A Deepwater Test of Subsea Wirelining Techniques

Abstract

ABSTRACT The paper presents the findings of an offshore test of subsea wireline techniques. It describes the applications for subsea wirelining and its advantages over more conventional means of providing wireline intervention in subsea completions. The test was predicated by uncertainty as to the feasibility of extending proven subsea wirelining technology from relatively shallow waters in the North Sea, to the deeper waters now being developed in the Gulf of Mexico. A test fixture was installed on the sea floor in approximately 1500 FSW and specific wireline manipulations were conducted to evaluate the effects of deepwater on wireline operator "feel". INTRODUCTION As the search for oil and gas takes the industry into ever increasing water depths, subsea production technology will play an important role in the development of these resources. Subsea completions are finding increasing acceptance as cost effective and reliable solutions to otherwise uneconomic field developments. There is however, one significant barrier to widespread use of subsea production. That is, the ability to provide a cost effective means of downhole intervention using commonly employed wireline techniques. Historically, floating drilling rigs have been used to tie-back subsea wells to the surface to gain access to the well bore. The high cost of rig mobilization and operation often make this approach prohibitively expensive for low productivity wells requiring frequent wireline work. In response to the need for less expensive and more efficient wireline workover techniques, several subsea wirelining systems have been developed for deployment from a diving support vessel (DSV).1,2 These systems do not tie the well bore back to the surface support vessel. A subsea lubricator assembly mounts directly on top of the subsea Xmas tree and the wireline extends, unprotected, through the water column to the surface. Subsea wirelining has been successfully utilized in the North Sea in water depths up to approximately 600 FSW. However, there has been much discussion as to the feasibility of this technology in significantly deeperwater. Concerns largely focus on the potential loss of operator "feel" essential to the surface manipulation of the wireline. Therefore, a simple test was developed to investigate the feasibility of subsea wirelining in deepwater. This paper describes and presents the findings of the test. In order to put matters in perspective, discussion of the test is prefaced by a brief description of subsea wirelining technology. SUBSEA WIRELINING SYSTEM DESCRIPTION Subsea wirelining systems were developed to provide a means, other than by a drilling rig, of re-entering satellite subsea completions to perform routine in-tubing work. Drilling rigs are expensive to mobilize and have far more equipment than required for a typica1 wire1ine job. The net result can often be a total job cost in excess of the remaining productive life of an individual well. Subsea wirelining techniques were designed specifically for dep1oyment from other, more readi1y mobilized and cost effective, offshore support vessels such as a DSV or even a supply boat.