TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMaximizing hole conservation while optimizing well economics in both conventional and deepwater wells is a continual challenge. Addressing these challenges with new technology has provided some significant solutions, but the uncertainty when utilizing new technology with no proven track record must be risk-weighted.Solid Expandable Tubulars (SETs) have been installed in both openhole and cased-hole wellbores from November of 1999, in a variety of environments in wells on land, offshore and in deepwater to solve a range of drilling and completion challenges.This paper will discuss the drilling case histories in depth including:• Descriptions of drilling challenges surrounding the use of SETs and their next best alternatives

Thermal effects on wellbore stresses can have a significant impact on effective fracture gradients. Changes in wellbore temperatures caused by various drilling operations provide for these thermal effects. For example, circulation on bottom usually results in lower bottom hole temperatures than the static geothermal temperature. This cooling effect reduces the wellbore stresses resulting in lower effective fracture gradients. Minimizing the cooling effect by increasing wellbore temperatures can increase effective fracture gradients and the corresponding pore pressure/fracture gradient margin avoiding costly lost circulation and additional unnecessary casing points. This paper presents results from leak-off tests taken at various temperatures which demonstrate the thermal effect on formation stress. This paper also examines the effects of operational factors on wellbore temperatures to minimize the cooling effect and/or increase effective fracture gradients. Software developed for thermal simulation of various drilling operations was used to perform the analysis. Introduction An investigation of historical lost circulation events, particularly in deepwater environments, resulted in considering the thermal effects on formation stress as a possible cause. A test was performed where leak-off-tests were taken at varying temperatures to confirm that the results would indeed be affected by wellbore temperature. The results of this test are presented in this paper. Subsequent analysis of historical lost circulation events in several deepwater wells indicated that at a minimum, there was at least a strong correlation between wellbore temperatures and a significant number of these lost circulation events for which several examples are presented in this paper. An understanding of the various factors that influence wellbore temperature was then needed to develop ideas as to how wellbore temperature might actually be managed to potentially prevent what can be referred to as thermally induced lost circulation. Thermal simulation software based on work by Mitchell and Wedelich1 was used to run a sensitivity analysis on a deepwater example well of the various controllable factors that influence wellbore temperatures. The results of this analysis are also presented in this paper. Thermal Effects on Formation Stress Timoshenko and Goodier2 presented an elastic theory which describes the effect of thermal stresses around an infinitely long cylinder containing a circular hole. In it, they showed that heating the inner wall of the cylinder will result in an increase in the compressive forces around the hole. Perkins and Gonzales3,4 discussed an analytical solution to the thermoelastic problem, showing that injecting large volumes of liquid that is colder than the in-situ reservoir temperature can significantly reduce the fracturing pressures in the formation. Tang and Luo5 presented model predictions of the effect on the near-wellbore stresses of differences in temperature between the mud in the wellbore and the formation. Figure 1 shows the results of their simulation of a 15 hour mud circulation period followed by a 15 hour noncirculating period. They predicted a tensile stress of 1015 psi around the wellbore after the 15 hour mud circulation period, followed by a gradual reduction in the tensile stress during the non-circulating period.

Maximizing hole conservation while optimizing well economics in both conventional and deepwater wells is a continual challenge. Addressing these challenges with new technology has provided some significant solutions, but the uncertainty when utilizing new technology with no proven track record must be risk-weighted. Solid Expandable Tubulars (SETs) have been installed in both openhole and cased-hole wellbores from November of 1999, in a variety of environments in wells on land, offshore and in deepwater to solve a range of drilling and completion challenges. This paper will discuss the drilling case histories in depth including:Descriptions of drilling challenges surrounding the use of SETs and their next best alternativesRisk analysis leading to the use of SETsDiscussion of the advantages and disadvantages of using SETsOperational lessons learned during installations of SETs Technology Overview Previously published papers and articles have discussed the concepts of Solid Expandable Tubular technology1 and the effect of the expansion process on the system's tubulars2,3 and connectors4. In this paper, the basics of SET technology will be briefly reviewed, emphasizing how the early products of this new technology have been applied in the drilling environment. Presentation of several case histories will demonstrate that Solid Expandable Tubular products can provide additional tools for the drilling "tool box", ultimately cutting drilling costs and bringing more dollars to the bottom line. As of this writing, 15 jobs have been performed, of which three were unsuccessful. Since learnings often are the results of problems, heavy emphasis will be placed on problems and the lessons learned. The Expansion System. The underlying concept of expandable casing is cold-working steel tubulars to the required size downhole - a process that, by its nature, is very unstable mechanically. Thus, there are many technical and operational hurdles to overcome when using cold-drawing processes in a downhole environment. An expansion cone, or mandrel, is used to permanently mechanically deform the pipe (Fig. 1). The cone is moved, or propagated, through the tubular by a differential hydraulic pressure across the cone itself and/or by a direct mechanical pull or push force. The differential pressure is pumped through an inner-string connected to the cone, and the mechanical force is applied by either raising or lowering the inner-string (Fig. 2). The progress of the cone through the tubular deforms the steel beyond its elastic limit into the plastic region, while keeping stresses below ultimate yield (Fig. 3). Expansions greater than 20 percent, based on the inside diameter of the pipe, have been accomplished. However, most applications using 4–1/4 inch to 13–3/8 inch tubulars have required expansions less than 20 percent.

fax 01-972-952-9435. AbstractThermal effects on wellbore stresses can have a significant impact on effective fracture gradients. Changes in wellbore temperatures caused by various drilling operations provide for these thermal effects. For example, circulation on bottom usually results in lower bottom hole temperatures than the static geothermal temperature. This cooling effect reduces the wellbore stresses resulting in lower effective fracture gradients. Minimizing the cooling effect by increasing wellbore temperatures can increase effective fracture gradients and the corresponding pore pressure/fracture gradient margin avoiding costly lost circulation and additional unnecessary casing points. This paper presents results from leak-off tests taken at various temperatures which demonstrate the thermal effect on formation stress. This paper also examines the effects of operational factors on wellbore temperatures to minimize the cooling effect and/or increase effective fracture gradients. Software developed for thermal simulation of various drilling operations was used to perform the analysis.