Enhancing the Effectiveness of Workover Interventions with Coiled Tubing and Real-Time Downhole Measurements

摘要

In offshore Mexico, operators have increased workover activity to maintain oil and gas production. The reservoir is a naturally fractured carbonate with gas and water flowing through the natural fractures, leaving oil trapped in the matrix. Controlling gas and water production is critical to prevent unwanted fluid from reaching the wellbore. Currently the combined progression of gas and water contacts has reduced the oil window from several hundred to as little as 40 m in some wells. In these conditions, and with rapidly advancing gas and water contacts, it is paramount to provide solutions to restrain unwanted fluid from reaching the wellbore. One of the most common workover interventions consists of isolating the water producing zone with coiled tubing deployed through-tubing inflatable-packers (CTD-TTIP) and perforating an upper oil-bearing zone. The problem is compounded by low reservoir pressure, resulting in heavy losses while drilling and cementing production zones; loss of zonal isolation as result of cement sheet failure through the producing intervals; and wells completed with a combination of large tubular sizes. Recently, operators and service companies in offshore Mexico have implemented an innovative workflow intended to enhance the effectiveness of water control interventions in this challenging work environment, through the utilization of realtime downhole measurements (RTDM) via coiled tubing equipped with optical fibers (CT-EOF) for accurate control of CT depth, the packer inflation process, packer differential pressure limits during the treatment injection, and fluid placement. This paper provides a technical analysis of the engineering process required to develop successful workover zonal isolation jobs with CTD-TTIP and RTDM in offshore Mexico, and presents a case history, lessons learned, conclusions, and recommendations from the experiences gained while performing CTD-TTIP with RTDM in offshore Mexico.