Selective Placement of Fractures in Horizontal Wells in Offshore Brazil Demonstrates Effectiveness of HydraJet Stimulation Process

Abstract

Summary Cased cemented completions have not been the preferred horizontal-well completion method in offshore Brazil. Lower-cost solutions such as uncemented preperforated liners were often used in completing horizontal wells offshore and are usually very effective. Often, however, low production rates mean that stimulation treatments become necessary for many wells. The use of conventional stimulation technology has generally been ineffective for these completions, which posed a challenge for the operator to find an effective solution for continuing developments in some fields. These challenges included reevaluating the more expensive cased cemented completions to allow more effective options for future stimulation, as well as trying to find newer stimulation techniques that can be effective with lower-cost completions (noncemented liners). In the attempt to find an economical yet effective stimulation solution, the operator chose to implement a unique and relatively new hydrajet stimulation technique that has a proven success rate in onshore applications. The technique can be applied in either sandstone or carbonate formations, which are commonplace in this field; therefore, stimulation plans in this area will include fracture acidizing as well as propped fracture stimulations that use a high concentration of proppants or curable resin-coated proppants (RCPs). This paper discusses the early results of this investigation. Wells that were completed and evaluated using different completion schemes are reviewed. Background As with vertical wells, underachieving wells are commonplace in horizontal completions. This situation can be caused by many things, such as unexpectedly low permeabilities in the area. However, among horizontal wells, underachieving wells are probably most often attributable to one or more of the following circumstances (McDaniel et al. 2002a; Surjaatmadja et al. 1994; Surjaatmadja et al. 2002a; Surjaatmadja et al. 2003; Abass et al. 1994, 1996):Permeability anisotropy (especially vertical permeability limitations).Skin damage or near-wellbore plugging of a natural fracture network.Ineffective stimulation techniques. The third circumstance is especially common in openhole horizontal wells, and even more so in wells that are completed using slotted or preperforated liners. Preperforated liners could even be deemed "unstimulatable" when conventional fracture-type stimulation techniques are being considered. Matrix-type stimulation or wellbore wall-cleaning techniques would probably be the only viable solution for production enhancement in this type of well. For moderate- to high-permeability reservoir applications, hydrajetting, when coupled with "squeeze" techniques (below fracturing pressures), has proved to be a very beneficial production-enhancement process (Rees et al. 2001; Surjaatmadja et al. 2002b). Unfortunately, because formation layers tend to be horizontal, horizontal wells tend to stay within one layer over a long distance, and permeability anisotropy becomes a serious problem. Another characteristic of horizontal wells is that they are often used in formations with very limited thickness; hence, their natural production performance has been artificially disadvantaged. Fracture stimulation techniques are believed to offer the best opportunity to achieve adequate stimulation under these conditions. One possible solution that has been attempted is the use of very high-rate water-frac treatments. These treatments have often produced a disappointing production response, and fracture-mapping techniques applied during some of these treatments have demonstrated the inefficiency of this treatment method when the operator attempts to create multiple fractures along the entire length of the wellbore (McDaniel and Willett 2002; Duttlinger 2001; Fisher et al. 2002; East et al. 2004). A logical continuation of this line of thought might lead to the use of sealing devices. Unfortunately, sealing devices such as inflatable packers tend to be ineffective when used in horizontal openhole completions, because fractures tend to jump over them, creating a passageway. For preperforated-liner applications, a passageway obviously has been established by the annulus region behind the liner. Based on these stipulations, the operator of an offshore Brazil field decided to implement a relatively new hydrajet fracturing process. This would be the first hydrajet fracturing stimulation performed offshore.

Consideration for Future Stimulation Options Is Vital in Deciding Horizontal Well Drilling and Completion Schemes for Production Optimization

“…This action may cause fluid to enter the formation matrix again at location "e" and from there directly enter the perforated liner. This type of completion "h" as been commonly used by some operators (McDaniel and Willett 2002;Surjaatmadja et al 2007). Similar outcomes can be achieved using expanded screens, uncemented liners, and prepacked liners.…”

Numerical Simulation of Jet Flow Field for Hydrajet Fracturing

“…Hyrajet fracturing technology was firstly put forward to resolve the problem of segmental fracturing for and the mechanism was recognized through corresponding study [1]. Henceforth, it was widely applied in oilfields [2][3][4]. Meanwhile, researches on fracture initiation and extension [5] as well as theories referring to annulus injection were conducted [6][7].…”

Mechanism and numerical simulation of pressure stagnation during water jetting perforation

“…Some laboratory experiments have been done to optimize the fl uid and the abrasive parameters in the AWJ perforation (Li et al, 2002;2006). Combining the AWJ perforation with fracturing, becomes a new technology, hydro-jet fracturing, in which packer can be eliminated, different intervals can be fractured, avoiding the risk of fracturing failure due to the packer sealing problem (East et al, 2005;McDaniel et al, 2004;Hoch et al, 2003;Rees et al, 2001;Surjaatmadja et al, 2007). The critical issue in this technology is that, at the blasting position, the pressure in the hole should be higher than that in the annulus (confi ning pressure).…”