The Brisbane Valley Rail Trail is 161km long disused rail line that starts at Wulkuraka Train Station (wheel chair friendly/station lifts/ramps/concrete footpaths - no toilets/water at the station) and heads north through the bush. The concrete path goes for about 5km and then transforms to an off road track. Depending upon your chair/scooter, there is many km of this trail that can be accessed. 
An electric assisted handcycle or recumbent would be suitable to use on the rail trail and transport along the trail can be arranged with Out There Cycling.
Check out the website for more information.
Some of the gullies may be too steep to traverse unaided and wheel chair accessible toilets are not always available in smaller towns.

Brisbane Valley Rail Trail

Ipswich Nature Park allows visitors to stroll, roll or walk around the park using cement paths and wooden walkways. A gold coin donation allows you to see wallabies, lizards, birds and other native Australian animals. Water bubblers and taps are available, as are shaded grassy areas and seats. Toilets are wheelchair accessible; the car park has 3 parking spaces for disabled permit holders and paths are about a metre wide. 

Ipswich Nature Centre