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

Abstract

Cased cemented completions have not been the preferred horizontal-wellcompletion method in offshore Brazil. Lower-cost solutions such as uncementedpreperforated liners were often used in completing horizontal wells offshoreand are usually very effective. Often, however, low producing rates meanstimulation treatments become necessary for many wells. The use of conventionalstimulation technology has generally been ineffective for these completions, which posed a challenge for the operator to find an effective solution forcontinuing developments in some fields. These challenges included re-evaluatingthe more expensive cased cemented completions to allow more effective optionsfor future stimulation, as well as trying to find newer stimulation techniquesthat can be effective with lower-cost completions (noncemented liners). In the attempt to find an economical yet effective stimulation solution, theoperator chose to implement a unique and relatively new hydrajet stimulationtechnique that has a proven success rate in onshore applications. The techniquecan be applied in either sandstone or carbonate formations, which arecommonplace in this field; therefore, stimulation plans in this area willinclude fracture acidizing as well as propped fracture stimulations that use ahigh concentration of proppants or curable resin-coated proppants (RCP). This paper discusses the early results of this investigation. Wells thatwere completed and evaluated using different completion schemes arereviewed. Background As with vertical wells, in horizontal completions underachieving wells arecommonplace. This situation can be caused by many things, such as unexpectedlylow permeabilities in the area. However, in horizontal wells, underachievingwells are probably often attributable to one or more of the followingcircumstances:1–6Permeability anisotropy (especially vertical permeability limitations)Skin damage or near-wellbore plugging of a natural fracture networkIneffective stimulation techniques The third point is especially true in openhole horizontal wells, and evenmoreso in wells that are completed using slotted or preperforated liners.Preperforated liners could even be deemed as "unstimulatable" when conventionalfracture-type stimulation techniques are being considered. Matrix-typestimulation or wellbore wall-cleaning techniques would probably be the onlyviable solution for production enhancement in these type wells. For moderate-to high-permeability reservoir applications, hydrajetting, when coupled with"squeeze" techniques (below fracturing pressures), has proven to be a verybeneficial production enhancement process.7,8 Unfortunately, becauseformation layers tend to be horizontal, horizontal wells tend to stay withinone layer over a long distance and permeability anisotropy becomes a seriousproblem. Another characteristic of horizontal wells is that they are often used informations with very limited thickness; hence, their natural productionperformance has artificially been disadvantaged. Fracture stimulationtechniques are believed to offer the best opportunity to achieve adequatestimulation in these conditions. One possible solution that has been attempted is the use of very high-ratewaterfrac treatments. These treatments often produced disappointing productionresponse, and fracture-mapping techniques applied during some of thesetreatments have demonstrated the inefficiency of this treatment method when theoperator attempts to create multiple fractures along the entire length of thewellbore.9–12 Logical progression of thought might lead to the useof sealing devices. Unfortunately, sealing devices such as inflatable packerstend to be ineffective when used in horizontal openhole completions becausefractures tend to jump over them, creating a passageway. Forpreperforated-liner applications, a passageway has obviously been establishedby the annulus region behind the liner.

Perforating for Fracturing—Best Practices and Case Histories

“…Applications of this technology and process are well documented and will not be repeated here; a few of the many available references are included in this paper's bibliography. [5][6][7][8][9][10] Most relevant to the HJ-Frac process in this paper is the hydrajet perforating step. Following the perforating step, the HJ-Frac technique will usually pump 100% of the proppant slurry through the jets and use the localized high-energy jetting to "hydraulically" isolate the frac slurry to enter only the fracture at the current jetting location from fractures previously placed below the current frac location, without the need for mechanical isolation methods.…”

“…If jetting continues as the wellbore pressure is increased when formation breakdown is desired, the actual pressure inside this tunnel will be hundreds of psi above the wellbore pressure to assist fracture initiation from the tunnel itself. [5][6][7][8][9][10][11][12][13] This would rarely happen in conventional perforations in hard or very low perm reservoirs.…”

Horizontal Well Completion and Stimulation Techniques--A Review With Emphasis on Low-Permeability Carbonates

“…Noncemented Well [20][21][22] The Macaé/Quissamã is a carbonate formation present in various fields (Bonito, Cherne, Congro, Enchova) in Campos basin offshore Brazil. The Congro field was discovered in 1977, in water depths from 190 m to 600 m, and started production in 1985.…”

“…The solutions to overcome these difficulties and other operational details were presented in previous papers 21,23 . The solutions to overcome these difficulties and other operational details were presented in previous papers 21,23 .…”

New Multiple-Interval Fracture-Stimulation Technique Without Packers

“…[2][3][4][5][6][7][8][9] The method incorporates hydrajet perforating and fracture initiation, followed by the fracture treatment, where generally all the treating fluid is pumped through the tubing string and out the jet nozzles (Fig. 1).…”