A computer model is presented for predicting downhole wellbore temperatures in flowing or shut-in fluid streams, in casing and cement, and in formations. Flowing options include injection/production, forward/reverse circulation, and drilling. Model predictions agree with field temperature data. The influences of temperature, flow rate, and depth on downhole temperatures are presented. Introduction Temperatures in a well are important for many aspects of drilling, completion, production, and injection. A few applications that require an understanding of the downhole temperature history in a well include (1) cement composition, placement, and setting time, (2) drilling mud and annulus fluid formulation, (3) packer design and selection, (4) logging tool design and log interpretation, (5) wax deposition in production tubing, (6) corrosion in tubing and casings, (7) thermal stresses in casings and tubing, (8) permafrost thaw and refreezing, (9) wellhead and production equipment design, (10) drill bit design, and (11) elastomer and seal selection. Of course, many other applications may exist. Two interesting possibilities are computing undisturbed formation temperatures from flowing stream temperature measurements and anticipating abnormal pressure zones from fluid temperature changes while drilling.Hostile environments present even more challenging needs for downhole temperatures, while making it more difficult to determine what temperatures to expect. Any unusual temperature conditions can make previous temperature experience and intuition unreliable. Abnormal temperature gradients can cause a rapid rise in flowing fluid temperature, and unusually deep wells expose fluids to hotter temperatures for longer times. In arctic environments, cool permafrost zones can cause unexpectedly low temperatures throughout the length of a well, both in and below the permafrost. Conversely, geothermal wells exist in unusually hot regions, resulting in abnormally high temperatures in a well. An understanding of downhole temperatures is needed in hostile environments for the same applications as more conventional wells and perhaps for additional needs, but determining those temperatures is more difficult.Determination of downhole wellbore and earth temperatures is a complex task. Many variables influence temperatures, which are continuously changing with time. Temperature recording devices have been developed, but these provide only isolated data points for a transient quantity and, furthermore, cannot provide sufficient information to establish the relative importance of variables influencing temperatures. Therefore, a means of computing downhole temperatures is needed to determine important design criteria, such as maximum temperature and time for exposure to high temperatures. Many simplified analytical techniques and some correlations of experimental data have been constructed in the past, each with limited success in predicting downhole temperatures. Experience has demonstrated that a computer model is needed to account for complexities of heat transfer in a well. JPT P. 1509^
A mathematical model of a buttress-threaded connection was developed to compute the strain limit of casing. The model results are compared with full-scale test results and predictions are made of the casing strain when the connection fails for various conditions of temperature, pressure, and connection assembly. Introduction Usually, well casing is designed so that the applied axial forces are not sufficient to cause yielding. However, for limited strain problems it is possible to load certain casing types beyond the yield point without causing a failure. Two examples of limited strain problems are soil subsidence and thermal expansion and contraction. For these types of problems, a displacement load is imposed and the stress is determined by the material properties. Permafrost soil subsidence caused by thawing induces a displacement-type load. To design for such loads, Atlantic Richfield Co. and Exxon Co., U.S.A.. have performed tests and calculations to determine the strain limit performed tests and calculations to determine the strain limit of 13 3/8-in., 72-lb/ft, N-80 buttress casing, which is used as surface casing in many Prudhoe Bay wells. Although full-scale casing connection tests have been conducted, the experimental measurements provide information for only a few special loading conditions. To investigate the effects of changes in loads, geometry, or material properties, the ability to calculate stresses and strains in the casing connection is needed. A computer model has been developed to perform a stress analysis of the threaded connection. Test data and model calculations establish the criteria for strain limit design of a 13 3/8-in., N-80 buttress casing. Model Description The problem of concern is diagrammed in Fig. 1. Since the geometry and loading are axisymmetric, an axial cross-section of the pipe may be analyzed as a twodimensional problem, with circumferential effects accounted for in the calculations. Moreover, a plane of symmetry exists at the center line of the collar. Therefore, it is possible to hold the center-line position rigid and apply the axial deflection across the end of the pipe section. pipe section.The mathematical model used to perform the stress analysis of the threaded connection was developed by Prototype Development Associates. The computer code Prototype Development Associates. The computer code uses the finite-element method to calculate stresses and strains for a given load system. Several features made the code adaptable to a threaded connection analysis. Mechanical properties may be approximated by a bilinear constitutive relation that accounts for yielding in the threads during deformation. The particular stress-strain relation selected for calculation is described in another section. Another nonlinearity is introduced by modeling the interface between mating teeth. This surface is capable of carrying a considerable compressive load, but the thread surfaces must separate without resistance under a tensile load. A special interfice element accounts for this nonlinearity and allows for resistance to shear motion, which is used to approximate frictional resistance to radial thread separation. This friction is most important near a failure condition where deformation is significant. The effects of connection assembly loads are modeled by specification of initial displacements that describe the appropriate interference fit between pipe and coupling. For the 13 3/8-in. buttress-connection analysis, approximately 2,000 finite elements and 2,200 nodes are used. JPT P. 355
This paper covers research funded by the API Production Research Advisory Committee (PRAC) on leak resistance of ~PI 8-~ou~d connectors. It details the sensitivity of leak resistance to variations in makeup turns, pipe diameter, grade, and applied tep-Slon. FIndIngs show that the leak resistance of the connector relative to pipe-body ratings increases with the number of makeup turns ~nd decreases as diameter and yield strength increase. Finally, tension is found to lower leak resistance in a manner that renders hydrotesting Insufficient for defining leak resistance in typical service conditions.
Temperature of cement is an important factor in properly cementing deep well production liners, yet current methods of determining cement temperatures do not account for all variables. In this paper a computer model predicts temperatures of cement while pumping and while waiting on cement, compares computed and measured temperatures, defines the importance of certain cementing variables on temperatures, and provides an explanation of difficulties encountered while cementing liner tops.
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