Wellhead Equipment Research Articles

The Strength and Minimum Wall Thickness of Wellhead Equipment for Ultrahigh-Pressure Oil and Gas Wells

Summary As oil and gas wells are drilled to greater depths, wellhead pressure is expected to exceed the 20 ksi (138 MPa) limit specified by API SPEC 6A and other industrial standards, necessitating the development of 25 ksi (172.4 MPa) equipment. This paper focuses on the strength design and analysis of ultrahigh-pressure wellhead equipment, reviewing various wall-thickness calculation formulas and design criteria based on basic mechanical theory. It traces the flange wall thickness calculations in API SPEC 6A, discusses issues with 25-ksi equipment, and analyzes safety factors, methods, and allowable stresses in different standards. The findings of the research indicate that for high-pressure equipment with a pressure of 25 ksi (172.4 MPa), the optimal ratio of outer diameter to inner diameter is 2, and the structure can meet the requisite strength requirements. The wall thickness design method for structures such as flanges in traditional American Petroleum Institute (API) specifications uses the maximum principal stress criterion for calculation, which is not applicable to high-pressure equipment. For high-strength steel with high yield ratio used in high-pressure equipment, yield strength and tensile strength should be combined in design and use, fully utilizing the material’s properties. It is recommended to use finite element analysis for high- and ultrahigh-pressure complex structures, following the latest design concepts such as elastic-plastic ASME standards. The research provides a theoretical basis for designing ultrahigh-pressure wellhead equipment.

Research on the impact of overflow well shut-in on wellbore integrity and safety

If an overflow occurs, the well must be closed immediately. To ensure the safety of the drilling wellbore in ultra-deep wells, it is critical to analyze the transient flow process and pressure fluctuations of the fluid in the annular space of the overflow well shut-in. This paper investigates the pressure fluctuation model of multi-phase fluid in the annular space after overflow occurs during gas well drilling, analyzes the influence factors of multi-phase fluid's pressure wave velocity, and simulates and analyses pressure fluctuation changes in the annular space in light of the impact of overflow well shut-in on wellbore safety. The model's correctness is verified by comparing it to experimental data published in the literature. The model is developed and examined using the example of a genuine gas well in western China. According to the study, as soon as the BOP closes, pressure rapidly increases to a high of 6.09 MPa at 5.89 s before falling to a valley of 4.68 MPa at 35.36 s. When the mild shut-in time lasts 20 s, the wellhead annular pressure reaches a maximum of 5.8 MPa. If the wellhead equipment can withstand the annular space's first pressure wave, a hard shut-in is recommended. To optimize the overflow well shut-in system and ensure wellbore safety, the change in pressure in the wellhead annular space as a result of varied shut-in timings and drilling fluid displacement is studied.

Development and Trends in Wellhead Equipment Detection Technology

Development and Trends in Wellhead Equipment Detection Technology

Methodical approach to determining the maximum permissible velocity of the gas flow with mechanical impurities using numerical modeling of erosion processes of the main technological elements of wellhead equipment

Long-term operation of gas fields is accompanied by changes in the stress-strain state of the productive reservoir, including irreversible processes of its destruction. The destruction of a productive reservoir is one of the reasons for the removal of mechanical impurities at the wellhead, abrasive wear, metal degradation, the appearance of defects in pipelines, equipment and wellhead binding. In order to avoid serious consequences from the development of defects due to the removal of impurities, various examinations are carried out using non-destructive testing methods. The need to monitor the actual condition of pipelines and wellhead equipment of wells operating the Cenomanian and Valanginian formations is due to the fact that during operation significant damage and destruction of the main elements of technological equipment may occur due to the removal of mechanical impurities, water, as well as the formation of hydrates, sand jams, etc., this can lead to serious economic losses, as well as the negative impact on the environment as a result of leaky connections and assemblies. Thus, in order to ensure reliable operation of producing gas wells in conditions of destruction of the bottom-hole zone of the well, it is necessary to choose a reasonable technological mode of operation, in which the risk of formation of sand and liquid plugs is reduced, and the negative impact of the removal of impurities on the condition of the equipment is minimized. Keywords: gas well; numerical modeling; bottom-hole zone; technological mode.

