A New Drilling Fluid System for Temporary Plugging of Low Permeability Carbonate Reservoirs Containing H2S and CO2

Abstract

Carbonate reservoirs in Asmari block of Missan oilfield are characterized by complex geological characteristics. Temporary plugging is commonly used for effective damage control caused by the working fluid when drilling in such complex multi-pressure reservoirs and for preventing leakage, blowout, and collapse in long open hole wells. In this paper a new temporary plugging drilling fluid formulation system is proposed, designed for the low permeability carbonate reservoir containing H2S and CO2 in the target block. The system contains a specially designed acid-soluble temporary plugging agent DSK-1 combined with HCOONa and modified biopolymer VS-A flow pattern regulator; modified starch water loss reduce agent, and DSP antioxidant. The parameters of the system, including temperature stability, resistance to formation water pollution, inhibition capacity, and stability to acids and acid gases, were evaluated in a series of experimental tests. The plugging ability was evaluated by experiments on cores received from the target block. The results showed that the plugging removal and recovery rate of the drilling fluid system was up to 86.3%, which can effectively meet the target requirements, and provide guidance and reference for the follow-up study of temporary plugging in low permeability carbonate reservoirs.