What are oil and gas industry wells?

Production wells are utilized to produce oil and natural gas from deep formations, anywhere from hundreds to thousands of metres deep below the surface. Oil and gas production from wells also contains saline water that was trapped in the same formation, and other impurities that must be separated.

At the time of initial discovery, a formation may have enough pressure for the fluid to flow to surface through a well into production equipment and pipelines. Formation pressure decreases over time with production, installation of equipment is required at the wellhead and within the well to bring the fluid to the surface.

Service wells provide supportive functions to production;

• Injection wells are used to inject fresh or produced water, or natural gas, into an oil pool to maintain pressure and increase production, typically doubling the total amount of oil recovered.
• Disposal wells are used to dispose waste water and natural gas impurities into deep formations, at similar depths to production, where it remains geologically trapped.
• Observation wells are used to measure and track reservoir pressure changes, sample reservoir fluids for changes, or place geophysical instruments below the surface to measure effects of oil and gas activities, such as seismic waves.
• Source wells are used to provide water for oil and gas industry use. The source may be either shallow fresh water or deep formation water. The principle uses of this water are to supply injection wells or for hydraulic fracture stimulation.

What is the difference between a conventional and unconventional well?

Gas and oil production in B.C. began in the mid 1950s. Vertical wells targeted highly porous formations which would flow gas and oil. These types of resources are now referred to as “conventional resources”.

In British Columbia, since approximately 2005, development activity has been predominantly in “unconventional resources” which do not readily flow gas and oil on their own. Many wells are now drilled vertically to the formation and then turned 90 degrees to drill horizontally for several kilometres within the formation. Due to the low natural porosity and permeability of the formation, hydraulic fracturing is required to create pathways for oil and gas to flow at an economic rate into the well. This change to development focus on unconventional resources has been similar across North America, now accounting for a large percentage of oil and gas production.

Historically, drilling a well had roughly a 75 per cent chance of being a successful producer; 25 per cent resulted in an unsuccessful “dry hole”, unable to produce at an economic rate. However, in unconventional resources, the success rate is now close to 100 per cent. This success rate is somewhat offset by the typically higher cost to drilling and complete an unconventional well. Another significant difference is the use of multi-well pads for the development of unconventional resources. The usual practice for conventional development consisted of a single well on a surface location, whereas unconventional development can include 20 or more wells on a surface location. The result is reduced surface disturbance for a similar number of wells and amount of production.

The technology of hydraulic fracturing was first used as a commercial application in the 1950s and has since been a common practice across oil and gas producing regions of North America for many decades. Thousands of wells in British Columbia have been subject to hydraulic fracturing.

What is induced seismicity?

Induced seismicity is earth tremors caused by the movement of pre-existing natural faults, triggered by human activities such as construction, mining, and oil and gas. For oil and gas, seismic events are associated with deep disposal of wastewater or hydraulic fracture stimulation. Induced seismicity events are of very short duration in comparison to natural seismic events like earthquakes. The vast majority of induced seismic events are not felt at the surface.

What are the different statuses of a well?

The status of a well identifies its current state of activity. Over the life of a typical well, it will have a progression of status changes – licensed > drilling > completed > production/injection/disposal > suspended > abandoned (decommissioned). The lifespan of a well can vary, from a few years, to many decades. A well may go directly from drilling status to abandoned status if it is unsuccessful in finding oil or gas.

The BC Energy Regulator maintains a public database of information on all wells that have ever been drilled and updates well status changes on a monthly basis.

How are these wells drilled?

Oil and gas wells are drilled utilizing portable steel drilling rigs, transported by truck in manageable pieces, which are assembled at a drilling site. Once assembled, it can take anywhere from a few days to several weeks to drill a single well, depending on depth, type of rock to be drilled through and challenges encountered.

Prior to the arrival of the drilling rig, a “drilling pad” is constructed by grading a site to manage rainfall runoff and heavy equipment traffic. In the past, a pad may have been used for drilling a single well, but for unconventional resources, would be used as a site to drill a dozen wells or more, using directional drilling technology. Some modern rigs can move, fully assembled, over short distances on a drilling pad to drill successive wells, either on a rail system or a self-supporting walking system, using hydraulics.

To drill a well, lengths of rigid drilling pipe are connected to one another with a specialized drilling bit rotating at the lead to break the rock into small chips. Drilling fluid called “drilling mud” is circulated down the centre of the hollow drilling pipe to cool the bit and lift rock chips to the surface through the annulus, the space between the outside of the pipe and wall of the hole. Various diameters and lengths of steel pipe, called casing, are run into the hole and cemented into place, to keep the hole from collapsing and to serve as a barrier to protect usable groundwater aquifers from contamination.

The depth of the well to be drilled will determine the size of the rig to be used, as deeper wells require heavier drill pipe and casing.

Over the life of a well it may be visited by a truck mounted “service rig”. These are used to maintain and modify the down-hole configuration of a well.

How deep are these wells?

Oil and gas wells vary from several hundred to several thousand of metres deep below the surface. The depth of a well can be quoted as either “true vertical depth” (TVD), as measured straight down from the surface, or as “measured depth” (MD) measured along the pathway of the well. Over 90 per cent of the wells now drilled in B.C., targeting the unconventional Montney formation, are drilled directionally, going down to a depth of 1.3 to 2.0 kilometres (TVD) and then out horizontally for 2 or 3 kilometres, for a total length (MD) of 3.3 to 5.0 kilometres.

What are the components of a well?

When a well is finished drilling, it will be composed of lengths of casing cemented into place to provide wellbore integrity and isolation of permeable zones from one another, including usable groundwater aquifers. Mounted at the surface is the wellhead, composed of valves and fittings to control pressure and fluid and connection of flow to surface equipment and pipelines.

Depending on the use of the well, features may include;

• perforations in the casing to allow oil and gas to flow into the well,
• a smaller diameter tubing and packer, to prevent contact of production or injection fluid with the casing,
• rods and pump attached to surface “pump jack” to lift liquids to surface,
• electrically-driven bottom hole pump,
• other valves and equipment for safety, flow control and ease of future well maintenance

This equipment may be pulled from a well and serviced as required, and a well reconfigured for production or service in a different formation at a different depth.

At the end of useful life of a well, it must be abandoned (decommissioned) in a manner approved by the BCER that ensures safety and the protection of the environment. This step includes the placement of plugs and cement within the well. The final phase is surface restoration of the well site back to pre-disturbance condition and receiving a Certificate of Restoration.

How many wells exist in B.C.?

How much do these produce?

Individual oil and gas wells vary significantly, in both the rate and total cumulative amounts, they produce. Oilfield units to describe gas production rate is millions of cubic feet per day (mmscf/d). Total cumulative production is quoted in billions of cubic feet (Bcf)

A typical conventional gas well might produce over a life of 20 years, starting at a rate of 2 mmscf/d, for a production total of 2 Bcf.

Improved technology is resulting in increasingly better production from new unconventional wells, in both production rate and total projected cumulative production. An unconventional well may commence production at a rate of 8 mmscf/d and be projected to produce 14 Bcf. A characteristic of unconventional resource wells is that a majority of the production occurs within the first two to three years, during a period of steep initial decline, however, this is followed by a long remaining life at a lower rate, which may last for many decades.