Observation technology of offshore oil environmental conditions

The environmental conditions of offshore oil are the natural environmental conditions for the survival and development of offshore oil, which can be divided into working environmental conditions, engineering design environmental conditions and disaster environmental conditions according to needs. Working environmental conditions refer to the environmental conditions required for offshore oil exploration, development and production operations. Engineering design environmental conditions refer to the engineering design environmental parameters (including extreme environmental conditions and operating environmental conditions) of offshore platforms, drilling ships, oil pipelines, mooring devices and oil and gas processing terminals; Disaster environmental conditions are natural disasters such as severe sea ice, tropical cyclone (typhoon), storm surge, disaster geology, earthquake and tsunami that may be encountered in offshore oil production and operation areas. These environmental conditions are solid foundation work, scientific basis for engineering design and important guarantee for safe production at sea, which are closely related to the survival and development of offshore oil. The environmental conditions of offshore oil is a new discipline that arises at the historic moment. With the development of offshore oil production and the continuous progress of science and technology, its practicability and social benefits are particularly remarkable.

I. Hydrometeorological Automatic Measurement System for Offshore Fixed Platforms

In the western South China Sea, due to special geographical conditions, strong tropical storms, strong cold air and strong winds, strong convective weather and typhoons (that is, "three strong and one soil") have always affected the normal operation of offshore oil and gas fields. According to statistics in recent years, Weizhou Oilfield stops production for about 25 days every year, and drilling operations stop for about 550 hours. In order to ensure the safety of offshore oil and gas field construction facilities and personnel, ensure the normal production of oil and gas fields in bad weather, check and correct the calculation formula of external load, and improve the design level of structures, it is necessary to master the temporal and spatial variation law of offshore meteorological and hydrological elements, which requires long-term continuous meteorological and hydrological observation.

It is an arduous task to obtain measured meteorological and hydrological data in bad weather at sea. In the past, meteorological and hydrological observations were obtained by dropping buoys; However, in the observation method of manual operation on the platform, once the operator encounters bad weather (typhoon, etc.). ), it is difficult to capture the complete data of typhoon. In order to solve the above problems, since the mid-1990s, China Offshore Oil Corporation has researched and established a set of meteorological and hydrological comprehensive observation system with a high degree of automation on a representative sea platform, adopted advanced foreign meteorological and hydrological sensors, developed an automatic data acquisition system, sent and received data through satellites, and equipped with emergency power supply equipment, so that meteorological and hydrological data observed in bad weather can be transmitted to shore stations through satellites in time. The shore station has a highly automatic receiving function, which can be provided to the engineering design and production departments at any time after computer processing.

(1) Measurement items and technical indicators

The main measurement items are 13, including wind speed, wind direction, air pressure, temperature and humidity. Hydrological measurement items include wave height, wave period, wave direction, (multilayer) velocity, (multilayer) flow direction, water level, water temperature and salinity. In addition, there are non-engineering auxiliary measurement items, such as platform latitude and longitude, system working voltage, fault alarm and so on. The added measurement items include multi-layer wind, corrosion, environmental protection, turbidity and so on.

1. Sensor selection

Determine the measuring range and accuracy of various sensors as required: ① introduce meteorological sensors into the automatic weather station, including sensors such as wind speed, wind direction, air pressure, temperature and humidity; (2) Hydrological sensors introduce wave, tide, temperature and salinity measuring instruments, including wave height, wave period, wave direction, velocity, flow direction, water level, water temperature and salinity sensors; ③ Multi-layer wave-current measuring instrument can measure velocity profile by introducing acoustic Doppler velocity profiler.

2. Install sensors on the production platform.

The installation scheme of sensors on the production platform is to ensure the long-term safe operation of the system under unattended conditions, so the following principles should be followed: ① It does not affect the operation of the production platform; ② The quality of measurement data can be guaranteed; ③ Complete data can be obtained when meteorological water temperature elements reach the limit; (4) Ensure that the instrument is not lost.

