Expandable tubulars (ET) are being used increasingly by the oil and gas industry during the drilling, completion and workover phases of wells. Expandable systems potentially offer great economic benefit by simplifying string design, reducing costs and allowing access to previously uneconomic wells, especially those in deep water.
The expansion process involves cold-working steel tubulars, a process that by its very nature is highly non-linear due to material yielding, tight contact, sliding and friction. The expansion process can have a significant effect on the expandable systems' material properties and behavior. In turn, this affects the materials' post expansion behavior and properties. The important parameters are the post-expansion properties of the tubular, such as collapse strength, change in length, wall thinning, and if a perforated or wire wrapped sandscreen is to be used, well engineers may want to calculate the increase in flow area or other changes to perforation geometry.
Complex analytical models have been developed and used by Technica-NNC to provide the manufacturers of expandable systems and tubular products with the data required to optimize system design. These complex models have been modified and redeveloped to provide output data in a format that can be utilized not only by the system designers but also by well engineers tasked with designing and implementing well applications. Access has been made efficient and easy through the development of a Web-based process called WellConstructor.
What is WellConstructor?
WellConstructor is a Web-based consultancy service that allows engineers to gain detailed insight into the post-expansion properties of ET. The program analyzes the information provided and produces output data that can be used by designers and well engineers while safeguarding the sensitive and client specific information generated by the original models. It is used to simulate the material properties of tubulars when exposed to the near-wellbore conditions in a predetermined wellpath during the deployment and expansion process, allowing accurate selection of the correct ET system.
The software bridges the gap between the system design stage and the field implementation process by providing the accurate data to minimize operational risks associated with ET applications. It can be applied to the analysis of both solid cone and rotary cone expansion methods, and incorporates an array of attributes to enable quick, systematic and accurate evaluation for well design solutions.
WellConstructor provides problem definition by converting client data into a detailed numerical model based upon a sophisticated finite element non-linear analysis code, combining material data such as Young's modulus, yield stress, etc. and relevant boundary conditions to accurately predict the tubular's expanded shape and residual stresses. The process takes into account the surrounding formations' influence on the expansion process and determines if differential sticking could be a problem. Formation stresses are synthesized using careful selection of appropriate formation models within the finite element code.
Hotline support is provided by experienced engineers/analysts in the form of telephone and e-mail. Work is performed under a mutually-agreed confidentiality agreement with solutions to standard problems provided within a fixed time scale (5 days) and at a fixed cost.
The system can be accessed either via the Technica-NNC Web site www.technica-nnc.com/wellconstructor or the specific WellConstructor Web site. Information can be input either by the individual or by sending the data to a Technica engineer. Secure passwords are required to allow data input, output data is sent by e-mail. Individual company specific sections can be included in the site to allow multiple users to access company specific data; alternatively the site can be modified for installation onto a company's server.
The Web-enabled interface allows well engineers to enter data that describes their expandable scenario in terms of tube geometry, tube material, expansion tool geometry and formation properties. If no detailed data are available, the engineers can choose generic data from the system. This allows a first pass analysis allowing high-level comparison, "optioneering" against conventional technology to be carried out. When the decision is made to go ahead with a well application then more accurate and application-specific data can be input.
The data required depends on the analysis requirements. A standard analysis requires details for the geometry of the well and tubulars, the material properties, fluid density, pressure and temperature, expansion system type and, if possible, configuration and how the constraint method is to be used. If a more complex non-standard option is required, then additional data are needed. For example, if analysis is required on a perforated sand screen application or representative formation, then perforation geometry or an appropriate description of formation properties is required.
Wellconstructor utilizes a solving engine based on advanced computational techniques, running on multiprocessor and Silicon Graphics workstations, which are able to compute the analyses quickly. It employs the computational technique finite element (FE) analysis and uses the well-established computer code ABAQUS. The program uses a carefully constructed parameterized script that can instantly create a model of the tubular and the expansion tool according to client's specifications, reducing the need for
in-house specialist analysts. Included in
the model are mathematical representations of:
boundary conditions representing how the tool and tube are constrained;
tubular geometry, including any perforations; and
material properties and, if required, formation properties.
Once the analysis has been completed, an electronic data sheet is output that lists the input data and the most important results from the program. The output data for a standard expandable analysis include the load required to initiate and sustain expansion, the change in tubular length as a result of expansion, the strain distribution (both axial and hoop) within the tubular and how this compares with the theoretical value that will cause rupture, the final shape of the tubular, the contact pressure experienced during the expansion process, torsional vibration, safety factors for loads and stresses and the residual stress in the tubular.
All data can be expressed graphically. Where input data are available, sophisticated 3-D outputs can be provided, for instance for a differentially-stuck liner or a perforated tubular.
Output Data Examples
Tool push load as a function of tool displacement through the tubular.
Change in liner length as a function of thickness of tubular wall (if using fixed push cone this is shortening, if rotary this is lengthening).
Liner rupture - comparison of the strain across the length of the tube with the percentage strain that would cause rupture.
Final shape - equivalent to plots relating to strain, but quoting absolute values.
Contact pressure - contact pressure along the length of the tube mid way through expansion process.
Stress plots - 2-D section though tube with contour plots showing residual stress.
Tubular thinning and elongation
To date, the process has been used as a design optimization service to identify and eliminate any weaknesses in client's system designs before manufacturing a prototype. The technology is used to maximize the reliability and working life of clients' products, expandable systems, tubular and thread components to bring them to the market place faster, at less cost and with greater confidence.
Technica-NNC has undertaken a large number of expandable analyses; all based upon the WellConstructor numerical analysis techniques. Comparison exercises have been performed, which demonstrated that program results compared well with physical tests.
Work is ongoing to link WellConstructor to the Technica-NNC probabilistic risk assessment software package, WellFocus, a risk-based decision-guiding tool to help identify the most economical and lowest-risk well engineering option, during planning and operations. The software is used to challenge technical limits and manage the mitigation of project specific risks. Designed by well engineers for well engineers, this program will capture, store evaluate and rank operational risk throughout the lifecycle of a well or series of wells. By using both programs, the package incorporates an array of attributes to enable quick, systematic and accurate evaluation design solutions, comprehensive triaxial design, working stress design for burst, collapse and axial installation and service life loads. These applied engineering approaches are supported through to delivery with a full multi-discipline risk based time and cost modeling approach to evaluate fully all operational risks. Both tools can be used, either at the high-level screening stage or at the detailed planning stage of an ET project.
The WellConstructor process is the first step to help take ET from the development stage to field implementation by providing well and drilling engineers with the information required to help reduce operational risks which presently exist. ET development is aimed at providing single-diameter well bores. The program will develop and evolve along with the technology to provide a design tool for slim/monobore wells. It is also hoped to develop a set of standard design rules and data for each type of tubular, thread connection and expansion method entering the market.