CALCULATION OF WELLHEAD PARTS

Wellhead rigidly connects the entire working column into a single system, takes the load arising from their weight, and transfers the entire load to the conductor. Provides insulation and tightness of the space between the columns, while at the same time allowing you to monitor the condition of the wellbore and perform the necessary technological operations. Wellhead serves as a pedestal for installing the production string lowered into the well. During drilling, blowout preventer equipment is installed on it, which is dismantled after drilling. The number of these elements depends on the number of working strings in the well. The casing head is positioned according to the sequence of running and cementing at the wellhead. They are selected during drilling taking into account the expected formation pressure after the drilled well interval. The operating conditions of the column head are quite difficult: In deep wells, the load from the weight of protective casings can exceed several hundred kilonewtons. The column head elements also absorb the pressure of the medium in contact with them. If there is H2S, CO2 in the formation fluid or gas, or if the formation water is highly mineralized, the casing is subject to corrosion. When the heating agent is injected in deep wells, their tubing head and casing head heat up to 150-250° C, and in the Northern conditions it cools down to -60° C. Violation of the reliability of the column head leads to serious accidents, and in some cases – fires and explosions In particular, the casing heads of multi-casing wells have a large mass and vertical size. Their high metal intensity and high demand require the expenditure of large amounts of steel, especially alloy steel, for their production. As the vertical size of the casing head increases, well maintenance becomes more complicated. Column heads for wellhead equipment are manufactured with different numbers of protective columns: three-, four- and five-post. The principle and design diagrams of such column heads are similar. Keywords: wellhead, casing hanger, equivalent tension, cylindrical part, flange.

Applications and functions of wet fountain fittings used in pre-salt cluster of santos basin

"Fountain fitting " - deep and ultra- deep in the waters oil and natural dig it up removal for needed which is main underwater of equipment is one Petrobras well in Brazil the mouth with (Wet Christmas Tree – fountain armature ) between WCT installed (Production Adapter Base - production adapter base ) (PAB) . This equipment is a wellhead equipment used to install oil and gas wellhead, control it and control the mode of operation. There are Fontan fittings for surface (for wells drilled on land) and subsea (offshore wells). According to its construction, it is horizontal and has three steps. Fountain accessories consist of tube and belt head, Christmas tree fountain. The belt head located at the bottom of the fountain shield is used to hang the protective belt, close the gap between the pipes, etc. It is for the Pipe head to hang and seal the pump compressor pipe lowered into the well attached to the belt head. The resource head directs the product from the well to the discharge line, enabling control and monitoring of the well. The fountain armature is equipped with a pressure gauge and thermometer. BOP and fountain of the armature absolutely different equipment that it is clarify need a lot people this two underwater equipment mix it up because it can each two of them the well in the mouth is installed . Dump Blow-Out Preventer (BOP) of wells digging , completion and processing during use which is security equipment . His main components drawers (rams), annular discharge against preventers and suffocation and don't kill are lines (choke & kill lines). Fountain pipes are lowered into the well where the fountain is expected to shoot. It is necessary to hang these pipes from something at the wellhead and direct the product of the well to the outside through it, and for this, it is necessary to mold the space between the fountain pipes and the production line. In order for the fountain to pump in an optimal mode, to regulate the use of reservoir energy, it is necessary to create counter pressure at the well mouth by any means. Therefore, the equipment at the mouth of the fountain well must be able to create any back pressure in the discharge line, including closing the well. In addition, the wellhead equipment should allow to measure the pressures behind the pipe, in the discharge line, and also to inject gas or liquid into the well if necessary.

Coupling Submarine Slope Stability and Wellbore Stability Analysis with Natural Gas Hydrate Drilling and Production in Submarine Slope Strata in the South China Sea

This research explores the geomechanical challenges associated with gas hydrate extraction in submarine slope zones, a setting posing a high risk of significant geological calamities. We investigate slope and wellbore deformations driven by hydrate decomposition within a subsea environment. Utilizing Abaqus, a fluid-solid-thermal multi-field coupling model for gas hydrate reservoirs was created. Hydrate decomposition during drilling is minimal, resulting in minor formation deformation near the wellbore. However, a year of hydrate production caused a maximum displacement of up to 7 m in the wellbore and formation, highlighting the risk of submarine landslides. This indicates the need for meticulous surveillance of formation subsidence and wellhead equipment displacement. In the aftermath of a hydrate-induced submarine landslide, both the hydrate layer and the overlying strata descend together, inflicting considerable damage on the formation and wellbore. Our study presents a holistic examination of the interplay between environmental geomechanics risks and engineering structure risks for submarine slope instability and wellbore stability during hydrate development, providing crucial insights for enhancing safety measures in hydrate drilling and production, and ensuring wellbore stability.

