Onland, drilling begins by ‘Spudding in’ – a process which forms the backbone of the whole drill site. When the desired depth of initial drilling is reach the hole is ‘cased’ with steel tubing. Cement is then pumped right to the bottom which backfills up the gap between the rock wall and the outside of the steel tube to lock it in place, providing essential strength and stability.
The casing and the cement form a non-porous barrier that prevents cross-contamination between the oil bearing rock formation and any overlying aquifers. The casing and cement are pressure–tested to ensure that they can tolerate higher pressures than those expected over the life of the well.
Most aquifers in New Zealand lie between 50 and 250 metres from the surface. These acquifers are drilled through in the very first days of drilling, and the well through the aquifer is subsequently cased with initially one and ultimately three or more layers of steel casing pipe and cement, to ensure aquifer integrity.
Even the shallowest wells in Taranaki are drilling down 1.5 kilometers to reach oil and gas reservoirs.There is no evidence to suggest acquifers have been compromised due to oil and gas activity in New Zealand.
As the drilling reaches certain depths, the size of the hole decreases. A hole that begins at around 50cm at the surface, finishes at the reservoir of oil at around 15 - 20cm. Each time the hole reduces in size another layer of casing and cement is installed.
That means when the well has reached it’s final depth, the hole back up to the surface has on average four layers of non-porous casing and cement to make sure the well is safe and stable for decades to come.
In New Zealand, onshore drilling depths can vary between 2 and 5 kilometers deep.
During drilling a blowout preventer (BOP) is fitted, which is a large, mechanical device that can control or shut the well if necessary to prevent a blowout (the uncontrolled release of crude oil and/or natural gas).
Once a well, or multiple wells within a field are producing a steady flow of oil, the field is considered to be in production.
Wells, production equipment and infrastructure like pipelines are installed in appropriate configurations and carefully maintained over the producing life of the field.
Generally, oil and gas continue to flow until the resevoir is depleted. This process can take decades.
Over the life of the field, as well flows begin to flow less quickly, pumps or other technologies may be employed to enhance flow rates and ensure that the maximum practical amount of oil and gas is extracted.
1. Petroleum wells must be plugged and abandoned in accordance with health and safety regulations and the well examination scheme. WorkSafe must be notified at least 20 days before well abandonment operations begin. They must be satisfied risks are identified and precautions are being implemented, and well operators must ensure independent examination of the well abandonment operation.
The site must be remediated to the specifications outlined in the resource consent. Remediation could include removal of infrastructure.