Oil Wells Design and Construction for Safety

Oil and natural gas deposits are found thousands of feet below the surface and are buried under many layers of soil and rock. At these depths, oil and natural gas are pressurized by the weight of the layers above. When drilling through the soil and rock layers to reach the oil and natural gas deposits, the pressure must be controlled, as it increases with respect to the depth of drilling.  Modern drilling techniques control this pressure to keep oil and natural gas from escaping into the environment.


Since 1924, The American Petroleum Institute (API) has been the leader in developing equipment and operating standards for the oil and natural gas industry. Each year, API works with leading industry subject matter experts to maintain our inventory of over 600 standards covering design specifications and recommended practices for conducting operations. Annually, API distributes over 250,000 documents worldwide and continues to strive to enhance operational safety, minimize environmental impact, improve quality assurance, and promote the global acceptance of petroleum products and best practices. API standards are designed to help industry professionals improve the efficiency and cost-effectiveness of their operations, promote product consistency, comply with legislative and regulatory requirements, safeguard health, and protect the environment. In conjunction with API’s Quality Programs, many of these standards form the basis of API certification programs.


With the accelerating changes in the energy industry and the increasing need to address upcoming workforce challenges, the petroleum industry has pursued improvement in operations and workplace safety through training. Among the important efforts to achieve this objective are the API University and the International Association of Drilling Contractors (IADC) WellCAP program.

Well Planning, Design, and Construction

All oil and natural gas exploration, development, and production operations are conducted to ensure that people and the environment are protected. Statutes and regulations have been implemented to ensure that oil and natural gas operations are conducted in an environmentally responsible manner.

Production wells must penetrate the rock formations above the target reservoir that have trapped the hydrocarbons and allowed them to accumulate. This means that stringent analysis, proper well construction, and integrity maintenance are of key importance in preventing potential leaks from occurring. 

Proper construction design incorporates the fundamentals of well preparation, mud removal, and casing and cement placement to provide barriers that prevent fluid migration. The casing forms a major structural component of the well and serves to maintain control of fluids and pressures encountered as the well is drilled, and to prevent the formation wall from caving into the well.

While drilling the well, and when production starts, the environment is protected from the contents of the well by a combination of steel casing and cement. The performance of this barrier system to isolate the hydrocarbons, thus protecting the environment, is of utmost importance.

All well designs and well plans include contingency planning. Although seldom needed, these contingency plans are in place to mitigate the risk of failure due to unplanned events, and, most importantly, to ensure the protection of people and the environment.

The Drilling and Completion Process

Drilling a typical oil or natural gas well consists of several intervals of drilling through soil and rock layers and installing equipment to ensure isolation between the well, the layers of rock and soil penetrated by the well, and the surface environment. When drilling a well, it becomes necessary at certain points to stabilize the drilled hole in order to prevent it from collapsing in on itself. At these points, drilling is stopped and casing is lowered into the hole.  Cement is then pumped into the area outside of the casing (known as the annulus) and the well is sealed off and stabilized.  Once the cement has hardened, drilling through deeper rock layers can continue until the oil and natural gas deposit is reached. Design and proper execution of the placing of steel casing, pumping of the cement, and evaluating the well’s construction throughout are key aspects of well construction and primary factors for success. Experts, who carefully execute highly technical processes, engineer a well’s casing and cement design.

Once the target hydrocarbons are reached, the final construction phase is well completion. Depending on the well type, this will include any number of techniques, some of which may allow for oil and natural gas to flow into the well and be delivered to the surface in order to go through a production processing system.

Blowout Prevention Systems

Modern drilling practices control well pressure to keep oil and natural gas from escaping into the environment. The primary ways to control subsurface pressure is by circulating weighted drilling fluid (drilling mud) down the drilled hole, and sealing off the rock layers with steel casing and cement.

As an added layer of protection against situations in which unexpected high pressure zones are encountered and the weight of the drilling fluid in not enough to control the pressure in the well, each well is equipped with a Blowout Prevention System (BOP). The BOP is a series of large valves and other devices that are installed on top of the well, and allows drillers to manage pressure increases or close the well, if necessary. By closing the appropriate valve or series of valves, the drillers can re-establish control of the well and adjust the drilling fluid weight to account for the increased pressure. Because BOPs are critical to the safety of the crew, the rig, and the well, they are inspected, tested, and refurbished at regular intervals.