After repeated presentations of a long inspection tone (800 or 1,000 msec), a test tone of intermediate duration (600 msec) appeared shorter than it would otherwise appear. A short inspection tone (200 or 400 msec) tended to increase the apparent length of the intermediate test tone. Thus, a negative aftereffect of perceived auditory duration occurred, and a similar aftereffect occurred in the visual modality. These aftereffects, each involving a single sensory dimension, are simple aftereffects. The following procedures produced contingent aftereffects of perceived duration. A pair of lights, the first short and the second long, was presented repeatedly during an inspection period. When a pair of test lights of intermediate duration was then presented, the first member of the pair appeared longer in relation to the second. A similar aftereffect occurred in the auditory modality. In these latter aftereffects, the perceived duration of a test light or tone is contingent-dependent-on its temporal order, first or second, within a pair of test stimuli. An experiment designed to test the possibility of cross-modal.transfer of contingent aftereffects between audition and vision found no significant cross-modal aftereffects.

Time-place discrimination has been shown reliably in several avian and insect species, but only occasionally in rats and fish. In the present experiments, we explored the effects of response cost on time-place discrimination by rats. In the first experiment, we increased the cost of making a choice and the cost of recovering from a wrong choice in two types of maze, a radial arm and a vertical maze. In the radial arm maze, we found only general place preference, whereas in the vertical maze, we obtained evidence of time-place discrimination. In the second experiment, we found that the proportion of rats showing time-place discrimination increased with the height and, therefore, the response cost of the vertical maze. These results suggest that rats do not automatically store and/or retrieve the time and place of reward events but that response cost is an important trigger for time-place discrimination.

Summary Underbalanced drilling with casing (UBDWC) is improving drilling performance dramatically in south Texas fields. This approach allows drilling of depleted and high-pressure sands intermingled within one hole section, resulting in significantly less-expensive well plans. Drilling cost reductions of 30% have been realized. Smaller-reserves targets are viable—a key advantage in the mature south Texas Vicksburg play. Introduction Shell has developed and operated gas fields in south Texas for the past 50years. These 10,000 to 16,000-ft, high-pressure/high-temperature wells normally have initial shut-in tubing pressures approaching 10,000 psi when virgin pressure sands are completed. The bottomhole temperatures range from 280to 400oF. Most wells have multiple low- permeability pay sands, which require massive hydraulic-fracture treatments to produce economically. Each pay interval is fracture treated in a separate stage, and the production from all the sands is commingled. Most current drilling activity is in and around mature fields in which large volumes of gas have been produced. Severe reservoir-pressure depletion intermingled with high pressure is often encountered. The presence and level of pressure depletion is difficult to predict because of complex geology, low permeability, and production commingling. The UBDWC approach was first applied to a slimhole re-entry program that began in 1995.These re-entries were either sidetracks to replace wells that failed because of casing damage or wells that were deepened to new objectives. The re-entries are normally half the cost of a new well, allowing smaller reserve targets to be drilled economically. The wells were sidetracked out of the existing 5- or 5½-in. casing and a new string of2?-in. casing was run and cemented. By 2000, the remaining re-entry candidates were difficult to drill, with lost-circulation and well-control problems more common. The program was becoming uneconomical because of the inability to set liners in the small hole size. UBDWC1-3 was applied to resolve these problems, and 10 re-entries have been drilled this way since2001.The low-permeability Vicksburg sands allow operations with a higher underbalance than would be possible in most other applications. The learnings from the re-entry program have been transferred to the drilling of new south Texas wells. This has allowed smaller casing programs and the elimination of liners, and trouble cost has been reduced, resulting in a cost savings of up to 30%.UBDWC requires little rig modification and standard off-the-shelf equipment; it has been applied on rigs equipped with rotary tables and top drives. Using the Intl. Assn. of Drilling Contrators' Underbalanced Operations Classification System, these operations are Level 5-B-5.