Bore

local function refuel()
    turtle.select(15)
    turtle.placeUp()
    turtle.suckUp()
    turtle.refuel()
    turtle.digUp()
    turtle.select(1)
end

local function drop()
    turtle.select(16)
    turtle.placeUp()
    for i = 1, 14 do
        turtle.select(i)
        turtle.dropUp()
    end
    turtle.select(16)
    turtle.digUp()
    turtle.select(1)
end

local function checkAndDrop()
    local needDrop = true
    for i = 1, 14 do
        if turtle.getItemCount(i) == 0 then
            needDrop = false
        end
    end
    if needDrop then
        drop()
    end
end

if turtle.getItemCount(15) == 1 or turtle.getItemCount(16) == 1 and not (turtle.getItemCount(15) == 1 and turtle.getItemCount(16) == 1) then
    --exactly one of our ender chests was in use.
    if turtle.getItemCount(15) == 1 then
        drop()
    else
        refuel()
    end
end

while true do
    if turtle.getFuelLevel() == 0 then
        refuel()
    end
    turtle.dig()
    checkAndDrop()
    turtle.forward()
    turtle.digUp()
    checkAndDrop()
    turtle.digDown()
    checkAndDrop()
end