REVIEW AND CRITICAL ANALYSIS OF THE CURRENT STATE AND WAYS TO IMPROVE REGULATED POWER SUPPLIES AND AUTOMATIC CONTROL SYSTEMS FOR ELECTRIC CENTRIFUGAL PUMPING UNITS IN INTERMITTENT OPERATION OF OIL WELLS

Link for citation: Kladiev S.N. Review and critical analysis of the current state and ways to improve regulated power supplies and automatic control systems for electric centrifugal pumping units in intermittent operation of oil wells. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 203-215. In Rus. Relevance. At present efforts are being made to convert low- and medium-flow oil wells to cyclical or short-term operation in order to reduce the excess pumping capacity that resulted from the reduction of well flow that is caused by reduced reservoir pressure during long-lasting exploitation of the deposit. The need for such a conversion requires justification for the use of more complex configurations of regulated power supply sources and automatic control systems of centrifugal pump units electric drives in automated process control systems. The local low-level automatic control systems for a mechanized electric drive method for lifting an oil-containing liquid from the well to the surface, namely the installation of variable-speed AC electric drives consist of ground-based devices and special submersible equipment. The ground-based devices are control stations with AC voltage and frequency converters with built-in telemetry units, external sine filter, step-up transformer. The special submersible equipment includes asynchronous induction electric motor, power cable, submersible telemetry unit, process sensors, centrifugal pump. The power supply of such a unit is provided from the external electric three-phase network of 6 kV through a reducing transformer substation of 6/0,4 kV. In the continuous mode of operation of oil pumping plants the electric pumps and other equipment, operate in quasi-static modes. Unregulated electric drive, as well as the open-loop controlled electric drive does not allow for smooth acceleration to the nominal performance of pumping equipment for pumping oil out of well in difficult conditions and its smooth regulation when reducing the well flow because of reducing oil flow to the slaughter. Therefore, the main way of smoothly reducing the excess performance of the submersible centrifugal pump is the periodic activation mode, which includes pumping the oil mixture out of the well and stop – for its accumulation and recovery of formation pressure. The introduction of cyclical technology shows that it is impossible to use the open-loop system of regulated electric drive everywhere, where acceptable quality indicators of transition comparable with the quality of closed-loop control systems are objectively unattainable. Due to the fact that the amount of pressure at the well intake created by a centrifugal pump, necessary to lift the well fluid to the surface, depends on the square of the rotation speed of the pump working stages, the operating pump productivity range Qmin... Qmax (m3/day) is obtained by varying the motor stator winding voltage (80…100) % from the nominal voltage value by using AC voltage controller with a phase control mode. If the stator voltage value is less than 80 % of Unom then the well fluid is not lifted to the surface and does not flow out of wellhead equipment. Therefore, when a frequency converter with Unom/fnom=const is used, the supply voltage and frequency of the motor should be varied in the same range. The price for using cyclic operation is a decrease in the reliability of submersible pumps. It is necessary to use special designs of submersible electric motors, improve power supply systems and synthesize closed-loop control systems of automatic control of electric drive of submersible pump. The purpose of the study is the review and critical analysis of the current state and ways to improve regulated power supplies and automatic control systems for electric centrifugal pumping units in intermittent operation of oil wells. Object: systems of power supply and automatic control of centrifugal pump units in intermittent operation of oil well, telemetry systems, energy-efficient submersible motors and centrifugal pump designs. Methods: methods of the theory of the automatic control system for developing the concept of operation of low flow of wells, analysis and synthesis of open and closed loop control systems of electric submersible centrifugal pumping units. Results. The paper introduces the scientific problem of development, implementation, models and methods of identification of technological processes, complexes and integrated control systems of oil extraction by electric drive method, taking into account the influence of a long submerged cable, low flow of wells and difficult operating conditions. The author proposed scientifically based technical solutions in the form of a structure of a power channel of an electromechanical system with a frequency-regulated induction motor, long submersible cable and indirect method of measuring state variable from ground-based measurements at load changes and measurement channel characteristics.