(2) Data collection and setting

1. Meteorological data

Meteorological data are observed every hour, every 1? Record a set of data, such as wind speed, record year, month, day, hour, minute, 1 "maximum wind speed, 3" maximum wind speed, 1? Maximum wind speed, 2? Maximum wind speed 10? Maximum wind speed, 30? Maximum wind speed and 60? Average wind speed, 2? Maximum wind speed, 2? Average wind speed, 2? Maximum wind direction, 2 hours ago? Insider 3? Maximum wind speed, 2? 1 inside? Maximum wind speed hours ago 10? Maximum wind speed hours ago 10? Average wind speed hours ago 10? Insider 3? Maximum wind speed hours ago 10? 1 inside? Maximum wind speed hours ago 10? Inside 2？ Maximum wind speed hours ago 10? Average wind direction, hours ago 10? Average temperature before hours 10? Average relative humidity hours ago 10? Mean air pressure. For the above *** 16 terms, the redundant channel using wind speed records has increased U terms compared with the original scheme, which is more convenient for calculating gust coefficient. The so-called 3 "maximum wind speed refers to taking a group of numbers every 3 seconds in 1 hour, and finding its average value, *** 1200, taking the maximum value; The so-called two hours ago? Insider 3? The maximum wind speed refers to 2 hours ago? Numbers within *** 120, in groups of three, average, ***40, choose the largest one, and so on.

2. Temperature and salinity data of waves, currents and tides

The temperature and salinity data of waves, currents and tides are generally observed about 8m below the average sea level, and the actual depth needs to be calculated according to the observed data. Observe the wave data every 3h, take a discrete value every 0.2s, and record 2048 wave discrete values each time. When is 2? When the maximum wind speed is greater than10.8m/s or the effective wave height hs is greater than or equal to 4.0m, it should be observed every hour instead. Record the surface velocity, flow direction, water level, water temperature and salinity every 10 minute.

3. Multilayer flow observation

When observing multi-layer flow, the instrument probe is placed at about 10m below the average sea level until the seabed, and the velocity and direction of each layer are observed every 2m. Record every 10 minute after hours.

(3) Microcomputer data acquisition and control

After processing, the collected data are sent to the shore station by satellite communication at 02: 05: 08: 1 1, 14: 00, 20: 00 and 23: 00 every day. At the same time, the original data were collected and stored in solid-state memory, with a capacity of more than half a year.

When is 2? Maximum wind speed is greater than10.8m/s or effective wave height hs >；; At 4.0m, the system will automatically encrypt when it exceeds the limit, and the data satellite transmission will be changed to once every hour. The overrun value can also be set automatically or manually.

1. Satellite data transmission

INMARSAT-C satellite communication is adopted between offshore oil platform and shore station to transmit various elements measured by the platform. The communication distance can satisfy the data transmission between offshore oil platforms in any sea area of China and shore stations anywhere. The average effective receiving rate of platform measurement data is not less than 90%. INMARSAT-C satellite transceiver system uses equipment imported from the United States.

2. Data receiving shore station

① The data satellite receiving shore station of the oil platform is located at the headquarters of Nanhai Western Petroleum Company; (2) The shore station has the functions of automatically receiving signals transmitted by offshore platforms, processing and printing various data; ③ The data received by the shore station is not only printed, but also stored in the hard disk, which is convenient for regular copying and archiving; ④ A set of shore station facilities can receive and process data sent by multiple oil platforms.

3. AC /DC power supply and emergency power supply system

Equipped with a set of power supply converted from AC to DC and an automatic switching control system, the system can work normally when the platform is unattended during the typhoon.

4. Shore station data processing software system

The data processing software system of the shore station can print the information received by the shore station into a report and draw the time process line.

The field test shows that:

A meteorological data is very safe with little external interference due to the high installation of sensors. Only one accident was caused by the fishing net winding S4 cable, which caused the serial port to burn, and the meteorological data record was interrupted. But this is not caused by the weather sensor itself.

