Hi scorps,
Yes it is possible to breed them indoors, but this is rarely achieved. To do it, you need to replicate the four seasons indoors. In summer you need higher water temperature, long daylight periods, a blazing heat lamp and depending on the species, some rain, the odd storm or two or maybe high humidity. All the features of a hot summer need to be re-created indoors.
Then, as you head towards winter, you need to gradually cool the tank, shorten the lighting periods so that they match the actual photoperiod of each day, reduce the intensity of the heat lamp according to the intensity of the sun, reduce feeding, etc. When you get to winter, the tank would need to reflect winter outdoors: very cold water temperatures, cold air temperatures, maybe winter rain or drizzle. Once you get past winter, you need to start the warming process, increase the artificial daylight length each day, bring up the intensity of the heat lamp, etc.
You would also need a suitable nesting site within the enclosure.
After several years of experimentation, you may find that your turtles would breed. However, most humans prefer to heat their house in winter and cool it in summer. The get turtles to breed indoors, you would need to have your house really cold in winter and really hot in summer.
The simpler solution is to keep the turtles in a large outdoor pond.
Regards,
Michael.