Prediction and Detection of Abnormal Pressures

Predictive Techniques:

· Geophysical Techniques

· Offset Data

Detection Techniques:

· Drilling Parameters (increasing ROP)

· Drilling Mud (gas volume, mudweight decrease, increase mud etc.)

· Drilled Cuttings (shale factor)

Overburden Pressure

The vertical pressure at any point in the earth is known as the overburden pressure. If not able to calculate the overburden can be assumed as 1 psi/ft.

Fracture Pressure

Consequence of underbalanced drilling

· Borehole Collapse

· Influx

Consequence of overbalanced drilling

1. Low ROP

2. Formation Fracture

3. Differential Sticking

 

Oil and gas gathering system

The well production a mixture of

· hydrocarbon gas

· condensate

· oil

· water

For the hydrocarbons (gas or liquid) to be sold, they must be: separated from the water and solids, measured, sold, transported by pipeline, truck, rail, or ocean tanker to the user.

Surface production operations covers the processing of all three streams from the well head.

The need for field processing of crude oil-gas mixture is justified for four main reasons:

· These mixtures are very difficult to handle, meter, or transport.

· It is unsafe and uneconomical to ship or transport such two-phase mixtures overseas to refineries and gas plants.

· Oil producers have to abide with the specifications set for shipping and refining

· Environmental constraints established for safe handling of HCs and the disposal of produced salt water

 

The equipment between the wells and the pipeline, or other transportation system.

· Its configuration depends on

· Oilfield size

· Landscape

· Physical and chemical properties of the oil

 

The main objectives of surface facility

· separate the gas, oil, and water produced from the well;

· process and treat the gas for sales, reinjection, or flaring;

· treat the oil for sales;

· treat the water for reinjection or disposal; and

· provide for well testing.

 

All facilities require safety system, including:

· safety instrumentation and shutdown system

· fire and gas detection

· fire-fighting equipment

· a means of evacuation, such as life rafts and escape capsules for offshore

· other equipment, depending on the location and complexity of the facility and whether it is manned

 

The process in a facility

· phase separation

· temperature changes

· pressure changes

 

Types of separator

· Cylindrical

1. Horizontal separator

─ for high-pressure and medium-pressure service

2. Vertical separator

─ for low-pressure service (generally)

· Spherical separator

─ more compact and cheaper

─ limited separation space and liquid surge capacity

─ for low-volume remote platforms

 

Separators are classified

" two-phase " if they separate gas from the total liquid stream and

" three-phase " if they also separate the liquid stream into its crude oil and water components.

After free water removal, produced oil often contains excessive impurities which are required to be reduced to a value acceptable for transportation or sales:

· Dehydration/Desalting

 

It is usually the first process in crude oil processing. It involves removal of salt dissolved in the water in the crude oil. It is achieved by a process unit called desalter

There are also electrostatic dehydrators which enhance coalescing of small water droplets and assist in settling

· Emulsion Treatment

For an emulsion to exist there must be two mutually immiscible liquids, an emulsifying agent, and sufficient agitation to disperse the discontinuous phase into the continuous phase.

A common method for separating this emulsion is to heat the stream thereby deactivating the emulsifying agent, allowing the dispersed water droplets to collide. This is achieved by heater theaters.

The purpose of a desalting system: reducing the salt content of the treated oil to

acceptable levels.

Separating water vapor from natural gas before the gas is transported by pipeline

Main processes of water removal in gas processing:

1. Glycol(absorption)

2. Solid desiccant(adsorption) dehydration.

Glycol absorption method of dehydration is very similar to using absorption for NGL extraction but the main difference is the use of a glycol instead of an absorption oil.

It also entails the oil making contact with the glycol (e.g. TEG), an hygroscopic substance in a glycol tower, the rich glycol re-boiled and stripped of its water component in form of steam, flashed of its dissolved gas in a flash tank and fed again into the tower.

Solid desiccants like activated alumina, silica gel are filled into adsorption towers

As the wet gas passes through the tower, water molecules are retained on the surface of these desiccant beds leaving the dry gas to exit the bottom of the tower.

To regenerate the desiccant, a high temperature gas is passed through the saturated desiccant bed and vaporizes the water in the desiccant tower, leaving it dry for further use.

 

Some wastes

· Produced water

· Onshore, produced water will normally be re-injected in the formation to serve as artificial lift for wells which cannot further achieve optimal production by its natural drive mechanism

· It can also be pumped into a disposal well when not needed

· Gas flares

· Compressed gas could also be re-injected into the formation through injection wells to lighten the column of fluid and allow the reservoir pressure to force the fluid to the surface.

· At high pressure, the gas could also be used in Industrial power plants to generate electric power in large quantities that can be supplied to end users

· At low pressure, it can be used in internal combustion engines to power locomotives.

· Other wastes like deck drains are collected in a gathering system, treated and disposed overboard or added to the treated produce water for reinjection.

· Waste lube oil and waste lube oil filters are usually sent to offsite reclamation plant

In conclusion, it is important to note that the significance of a production facility is to separate the well stream into three components, typically called phases (oil, gas, and water), and process these phases into some marketable product(s) or dispose of them in an environmentally acceptable manner.

To achieve optimal production each process must be carried out efficiently.