Study On Temporary Plugging And Self-unblocking System In Low-pressure Oil And Gas Fields

Temporary plugging agents often play an important role in oil-gas field development.Whether in the drilling or workover process,or even in the course of deviating some special well-injection fluids,temporary plugging agents contribute to temporarily sealing the formation.And after a certain period of time,the plugging can be released.Therefore,performance requirements for temporary plugging agents include:low fluid loss,low residue,and quick return to reduce formation damage.For low-pressure oil and gas wells,it is necessary to consider not only the temporary sealing of the formation,but how to reduce the clogging for the pores after the gel-breaking and the thorough return of the broken gel to the top priority.Conventional gel type temporary plugging agents can find various applications according to different downhole conditions in terms of water plugging rate,compatibility,portability,salt resistance,and temperature resistance.But for low pressure oil and gas wells,there is a general problem of poor ability to return.Because of the deficiency of the formation energy or the special formation environment,the pressure coefficient of the formation is far below the normal level.It is difficult to return the broken gel through formation pressure after the temporary plugging agent breaks the gel.The temporary plugging agent system developed in this paper is aimed at low-pressure oil-gas wells,which can automatically break the rubber and voluntarily generate gases to discharge in certain time.Different from the conventional temporary plugging agent,the agent in this paper can automatically achieve uniform gel breaking within a certain period of time by controlling the latent acid content and with the help of the formation temperature.In addition,inert gas(N2)is generated during the gel-breaking process,which can increase the formation energy for low-pressure gas wells,and play an auxiliary role to discharge.Through the screening of the plugging agent,the temporary plugging gel system with AP-P4/chromium acetate,hydroxypropyl phthalate/inorganic boron as thickener and crosslinker was determined.By doing laboratory experiments,the effects of different thickening agents and crosslinker addition on the system were studied.The addition amount of each part of the two systems was determined and the plugging capacity was tested.The experimental results show that both temporary plugging systems can achieve complete plugging effect within a certain pressure range.The less active ammonium persulfate was worked as the oxidant breaker at medium and low temperatures,and the ability to rapidly break the gel at temperatures above 60℃ were used to screen NH4++NO2-which worked as an autonomic thermal system.We managed to bring gel breaking time under control by controlling the hydrogen ion concentration and autonomic thermal system.Among these reaction process,the concentration of hydrogen ions is controlled by the amount of latent acid added.The heat generated in the self-generated heat system helps to accelerate the gel breakage.The gas generated contributes to the backflow of the gel-breaking liquid by increasing the formation energy.A study on the compatibility of the two temporary plugging systems with the self-ignition/heat system found that the AP-P4 temporary plugging system was limited by the salt tolerance of the polymer,and that the amount of self-ventilation/heating system tolerated was lower than 3.5%,the applicable formation temperature condition is 55℃;due to its good salt resistance performance,the silicone temporary plugging system can be stabilized into a rubber when the amount of self-ignition/heat system addition is 10%,and the amount thereof is increased.It does not affect the gel-breaking performance of plugging agents.The applicable formation temperature conditions of the silicone temporary plugging system are between 40℃ and 55℃,which is more suitable for abnormally low-pressure oil-gas wells(pressure coefficient<0.3).Two types of spontaneous gas and self-degradation temporary plugging agents were tested for plugging.Both types of temporary plugging agents can effectively seal the formation and the damage rate to the core is below 10%respectively.Two kinds of temporary plugging systems have realized the integration of cross-linking,temporary plugging,self-heating and plastic-breaking,and self-supporting rowing.The utility model addresses the problem that the conventional temporary plugging agent needs additional gel breakers to achieve the additional work steps of breaking the rubber.At the same time,on the basis of achieving the gel breaking,the generated gas can provide energy for the low pressure gas wells and help the broken gel to completely discharge out of the ground in an effort to reduce the damages caused by residues in the formation.