Jim B. Surjaatmadja

Successful Pinpoint Placement of Multiple Fractures in Highly Deviated Wells in Deepwater Offshore Brazil Fields

The application of hydrajet technique to stimulate highlydeviated and horizontal wells has become a successful method to improve well productivity for different field conditions in the world. In the past 2 years, an operator company has successfully implemented a relatively new hydrajet stimulation technique in shallow waters off Brazil. In deepwater locations, additional problems had to be overcome, which proved achievable using this new technology. This paper discusses a reservoir-based methodology to determine the optimum number of transversal fractures for a horizontal deepwater well. The method starts with the review of geology and stratigraphic aspects of the field to better understand the relationship between fracture orientation, geological faults, and regional tectonic effects. With this preliminary characterization, well-log interpretation of the pilot well and horizontal wellbore is performed to identify porosity and permeability index of the carbonate formation being drilled. A study using well testing and nodal analysis is conducted to verify reservoir properties based on real production data. Next, a numerical simulator is used to obtain a production forecast varying the number of transverse fractures intersecting the well. Finally an economic evaluation of net present value vs. number of fractures is performed to determine the optimum number of transversal fractures. Production results are then evaluated and compared to the other stimulation attempts in offshore horizontal completions in the area.

First Applications of a Multiple Fracturing Method in Noncemented Horizontal Offshore Wells

This paper presents the first offshore applications, both in platform and subsea wells, of a multiple fracture creation process in openhole horizontal wells, previously applied in onshore scenarios. The applications had to overcome many challenges typical of workovers on mature field offshore wells. The paper covers detailed workover planning, multiple fracturing designs, operations data, and the stimulation results. The campaign comprised three horizontal slotted liner wells offshore Brazil as part of a research project to evaluate selective stimulation methods for horizontal wells. It was proved that the method can be successfully applied in platform and subsea wells (a first). The economic results were very attractive, making the method an alternative for hundreds of noncemented offshore horizontal wells.

First Implementation of HydraJet Fracture Acidizing in Deepwater Offshore Brazil Fields

The placement of multiple fractures in horizontal, deviated wells is usually more difficult than placement in vertical wells. When completed with uncemented preperforated liners, such treatments become much more difficult and often are ineffective using conventional stimulation methods. When found in offshore locations, these wells present even more problems. Recently, in the shallow waters offshore Brazil, a relatively new hydrajetting technology was used with great success. However, additional complications arose when hydrajet fracturing was elected to stimulate a subsea well. This process requires dual high-pressure connections to the wellbore, including placement of a tubing string inside the full length of the well. Maintaining the hydrajet tool in position during each fracturing stage was a big issue in a floating rig. The need to pull tubing between stages of the stimulation process also poses a challenge. Because this operation occurred in a subsea well, it was the first such application ever attempted worldwide. Extremely detailed planning was essential to the ultimate success of the operation. This paper discusses the rigorous planning involved in implementing multistage hydrajet fracture acidizing in a subsea well offshore Brazil. During the operation, all challenges, mechanical or otherwise, were meticulously scrutinized, including the proper operation of the stimulation vessel and riser motion. This paper also presents posttreatment production results evaluated and compared to other stimulation attempts in offshore horizontal completions in the area.

Finite Element Analysis Shows Screenout Development and Cement Bond Destruction in Horizontal Wells

Premature screenouts during proppant placement have often interfered with fracturing treatments of cased horizontal wells. Fractures and tortuosities are believed to cause reduced fracture widths, which in turn are believed to be the primary causes of screenouts. No one can be certain which (or if either) of these two phenomena is the primary cause of screenout. This paper investigates a theory that could a furnish third factor causing screenouts, even after treatment engineers take extreme precautions to avoid tortuosities and multiple fractures. This investigation focuses on the complex interaction of the fracturing fluid flow and the mechanics of the fracture using finite element analysis. The modeling primarily addresses the radial fracture occurring perpendicular to the borehole of a cased horizontal well. The Darcy-Weisbach relationship is used to analyze the fracturing fluid that flows radially in the fracture while it drains into the producing formation. From this analysis, pressure distribution across the fracture can be computed and used as inputs to the finite element model. By using this technique, fracture-width development may be evaluated, so that screenout predictions may be made before the job. Possible solutions to avoid such screenouts are also evaluated using the Finite Element Analysis (FEA) technique. Finally, different tools and solutions, such as expansion joints and hydrajet perforating are also analyzed using this approach and are presented in this paper.

