Drilling
Definition
Drilling is a process whereby a hole is bored using a drill bit to create a well for oil and natural gas production. There are various kinds of oil wells with different functions:
• Exploration wells (or wildcat wells) are drilled for exploration purposes in new areas. The location of the exploration well is determined by geologists.
• Appraisal wells are those drilled to assess the characteristics of a proven petroleum reserve such as flow rate.
• Development or production wells are drilled for the production of oil or gas in fields of proven economic and recoverable oil or gas reserves.
• Relief wells are drilled to stop the flow from a reservoir when a production well has experienced a blowout.
• An injection well is drilled to enable petroleum engineers to inject steam, carbon dioxide and other substances into an oil producing unit so as to maintain reservoir pressure or to lower the viscosity of the oil, allowing it to flow into a nearby well.
The process of drilling an oil and natural gas production well involves several important steps:
• Boring – a drill bit and pipe are used to create a hole vertically into the ground. Sometimes, drilling operations cannot be completed directly above an oil or gas reservoir, for example, when reserves are situated under residential areas. Fortunately, a process called directional drilling can be done to bore a well at an angle. This process is done by boring a vertical well and then angling it towards the reservoir.
• Circulation – drilling mud is circulated into the hole and back to the surface for various functions including the removal of rock cuttings from the hole and the maintenance of working temperatures and pressures.
• Casing – once the hole is at the desired depth, the well requires a cement casing to prevent collapse.
• Completion – after a well has been cased, it needs to be readied for production. 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 or gas to flow.
• Production – this is the phase of the well’s life where it actually produces oil and/or gas.