s 500 s fn ! 4 0 0 , fn W 3 0 0 ' 0 0: NUMBER of papers' -3 have been published concerning the A deleterious effect of post-production heating on both virginfibers and pristine rods. The glasses discussed in these papers showed a noticeable decrease in room-temperature strength after heating in air in the range 50" to 220"C, the strength reduction increasing with rising temperature. The cause of the strength reduction is still not clear although work by Sakka2 indicates that a degradation of the surface is involved.The purpose of this note is to demonstrate that lightly damaged fibers, when heated in air, undergo strength reduction similar to that of virgin fibers and that this strength reduction is not affccted by a heating atmosphere of dry inert gas.A continuous E-glass filament, with a nominal diameter of 0.00037 in., spirally wound on a Bakelite tube so that adjacent spirals were not in contact, was supplied by the Owens-Corning Fiberglas Corporation. It was anticipated that the filament would be damaged slightly by contact with the Bakelite; however, further mechanical contact was prevented. Four groups of specimens, tested directly from widely separated segments of the filament, gave mean tensile strengths of 459, 472, 473, and 473 kips/ima (ksi). The 113 specimens comprising these four groups h:td an overall mean strength of 467 ksi with a coefficient of variation of 13.4%. The specimen preparation and testing procedures have been detailed el~ewhere.~The lengths of filament to be heated were wound loosely on aluminum frames and placed in a gastight box having inlet and outlet valves. For air-heated fibers, both valves were opened and the box was placed in a resistance furnace and heated for 40 to 60 rnin. For inert gas heated fibers, a cylinder of pressurized argon gas was connected to the inlet valve by a copper coil, the box was flushed with argon,* and then the outlet valve was adjusted to give a 1 psi gage pressure of argon in the box. The box was then placed in the furnace with the copper coil which heated the argon before it entered the box. After heating for 40 to 60 min., the box was quickly cooled almost to room temperature and the filament was removed and made into tensile specimens. The strengths after heating are shown in Fig. 1. Each data point represciits 28 to 35 specimens; all strength tests were conducted a t 75°F and 45y0 rh a t a strain rate of 0.7 in./in./min. The group heated in air a t 66°C was stronger than the unheated group. This may be due to a healing of pre-existing flaws by mild corrosion coupled with the likelihood that the section of filament from which this group was made was initially less damaged than the other lengths removed from the Bakelite tube. For the heating times and temperatures studied, there is no difference between the fibers heated in air and those heated in argon. * 0°5 0 +------0 Haated in olr 0 Heated in orgon 2 0 0 1 i 95% conffdance limits on mean 100
Fourth Period: I," Kinetika i Katuliz, 3 [ l ] 81-90 (1962); Kinetics Catalysis (USSR) (English Transl.), pp. 65-72. The scatter usually seen in strength data for virgin Eglass fibers can be reduced to a very low level by controlling the thermal history of the glass melt from which the fibers are formed. Provided the glass melt is heated substantially above the drawing temperature, strengths of subsequently produced groups of 10 specimens will have a coefficient of variation of -1%. Unless glass is prevented from stagnating in the nozzle of the fiber-forming apparatus during a pause in the drawing operation, a secondary effect, associated with the spontaneous creation of defects in the glass in the nozzle, causes fibers produced immediately after such a pause to exhibit low strengths and high scatter. mental Treatments on the Strength of E-Glass Fibers," Ph.D. Thesis, University of Illinois, February 1965. Univ. Murojums (Ann Arbor, Mich.), Order No. 65-7082, 164 pp.; Dissertation Abstr., 26 11) 246 (1965). Journal of The A m e r h n Ceramic Sockty-KivZighnVol. 49, No. 3
A distinct shift in wellbore fracture stimulation events has occurred within the Western Canadian Sedimentary Basin (WCSB) over the last 5 years. New designs, commonly referred to as "increased fracture intensity designs," are characterized by an increased number of fracture stages, decreased fracture spacing, and resulting increases in water and proppant required per stimulation. Existing technology applied in increased fracture intensity designs include: Open Hole Ball and Seat technology, Coil Activated sleeves, Plug and Perforating, as well as hybrid designs that combine several technologies. Increased fracture intensity designs have contributed to improved production rates and increased reserves and, as a result, have quickly become the preferred approach to hydraulic fracture stimulation of the reservoir. Promising hydraulic fracture designs and decreased spacing designs run the risk of being applied broadly without discrimination. Without proper retrospective or hindsight, there is a risk of over applying this new approach with false assurances of its success rates. It is therefore important to determine whether and at what point increasing fracture intensity generates diminishing returns. This paper provides 3 retrospective case studies within the regions of the greater Montney and Cardium formations where increased fracture intensity designs have led to decreased well production as well as decreased reserve allocation. We further examine the various components of increased fracture intensity designs to pinpoint areas where design optimization may have prevented these outcomes.
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