M Huiyun,Yu Chenggng,Dong Lingling,Fu Yukun,Shui Chungng,Sun Hnwen,Zhu Xiohu,*

a Engineering Technology Research Institute,PetroChina Southwest Oil & Gas Field Company,Chengdu,610017,China

b School of Mechatronic Engineering,Southwest Petroleum University,Chengdu,610500,China

ABSTRACT Intelligent well technology is an oil and gas well optimization completion technology integrated with underground real-time monitoring,data analysis decision-making and remote control of downhole tools.It's of great significance to the transformation and innovation of China's oil and gas development projects.The author of this paper expounds the definition,principle,composition and characteristics of intelligent well technology,and introduces the development status quo of intelligent well technology abroad,including mature intelligent well system,key technology research of intelligent well and its application technology.After the introduction to the related technology research of intelligent well in China,the author puts forward some opinions on the development of our own complete intelligent well system.

Keywords:Intelligent well technology Development System composition Field application

1.Introduction

Oil and gas exploration engineering is one of the most complex projects as it often comes across problems such as large depth,small space,complicated environment and monitoring difficulty.With the gradual development of easy-to-exploit oil and gas resources,many oil and gas fields feature high recovery and water cut,aggravating oil and gas exploration.In order to cope with the challenges associated with oil and gas development,foreign countries have first proposed intelligent well technology (i-well)based on mechatronics and digital communication technology [1,2].In recent years,it has been popularized and even gradually demanded as a conventional means of oil and gas exploitation.Domestic intelligent well technology research started late.And only part of foreign intelligent well technology can be introduced,but at a high price.In recent years,the problems such as difficult exploitation,regulation and monitoring of oil and gas exploitation in China have become more and more serious,and the exploitation technology needs to be innovated urgently.A large number of oil and gas development researchers have gradually realized the superiority of intelligent well technology.As a result,it's an urgent need for China to develop a complete set of intelligent well system.The mature intelligent well systems abroad and the research and development of key technologies of intelligent well at home and abroad will be introduced herein.Considering the characteristics of oil and gas resources in China,the author puts forward some thoughts on the development of intelligent well,hoping to contribute to China's early entry of the era of intelligent oil and gas resources development.

2.Introduction to intelligent well technology

2.1.Definition and principle of intelligent well technology

Intelligent Well Technology,or Intelligent Completion,is a complete system of the production well that enables continuous and realtime reservoir management.The core of the technology is to form a closed-loop control.Therefore,the data such as downhole temperature,pressure,flow,composition collected by the well sensor is fed back to the uphole system in real time.And then,the same data will be deeply processed,analyzed and judged on the software platform.After that,a reservoir management decision instruction is formed and transmitted to the downhole production tool for remote operation via the wireless communication control system.

Intelligent well technology helps to connect the surface with the downhole.Its specific application in reservoir development is mainly to optimize production and control the occurrence with the goal of maximizing recovery.Faced with more and more complex reservoir production projects,multi-layer combined production can give full play to the production capacity of oil well,which is better than sequential production.

Fig.1.Architectural diagram of intelligent well technology.

The application of intelligent well technology can shut down the produced water that affects the production in time.When the pressure is not balanced,the intelligent downhole throttling technology and time balance can be adopted.The complete intelligent well system needs to have factors such as interlayer isolation,flow control,mechanical oil recovery,permanent monitoring and sand control taken into account.In this way,engineers can monitor and control the oil and gas production of single-well multi-segment oil and gas production or singlebranch wellbore in multi-branched well in real-time.The resultant realtime reconfiguration of the well structure will help to improve well production and cut operating costs.

2.2.Composition of intelligent well technology

Fig.2.Architectural diagram of intelligent well technology.

The intelligent well system is mainly composed of two parts: ground equipment and downhole equipment,including downhole information detection and acquisition system,production fluid control system,data information transmission system and uphole data analysis system[3-6],as shown in Fig.1 and Fig.2.The production fluid control system is an integral part of intelligent well technology.When the formation pressure is insufficient,the reservoir energy can be restored by adjusting the production rate.It may thus effectively control the interlayer interference,delay the water breakthrough,inhibit the water content,prolong the high-efficiency mining time of the reservoir,optimize production of the oil well,and enhance oil and gas production [7,8].

