Improve Injection Profile by Combining Plugging Agent Treatment and Acid Stimulation

Plugging agent treatment and acid stimulation has completely different mechanisms for improving injection profiles. In this paper, a hybrid procedure is introduced to reduce the damage of plugging agent to low and medium permeability zones and the penetration radius of acid into high permeability zones. The procedure is: first inject plugging agent to block high permeability zones, and then inject acid to remove plugging agent damage from the low and medium permeability zones and stimulate them. For performing this procedure successfully, three kinds of plugging agents were screened out for using in different reservoirs: Strong strength plugging agent for the wells with fractures or high permeability streaks; Weak gel for those with thick layer in which serious heterogeneity exists; Temporary plugging agent for those in which the absorption ability of high permeability zones needs maintaining. Several acid systems were evaluated to be compatible with the three kinds of plugging agents. The objectives of this paper are: (1) To show the screen results about the compatible plugging agent and acid; (2) To show how to optimize the operation process; (3) To tell some experiences learnt from the oilfield applications of this technique. From Jan. 2001 to Dec. 2002, 46 operations using this procedure were carried out in Weicheng and Mazhai Oilfields of SINOPEC. Results show that the average benefit/cost ratio is over 3.5. Experience learnt from these applications was summarized in the paper