Distributed fiber optic monitoring system application for oil well temperature, pressure, flow rate and other solutions

Fibra optika temperaturo-sensilo, Inteligenta monitora sistemo, Distribuita fibro-optika fabrikisto en Ĉinio

The bottomhole pressure, temperature and other data of oil and gas wells are necessary basis for dynamic analysis of oil and gas field development and formulation of development adjustment plans. Tial, frequent testing operations are needed in the production process of oil and gas wells to obtain relevant data. Tamen, with the deepening of refined oil and gas field development, intermittent single point data can no longer effectively support timely adjustment of oil and gas wells. Permanent pressure monitoring and fiber optic monitoring technology can continuously monitor oil and gas wells for a long time, obtain real-time curves of bottomhole pressure and temperature, and guide oil and gas wells to carry out production under reasonable pressure differences in real time. Through stable or unstable well testing, dynamic reserves, permeability, skin factor, ktp. of a single well can be calculated, and multi-point control can be used to test the connectivity of production layers between wells.

The permanent downhole pressure monitoring system adopts advanced pressure sensors and electronic chips. After more than a decade of on-site application in oil fields in countries such as Canada, the United States, Iraq, Iran, Russia, Malaysia, etc., it has fully demonstrated its superiority in oil and gas well testing technology. In the mid-1980s and early 1990s, 12 units jointly initiated research on the application of fiber optic sensor technology in permanent monitoring of oil reservoirs. Currently, fiber optic monitoring systems such as temperature and pressure measurement systems and distributed temperature measurement systems have matured and are used for monitoring oil well temperature, pressure, flow rate, ktp.

At present, interval steel wire operation is mainly used in China to measure the pressure and temperature data at the bottom of oil and gas wells, and continuous monitoring technology is rarely applied. This article will focus on summarizing the basic principles and adaptability of different testing methods, providing reference for the selection of testing methods for oil and gas wells, especially for key oil and gas well testing methods such as high temperature and high pressure.

The conventional interval testing method tests oil and gas wells at specific times according to production needs. A pressure gauge is inserted into the well using steel wires or cables to obtain bottomhole pressure and temperature data during the testing operation. After the operation is completed, the pressure gauge is lifted out of the wellhead. The advantage of this method is that the cost of a single testing operation is low, but it cannot obtain long-term continuous pressure and temperature data. Samtempe, the pressure gauges used are mainly gemstone or quartz electronic pressure gauges, with a pressure range of about 105 MPa and a temperature range of about 177 ℃, which can no longer meet the testing requirements of high temperature and high pressure wells.

There are currently three commonly used testing processes:

(1) Steel wire lifting and storage type: First, program the electronic pressure gauge and connect it with electricity. Use steel wire equipment to lower the pressure gauge into the target layer. After the test is completed, the pressure gauge is lifted out of the wellhead along with the steel wire, and pressure and temperature data is replayed on the ground.

(2) Steel wire salvage storage type: After programming the electronic pressure gauge and connecting it with electricity, it is lowered into the target layer with the steel wire, released from the pressure gauge, and lifted out of the steel wire. At the end of the test, use steel wire tools to salvage the pressure gauge and replay pressure and temperature data on the ground.

(3) Cable lifting and direct reading type: Connect the electronic pressure gauge to a single core cable, use a winch to send it to the target layer at the bottom of the well, and supply power to the underground pressure gauge on the surface. The test data is transmitted back to the surface in real time through the cable, and the pressure gauge is lifted after the test is completed.

The storage testing method uses batteries to power the pressure gauge, while the direct reading testing method uses cables to power the underground pressure gauge. The testing time is no longer limited by battery energy, but there is a problem with sealing the testing wellhead. At present, the main method for testing operations is to use a steel wire lifting and storage method, which converts the pressure and temperature at the depth of the oil layer based on the wellbore pressure gradient curve measured during the steel wire lifting process.

