A Compound Acid for Medium to High Water-cut Screen Pipe Completed Wells in Wenchang Oilfield

Some oil wells in the Wenchang Oilfield (located in the west of South China Sea), which were completed with screen pipe, are now having high water-cut. In acidizing operations, acids are difficult to be distributed evenly, thus the production of fluid is increased, while the production of oil remains low. Based on the characteristics of the reservoir rocks and the well completion method used, a compound acids, formulated with a self-diverting acid WZX-02 and a retarding acid WHS-05, was developed to deal with the said problems. The compound acids are able to control themselves from entering into formations of high permeability, thereby avoiding water-cut increase after acidizing operations. The compound acids have been pilot tested on the Well D in Block M in Wenchang oilfield. Prior to acidizing, the well had liquid production of 68 m³/d, oil production of 32 m³/d, and water-cut of 53%. After acidizing, the liquid production increased to 207 m³/d, oil production to 117 m³/d, and water-cut reduced to 43%, demonstrating that the compound acids had remarkable ability in oil production enhancement, and can be used in acidizing screen pipe completed wells with high water-cut.