Innovative Method to Control Acid Placement during the Stimulation of Wells with High Water Cut

Abstract

Abstract Water production is a serious challenge when stimulating wells in mature reservoirs. Production results after acidizing sometimes reveal a higher water cut; in some cases this change is significant enough that the well is no longer able to flow unassisted. A typical acid stimulation in the field follows a predetermined pumping schedule, where diverter is squeezed into the high water cut interval prior to injecting acid into oil zones. The diverter volume is based on a rule of thumb and the acid is pumped after assuming that the diverter is efficiently sealing the high water cut zone. Several coiled tubing (CT) matrix stimulation jobs have yielded production results of 100% water cut. Prior to stimulation (a period of months or years), diagnostic logs were conducted to identify water producing intervals. Although, in some cases, the post-stimulation water cut may be as high as or higher than the water cut prior to the stimulation, suggesting that the diverter volume was not enough to seal the water zone. An innovative method is needed to confirm the isolation of high water cut zones before pumping acid, which would lead to increased oil production and reduce the risk of unintentionally stimulating water producing zones. This paper shares a case history of a cased and perforated vertical oil well from a field in which the operator was able to reduce the risk of acidizing a high water cut interval through the innovative use of a fiber optic enabled coiled tubing (FOECT) string and a pressure-temperature casing collar locator real-time downhole measurement tool. The distributed temperature surveys (DTSs) recorded with the fiber optic cable were used as an innovative method to identify the water producing zone. This method correlated with the water producing interval identified by a wireline log run some period prior to the CT job. DTS allows the assessment of diverter efficiency and the tracking of fluids placement. In this case study, acid was confirmed to have been squeezed only in the upper oil zone. As a result, the well production increased significantly without any increase in the water cut.