Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2001-09-07
2004-09-21
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C166S250100
Reexamination Certificate
active
06795773
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to well completion methods and more particularly to methods of defining fracturing treatments for oil or gas wells.
In completing an oil or gas well after the wellbore has been drilled, a procedure referred to as “fracturing” may be performed to enhance the productivity of the well. Fracturing in essence creates in the oil or gas-bearing formation an enhanced conductive path through which the oil or gas can flow more readily than through the unfractured formation rock itself.
Although fracturing may increase oil or gas flow from the formation into the wellbore, achieving this result may not be economically efficient if the cost of fracturing is more than the revenue that will be obtained from the increased production. Even if a fracturing process is economical for a particular well, the design of the fracturing job should be carefully made to ensure its success. The advent of the Three Dimensional Fracture Simulators (3-D) has helped optimize fracture treatments by predicting fracture growth in height. This has shown that many times the fracture grows out of the desired formation and thus reduces the effectiveness of the fracture treatment. This 3-D growth is key to fracture optimization and can be used to determine when the fracturing process is no longer achieving the fracture length growth and thus reducing the economic impact of the treatment.
A traditional way of creating a fracturing treatment design has depended upon the ability of a skilled person to select a fracturing fluid with which to hydraulically fracture the formation and a proppant which is to be carried into the fracture by the fracturing fluid and left there to prop the fracture open after the hydraulic pressure is released. The details and quality of a particular design of such a fluid system have depended upon the knowledge and experience of this person. Typically, that knowledge and experience are applied to select a fracturing fluid and proppant with whatever factors the individual designer has come to rely on. Maybe more than one such design is conceived, and maybe the designs are tested in a fracture modeling simulator to see what the simulator projects will be the resultant fracture for each of the designs. Economic analyses can be made for the various simulations using, for example, return on investment (ROI) or net present value (NPV) from a reservoir simulation of production results from each proposed treatment and cost of the treatment. From these cost versus production analyses, one of the designs is selected and used in controlling the pumping of the selected fracturing fluid and proppant into the well. If the skilled individual is at the well site during the fracturing treatment or otherwise in real-time communication, changes to the design might be made “on-the-fly” based on conditions that are monitored during the fracturing job.
One shortcoming of the aforementioned traditional technique for designing a fracturing job is that it significantly depends on the individual skill of the person who is designing the treatment schedule for the job. Thus, each fracturing job to be performed in this manner depends on the availability and ability of a particular person. This limits the design by a person's own shortcomings, and it hinders the transfer of knowledge gained from one area/formation into other areas or formations. This approach does not necessarily mean that the “optimum” fracturing treatment has been designed and delivered. One has to realize that the optimum treatment does not necessarily mean the largest. This type of approach also can provide a myriad of different possible designs to be analyzed by the simulator and economic factors.
In view of at least the foregoing shortcomings, there is a need in the well completion field, and specifically the fracture treatment design field, to reduce the dependency on specific individuals with unique knowledge, experience and ability; however, there is also the need to make such expertise more widely available so that it can be used consistently for more wells. There is also the need for a design technique that more easily arrives at one or more possible solutions than may be required for a human to directly create such design. There is also the need to arrive at possible fracturing treatment solutions based on actual well data and consistent, predetermined analytical factors. There is also the need to provide the ability to optimize a design, including economic optimization. Towards this goal we need to apply the knowledge gained through theory in a practical fashion reaching the right mix of sound fundamental work and field gained experience.
SUMMARY OF THE INVENTION
The present invention overcomes the above-noted and other shortcomings of the prior art and meets the aforementioned needs by providing a novel and improved optimization process for well completions in general and for fracturing treatments in particular. This process is to optimize the materials used (fluid, proppant, breakers, etc.) in the fracturing treatment as well as the height, length and width of the fracture to achieve the optimized fracture treatment based on the desired economic drivers. The stresses within the oil or gas bearing formation as well as the surrounding formations control the geometry of the fracture created. These stresses will determine the geometry of the fracture and can be modeled in a 3-D fracture simulator (FracPro®, FracProPT™, StimPlan™, M-Frac™, etc.) and this geometry is key to optimizing the fracture treatment.
Instead of starting with various fracturing materials based on some individual's personal knowledge or preferences and running simulations and economic analyses to project possible resulting production and cost, the present invention starts by determining a conductivity profile (preferably an optimum one) for the given reservoir to be fractured. Once the conductivity profile, for a constant pressure drop down the fracture, is determined for the given reservoir conditions, along with any other losses like multi-phase flow or gel damage, the materials needed to obtain this conductivity profile are determined by the respective material's performance and economics. The materials selected are based on their ability to meet the conductivity objective and their rank based on economic value to the fracture conductivity objective (for example, proppant judged on strength and cost/conductivity for given reservoir conditions, stress, temperature, etc.). In this way unsuitable materials are eliminated early in the analysis so that the materials to evaluate in the desired design are only those capable of achieving the final conductivity goal in an economical manner. Whereas a prior approach might result in a very large number of combinations of materials to evaluate to achieve the desired results by trial and error, the new approach of the present invention significantly reduces the combinations of materials for the design process and ensures that the materials in the evaluation process are only those that should be considered for the reservoir conditions. This ensures that the final simulations use the technically appropriate materials and are the best value materials for the desired conductivity objectives. The theoretical length desired for the formation to be stimulated should be verified by 3-D simulation for height, length and width before the appropriate materials are selected and the preferably optimized fracture geometry determined.
Adding a further step in the new approach of the present invention gives the designer a pumping schedule to be performed on the surface after an initial test in the actual well. This differs from the old approach in which a pumping schedule is first prepared and pumping of the job begun and then evaluated as to how close the pumping schedule comes to producing the desired conductivity profile needed for the reservoir conditions. Waiting until after a test is run on the actual well to provide a pumping schedule as done in the present invention
Byrd Audis C.
Soliman Mohamed Y.
Barlow John
Gilbert, III E. Harry
Halliburton Energy Service,s Inc.
Kent Robert A.
Le Toan M.
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