Nanoarchitectonics and performance evaluation of a Fe3O4-stabilized Pickering emulsion-type differential pressure plugging agent

Abstract With the rapid growth of natural gas consumption capacity, the important role of gas storage in seasonal peak shaving and emergency response is gradually emerging. Long-term forced production and injection of gas storage will lead to problems such as wellhead equipment leakage and string seal failure. Replacing the string is not only costly but also takes a long time. Aiming at thread leakage caused by multiple rounds of forced production and injection in gas storage, a Pickering emulsion differential pressure plugging agent with a self-sealing function under a certain pressure difference was developed. We selected carboxyl nitrile latex with a self-polymerization function and modified the nano-stabilizer Fe3O4@SiO2. The Pickering differential pressure plugging agent with excellent plugging performance was prepared by the combination of modified particles and non-ionic emulsifier OP-10. The plugging test was carried out for the simulated oil pipe thread. When the leakage rate was 50 mL/min, no leakage occurred under a pressure of 20 MPa after plugging. The differential pressure plugging agent is expected to achieve plugging without moving the pipe string and rebuild the integrity of the wellbore.

Research on the Stress Characteristics of Wellhead Bolts

Bolts are important connectors in the wellhead oil pipe spool, and the safety of wellhead bolts is an important guarantee for the operation of the oil pipe spool. Taking the wellhead oil pipe spool as the research object, a three-dimensional fluid model and a structural model of the wellhead equipment and its bolts were established. Through finite element numerical simulation, combined with the basic theory of fluid solid coupling, the equivalent stress and dangerous bolt distribution of the oil pipe spool bolts were studied. The study showed that under two different working conditions, the average equivalent stress on the bolt as a whole increased as the bolt position approached the outlet of the side flow channel, The most dangerous bolt in the wellhead tubing spool appears near the outlet; The stress distribution of bolts in different sections is uneven, and the stress at the bolt head, thread, and smooth rod intersects is greater than that at the middle section of the bolt. The bolt also bears both axial and bending stresses.

THE STUDY OF THE CAUSE OF FAILURE OF THE MAIN ELEMENTS OF THE CHIRTMAS TREE AND EFFECTIVE SOLUTION WAYS

The article is devoted to the study of the causes of failures of fountain fittings in the process of operation, the measures taken to eliminate failures, increase efficiency and increase the overhaul period. İn order to improve the efficiency of the fountain fittings, the works that can be performed during major and current repairs are investigated. The main purpose of this article is to increase the reliability of the design of the fountain fittings. This article explores the causes of failure that may occur in wellhead christmas trees, their causes and solutions. The general design of x-mas trees is shown. Basically, christmas tree fittings are cross-shaped, three-necked and, depending on the design, for a working pressure of 21, 35, 70, 105, 140 MPa. x-mas trees perform the main and most important work, such as hanging tubing, shutting off the wellhead, providing the necessary pressure on the wellhead, and regulating oil production. As is known, during the operation of oil and gas wells, along with the main product, clay, sand and abrasive particles are removed from the well. Among these impacts, christmas trees are exposed to the corrosive attack of sand flowing with oil, gas and water during operation. It is the cross and the connecting elements of the x-mas tree - closing valves, the cross, the christmas tree, a pair of gates - saddles, the sealing elements that are most susceptible to eating (wear). Due to the fact that these processes occur under high pressure, a number of important requirements are imposed on the design of x-mas trees. İmproving the design of x-mas trees, which is wellhead equipment, is always one of the most important tasks in operation. In order to improve the efficiency of x-mas trees, the works that can be performed during major and current repairs have been studied. The main purpose of this article is to study the improvement of the reliability indicators of the x-mas tree design, increase the overhaul period. Keywords: Christmas tree, stem, valve, globe valve,packing element, shut-off valve, disc - saddle pair.

INCREASING THE FLUSHING SAFETY OF THE DRILLING PROCESS AND THE PERFORMANCE OF SEALING ELEMENTS OF BLOW OUT PROTECTION EQUIPMENT

