An operating company successfully executed two wireline through tubing gas shutoff (GSO) workovers in high angle openhole gravel pack (OHGP) completions to isolate high gas oil ratio (HGOR) zones, resulting in significantly increased oil production. This paper summarizes the GSO concept, production logging results, completion modeling, job planning, and prejob surface testing of the completion equipment, job execution, and production results.

The GSO workovers were performed on a tension leg platform (TLP) in a deepwater offshore field. Isolation of HGOR zones was achieved by installing a wireline deployed stackable straddle system across the heel of the OHGP interval. Although both wells have OHGP completions for sand control, effective isolation of the gas zone was predicted using completion modeling and was validated by sustained production performance. These wells do not have external casing packers (ECPs) to prevent flow through the gravel pack interval. Isolation of the gas along the annulus is provided only by increased hydraulic resistance in the gravel packed annulus.

The candidate wells had unfavorably HGORs attributed to gas breakthrough from ongoing gas reinjection. To evaluate if production could be improved by reducing gas production, detailed mathematical modeling of an isolation straddle's impact to inflow from the reservoir through the completion was performed. Results suggested that internal isolation could provide effective GSO without ECPs. Optimal straddle length was determined to help minimize production from the HGOR zone without affecting low GOR zones. In preparation for the workovers, multiple surface tests were conducted to test installation and retrieval of the completion equipment as well as integration and function of tools and equipment from multiple service companies. Work on the first well included the first use of coiled tubing (CT) by the operator on a TLP for a workover. After the CT milling of downhole restrictions, 16 components were sequentially installed by means of electric line (e-line) of a stackable straddle system across the high gas zone. After straddle installation, both wells transitioned from being cycled to continuous lower GOR production. The first well produced 5,000 BOPD at 6,000 GOR before the GSO, and was increased to 10,000 BOPD at 1,000 GOR. The second well produced 6,000 BOPD at 6,000 GOR before the GSO, and 10,000 BOPD at 500 GOR afterward.

The keys to success involved strong teamwork and support from multiple service companies using CT milling, completion equipment, wireline, slickline, and conveyance tools. Significant scalability was achieved during planning of the second workover based on observations from the first.

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