Before an oil company can start with construction, drilling or modification of onshore oil and gas production fields, it needs to obtain approvals from various government agencies. In addition to building and drilling permits, legal hurdles include air emissions, discharges to surface water systems, injection activities, impact on the threatened or endangered biosphere, stormwater runoff, and impact to various cultural resources. Before commencing with operations, oilfield operators need to ensure that all permits are secured, as well as to conduct the operations in line with local, state, or federal regulations.
Emissions and discharges
Oil and gas production and transport are associated with various atmospheric and marine discharges. The volume of CO2 emitted by the individual field through transportation and gas flaring depends on operational and natural conditions, and to a lesser degree on the scale of production. For example, in Europe, offshore installations exceeding 20MW are covered by the European CO2 allowance scheme. In addition, small quantities of chemicals, including oil residues and subsoil materials are inevitably discharged into the sea as a result of oil and gas extraction, and drilling of new wells.
Every oilfield road needs to be site-specific, taking into account the unique terrain, safety, operational, and maintenance requirements. Planning in advance should enable proper and timely review of any environmental concerns. The construction itself needs to be timed to minimize undesirable effects on sensitive habitats, with special consideration to seasonal restrictions, such as freeze-thaw cycles, potential flooding, and wildlife migration. During construction, the operator should consider the use of geotextiles and geosynthetics, as these materials help to stabilize the road and decrease the use of roadbed and surface materials. In planning the road route, the number of river, stream, and wetland crossings should be minimized, with bridges and culverts used to enable a free flow of water where drainage ways are disturbed.
Production in injection and disposal wells
Planning for a new well site needs to include the latest guidelines for waste management, pit location, and construction, as well as handling waste disposal and water discharges. The location and size of new pits need to ensure minimal disruption of surface resources, retaining the potential for reclaiming the site. Existing oilfields, pits, and production equipment, on the other hand, need to be assessed and reviewed periodically, to determine if the current condition of the facility is suitable for intended extraction operations. The waste management plan should tackle the specific waste types which are produced by a specific operation, but also address the actions taken in case of unexpected and hazardous waste materials.
Equipment used for carrying out well completion and workover operations should be installed in a way that uses the smallest practical area for oil and gas operations. Injection and disposal wells should be executed so that the injected fluids enter the desired formations, avoiding drinking water zones. For this, three levels of protection are used: surface casing and cement, long string casing, and tubing and packer. Quality solids control oilfield equipment should be used to capture and remove all produced fluids, drill cuttings, NORM scale, cement, cement returns, and other solids, separating the hazardous waste from non-hazardous to prevent cross-contamination.
In addition, all oilfield equipment should be inspected on regular basis for leakage, with corrective actions ensuring safe and environmentally-acceptable operation. The tubing-casing annulus pressure of injection and disposal wells should be monitored periodically for integrity. If a well is not equipped with tubing and packer, the operator can use tracer logs or temperature logs to make sure the injected fluids are forming properly. The frequency of equipment testing often depends on the operation conditions, for example, the mechanical integrity testing should be more frequent in a damp area that has had a high number of failures due to corrosion.
Plugging and abandonment
A well can be abandoned permanently when it has no further utility, in which case it’s sealed permanently against fluid migration and ingress, or temporarily when a wellbore has future utility but needs to be maintained in a condition that enables restoration of workover operations. In both cases, there are environmental concerns that need to be addressed. Apart from protecting freshwater aquifers and isolation of downhole formations containing hydrocarbons used in injection operations, there are additional issues like protection of surface soils and bodies of water.
Environmental issues concerning oil and gas industry operations can be solved through sound management processes and technical solutions that reduce the impact of oilfields and the associated infrastructure. While government legislative bodies are passing stricter regulations, equipment manufacturers are improving their products, ensuring that workover operations are carried out effectively and with a minimal impact.