(1)Downhole information detection and acquisition system: It's mainly composed of downhole permanent or semi-permanent sensors.Several sensors,including electronic sensors,fiber optic sensors,and quartz sensors,are distributed throughout the wellbore to detect and collect real-time data such as downhole temperature,pressure,flow,displacement and time.

(2)Production fluid control system: It mainly consists of a series of downhole tools wireless controlled,including packers,throttle valves,flow control valves and branch wellbore sealing switch devices.Hydraulic and hydraulic-electric control methods are mainly used.But in recent years,all-electric control systems have emerged.

(3)Data information transmission system: It is an important bridge between production fluid control system and data analysis system.It plays the role of communication between real-time downhole data acquisition and transmission of control instructions to downhole.Generally,it is realized by cable or optical fiber.In recent years,it also transmits information by means of pressure pulse or electromagnetic wave decoding.

(4)Uphole data analysis system: It's used to process the raw data collected by the downhole sensor,and is summarized and screened by the software system to help the user to clearly understand the downhole occurrence.At the same time,the analysis software adopts reservoir engineering method,optimization method and reservoir numerical simulation and prediction technology to analyze and collect the production dynamic data and help users make corresponding adjustment decisions.

2.3.Characteristics of intelligent well technology

Compared with traditional completion technology,intelligent well technology has significant advantages in accuracy,continuity,convenience and efficiency [3,7-9].Its main embodiments:

(1)Real-time downhole condition monitoring and data acquisition:Compared with the discontinuity and instability of the traditional logging technology,the data measurement of intelligent well technology is continuous and steady.It helps to ensure highers accuracy,avoid the impact of traditional logging on normal production and secure higher efficiency.

(2)Intelligent reservoir production simulation and convenient production engineering management: Through continuous,long-term,real-time and accurate downhole information data,the ground system simulates and analyses reservoir occurrence.It helps engineers to judge downhole conditions and make decisions,facilitate accurate management of production,improve production efficiency and mitigate safety hazards.

(3)Ground system analysis and decision making and closed loop control of downhole tools: Logging and control in traditional technology are two independent projects.They cannot be carried out at the same time.The well still changes continuously between the completion of logging and the start of regulation,leading to the inaccuracy of traditional technology in production optimization.The test and control of intelligent well technology can be carried out simultaneously.It not only has advantages in decision accuracy,but also reduces the workload and working time of logging and lifting tools,greatly improving production efficiency and cutting production costs.

In spite of manifest advantages of intelligent well technology,its development is also challenging.First,the establishment of intelligent well system has the same difficulties as traditional completion technology: small space,large depth and complex environment.Compared with digital coal mining,the underground space is sufficient for people to open to traffic,while the oil and gas well underground takes millimeter as the basic unit.The coal mines generally have a depth of 1000 m,with 1500 m as the standard for a deep well.Oil and gas well needs 3000 m-4000 m long-distance communication and control.The underground visibility of the coal mine well is better and the environment is well understood,while the oil and gas underground environment measurement is difficult and incomprehensible.

In addition to the difficulties inherent in oil and gas well,intelligent well technology has its own unique problems: The underground working environment features high temperature,high pressure,corrosion,electromagnetic interference,etc.,posing higher requirements for the sensors and actuators placed underground.And again,the components of domestic intelligent well technology are solely imported at present.Their high costs also curb the development of intelligent well technology.

2.4.Limitations of intelligent well technology

(1)Input-output ratio.The cost of the whole intelligent completion system is high,even the application of one of the key technologies requires a high initial investment.For some wells with small production,there may be a smaller comparison between cost and benefit output,which in turn reduces the final economic benefits.Even some wells have an input-output ratio of less than 1,resulting in a loss.Therefore,when using the intelligent well technology,the expected production of the well is limited.In addition,the cost of intelligent well technology does not increase linearly,it has a higher investment in the initial stage.Even if the expected production of the well is high and the daily production is insufficient,the investment return period will be prolonged,and the final economic benefit will be reduced.Based on the two considerations above,it is generally believed that the daily production of the well using the intelligent well system should not be lower than 68 t.

