MULTI-STRING TUBINGLESS COMPLETION TECHNIQUE

摘要

Method and apparatus for completing multi-string tubingless underwater wells with through flowline (TFL) pumpdown tool servicing capability. A subsea borehole is drilled through the productive oil and/or gas formations. At least two parallel small diameter casing strings are run into the borehole guided by a riser assembly. These casing strings have a common hanger at their upper ends and are connected together at various levels with a plurality of gas-lift crossover mandrels and at least two (upper and lower) circulation crossover mandrels for tool circulation. Then a Xmas tree is lowered on a disconnectable running pipe to a wellhead guided by guidelines. The Xmas tree has at least two parallel small diameter casing strings extending from the lower end thereof. These upper casing strings have a common connector on their lower ends for connection to the hanger. Each upper casing string fluidly communicates with a lower casing string through the connector and hanger. A tensioner located in the Xmas tree applies tension to both the upper and lower sections of casing strings and properly spaces out the upper ends of the upper sections of casing strings in the Xmas tree. The upper ends of the casing string sections in the Xmas tree are connected to a production manifold. Suitable control fluid conduits are lowered with the Xmas tree for operation of the tensioner and for operation of safety valves located in each of the upper sections of casing strings. The lower circulation crossover port between two of the casing strings is then opened for perforating operations. A perforator gun is landed in a landing nipple adjacent a formation and is reciprocated until it rotates to the proper direction to avoid perforating the other pipe string in the borehole and then is fired. After each of the formations has been perforated, production of the formation may be maintained by natural formation energy. Various well servicing operations may be carried out using pump-down tools and techniques. A producing formation or zone may be blocked off using a pump-down patch tool and the well fluids may be artificially lifted by positioning pump-down gas-lift valves in one of the casing strings.