Figure 6-20 Schematic Diagram of Gathering Process
1 Oil and gas gathering and transportation system
In the oilfield, all oil and gas production processes from wellhead to crude oil and natural gas export belong to the category of oil and gas gathering and transportation.
Main contents of oil and gas gathering and transportation work:
(1) Oil and gas metering, including the metering of oil, gas and water of single well products, as well as the metering of oil and gas during processing and before export to users. Oil gathering and gas gathering, that is, the mixture of oil, gas and water measured by a single well is collected to a processing station (joint station), or the water-bearing crude oil and natural gas are collected separately and sent to a crude oil processing station and a natural gas gathering station.
(2) Oil-gas-water separation, that is, the oil-gas-water mixture is separated into liquid and gas, the liquid is separated into water-containing crude oil and oily sewage, and solid impurities are separated if necessary.
(3) Dehydration of crude oil, that is, demulsification, sedimentation and separation of water-bearing crude oil to make the water content of crude oil reach the standard.
(4) The crude oil is stable, that is, the light components such as C 1 ~ C4 in the crude oil are removed, so that the saturated vapor pressure of the crude oil reaches the standard.
(5) Crude oil storage, that is, storing qualified crude oil in oil tanks to maintain the balance between production and sales of crude oil.
(6) Natural gas dehydration, that is, removing water from natural gas to ensure its safety during transportation and cooling.
(7) Natural gas light hydrocarbon recovery, that is, part of C2, C3, C4 and C5 components in natural gas are removed as required to ensure that no liquid hydrocarbons are precipitated during pipeline transportation.
(8) Liquid hydrocarbon storage. Liquefied petroleum gas (LPG) and liquefied natural gas (NGL) are respectively packed in pressure tanks to keep the balance between production and sales of liquid hydrocarbons.
(9) Oil and gas transportation. Crude oil, natural gas, liquefied petroleum gas and natural gas are metered and exported or distributed to oilfield users.
2 Oil and gas gathering and transportation project scale
The production characteristics of oil fields are that the oil and gas production shows several stages of rising, stabilizing and declining with the development time, while the water content of crude oil increases year by year, which reflects that the surface gathering and transportation system is not only a change in quantity (oil, gas and water production) but also a change in quality (such as the physical properties of crude oil), so it is necessary to consider a small amount of changes in surface production facilities to meet the requirements of different stages of oilfield development in a certain period. Generally, the service life of oil and gas gathering and transportation project in oilfield is 5 ~ 10 years, and the production scale is determined according to the annual changes of oil production, gas production, gas-oil ratio and water cut and the maximum handling capacity of 10 years.
1) Oil and gas gathering and transportation process
Oil and gas gathering and transportation technology is a general description of the oil and gas flow direction of oil and gas fields, including all technological processes from the wellhead of oil and gas wells to the first station of mine crude oil depot or oil and gas pipeline. Oil and gas gathering and transportation technology is formulated according to the geological characteristics, oil production technology, physical properties of crude oil and natural gas, natural conditions and construction conditions of each oilfield.
2) Oil-gas separation
The well fluid from the wellhead is mainly a mixture of water and hydrocarbons. Under the conditions of high temperature and high pressure in reservoirs, natural gas is dissolved in crude oil. During the upward flow of well fluid from underground along the wellbore and gathering pipeline, with the decrease of pressure, the gas dissolved in the liquid phase is continuously precipitated to form a gas-liquid mixture. In order to meet the needs of product measurement, processing, storage, transportation and use, they must be separated, which is oil-gas separation. See fig. 6-2 1 for the tertiary oil-gas separation process.
Figure 6-2 1 Schematic Diagram of Three-stage Oil-gas Separation Process
1- Oil-gas mixture from wellhead; 2- Oil-gas separator; 3- Balanced gas; 4- crude oil; 5— storage tank; 6 pump