Recent Innovations in Offshore Completion and Workover Systems

ABSTRACT Humble Oil &Refining Company has developed an offshore completion and workover system, for use with multi-well fixed platform development, which utilizes the tubingless completion and concentric tubing concept to effectively reduce completion and workover costs. Offshore drilling and completion technology has been improved to take advantage of the dual and triple 3-1/2-inch OD tubingless system. Sand consolidation and cementing techniques have been developed especially to take maximum advantage of concentric operations. Concentric 2-l/16-inch tubing has been used successfully as production tubing inside 3-1/2-inch casing to provide artificial lift capability and for higher pressure well installations. A recent innovation in self-contained rig design involving the use of a combination drilling concentric completion rig has been successfully employed to permit concurrent drilling and completion operations and to eliminate production delays which can result if concentric completion operations are deferred until the drilling rig moves off the platform. This "piggy-back" rig utilizes a small separate drawworks and crown block for handling concentric pipe inside the same 30' by 40' derrick and substructure used by the drilling rig. Additional speed, economy and versatility is anticipated with further system developments such as the coiled tubing unit. This completion workover unit can work on live wells safely and has smaller space requirements than concentric rigs. The coiled tubing concept may lead to other significant improvements in storm-choke technology, paraffin control, and artificial lift in offshore wells. INTRODUCTION Tubingless completions have been utilized in the oil industry for many years. During the late 1950's this type of miniaturization became the key development system for some of the most active drilling areas. Completion of wells by this technique is the cumulative result of developments in permanent-well completion techniques, modified cement, through-tubing jet perforating guns, optimum perforating conditions, and a large number of additional developments in equipment and techniques by the operating and service companies.1 The tubingless completion was more slowly adapted to offshore wells because of directional holes and different operating conditions. The offshore well is a more difficult application of tubingless completion techniques, but a look at offshore economics highlights the multiplied incentive for such major cost cutting. The higher investments warrant additional consideration for every aspect of offshore completions, but tubingless completions are available which are as safe or safer than the industry's typical conventional completion, and without the loss of both the operating and economic advantages of the tubingless well and with no compromise to the integrity of the well. Aside from initial completion savings, the cost of subsequent workover operations are grossly reduced, artificial lift maintenance is lower, and lost production from the other zones of multiple wells during workover or servicing of a given zone are materially reduced 2. Humble developed the tubingless completion and concentric tubing concepts further to obtain a new offshore completion and workover system, especially adapted to multi-well fixed platform development. The objective is an effective reduction in the total cost of reserve exploitation, including drill and complete, production, artificial lift, workover, and well servicing costs.