stratum.It is prone to crack-type malignant leakage during drilling.Conventional plugging technology is difficult to form plugging quickly and effectively,prolonging the drilling cycle and increasing drilling costs.Aiming at this problem,a high-temperature reservoir plugging gel system was developed to effectively block the malignant leakage of oilfield reservoirs and improve drilling efficiency.The plugging gel technology is a kind of plugging method that utilizes a cross-linked polymer to form a spatial network structure by cross-linking reactions,and fills the lost space to achieve plugging.At present,the researches on polymer plugging gel are concentrated on the sealing effect,etc.,and there are few studies on gelation time or gel breaking control,thus the applicability to the deep buried reservoir segment is low.Based on literature research,geological conditions and laboratory experiments,this study uses partially hydrolyzed polyacrylamide as the cross-linked polymer,and methylparaben with hexamethylenetetramine as crosslinkers to make a kind of high-temperature reservoir plugging gel system.The gel system has good rheology before gelation,and the density can be adjusted to 1.35 g/cm~3 to cope with deep complexities and is not easily diluted by other fluids.At 140?,the gel system can be gelatinized within 4 to 10 hours by changing the mass fraction of oxalic acid.The plugging capacity of the gel system was evaluated by using a plugging evaluation device and a cracked steel core(length 5 cm,diameter 2.5 cm).The plugging pressure was 2.5 to 1.2 MPa in the core with a slit width of 2 to 5 mm.When the temperature was around 140°C.In the first 15d,it can maintain good sealing ability.After 30 days,it can realize natural complete gel breaking.It can also use a small amount of gel-breaked agent to break the gel within 8h,and then flow back under a small return pressure.