Blowout

In the name of God

Course Instructor :

Dr. Mohammad Ghavidel Syooki

Introduce by:

Mohammad Javad Derakhshan

History of Blowout

• Gushers were an icon of oil exploration during the late 19th and early 20th centuries. During that era, the simple drilling techniques such as cable-tool drilling and the lack of blowout preventer meant that drillers could not control high-pressure reservoirs. When these high pressure zones were breached, the oil or natural gas would travel up the well at a high rate, forcing out the drill string and creating a gusher. A well which began as a gusher was said to have "blown in": for instance, the Lakeview gusher ”blow in” in 1910. These uncapped wells could produce large amounts of oil, often shooting 200 feet (60 m) or higher into the air.

Blowout

• A blowout is the uncontrolled release of crude oil and/or natural gas from an oil well or gas well after pressure control systems have failed.

Cause of blowout

• Reservoir Pressure

• Formation kick

Reservoir pressure • Because most hydrocarbons are lighter than rock or water, they often migrate upward through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as reservoirs) by impermeable rocks above. The down hole pressures experienced at the rock structures change depending upon the depth and the characteristic of the source rock.

Formation kick

• The down hole fluid pressures are controlled in modern wells through the balancing of the hydrostatic pressure provided by the mud used. Should the balance of the drilling mud pressure be incorrect then formation fluids begin to flow into the wellbore and up the annulus and/or inside the drill pipe. This is commonly called a kick. If the well is not shut in the closing of the a kick can quickly escalate into a blowout when the formation fluids reach the surface, especially when the influx contains gas that expands rapidly as it flows up the wellbore, further decreasing the effective weight of the fluid. In other petroleum engineering words, the formation pore pressure gradient exceeds the mud pressure gradient.

Formation kick

Early warning signs of a well kick are :

• Sudden change in drilling rate;

• Change in surface fluid rate;

• Change in pump pressure;

• Reduction in drill pipe weight;

• Surface mud cut by gas, oil or water;

• Connection gases, high background gas units, and high bottoms up gas units in the mudlogging unit.

Types of blowout

• Surface blowout

• Subsea blowout

• Underground blowout

Surface blowout

• Blowouts can eject the drill string out of the well, and the force of the escaping fluid can be strong enough to damage the drilling rig. In addition to oil, the output of a well blowout might include sand, mud, rocks, drilling fluid, natural gas, water, and other substances.

Subsea blowout

• Subsea wells have the wellhead and pressure control equipment located on the seabed.

• The deep water horizon well blowout in the Gulf of Mexico in April 2010, in 5,000 feet (1,500 m) water depth, is the deepest subsea well blowout to date.

Underground blowout

• An underground blowout is a special situation where fluids from high pressure zones flow uncontrolled to lower pressure zones within the wellbore. Usually this is from deeper higher pressure zones to shallower lower pressure formations. There may be no escaping fluid flow at the wellhead.

Blowout control

• Drilling relief wells

• Using blowout preventer

Relief wells

• Sometimes, blowouts can be so forceful that they cannot be directly brought under control from the surface .In such cases, other wells (called relief wells) may be drilled to intersect the well or pocket, in order to allow kill-weight fluids to be introduced at depth.

• The first use of a relief well was in Texas in the mid-1930s when one was drilled to pump water into an oil well that had cratered and caught on fire.

Blowout preventer

• A blowout preventer or B.O.P is a large, specialized valve or similar mechanical device, usually installed redundantly in stacks, used to seal, control and monitor oil and gas wells. Blowout preventers were developed to cope with extreme erratic pressures and uncontrolled flow (formation kick) emanating from a well reservoir during drilling.

Blowout preventer

• When a kick (influx of formation flow) occurs, rig operators or automatic systems close the blowout preventer units, sealing the annulus to stop the flow of fluids out of the wellbore. Denser mud is then circulated into the wellbore down the drill string, up the annulus and out through the choke line at the base of the BOP stack through chokes (flow restrictors) until downhole pressure is overcome.

Blowout preventer

The primary functions of a blowout preventer system are to:

• Confine well fluid to the wellbore;

• Provide means to add fluid to the wellbore;

• Allow controlled volumes of fluid to be withdrawn from the wellbore.

Blowout preventer

Additionally, and in performing those primary functions, blowout preventer systems are used to:

• Regulate and monitor wellbore pressure;

• Center and hang off the drill string in the wellbore;

• Shut in the well (e.g. seal the void, annulus, between drillpipe and casing);

• Kill the well (prevent the flow of formation fluid, influx, from the reservoir into the wellbore) ;

• Seal the wellhead (close off the wellbore);

• Sever the casing or drill pipe (in case of emergencies).

B.O.P categories

• Two categories of blowout preventer are most prevalent: ram and annular. BOP stacks frequently utilize both types, typically with at least one annular BOP stacked above several ram BOPs.

Ram blow out preventer

•  The rams extend toward the center of the wellbore to restrict flow or retract open in order to permit flow. The inner and top faces of the rams are fitted with packers (elastomeric seals) that press against each other, against the wellbore, and around tubing running through the wellbore. Outlets at the sides of the BOP housing (body) are used for connection to choke and kill lines or valves.

Types of Ram blowout preventer

• Pipe rams close around a drill pipe, restricting flow in the annulus between the outside of the drill pipe and the wellbore, but do not obstruct flow within the drill pipe. Variable-bore pipe rams can accommodate tubing in a wider range of outside diameters than standard pipe rams, but typically with some loss of pressure capacity and longevity.

• Blind rams (also known as sealing rams), which have no openings for tubing, can close off the well when the well does not contain a drill string or other tubing, and seal it.

Types of Ram blowout preventer

• Shear rams cut through the drill string or casing with hardened steel shears.

• Blind shear rams (also known as shear seal rams, or sealing shear rams) are intended to seal a wellbore, even when the bore is occupied by a drill string, by cutting through the drill string as the rams close off the well.

Ram blowout preventer

Blowout Preventer diagram showing different types of rams.

(a) blind ram

(b) pipe ram and

(c) shear ram.

Annular blowout preventer

• An annular-type blowout preventer can close around the drill string, casing or a non-cylindrical object, such as the kelly. Annular blowout preventers are also effective at maintaining a seal around the drillpipe even as it rotates during drilling. Annular preventers are generally not as effective as ram preventers in maintaining a seal on an open hole. Annular BOPs are typically located at the top of a BOP stack, with one or two annular preventers positioned above a series of several ram preventers

Annular blowout preventer

Diagram of an Annular blowout preventer in open and fully closed configurations. The flexible annulus (donut) in blue is forced into the drillpipe cavity by the hydraulic pistons.