The testing operation is a wellhead pressure operation, and the high-temperature and high-pressure well testing operation requires high pressure levels for well control equipment such as blowout preventers and spray pipes. Due to the heavy weight of the steel wire tool string, high requirements are also placed on the tensile performance of the steel wire, which poses a high risk for the testing operation.

The Permanent Downhole Monitoring System (PDMS) is a technology that places an electronic pressure gauge into a pressure gauge holder connected to an oil pipe, and lowers it into the well along with the oil pipe. The high-precision sensors in the pressure gauge sense the pressure and temperature underground, and the processed pressure and temperature signals are transmitted to the surface through cables. The surface data acquisition system controls and stores the underground pressure and temperature signals transmitted to the surface, and real-time pressure and temperature data is recorded. PDMS can use ground direct reading to monitor oil reservoirs and well conditions in real-time, continuously, and long-term, facilitating timely understanding of oil and gas well production dynamics, optimizing oil and gas well working systems and lifting parameters.

The system mainly consists of two parts: underground and surface. The ground part consists of a cable wellhead lead out device, a data acquisition system, and a solar automatic power supply system. The underground part consists of an electronic pressure gauge, a pressure gauge support cylinder, armored cables, and cable protectors.

The ground data acquisition system is used to supply power to the underground pressure gauge and issue control commands to it, change the sampling interval of the underground electronic pressure gauge, and collect and store pressure and temperature data transmitted by the underground pressure gauge. The data is stored using an SD card, with a storage capacity of up to 15 million sets of data. The solar automatic power supply system provides reliable power to the surface data acquisition system and underground pressure gauge. Reserve cable exit holes on the tubing hanger and Christmas tree, install cable wellhead lead out devices, and the main function is to seal the cables that pass through the wellhead. The sealing pressure is 20kPsi, and the material is Inconel 718. It adopts full metal sealing, which can ensure long-term sealing effect and is suitable for high-pressure and high-temperature oil and gas wells.

A cable is a transmission channel for power and data, with solid copper wires inside, an inner insulation layer and an insulation filling layer in the middle, and a metal packaging layer on the outermost layer. The steel pipe material is Incoloy 825 (high nickel alloy), with a maximum working pressure of 25kPsi, a maximum working temperature of 200 ℃, a tensile strength of 1000kg, and a core wire specification of 18 AWG. It has good resistance to compression, abrasion, and corrosion, and is suitable for long-term use underground. Cable protectors are used to attach cables to oil pipes and provide protection for cables at pipe couplings. There are options for stamping type lightweight protectors and cast steel heavy-duty cable protectors. Heavy cable protectors are usually used at the lower end of the oil pipe string and in special wellbore structures. They can resist wear and withstand large external impact forces, protecting the cable from being completely damaged by the harsh underground environment; Lightweight cable protectors are usually used at the upper part of the oil pipe string, which can not only fix the cable but also withstand the usual downhole impact force.

The electronic pressure gauge is the core part of the PDMS system underground, using high-precision and high-resolution quartz pressure and temperature sensors. The production design of the circuit is based on the latest hybrid circuit technology and packaged using vacuum welding technology. The sealing between the electronic pressure gauge sensor and the outer cylinder of the circuit is done using ion beam welding technology. The outer cylinder material is made of ultra strong anti-corrosion nickel based alloy Inconel 718, with a maximum outer diameter of 0.875 inches and a maximum pressure rating of 25000 Psi. It can work continuously for more than 10 years at high temperatures of 200 ℃/392 ℉, and can work for a long time in harsh well conditions such as high temperature and high pressure.

The pressure gauge support cylinder provides installation position and mechanical protection for the pressure gauge. The seal between the pressure gauge and the support cylinder is a metal seal. The pressure inside the outer casing of the support cylinder can be monitored or the pressure inside the oil pipe can be sensed and monitored through the pressure transmission hole. Two pressure gauges can also be installed simultaneously on one support cylinder.

