Unit 12 How are oil and gas produced.

Words to be remembered:

 

once – как только

to assess - оценить (потенциал коллектора)

casing – обсадные трубы, крепление обсадными трубами

reservoir – коллектор

because of – из-за

to avoid – избегать

"gushes" – «фонтан»

a series of valves – несколько задвижек, клапанов

to install – устанавливать

wellbore – скважина

pressure differential – разница в давлении, перепад давления

artificial lift – искусственный подъем

to recover = to produce = to extract – добывать

producing well = production well – добывающая, эксплуатационная скважина

to contaminate – загрязнять  

predictable – предсказуемый  

decline curve – кривая падения (добычи), кривая истощения (пласта) 

waterflooding - заводнение (нефтяного месторождения) 

to convert – трансформировать, превращать 

injection well – нагнетательная скважина 

enhanced oil recovery (EOR) – добыча нефти вторичным методом 

 

Once an oil or gas reservoir is discovered and assessed, production engineers begin the task of maximizing the amount of oil or gas that can be recovered from it. Oil and gas are contained in the pore spaces of reservoir rock. Some rocks may allow the oil and gas to move freely, making it easier to recover. Other reservoirs do not part with the oil and gas easily and require special techniques to move the oil or gas from the pore spaces to a producing well. Even with today's advanced technology, in some reservoirs more than two-thirds of the oil in the reservoir rocks may not be recoverable.

Before a well can produce oil or gas the borehole must be stabilized with casing cemented in place. The casing also serves to protect any fresh water intervals, so that oil cannot contaminate the water.

Reservoirs are typically at high pressure because of underground forces. To avoid the "gushes" of the early 1900s, a series of valves and equipment is installed on top of the well.

Early in its production life, the underground pressure will often push the hydrocarbons all the way up the wellbore to the surface, much like a carbonated soft drink that has been shaken. Depending on reservoir conditions, this "natural flow" may continue for many years. When the pressure differential is insufficient for the oil to flow naturally, mechanical pumps must be used to bring the oil to the surface. This process is called artificial lift.

Most wells produce in a predictable pattern called a decline curve. Production will increase for a short period, then peak and follow a long, slow decline. How high the production peaks, and the length of the decline depend on reservoir conditions. Some wells may stop producing in economic quantities in a few years. In the U.S., 8 oil and gas fields have been producing for more than 100 years.

As a field ages, the company may choose to use a technique called waterflooding. In this case, some of the wells in the field are converted from production wells to injection wells. These wells are used to inject water (often produced water from the field) into the reservoir. This water tends to push the oil out of the pores in the rock toward the producing well. Waterflooding will often increase production from a field.

In more advanced cases, the company may use more sophisticated techniques, collectively referred to as enhanced oil recovery (EOR). Throughout their productive life, most oil wells produce oil, gas, and water. This mixture is separated at the surface. Initially, the mixture coming from the reservoir may be mostly oil with a small amount of water. Over time, the percentage of water increases. 

Natural gas wells usually do not produce oil, but do produce some amount of liquid hydrocarbons. These natural gas liquids are removed in the field or at a gas processing plant (which may remove other impurities as well). Natural gas wells also often produce water, but the volumes are much lower than is typical for oil wells.

Once it is produced, oil may be stored in a tank and later moved by means of truck, barge, or ship to where it will be sold or enter the transportation system. Natural gas is almost always transported through a pipeline. Many years ago, the gas may have been wasted as an unwanted byproduct of oil production. Now the industry recognizes the value of clean-burning natural gas and is working on improved technologies for getting gas from the reservoir to the consumer.

 

Questions on the text:

 

  1) Where are oil and gas contained? 2) What must be done before a well can produce oil or gas? 3) What is casing and what does it serve to? 4) Why are reservoirs often at high pressure? 5) What is done to avoid “gushers”? 6) How long may a natural flow of the hydrocarbons continue? 7) What is an artificial lift and when is it applied? 8) What can engineers do to affect a well’s decline curve? 9) When is the technique of waterflooding used? 10) Describe the waterflooding technique. 11) What is enhanced oil recovery (EOR)? 12) How much water is produced from oil wells in the USA? 13) Was natural gas considered for many years as an unwanted byproduct of oil production? 15) What happens to produced natural gas today?