The article is devoted to the study of the choice of the most effective control of technological processes for the prevention and elimination of gas, oil and water intrusions based on establishing the reliability, performance and durability of blowout control equipment. In this regard, the technical condition of the sealing elements of rams preventers, which generally meet all the requirements for the normal performance of blowout safety tasks, is of paramount importance.In order to evaluate and predict the performance and durability of the ram preventer's sealing elements, the basis for conducting experimental studies of their technical condition should be developed.To develop the basis for conducting experimental studies of the technical condition of the sealing elements of ram preventers in order to assess and predict their performance and durability. In this regard, for research, the main parts and components of the stand for testing standard drilling oilfield equipment were developed and manufactured. Structurally, the stand consists of two test wells with a depth of 2000 and 2500 meters, respectively. The structure of the wellhead equipment of each well includes a casing head with installed anti-blowout equipment (ram and annular hydraulic preventers together with a hydraulic drive station). A standard drilling rig and a rig for running a drill string into a pressurized well are installed at the test wellheads. In addition, the stand includes specially designed and manufactured additional components and assemblies: pumping units, suction and discharge manifolds, a circulation system equipped with a number of additional devices and mechanisms, etc. Moreover, an integrated hardware and software complex has been developed specifically for the stand for monitoring and recording information during experimental studies. This complex ensured fast processing of the results of experimental studies on a computer, reliable storage and retrospective access to data, quick readjustment and the possibility of parallel work with several test objects. It is a guide for the experimental study of the productivity and durability of the sealing elements of ram preventers and provides a set of measures for determining the technical condition of BOP during operation based on objective indicators. Keywords: Blowout preventer, ram, preventer, sealing element, heavy-duty.

Influence of shock-vibration loads of drilling equipment on the drilling indicators of oil and gas wells

When drilling oil and gas wells, downhole and drilling wellhead equipment is subject to the influence of significant vibration processes of different directions with different amplitude-frequency characteristics. The paper describes the main sources of vibration of drilling equipment, which have a downhole origin. In this paper an amplitude-frequency characteristic of oscillatory processes of a drill string and their influence on drilling performance are given. In addition to the sources of fluctuations of the bottomhole nature of origin, sources of the wellhead nature can also be distinguished. Thus drilling mud pump is a generator of pulsations and beats of the pressure of drilling fluid, which in turn leads to the increase in the dynamics of the drilling tool, the appearance of torsional vibrations of downhole motors and bits. We established the negative influence of vibrations of the bottomhole assembly and drilling mud on the stability of the operation of hydraulic downhole motors, penetration on the bit, durability of the elements of the string and energy indicators of drilling. The proposed device allows reducing the amplitude of pressure fluctuations of the drilling fluid and drilling tool.

RESEARCH ON THE RESERVES FOR REDUCING THE METAL INTENSITY OF COMMERCIALLY AVAILABLE DOWNHOLE SUCKER-ROD PUMPING UNITS

A modern well pumping unit (WPU) consists of downhole equipment, including a downhole sucker-rod pump (BHP), tubing string and pump rods, and surface equipment, including the drive of the downhole sucker-rod pump and wellhead equipment. Each of these elements is serially produced by oil industry in accordance with state standards. In the given article with the purpose of finding out the possibility to decrease metal consumption of serial rocking units the possibility of transition to one-beam welded design of the rocking unit balancer is investigated. Keywords: rocking-type machine, rocker, single-beam design, metal-intensity,

COMPLICATION DURING WELL DRILLING AND THEIR PREVENTION

The article provides a brief analysis of the complications that occur during the drilling of wells and their prevention. Violation of normal working conditions during drilling of wells occurs as a result of the impact of geological factors, disruption of technical and technological processes, as well as improper organization of work. Improper organization of work means a lack of manpower in the rig, failure to bring the necessary materials and tools to the rig, timely elimination of defects in the installation work. Due to technical failures of surface and wellhead equipment, long-term oil and gas-water fountains, as well as wells may be seriously complicated. Many complications occur as a result of incorrect technological process. These include the bending of the wellbore, the collapse of the well wall, the formation of a groove in the wellbore, and the occurrence of oil-gas-water through the protective belts. A lot of time and money is spent to prevent complications, which reduces the technical and economic performance of drilling. A number of measures should be taken in advance to prevent complications, as it is very difficult to prevent complications once they occur. Keywords: Drilling of wells, complications in the well, disruption of technological processes, disruption of the wellbore, protective belt, collapse of the well wall.

