What is done to land after oil is drilled from it?

It depends; often nothing is done, frequently it is sold and developed.

Producing wells are capped and old wells have the pipe removed and the hole is often filled in with concrete, but the land itself is hardly touched by modern techniques. Large areas of Houston are built over old and existing oil wells; the land was purchased for drilling and then sold to the city or developed so that it could be used by others. The oil company retained the mineral rights and sold the rights for the land itself.

I grew up in a neighborhood that was built over land that had been originally purchased for oil exploration and drilling.

However, one technique for making poor oil wells produce more is to inject water, steam or CO2 into the ground to force the oil out.

According to Wikipedia: http://en.wikipedia.org/wiki/Oil_drilling

"From the 9th century, oil fields were exploited in the area around modern Baku, Azerbaijan, to produce naphtha for the petroleum industry of the medieval Islamic world. These fields were described by al-Masudi in the 10th century, and by Marco Polo in the 13th century, who described the output of those oil wells as hundreds of shiploads.

Shallow pits were dug at the Baku seeps in ancient times to facilitate collecting oil, and hand-dug holes up to 35 meters (115 feet) deep were in use by 1594. These holes were essentially oil wells, which makes Baku the first true field. Apparently 116 of these wells in 1830 produced 3,840 metric tons (about 28000 barrels) of oil. Later, Russian engineer F.N. Semyenov used a cable tool to drill an oil well on the Apsheron Peninsula, ten years before Colonel Drake's famous well in Pennsylvania. Also, offshore drilling started up at Baku at Bibi-Eibat field near the end of the 19th century, about the same time that the "first" offshore oil well was drilled in 1896 at Summerland field on the California Coast.

The earliest oil wells were drilled percussively by hammering a cable tool into the earth. Soon after, cable tools were replaced with rotary drilling, which could drill boreholes to much greater depths and in less time....

The well is created by drilling a hole 5 to 30 inches (13 – 76 cm) diameter into the earth with an oil rig which rotates a drill bit. After the hole is drilled, a steel pipe (casing) slightly smaller than the hole is placed in the hole, and secured with cement. The casing provides structural integrity to the newly drilled wellbore in addition to isolating potentially dangerous high pressure zones from each other and from the surface....

After drilling and casing the well, it must be 'completed'. Completion is the process in which the well is enabled to produce oil or gas.

In a cased-hole completion, small holes called perforations are made in the portion of the casing which passed through the production zone, to provide a path for the oil to flow from the surrounding rock into the production tubing. In open hole completion, often 'sand screens' or a 'gravel pack' is installed in the last drilled, uncased reservoir section. These maintain structural integrity of the wellbore in the absence of casing, while still allowing flow from the reservoir into the wellbore. Screens also control the migration of formation sands into production tubulars and surface equipment, which can cause washouts and other problems, particularly from unconsolidated sand formations in offshore fields.

After a flow path is made, acids and fracturing fluids are pumped into the well to fracture, clean, or otherwise prepare and stimulate the reservoir rock to optimally produce hydrocarbons into the wellbore. Finally, the area above the reservoir section of the well is packed off inside the casing, and connected to the surface via a smaller diameter pipe called tubing. This arrangement provides a redundant barrier to leaks of hydrocarbons as well as allowing damaged sections to be replaced. Also, the smaller diameter of the tubing produces hydrocarbons at an increased velocity in order to overcome the hydrostatic effects of heavy fluids such as water.

In many wells, the natural pressure of the subsurface reservoir is high enough for the oil or gas to flow to the surface. However, this is not always the case, especially in depleted fields where the pressures have been lowered by other producing wells, or in low permeability oil reservoirs. Installing a smaller diameter tubing may be enough to help the production, but artificial lift methods may also be needed. Common solutions include downhole pumps, gas lift, or surface pump jacks. The use of artificial lift technology in a field is often termed as "secondary recovery" in the industry. Many new systems in the last ten years have been introduced for well completion. Multiple packer systems with frac ports or port collars in an all in one system have cut completion costs and improved production, especially in the case of horizontal wells. These new systems allow casings to run into the lateral zone with proper packer/frac port placement for optimal hydrocarbon recovery....

When the well no longer produces or produces so poorly that it is a liability, it is abandoned. In this process, tubing is removed from the well and sections of well bore are filled with cement to isolate the flow path between gas and water zones from each other, as well as the surface. Completely filling the well bore with concrete is costly and unnecessary."