Experimental Study On Acid-Soluble Magnesium Cement Plugging Materials In Carbonate Reservoirs

Due to the unique geological structure of the Ordovician carbonate reservoirs in the Tahe Oilfield,the fracture development is prone to well leakage.The current plugging materials usually do not have the role of reservoir protection,which cause waste of oil and gas resources.Acid-soluble magnesium cement(ASMC)is expected to solve the leakage loss of carbonate reservoirs.This paper is based on the carbonate reservoirs in Tahe Oilfield,research the possibility of ASMC application from the basic characteristics and the modification properties of ASMC.The experiment was carried out,and the following conclusions were mainly obtained:(1)ASMC can effectively deal with the loss of Ordovician carbonate reservoirs,the density is low so the ground disturbance is small.Low viscosity allows it to flow or penetrate into the fractures of the formation to prevent most of the loss.It has high compressive strength and can withstand two-direction pressure to better resist or prevent the failure of plugging caused by deformation.The thickening process is characterized by “right-angle thickening”,which is conducive to construction safety and cost savings.(2)Experimental research on the pumping,water resistance,thickening time and acid solubility of ASMC by adjusting the drag reducer,water resistance agent and retarder.The test results show that ASD-5 drag reducer,sodium citrate,boric acid and borax are effective reagents for adjusting the performance of ASMC.Borax,boric acid and triethanolamine are effective high-temperature retarding additives.The thickening time of ASMC can be maintained at 120? and 140? for more than 240 min to ensure the safety.The amount of retarder added at 120°C was 21% borax + 21% boric acid;at 140? was 31% borax + 31% boric acid + 21% triethanolamine.(3)ASMC can be completely dissolved in HCl solution,static acid dissolution,dynamic acid dissolution and dynamic intrusion depth test on ASMC modified by retarder to simulate modified ASMC in static condition,external disturbance condition,limited surface contact condition.The acid dissolution rate and acid solubility rate show that the modified ASMC still has acid-solubility characteristics,the acid solubility rate is close to 100%,and the acid dissolution rate was also improved.ASMC has good resistance to salt pollution and has good compatibility with water-based drilling fluids and oil-based drilling fluids.