(2)Requirements for well conditions.Since the downhole space of the oil and gas well is small,and the intelligent well system has more equipment and facilities,there are certain requirements for the well condition.In the implementation of intelligent well,interlayer packer,inflow control tool and multiple cables shall be installed in the well bore.In terms of the packer size of intelligent well system products,the well bore size is generally not less than 117.8 mm.Intelligent wells are generally suitable for self-drilling wells,gas lift wells and installation of large displacement pump wells (such as electric submersible pumps).Non-self-injection wells need to be equipped with more wellbore tools,which will lead to further reduction of downhole space,affecting the installation of intelligent well equipment and tools.As a result,the intelligent well system cannot perform its full function or even function properly.

(3)Technical research.The complexity of the intelligent well system is higher than any previous downhole tool,and the unpredictable downhole environment makes the development of the intelligent well system more difficult.Until today,we still can't guarantee that any intelligent well system can improve production stably and safely.Therefore,we need to attach great importance to the development of key technologies of intelligent well technology.

3.Development status quo of intelligent well technology at home and abroad

3.1.Overseas mature and complete intelligent well system products

In the 1990s,the concept of intelligent well technology has been put forward abroad,and at the end of the 20th century,a number of complete sets of intelligent well technology products have been developed and put into production [10-19].After decades of development,foreign large-scale oil and gas production equipment enterprises led by Schlumberger and Beckhughes have further improved the technology of intelligent well from the aspects of electrification,electronics,remote communication and hierarchical control.At present,the representative mature intelligent well technology products are shown in Table 1.

3.2.Development status of key technologies for intelligent well

At present,the relatively mature and complete intelligent wellsystem is relatively few.In order to improve this complex system,many workers conduct targeted research on key technologies.In fact,most oil and gas well using intelligent well technology do not have a complete set of intelligent well technology.In spite of the application of only or several key technologies,the improvement of production and efficiency is obvious.

Table 1 Typical intelligent well technological products abroad.

Table 2 Intelligent well monitoring technology abroad [16,30,31].

3.2.1.Monitoring technology

Downhole data monitoring technology is the “eye” of intelligent well technology.Unlike the traditional method of processing the downhole data through the calculation of the data on the well,the intelligent well monitoring technology is to obtain the downhole realtime data directly.In the 1960s,the first batch of permanent downhole instrumentation (PDG)was formally used.It heralded that oil and gas development has entered the era of digital intelligent monitoring.The development status quo of intelligent well monitoring technology is shown in Table 2.

3.2.2.Data processing technology

Data processing technology is the “brain” of intelligent technology.The intelligent well monitoring technology continuously acquires data in the well for a long time.Original data are characterized by massive data set,including abnormal points and noise,multiple stages of pressure rise and fall.Such data cannot be directly used for reservoir modeling or interpretation with existing well test interpretation theory.In order to effectively utilize the huge data set,appropriate data processing technology is indispensable.The development status quo of data processing technology for intelligent well abroad is shown in Table 3.

3.2.3.Flow control valve

Flow control technology is the “hands” of intelligent well technology.The ultimate goal of intelligent well technology is to regulate and reorganize production,relying on the wireless control throttling device.At present,hydraulic control valves are widely used,including full-open and fully-closed control valves,as well as step-wise and fineadjustable control valves.With the advancement of mechatronics technology,electric-hydraulic integrated control valves have been gradually developed,exhibiting great advantages in deep well (see Table 4).

3.2.4.Optimization method

The optimization method is the “blood” of intelligent well technology.The excellent optimization method can make each component of the intelligent well system better connected,apart from a better communication with users.Production optimization methods are mainly divided into reactive strategies and proactive strategies.The difference between the two is that the former is to adjust and control after encountering production problems,while the latter is to formulate a set of cautionary plans (see Table 5).

