Effect of Pump Rate in Fracturing Treatments
Pump rate is a critical component of any successful hydraulic fracturing treatment. In application, once the formation in situ stress is overcome and fracture initiation occurs, the pump rate must be sufficient to overcome the natural formation leak off rate just to hold the fracture open. Additional pump rate is then required to increase downhole pressure and facilitate further propagation of the fracture. Conventional fracture geometry models utilize pump rate as a variable and generally predict greater fracture length, height, and width with increased pump rates.
Higher leak off rates are often observed in naturally fractured reservoirs thus requiring higher pump rates to propagate fractures. Studies have indicated that in naturally fractured reservoirs, fractures not only initiate near wellbore but higher pump rates can also induce additional propagation at natural fracture interfaces further from the wellbore. Thus increased pump rates tend to improve the overall fracture network efficiency within naturally fractured reservoirs.
Pump Rates in Limited Entry Applications
The most common Limited Entry technique is the Plug and Perf Completion (PnP). In this particular application, multiple perforation clusters are treated simultaneously within each stimulation stage. Due to heterogeneity within the formation, individual perforation clusters may be exposed to different in situ pressures and frac gradients. This can subsequently result in a lack of uniformity during the stimulation treatment. If fracture initiation occurs first at one perforation cluster then any additional pump rate may divert to this location and propagate this fracture rather than contributing to fracture initiation at the other clusters.
In order to initiate and propagate fractures at other clusters, a substantially higher pump rate is required as compared to stimulating one cluster at a time. The progressive nature of this scenario can lead to very high pump rate requirements in an attempt to achieve stimulation of all clusters. Even so, the lack of control during treatment of multiple clusters can result in over stimulation of one or more clusters while little or no stimulation occurs at other clusters within the same stage. As a result, high horsepower demands are typically associated with PnP completions in order to generate very high pump rates.
Pump Rates in Single-Point Entry Applications
Single-point entry techniques can be configured to allow stimulation treatment of one cluster at a time within each stage. Treating each perforation cluster individually results in lower pump rate and horsepower requirements per stage as compared to PnP completions. Individual treatment also allows more control over the fracture modeling and affords a better capability to make any needed changes in real time during each pumping stage. Examples of this type of completion are coiled tubing deployed systems and ball drop completions.
The Stage Completions systems offer a potential pumping advantage from a mechanical standpoint when compared to other Single-point entry systems. Both the SC Bowhead and SC Bowhead II systems utilize large bore collet sleeves throughout the length of the wellbore. Additionally, the SC Bowhead II utilizes a dissolvable ball and collet activated fracturing sleeve system which has an equal large bore diameter through each collet.
The resultant larger flow area through the lateral section can result in reduced friction loss during pumping as compared to other systems. By comparison, coiled tubing deployed systems require coiled tubing to remain in the hole during pumping and the net flow area of the lateral is reduced by the cross sectional area of the coiled tubing string. Likewise, ball drop systems require a series of ball seats with graduated inside diameters. As the seat diameters are reduced along the lateral section, net flow area becomes restricted and additional pumping friction can be introduced to the stimulation treatment.
In many cases, less horsepower has been required to pump the treatment once implementing Stage Completions systems. The reduced horsepower requirement has resulted in potential cost reductions for fracturing operations. Operators have also experienced better real time control during pumping operations, and more accurate treatment modeling has translated itself into improved production results across the board.
Forward Thinking Industry Leaders Recognize the Advantages of Single-Point Entry Technologies
Single-point entry completion technology offers clear technical advantages in regard to controlled fracture placement and stimulation efficiency as well as the ability to fracture each individual stage at a higher rate. The trending emphasis on choosing the best completion practice for each well application should lead the industry as a whole to give serious consideration to these systems, and Stage Completions strives to remain an innovator and pioneer in this arena as the industry continues to adopt these technologies.
As the global demand for fracking continues to climb, new pumping technologies must be developed to ensure service companies can efficiently operate in more complex geological formations. Innovation will remain the key to success in the oilfield.
About this Blog
In this blog, we hope to engage the oil and gas community with information about multistage fracturing. We think analyzing and offering our expertise about the ways our industry is evolving will help others seek the most innovative technologies and practices as they become available. If there’s a subject you’d like to know more about, please let us know. Thank you for joining us in the conversation.