Petroleum engineering is an engineering discipline concerned with the activities related to the production of hydrocarbons which can be either crude oil or natural gas and there is subsurface activities that presume to fall within the upstream sector of oil and gas industry which are activities of finding and producing hydrocarbons(refining and distribution to a marked are referred to as the downstream sector)explored by earth scientists and petroleum engineering are the oil and gas industry’s two main subsurface disciplines in which focus on maximizing economic recovery of hydrocarbons from petroleum of engineering focuses on estimation of the recoverable volume of the recourses using a detailed understanding of the physical behavior of oil , water and gas within a porous rock within a very high pressure and The combined efforts of geologists and petroleum engineers throughout the life of a hydrocarbon accumulation determine the way in which a reservoir is developed and depleted, and usually they have the highest impact on field economics. Petroleum engineering requires a good knowledge of many other related disciplines, such as geophysics, petroleum geology( drilling, economics, reservoir simulation,well engineering, artificial lift systems)
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The Drill is a machine which creates holes (usually called boreholes) and shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person. They sample sub-surface mineral deposits, test rock, soil and groundwater physical properties.
A drilling fluid is any fluid which circulates through a well in order to remove cuttings from a wellbore. This section will discuss fluids which have water or oil as their continuous phase. Air, mist and foam, which can be used as drilling fluids, will not be discussed at this time and drilling fluid must fulfill many functions in order to drill a well successfully, safely, and economically. The most important functions are:
- Remove drilled cuttings from under the bit.
- Carry those cuttings out of the hole.
- Suspend cuttings in the fluid when circulation is stopped.
- Release cuttings when processed by surface equipment
- Allow cuttings to settle out at the surface.
- Provide enough hydrostatic pressure to balance formation pore pressures.
- Prevent the bore hole from collapsing or caving in. 8. Protect producing formations from damage which could impair production.
- Clean, cool, and lubricate the drill bit
Occasionally, these functions require the drilling fluid to act in conflicting ways. You can see that items #1-3 are best served if the drilling fluid has a high viscosity, whereas items #4-5 are best accomplished with a low viscosity. In its most basic form a drilling fluid is composed of a liquid (either water or oil). If nothing else is added, whenever the hydrostatic pressure is greater than the formation pore pressure (and the formation is porous and permeable) a portion of the fluid will be flushed into the formation. Since excessive filtrate can cause borehole problems, some sort of filtration control additive is generally added. In order to provide enough hydrostatic pressure to balance abnormal pore pressures, the density of the drilling fluid is increased by adding a weight material (generally barite).
Preparation: The oil drilling process starts with finding the land to drill on. After selection, there are normally environmental studies to ensure no damage is done. The mineral rights will need to be acquired as well. A water source will have to be established, if one isn’t nearby, and the site will need to be cleared of debris, trees and other objects. A hole is then dug where the main drilling will be.
The Base Liquid:
- Water – fresh or saline
- Oil – diesel or crude
- Mineral Oil or other synthetic fluids
- Dispersed Solids:
- Colloidal particles, which are suspended particles of various sizes.
Usually salts, and their effects on colloids most is important and all drilling fluids have essentially the same properties, only the magnitude varies. These properties include density, viscosity, gel strength, filter cake, water loss, and electrical resistance. Though this type of drilling fluid is easy to describe, it is hard to define and even more difficult to find. In the field, a normal fluid generally means that there is a little effort expended to control the range of properties.
General rules include:
- It is used where no unexpected conditions occur.
- The mud will stabilize, so its properties are in the range required to control the hole conditions.
- The chief problem is viscosity control Formations usually drilled with this type of mud mainly sands.
Since viscosity is the major problem, the amount and condition of the colloidal clay is important. To do this, two general types of treatment are used:
Water soluble polyphosphates:
- They reduce viscosity
- You should use it alone or with tannins
Caustic Soda and Tannins:
- They also reduce viscosity.
- You have to use it under more severe conditions than phosphate treatment.
The drilling fluids are made to combat particular abnormal hole conditions or to accomplish specific objectives. These are:
- Faster penetration rates.
- Greater protection to producing zones.
Abnormal Hole Conditions:
- Long salt sections.
- High formation pressures.
Lime Base Muds:
- Water base mud.
- Treated with large amounts of caustic soda, que-bracho, and lime.
- Ratio of 2 lb caustic soda, 1.5 lb quebracho and 5 lb lime per 1 barrel of mud.