3.3.Application of intelligent well system

In 1997,the first electronic hydraulic intelligent well system SCRAMS [20],developed by Halliburton and Beihai Petroleum Service Engineering Company,was installed on the Saga Tension Leg Platform in Beihai.Since then,intelligent well technology has developed rapidly in the field of foreign oil and gas development: in the first 10 years,the production well with intelligent well systems has grown at a rate of 27% per year,and more than a thousand production wells have been intelligently transformed.In the second decade,large foreign oil and gas development enterprises,including Shell Petroleum Company,have adopted the technical requirements of intelligent well as conventional means of production.The successful application of intelligent well technology exists in multi-layer production,automatic gas lift,water and gas injection,deep-water ocean,heavy oil exploitation,thin reservoir,multi-branch well and marginal reservoir development.Morethan 300 production wells have been equipped with complete intelligent well system,and tens of thousands of other production wells have adopted incomplete intelligent well technology such as downhole monitoring technology and downhole flow control technology.Although most intelligent well systems are used at sea,the intelligent digitization of land-based oil and gas exploration has become a trend[21,22].The application situation of the intelligent well system abroad is shown in Table 6.

Table 3 Data processing technology of intelligent well abroad [32-45].

Table 4 Flow control technology of intelligent well abroad [32,46,47].

3.4.Development and application status of domestic intelligent well technology

With the development of oil and gas development projects,China's oil and gas exploitation has expanded from the initial land area to the sea and desert.The traditional completion technology can't reach the set target when dealing with such complex reservoirs,and the introduction of a foreign intelligent well system is priced between US$2 million and US$5 million,resulting in a sharp increase in development costs.Most production wells in China cannot afford such a high cost because their production capacity is not big enough.

Domestic research on intelligent well technology is still in its infancy.Faced by the blockade of import of intelligent well technology,the Chinese government has spent plenty of money and time on its research and development.Starting from basic hardware,China has carried out research on key technologies of intelligent well including intelligent downhole throttle valves,remote bidirectional communication and permanent downhole intelligent monitoring.We are committed to partial intelligent digitization of domestic oil and gas production well before embracing complete intelligent well system in the future [48,66-70].At present,the domestic research on intelligent digital completion technology is shown in Table 7.

The downhole data transmission system and electronic sensors independently developed by Southwest Oil and Gas Company can monitor downhole temperature and pressure and transmit them to the ground in real time.

The distributed FBG temperature and pressure sensors of Beijing Ulanshi Company are divided into two kinds: single-point sensor and double-point sensor.Both of them can perform downhole temperature and pressure measurement.Single-point sensor can measure the temperature and pressure of tubing or annulus separately,and double-point sensor can monitor the temperature and pressure of tubing and annulus simultaneously.The supporting brackets of sensors are also divided into single-point type and double-point type,helping to better fix the supporting sensors and fully protect the sensors in the working process and effectively securing the safety and reliability of sensor signal transmission.

Daqing Petroleum Company's horizontal well intelligent well technology can be used to help judge the aquifer interval according to the downhole pressure and water injection curve.And again,increment of the annulus pressure is leveraged to switch the bottom hole valve for regulating the downhole flow.It may thus control the production state of oil well in low aquifer.

From 2011 to 2012,Xi'an Petroleum University designed two sets of intelligent well completion systems,namely “directhydraulic + downhole electronic measuring instrument” and “direct hydraulic + downhole optical fiber measurement”.A downhole fluid control valve and a traversing packer are designed and they can traverse six 1/4 inch hydraulic pipelines or optical cables with inner diameter not less thanand outer diameter less than.A fiber optic measurement system with a 3-point horizon and measurable in-column and annulus parameters was designed.

Table 5 Development status of production optimization methods for intelligent wells abroad [49-65].

Table 6 Application situation of the intelligent well system abroad [13,15-18,23-29].

Table 7 Domestic research on intelligent digital completion technology.

In Liaohe Oilfield,a fiber optic pressure sensor with metal insulation and wavelength demodulation is developed.Laser fusion technology is applied in the probe for stable operation of the pressure sensor in the downhole condition with high temperature and pressure.

Based on the “863” project “Key Technologies for Intelligent Well in Deepwater Oil and Gas Fields”,Weide Petroleum Technology Development Co.,Ltd.carried out mechanical design covering downhole inflow controller,interlayer packer,wellhead passer,and downhole fluid control valve.And the intelligent well production forecast software was developed to guide and optimize the intelligent well production strategy.

