Multistage Fracturing System: Improving Operational Efficiency and Production
- Rocky Allen Seale (Packers Plus Energy Services) | John Donaldson (D & J Oil Co.) | James Athans (Packers Plus Energy Services)
- Document ID
- Society of Petroleum Engineers
- SPE Eastern Regional Meeting, 11-13 October, Canton, Ohio, USA
- Publication Date
- Document Type
- Conference Paper
- 2006. Society of Petroleum Engineers
- 4.2.3 Materials and Corrosion, 2.5.3 Fracturing Equipment, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4.3 Sand/Solids Control, 1.2 Wellbore Design, 2 Well Completion, 1.10 Drilling Equipment, 1.6.6 Directional Drilling, 1.8 Formation Damage, 2.5.4 Multistage Fracturing, 1.6 Drilling Operations, 1.14 Casing and Cementing, 4.1.2 Separation and Treating, 3 Production and Well Operations, 5.8.2 Shale Gas, 2.2.2 Perforating
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Over the last several years there have been many technical developments in horizontal completion methods. These developments have been designed to better stimulate the entire horizontal interval. For cased and cemented applications, composite plugs have provided the ability to segment the horizontal wellbore into sections and divert the stimulation as designed. However, the process of setting a plug on coiled tubing (CT), perforating, stimulating and then repeating the process for the required number of stages to optimize production and then running back in with CT to remove the plugs can take weeks to complete. For open hole applications, horizontal stimulations have relied solely on bullheading in stages in an attempt to generate multiple fractures. This has proven in many cases to only stimulate certain sections of the wellbore leaving much of the horizontal section unstimulated.
A new completion system has been deployed in over 300 wellbores in various producing formations, such as sandstone, limestone, shale, dolomite and coal. This system uses a series of mechanical open hole packers deployed on the production liner with fracturing or stimulation ports located between the packers that allow for stimulation in each desired interval. Without the requirement of cementing the liner in place, all the problematic issues associated with cementing are eliminated. Additionally, the use of mechanical packers provides positive mechanical diversion at high differential fracturing pressures. The system has also been designed, so all of the fracturing or stimulation treatments along the horizontal wellbore can be pumped in one continuous operation, thus minimizing the associated risks and optimizing the efficiencies of both the personnel and equipment needed to perform the work. This paper will detail the operational efficiencies and reliability of this novel completion system, as well as analyze the cost benefits and production increases that have been noted.
Horizontal drilling has maintained steady growth for well over a decade and in many cases has become the exploitation method of choice for infill drilling and reservoir depletion. However, there were certain technology voids that were slowing the growth of horizontal drilling. These technology short comings were the ability to effectively stimulate or fracture the horizontal wellbore from the toe to the heel, particularly in reservoirs that were not naturally fractured. The use of limited entry and bullheading techniques provided little if any benefit compared to vertical wells. Post production analysis on the deliverability of horizontal wells in reservoirs such as matrix, heterogeneous and non-conventional formations showed a direct correlation to the completion and stimulation methods employed and their shortcomings in horizontal applications. Thus, the added expense of a horizontal well was not justified by the equal to or slightly better production results versus vertical wells.
For cased and cemented liner applications this issue was addressed some years back by limited entry techniques and then later by the use of composite bridge plugs set on coiled tubing (CT), followed by perforating and then stimulating the well. The cement provides the mechanical diversion in the annulus and the bridge plug provides the mechanical diversion in the liner. This process is then repeated for the number of stimulations desired for the horizontal wellbore. (Figure 1) After all the stages have been completed, CT is used to drill out the composite bridge plugs and establish access along the horizontal.1 Although effective, the inherent cost of multiple interventions with CT, perforating guns and deployment of fracturing equipment needed for each stage are extremely high, not to mention very inefficient and time consuming. This coupled with the associated mechanical risks often does not allow for the optimum number of fractures to be placed along a given horizontal interval. Production using this method can also be limiting, as cementing the wellbore closes many of the natural fractures and fissures that would otherwise contribute to overall production. Additionally, there is the issue of re-fracturing at a later date. With all the perforations open, the only feasible method for re-fracturing is to run packers and plugs on a workstring using a rig, which introduces added frictional forces, thus limiting the flow rate during the fracture so the optimum design cannot be accomplished. There is also the added expense of using a rig to perform this operation. Higher temperatures and pressures only exacerbate the problem with additional and repeated exposure for personnel and equipment.
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