The permanent downhole monitoring system can continuously monitor the bottomhole pressure and temperature of oil and gas wells for a long time. It is used for dynamic analysis of oil and gas well production, well testing analysis, numerical simulation of oil and gas reservoirs, optimization of artificial lifting working parameters, prevention of formation sand production, and other research issues. Its main characteristics are: (1) it has long-term stability in operation. The solar power supply system can ensure continuous and reliable operation of the system; Adopting ultra large scale integrated circuit design, it has strong seismic and anti-interference capabilities; The latest pressure sensor technology and circuit technology are adopted, and the continuous monitoring time can reach more than 10 years, with high working stability and reliability.

(2) Suitable for monitoring high temperature and high pressure wells. The maximum pressure level of the electronic pressure gauge can reach 25kPsi, and it can work continuously for more than 10 years at high temperatures of 200 ℃/392 ℉. It can be used for monitoring harsh well conditions such as high temperature, high pressure, and high corrosiveness.

(3) Continuous real-time monitoring of multi-layer pressure. The permanent underground monitoring system can not only achieve single-layer pressure monitoring, but also achieve simultaneous and real-time monitoring of single well and multi-layer underground data. In addition, it is possible to choose to monitor the pressure inside the casing outside the support tube or the pressure inside the oil pipe inside the support tube.

Permanent fiber optic monitoring technology fiber optic sensing technology is a new type of sensing technology that uses light waves as carriers and optical fibers as media to perceive and transmit external measured signals. The permanent fiber optic pressure/temperature monitoring technology is to lower the fiber optic sensor into the well along with the completion string. The wellhead laser emits a laser, and the optical signal reaches the downhole sensor through the fiber optic. The sensor modulates the temperature and pressure information on the reflection spectrum. The wellhead detector receives the spectrum reflected back from the sensor and obtains temperature and pressure data through analysis of the interference spectrum. Permanent fiber optic monitoring can achieve real-time, long-term, and stable monitoring of bottomhole pressure and temperature data in oil and gas wells. Through regional and multi well point data monitoring, it can provide a basis for formulating oil and gas field development plans.

The commonly used optical fiber sensors underground include distributed optical fiber temperature sensors (DTS) and optical fiber pressure sensors (PT). The measurement basis of DTS is the influence of temperature on the light scattering coefficient. By detecting the disturbance information of external temperature distribution on the fiber, temperature information is obtained to achieve distributed temperature measurement. The technical basis of measurement is fiber Raman scattering technology. The laser emits light pulses along the fiber optic, which are divided into two beams through a splitter. Two filters with different center wavelengths are connected below to filter out Stokes light and anti Stokes light, which are converted into electrical signals by photodetectors and sent to the data acquisition and processing unit. After detection and processing, the temperature value is finally output.

Based on the principle of constant speed of light, the precise depth of reflected light signals from optical fibers can be measured

Most fiber optic pressure sensors use pressure gauges based on the principle of Fabry Perot interferometer. The cavity formed by two fiber end faces is called a Fabry Perot cavity in optics, abbreviated as a Fabry Perot cavity. When the laser enters the Faber cavity from one end of the fiber, some of the light energy is reflected on the end face of the fiber at that end; The remaining optical energy continues to propagate forward, then is reflected from the second fiber end face and enters the first section of the fiber in the opposite direction. The laser reflected twice forms interference on the surface of the detector, and the interference spectrum is uniquely determined by the length of the Fabry cavity, which is a sine wave in the frequency domain. By measuring the period and phase of the sine wave, the cavity length can be accurately determined. The external pressure P will compress the Faber cavity, causing the cavity length of the Faber cavity formed between the two fiber end faces to change with the change of external pressure. Tial, by measuring the length of the Faber cavity, the external pressure P can be inferred.