The interruption of BSS4 data was affected by the hook twice and the fishing net once, not by the S4 instrument itself. However, the salinity data in the data is unstable and the data is not good. The sensor may be faulty, and the whole machine has been sent back to the manufacturer for repair, and then installed on the platform for use.

C ADCP data limited by installation conditions is available at first, but about 5 floors are affected by pile legs, and the flow data is not good. After that, ADCP was moved out to solve the above problems, but the loss accident happened. After refitting the instrument bracket, the instrument has been extended by about 70cm, and the data has been greatly improved. Now it is basically unaffected by pile legs.

D. The operation of the shore station is relatively normal, only affected by factors such as solar activity, and there are two errors in meteorological data, ***7.9 days, with an error rate of 2% ~ 3% and an intact rate of 97.7%, far exceeding the requirements of more than 90% in the contract.

(4) Instruments

It mainly includes: ① a set of ①YOUNG-4X automatic weather station (including 1 host and display, 1 wind speed and direction sensor, 1 air temperature and humidity sensor, 1 louver); ② 1 block ②S4ADW wave meter; ③ 1 piece ③300kHz Doppler profile current meter; ④ 1 data acquisition instrument; ⑤ 1 emergency power supply; ⑥ 1 satellite transmitting antenna; ⑦ 1 set of anchoring system; ⑧ 1 set of cables and accessories.

After three and a half years of research, sensor selection, data acquisition and processing system development, research and installation, anchoring scheme, indoor test and offshore test, a complete set of instruments was installed on the W 1 1-4 oil production platform in 2000, which was used for field tests from 65438 to 065438. S4 9.2 months' data; The ADCP data is 6.7 months, and the meteorological data received by the shore station is 1 1.3 months.

Second, the seabed mud temperature survey

The investigation of submarine mud temperature is a pioneering work. There is no precedent in the history of marine survey in China to detect the seabed temperature through tens or even hundreds of meters of seawater. It is the first attempt to investigate the mud temperature, water temperature and air temperature of JZ20-2 submarine pipeline and SZ36- 1 oilfield in Bohai Sea. In order to provide the real design parameters of submarine mud temperature (in previous engineering design, it was assumed that the water temperature at the bottom of the ice was the submarine mud temperature). The investigation results show that the true minimum temperature of submarine mud is 4 ~ 6℃ lower than the water temperature at the bottom of ice, which greatly reduces the project cost and has remarkable economic and social benefits.

(1) observation of mud temperature and water temperature in the sea area of platform site and submarine pipeline route of Qinhuangdao (QHD)32-6 oilfield.

1. Survey

The observation time is1998165438+1October 10 ~ 22, and the observation point of submarine mud temperature and water temperature 17 is located in the site of QHD32-6 oilfield platform and the sea area where submarine pipelines are routed.

The water temperature should be observed in three layers (surface layer: 0 ~1m; Middle layer: 0.6H；; Bottom layer: 0 ~ 1m from the seabed), mud temperature observation is divided into five layers: surface layer 0.5 and surface layer 1. O, surface layer 2. O and surface layer 3. Om***。

2. Result analysis

Through the statistics and calculation of field measured data and historical data, the statistical parameters of mud temperature and water temperature are given in the report, and the extreme value of mud temperature once in many years is calculated (table 17- 1).

Table 17- 1 Extreme mud temperature (℃)

3. Observation instrument

The instruments used in the investigation of submarine mud temperature are the water temperature sensor produced by Andra Company in Norway and the vibrating mud temperature tester modified from the mud temperature sensor, with the same accuracy as above.

(2)SZ36- 1 Seasonal fixed-point observation of submarine mud temperature

1. temperature observation of submarine mud

65438+February 20th to March 6th, May 28th to June 1 1, August 18 to September 1, June10 28th to1. Observe it three times a day, at 8: 00, 14: 00 and 20: 00 respectively.

2. Analysis of submarine mud temperature

According to the obtained data, the highest, lowest and average values of five grades and four representative months are counted. The vertical structures of water temperature and mud temperature are different in four seasons, which will be discussed separately below.

