In the past, a casing string would be cemented, followed by a perforation procedure initiated after a specific zone is isolated from the wellbore through the use of packers. Thereafter, when production is required from other zones in the well, the procedure is repeated and the new zone for production is isolated with packers and perforated with a gun. Thereafter, the customary steps of stimulation, reversing, and setting a completion packer are accomplished and the work string is removed. Thereafter, production can begin. A 1989 paper by Damgaard given to the Society of Petroleum Engineers, Paper No. SPE-19282, describes a system wherein multiple zones are perforated and isolated individually with packers and sleeves. The production can be from one zone or multiple zones. Subsequently or at about the same time, the use of casing sleeve valves evolved such that access to the formation could be obtained through dissolvable plugs located behind sliding sleeve valves in the casing. Typical of such applications are U.S. Pat. Nos. 4,880,059 and 4,991,654, Such designs had several shortcomings as far as being able to orient sufficient fracture pressure into the formation. The internal pressure built up in the casing to begin the dissolving process of the plugs illustrated in U.S. Pat. No. 4,880,059 could tend to unevenly erode the plugs, creating flow short circuits. This would reduce the differential pressure on undissolved plugs and would tend to impede their rate of dissolution. The additional resistance offered by the plugs which slowly dissolve would decrease the available pressure into the formation by the fluid in the casing. This was because any pressure drop taken across the plugs which have yet to fully dissolve would decrease the available pressure drop into the formation from the fluid in the casing. The lack of a conduit for communication for the flow that ultimately penetrates the dissolving plugs also tended to reduce the concentration of force applied to the formation through the opening in which the dissolving plug was mounted and thereby reduce the overall stresses applied to the formation in an attempt to fracture the formation. Much earlier, telescoping access ports were disclosed in U.S. Pat. No. 3,359,758. In that patent, multiple tubing strings were run, each of which had a telescoping outlet at a different depth. The wellbore was then filled with cement, with each tubing string swabbed to induce any obstructing cement over the telescoping openings back into the wellbore so that it can be removed to the surface. Thus, the telescoping openings were used more for positioning of the tubing rather than as a mechanism for inducing formation stress. These telescoping outlet assemblies did not contain a prepackaged fluid which could move out with the telescoping conduit to keep it free of cement or wellbore fluids.
The apparatus and method of the present invention allow access at multiple levels without perforation. The movable pistons extend outwardly to create fracture stresses in the formation. Through pressure in the tubing, in combination with the disclosed rupture disc assemblies, additional stress is put on the formation from fluid force coming behind the bursting of the discs. Further, the pressure acts to drive the movable pistons further into the formation to the extent they have not achieved their full outward movement by the time they are displaced toward the formation prior to breakage of the rupture discs. The fluid energy is transmitted directly to the formation through the flowpath created by the pistons to further aid in fracturing the formation for subsequent production from the well.
When a specific zone is played out, a valve adjacent that zone may be closed and a separate valve opened with a shifting tool to allow access for production from a different zone or from a different location of the same zone. The single packer above the highest completion is used, regardless of which zone is aligned for flow into the casing.
The method of the present invention also facilitates rotation of the casing during the cementing procedure.