Composition of a permanent fiber optic pressure/temperature monitoring system

The ground part mainly includes buried optical cables and modulators, while the underground part mainly includes fiber optic sensors, sensor supports, optical cables, and cable protectors. The ground spectral demodulator emits a continuous wavelength scanning laser of 1510-1590nm. The laser is transmitted to the F-P cavity pressure sensor and FBG temperature sensor underground through a signal fiber, and then the laser is reflected by the F-P cavity and FBG to form a reflection spectrum. The reflection spectrum carries the pressure and temperature information near the sensor back to the demodulator along the same fiber, and the demodulator sends the spectral signal to the computer. The computer calculates the pressure and temperature values underground according to the demodulation program, and displays, stores or remotely sends them in real-time according to the required database format.

The ground control unit consists of a demodulator and a laptop computer, and the software that matches the demodulator is built-in to the computer. A demodulator is a device that interprets the spectral signal reflected back by the downhole temperature and pressure sensor into a visible temperature and pressure value for the user. It can sequentially demodulate the pressure and temperature signals of 16 channel sensors, and display and store the current temperature and pressure. Buried optical cables are mainly used to transmit optical signals from the wellhead to the equipment, and are generally constructed in a buried manner. Armored optical cables provide a channel for signal transmission between sensors and ground demodulators. The outer armor material is 316L or Inconel825, and the middle hydrogen resistant metal layer can delay hydrogen loss by about 140 times, greatly extending the service life of optical cables under high temperature conditions. The service life of optical cables can reach more than 10 years.

Fiber optic sensors are the core components of a permanent fiber optic pressure/temperature monitoring system underground, with a maximum working pressure of 15kPsi and a maximum working temperature of 300 ℃.

The advantages of permanent fiber optic monitoring technology mainly include:

(1) The sensor is small in size, lightweight, with very few components and no moving parts. The optical sensor has a lifespan of more than 15 years.

(2) Fiber optic is both a sensor and a signal transmission medium, without underground electronic devices, resistant to strong electromagnetic interference, and highly reliable.

(3) All quartz structure, stable chemical properties, laser micro processing technology, reliable performance.

(4) The armored optical cable is made of 316L or Inconel825 alloy material, which is resistant to H2S/CO2 corrosion.

(5) There are multiple measurement points, which can be connected in series or parallel to monitor the pressure and temperature of multiple layers in a single well. A 1/4 “fiber optic cable in a single well can provide up to 12 pressure and temperature signals, and a set of wellhead equipment can connect 16 temperature and pressure sensors simultaneously.

(6) Can be used for high temperature/high pressure wells: can withstand 300 ˚ High temperature, 15000Psi pressure, and vibrations and impacts generated by high-yield airflow.

Steel wire operation is suitable for testing vertical wells and small inclination wells. Its advantage is that the cost of a single operation is low, but the subsequent cost increases with the number of operations. It can be used for temporary monitoring of low-temperature and low-pressure ordinary development wells. Permanent pressure monitoring and fiber optic monitoring are suitable for vertical and horizontal wells, with high initial investment but no subsequent operating costs. Cluster/platform wells can share surface equipment, greatly reducing overall costs. They can be used for real-time and continuous monitoring of high-temperature, high-pressure or key wells.

(1) Continuous monitoring technology provides strong data support for the refined management of oil and gas wells, which helps to optimize the working system of oil and gas wells in a timely manner, prevent sand production in reservoirs, and suppress the rapid coning of edge and bottom water.

(2) Permanent pressure monitoring technology and fiber optic monitoring technology can effectively solve the dynamic monitoring problem of high-temperature and high-pressure wells, and can reduce the engineering accident rate of testing operations while providing dynamic data of oil and gas wells.

(3) Taking into account technical and economic factors, it is recommended to conduct long-term continuous monitoring of key wells. Permanent pressure monitoring technology should be used for high-pressure wells, and fiber optic monitoring technology should be used for high-temperature wells.