In terms of technical application,the segmented completion technology using the uniform liquid feeding sieve tube and data acquisition technology developed by Shengli Oilfield has been applied 50 times,exerting obvious water control effect.The permanent downhole temperature and pressure monitoring technology developed by Southwest Oil and Gas Field Company has been successfully tested in J17 and Z7 wells of Shunan Gas Mine in April and May 2004 respectively.In early 2016,the M03 and M08 injection wells of the Penglai 19-3 oilfield in Bohai were inserted into the hydraulic intelligent completion system of the Halliburton Company,Smart Well.It was the first time that the intelligent water injection completion technology was used for layered injection,marking the digital intelligent production of China's unmanned offshore platform.

4.Thoughts on the domestic development of intelligent well technology

Domestic research on the key technologies of intelligent well has achieved some success,but these achievements only have some functions of intelligent well system.And there is still a big gap compared with the mature and complete intelligent well system abroad.The British Shell Group has summarized the research direction of intelligent well technology in the future [70]:

(1)Production control of multiple reservoirs can be realized by a single well;

(2)Intelligent well technology should minimize the number of workovers in daily production;

(3)Rather than just the optimization of the basic production unit,the whole oil field production system should be optimized from a systematic point of view,so as to achieve excellent compatibility between downhole tools and ground equipment;

(4)Automatic production of oil well and optimization of production strategy of oil well;

(5)The continuous service life of the intelligent well system after putting into use should be 10 years,and the reliability should be more than 95%.

From this we realized that there has been great progress in Article 1 and 2 in China.However,we are still limited to the optimization of production units,which is to optimize production by improving one or several important hardware,that is to say,we are still not doing enough for Article 3.One of the important reasons is that Article 5 is not well done.The reliability of downhole and other components is the potential requirement of Article 5,the quality and performance of domestic downhole components are currently difficult to guarantee.At present,the quality and performance of domestic downhole components are difficult to guarantee,and expensive imported components increases the cost of research and development,largely restricting the development and application of intelligent well technology in China.In addition,due to the difference in geological conditions,unlike the highyield well with long self-blowout period abroad,the reservoir energy in China is relatively low.Although there are some high-yield well,the self-blowout period is relatively short,posing higher requirements for the design of our intelligent well technology.After years of intensive injection and production,the contradiction between layers of oil and gas well is becoming more and more serious.The economic benefit of oil field is declining due to the decrease of production and the increase of liquid water content.China urgently needs to innovate the completion technology.China's intelligent well technology catches up with the trend of “China Creation”.The author puts forward the following considerations for the development of intelligent well technology in China:

(1)The key technology is the core,and the basic components are flesh and blood.Parallel with vigorous development of key technologies,we should also pay attention to the underground electronic components resistant to high temperature,high pressure,electromagnetic interference and corrosion.These components will be the foundation of the Baizhang Tower,the flesh and blood of the technology giant.

(2)Our own intelligent well technology should be of Chinese characteristics.We should understand more about the oil and gas well,design and improve non-self-blowout well with low reservoir energy but high expected production,so that intelligent well can adapt to China's geological conditions.

(3)Intelligence is the means and efficiency improvement is the goal.We should always remember that intelligent well technology is designed to optimize production and improve efficiency.If the current intelligent well technology is applied to a well of about 4000 m,an input of nearly RMB 8 million is required.It is generally believed that the daily production of oil and gas well should not be less than 68 tons.Otherwise,the higher initial investment in installing the intelligent well system will lead to lower production and longer return period.Therefore,in order to develop and promote intelligent well technology,we shall make sure that the cost is kept at a reasonable level.Otherwise,the intelligent well is just flashy.

Acknowledgements

This research was supported by PetroChina Co Ltd.Science and Technology Major Project (2016E-0612),Ministry of Education(Southwest Petroleum University),Scientific Research Starting Project of SWPU (No.2017QHZ012),Sichuan science and technology program(2019YFG0305,2018GZ0429,2018CC0098),National Research Council of Science and Technology Major Project (2017ZX05023-002).

Appendix A.Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.petlm.2019.11.003.