Horizontal drilling and completion advances in tight gas and shales have allowed access to significant new resources both in existing fields and new plays. Open hole multi-stage fracturing (MSF) technologies using ball operated sleeves and openhole packers have generally been effective in delivering high productivity wells, worldwide. Successful case histories treating tight shale gas with MSF completions abound in current literature, however, it is important to note that a majority of these case histories deal with reservoirs with high pressures. Often tight gas reservoirs are initially found to be over-pressured (higher than water gradient), but as with all depletion drive systems, the reservoir pressure depletes with the removal of fluids. Pressure depletion brings along with it its own set of challenges. The wells cease to have the ability to flow naturally to surface, liquid loading, and artificial lift are issues that come to the forefront. Conventional multi-stage stimulation that was seemingly fast and efficient in high pressure environment loses its appeal in sub-hydrostatic pressure wells. The time spent between each stimulation stage to the onset of well flowback becomes long and detrimental to the recovery of the well. The fracturing fluid lost to the formation can negatively alter the relative permeability of gas in the reservoir and the longer the time spent to recover the fluids the damage tends to get irreversible. Quick and efficient clean-up of fracturing fluid is indispensable to maintain a well's productivity in tight, low pressure gas reservoirs. A new generation of multi-stage completion systems is discussed in this paper. These multiple stage tools are operated by a single ball that opens several of the treating sleeves in one run thus allowing a large section of the reservoir to be treated simultaneously. The stimulation fluid placement is enhanced by pumping through limited entry ports of the stimulation sleeves at optimum injection rates supported by modern particulate diverting agents, and energized fluids. The operation time between the first stimulation (acid) stage hitting the formation to the well being flowed back can be cut down to a matter of few hours from an otherwise operation of a few days. The results from this step change in completion and stimulation design have been spectacular providing several folds of productivity improvement. This application provides a fundamentally sound solution for treating low pressure, tight reservoirs.

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This paper describes a game-changing solution regarding the use of metal expandable annular sealing systems in a high pressure multistage frac well. The design and engineering of this technology resulted in the development of fit-for-purpose equipment that overcame challenges often encountered in a high-pressure stimulation environment. The metal expandable annular sealing system was custom designed in order to provide high expansion that can be set in potentially washed out wellbores. The design included a long multi-element sealing system with built-in redundancy to account for fracturing fluid chemical reaction with the rock behind the seals. The system is just under 4 meters, complemented with multi-elastomer seals, each delivering full Delta P capability within a washed-out hole up to 6.5". The unique design allows full rotational capabilities during deployment, minimizing operational risks. The system was run in combination with multi open-close fracturing sleeves and a pressure activated toe sub rated to 10,000 psi for acid fracturing in three zones of a vertical carbonate well – the well was known for its heterogeneity and high reservoir pressure contrast. The use of mechanical packers with short sealing elements would have been challenging and increases the risk of unwanted communication between zones. Successful installations, activation of the sleeves and subsequent hydraulic fracturing were achieved, which enabled operational flexibility, reliable isolation and high expansion benefits. Acid fracturing treatment data from each of the stages were analyzed and used to confirm that the zonal isolation integrity. This paper includes the challenges of providing zonal isolation with conventional packer designs and details the design, testing and qualification of the solution as well as further design modifications for higher fracturing pressure rating.