- Will go through a highly viscous stage, but will become stable at a low viscosity.
- Can tolerate large amounts of contaminating salts.
- Remains fluid when solids content gets high.
Weakness – it has a tendency to solidify when subjected to high bottom-hole temperatures.
Similar to lime based mud – differ only in degree.
A compromise attempt at overcoming the high temperature gelation problem.
- Use less lime than lime-base mud.
- Not nearly so resistant to salt contamination.
Emulsion Muds – Oil in Water:
- Oil can be added to any of the normal or special mud with good results
- No special properties necessary
- Natural or special emulsifying agents hold oil in tight suspension after mixing.
Oils used are:
(a) Crude oils. (b) Diesel. (c) Any oil with API gravity between 25 and 50.
Oil content in mud may be 1% to 40%.
- Very stable properties.
- Easily maintained.
- Low filtration and thin filter cake.
- Faster penetration rates.
- Reduces down-hole friction.
Major objection is that the oil in the mud may mask any oil from the formation.
- Mud with inhibited filtrates.
- Large amounts of dissolved salts added to the mud.
- High pH usually necessary for best results.
- Designed to reduce the amount of formation swelling caused by filtrate – inhibit clay hydration.
- Needs specialized electric logs.
- Requires much special attention.
- Low mud weights cannot be maintained without oil.
- Hard to increase viscosity.
- Salt destroys natural filter cake building properties of clays.
Gypsum Base Muds
A specialized inhibited mud:
- Contains large amounts of calcium sulfate.
- Add 2 lb/bbl gypsum to mud system.
- Filtration controlled by organic colloids.
- Mud is stable.
- Economical to maintain.
- Filtrate does not hydrate clays.
- High gel strength.
Disadvantages: (a) fine abrasives remain in mud. (b) Retains gas in mud.
Oil Based Muds:
- Oil instead of water used as the dispersant.
- Additives must be oil soluble.
- Generally pre-mixed and taken to the well-site.
- To increase aniline value, blown asphalt and un-slaked lime may be added.
- Will not hydrate clays.
- Good lubricating properties .
- Normally higher drill rate.
- Dirty to work with.
- Requires special electric logs.
- Viscosity varies with temperature.
1. Water in oil emulsion. Oil largest component, then water added.
Order of addition is important
2. Have some of the advantages of oil muds, but cheaper.
Oil-Based Mud Systems:
There are two types of systems: 1) invert emulsion, where water is the dispersed phase and oil the continuous phase (water-in-oil mud), and 2) emulsion mud, where oil is the dispersed phase and water is the continuous phase (oil-in-water mud). Emulsifiers are added to control the rheological properties (water increases viscosity, oil decreases viscosity).
Air, Mist, Foam-Based Mud Systems:
These “lower than hydrostatic pressure” systems are of four types: dry air or gas is injected into the borehole to remove cuttings and can be used until appreciable amounts of water are encountered, mist drilling is then used, which involves injecting a foaming agent into the air stream, foam drilling is used when large amounts of water is encountered, which uses chemical detergents and polymers to form the foam, and aerated fluids is a mud system injected with air to reduce the hydrostatic pressure.
Workover Mud Systems:
Also called completion fluids, these are specialized systems designed to minimize the damage formation, be compatible with acidizing and fracturing fluids and reduce clay/shale hydration and They are usually highly treated brines and blended salt fluid.
Set Up and Drilling: The main hole is dug wide at the top and is drilled down with just a basic small drill. Two other holes are also dug to store equipment and dirt. Next the main rig is brought in and set up over the main drilling hole. The basic rig is made up of a drill bit and piping that sends the drill further and further down, scaffolding with cable and pulley to bring the drill up and an engine to turn the drill. The drill is sent down, where it chews up the earth. The mud is moved up the piping into a hole built for storage. As the drill goes down, more piping is added, and when a drill wears out, it is pulled up and replaced.
Once mud, being pulled up from the drill site, shows signs of oil residue, the drill is removed and testing is done. Core samples are taken as well as pressure and gas tests. When it is confirmed that the oil has been found, an explosive charge is sent down in the form of a perforating gun. This will crack the rock so that oil can flow into the drill area. After the rock is cracked, a pipe is lowered down for the oil to be collected. The hole is then capped off to avoid spillage and a pump is set up to pull the oil out of the ground.
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