(1) Winter type (February)

The vertical distribution of water temperature is basically uniform, and the surface layer is slightly lower than the bottom layer 65438 0℃, with an average of -0.78℃, which is the lowest water temperature in a year. However, the vertical distribution of mud temperature has obvious gradient, showing the characteristics of low surface mud temperature and high lower mud temperature.

(2) Spring type (May)

The sea surface began to heat up in April, and the average surface water temperature in May was about 9.4℃ higher than that in February. The water temperature changes in a gradient in the vertical direction, and the average difference between the upper and lower water temperatures is about 65438 0.65438 0℃. Due to the increase of water temperature, the mud temperature on the bottom surface of the pool also began to increase. In May (in fact, in early June), the temperature of bottom surface mud increased by 65438 00.3℃ compared with that in February, and the vertical gradient of mud temperature decreased obviously. At 2m below the bottom surface, the mud temperature at the bottom surface is higher than 65438 0.7℃.

(3) Summer type (August)

At this time, the water temperature has formed an obvious gradient in the vertical distribution, and the surface water temperature is about 6.8℃ higher than the bottom water temperature. The vertical structure of mud temperature is just the opposite to that of winter type, that is, the bottom mud temperature is high and the lower mud temperature is low, and the difference between the upper and lower layers is about 5.6℃.

(4) Autumn type (165438+ 10 month)

From September, the sea surface began to cool down. In June, the sea surface temperature was lower than that in August 1 1.4℃, and the vertical distribution of water temperature was uniform. With the decrease of water temperature, the temperature of mud on the seabed surface began to decrease. At the end of June 1 1, the surface mud temperature is about 2.2℃ lower than that in August, while the mud temperature in the 2.0m layer is 2.6℃ higher than that in August, indicating that the mud temperature in the 1 1.0m layer is the highest in a year, because the heat conduction of the bottom mud is slower than that of seawater.

Generally speaking, the mud temperature is closely related to the water temperature, and changes with the change of the bottom water temperature. The vertical distribution of mud temperature in winter and summer presents obvious gradient. In winter, the deep mud temperature is high and the bottom mud temperature is low, and the difference between them can reach about 7.7℃. In summer, the mud temperature at the bottom is high, and the mud temperature in the deeper layer below is low, and the difference between them can reach about 5.6℃. In spring and autumn, the vertical temperature difference of mud temperature is about 65438 0 ~ 2℃. See table 17-2 for details.

3. Extreme value distribution of mud temperature

Correlation analysis between (1) water temperature and mud temperature

A. First, make correlation analysis on the bottom water temperature and mud temperature of each layer in the same period. Let the bottom water temperature be x and the mud temperature be y, and the relevant formula and corresponding correlation coefficient r are as follows:

High-tech and Practice of Offshore Oil in China

High-tech and Practice of Offshore Oil in China

It can be seen from the above results that the correlation coefficient between the bottom mud temperature and the bottom water temperature is very high, and it will obviously deteriorate when it reaches 0.5m, 1.0m, 1.5m and 2.0m.. ..

B. Correlate the monthly average mud temperature of 1 1 in February, May and August with the monthly average bottom water temperature of n(n=0,1…1) months ago, and extract the one with a large number of relationships. The results are as follows:

High-tech and Practice of Offshore Oil in China

The mud temperatures of 0.5m, 1.0m and 2.0m layers thus obtained have a good correlation with the bottom water temperature, and the correlation coefficient increases with the increase of depth. They are the results of n= 1 respectively. This shows that the change of mud temperature in each layer below 0.5m lags behind the change of seawater by about 1 month.

From the formulas (17- 1), (17-7), (17-8), (17-9) and (17-/kloc)

(2) Extreme value distribution of mud temperature

According to the relevant formula obtained in the previous section, the annual recurrence value of water temperature can be calculated, and the extreme value distribution of mud temperature can be calculated. The results are listed in Table 17-3 and Table 17-4.

Table 17-3 Maximum mud temperature in different return periods (℃)

Table 17-4 Minimum mud temperature in different return periods (℃)