Harvesting Downstream Energy to Improve Efficiency: Creating Apparent Discharge Coefficients of Jet Nozzles Greater Than 1.3

Fluid movement devices use upstream energy to move fluid from one location to another. Flow nozzles that slightly accelerate fluid motion, especially into the same direction, often exhibit discharge coefficients greater than 1.0. Jet nozzles, however, by definition, create a jet stream that is much faster than the upstream fluid, often exceeding 100-fold higher velocities. Energy used to move this fluid is often very high; jetting efficiencies are generally less than 1.0 and will only approach 1.0 if the shape of the entrance is such that there is no “vena contracta” within its flow regime inside the nozzle.High-pressure nozzles require high horsepower to generate high-velocity fluids. As is commonly performed, power is created using high-powered pumping equipment. Oftentimes, nozzles are used to jet in locations that have high ambient pressures, such as at the bottom of the ocean or inside a deep oil well. At these locations, the hydrostatic pressures could be very high. Pressure at the upstream side of the nozzle would be even higher.This paper discusses the design and use of a unique nozzle that uses the hydrostatic (potential) energy to accelerate the fluid velocity of the jet. In essence, the nozzle uses the downstream energy to perform part of its job, thus, substantially reducing the upstream pressure requirement. This phenomenon was proven to occur using CFD analysis. Laboratory tests have shown apparent discharge coefficients between 1.38 and 1.69, depending on the downstream pressure.Copyright

Mechanical Engineering in Stimulating Well Production in the Oilfield

A mechanical oil field engineer could very well be the most diverse position within the industry. Various tasks, such as entering a wellbore to a depth of 25,000 ft to deliver equipment capable of pumping sand slurries at pressures greater than 15,000 psi and temperatures often higher than 350°F, are unique to the job. Yet, there are even more areas where the mechanical engineer could excel, to include stimulation (including fracturing/fracking), rock mechanics (static or dynamic), or even geomechanics.This paper discusses examples of mechanical engineering improving traditional approaches to well stimulation technologies. In one example, the commonly known Bernoulli equations were used to formulate a unique formation fracturing technique. Using this technique, fracturing fluid zonal distribution, which traditionally has been performed using mechanical wellbore sealing devices, was diverted using dynamic isolation of a high-pressure wellbore operation (i.e., sealing using fluid velocity). The effectiveness of such a process was demonstrated by completing the task in less than one tenth of the time required when using conventional (mechanical) techniques.In another example, fluid rheology parameters were applied to formation rock response, simulating the formation movements as if they were a very viscous, non-Newtonian fluid. The rock could hence be modeled as if it were plastic, using the Kelvin-Voigt relationship. The primary intent of this exercise was to provide an improved stimulation technique to the oil industry, thus providing much better producing wells in the future.Copyright

High-Reduction, High-Torque Gear Reducer Design Emphasizes Compactness

The design of high-torque, high-reduction gear reducers often requires the use of multi-stage gearing, planetary gear systems, or both. Because these systems contain many independent parts, they often become bulky. When these systems will be used in downhole oilfield equipment, compactness can become a crucial factor. Moreover, downhole oilfield equipment generally requires that areas of the system be reserved to provide some fluid flow-path around the equipment. A unique gear reducer was designed to accommodate this need for compactness. The new reducer system consists of only four gears, two of which are built as a single part. All four gears are positioned roughly concentrically within a donut-like space, and the open center accommodates fluid flow. Unlike other gear reducer systems, this system employs not only a ratio (divisional) method, but also a unique subtraction method. Consequently, a reduction of more than 2000:1 is possible. With this radical design, conventional gear teeth cannot be used if good meshing is desired. Subsequently, a special gear tooth shape was designed to provide surface contact between the teeth. With this special shape, full contact of more than 30% of the teeth can be achieved, compared to one or two teeth in standard designs. Thus, the new system also improves load-transmitting capacity. In this paper, the design of the new gear reducer is discussed in detail. A specific application in which high-pressure, sand-laden slurry is pumped through the center of this gear reducer is also discussed.Copyright