Statistical analysis of the relative position of the rod hanger and the wellhead

One of the leading methods of exploitation of oil fields is oil production with the help of downhole rod pumping units (DRPU). Over 80 % of the operating well stock of Azneft PA is equipped with deep well pumps and about 30 % of oil is produced in the country with their help.
 The widespread use of DRPU is associated with a fairly high maturity of installations, simplicity of its design and maintenance, repair in field conditions, ease of adjustment, the possibility of servicing the installation by unskilled workers, a small effect on the operation of DRPU of the physical and chemical properties of the pumped liquid, as well as high efficiency.
 However, along with the high efficiency of the applied DRPU, there are also complaints regarding the need to increase the reliability and resource of wellhead equipment, including in order to improve the environmental situation in the oil fields.
 One of the conditions for ensuring high reliability of the ground equipment of the DRPU is to ensure the tightness of the wellhead rod-wellhead stuffing box assembly, the violation of which is not only a failure of the installation, but also leads to environmental pollution.
 This is facilitated by inaccuracies in the assembly and installation of DRPU at the wellhead. When mounting the pumping unit, for many reasons, the tolerance of the wellhead rod with the suspension point of the rod string to the balancer head is not ensured.
 In this regard, in the requirements for the accuracy of mounting the pumping unit at the point of application, a certain mismatch of the axes within the circular coordinates is allowed. So, for widely used pumping units of the CK8 type, the permissible mismatch between the axis of the wellhead rod and the suspension point of the rods is determined by the conditions under which the projection of the suspension point of the rods onto the plane of the base of the pumping unit at any position of the balancer is allowed within a circle with a diameter of 25 mm.

Well-Integrity-Management Approach in HP/HT Gas Field Ensures Stable Production

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208443, “Integrity Evaluation and Management in High-Temperature, High-Pressure, and High-Production-Rate Wells in Southwest China,” by Dajiang Zhu, Yu Fan, and Huali Zhang, PetroChina, et al. The paper has not been peer reviewed. The Longwangmiao (LM) gas field in southwest China features high-pressure (HP; approximately 75–76 MPa), high-temperature (HT; approximately 144–156°C), and high-production-rate (approximately 700 000–1 million m3/d) characteristics. Serious well-integrity problems were encountered in the development process. Wellhead growth was present in 33 wells, and four wells exhibited gas leakage through wellhead valves. A well-integrity-management system was developed based on annulus-pressure-management technology, wellhead-growth-risk analysis and control, downhole leakage detection, and wellhead corrosion and erosion detection, ensuring the safe and stable production of gas wells. Introduction In the four wells that experienced gas leakage after well completion, this mainly consisted of damage to and leakage of the wellhead valve stem seal, tail rod, and flange connection (Fig. 1). In addition, corrosion and internal leakage in six wellhead valves with a material level rating of FF also was detected. The corrosion and leakage of wellhead equipment has become a restrictive factor for the rapid and safe development of the gas reservoir. In addition, because the average gas-production rate of a single well is greater than 700 000 m3/d, and the wellhead temperature is greater than 90°C during production, the wellhead generally is lifted. After the gas reservoir was put into operation, under the influence of the rise of wellbore temperature, 33 of the 56 production wells were monitored for wellhead growth. The average growth was 4 mm for production wells, and the maximum value was nearly 30 mm.

INCREASE THE RELIABILITY OF A WELL HEAD

The article describes the completion of drilling a well, lowering and cementing the production line, as well as after digging the cement plug in the casing (the height of the rise of the cement behind the belt if it is determined that there is a cement plug in the casing when determining with an electric thermometer)used to hang safety belts during wellhead equipment information on casing heads, their types and the study of the sealing element. Keywords: casing head, casing hanger, hermetic knots, casing spool, rubber sealant, metal sealant.

Strategy Targets Risk Management for CO2 Waterless Fracturing

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30437, “Risk Management and Control for CO2 Waterless Fracturing,” by Siwei Meng, Qinghai Yang, SPE, and Yongwei Duan, PetroChina, et al., prepared for the 2020 Offshore Technology Conference Asia, originally scheduled to be held in Kuala Lumpur, 2–6 November. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. Given shortages and uneven distribution of water resources in China, efforts must be made to develop waterless fracturing techniques. The fluid experiences high pressures and low temperatures during carbon dioxide (CO2) waterless fracturing operations, which can lead to accidents and environmental pollution. In the complete paper, a safety-management approach and a contingency plan for such operations are developed. At the time of writing, this CO2 waterless fracturing methodology has been completed successfully more than 20 times. Surface Process Work Flow of CO2 Waterless Fracturing The basic process of a CO2 waterless fracturing operation is shown in Fig. 1. First, several CO2 storage tanks are connected in parallel. The booster, sealed blender, fracturing pump (all mounted on trunks), and wellhead equipment are connected. The measuring trunk communicates with each vehicle to monitor operation status. Proppant is put into the sealed blender, into which liquid CO2 is injected for pre-cooling. Pump testing is conducted on the high-pressure line and the wellhead and the low-pressure liquid supply line is pressure-tested. Operation does not proceed until pressure-testing results are positive. Afterward, liquid CO2 is injected into formations to fracture them and, moreover, extend created fractures. The sealed blender is enabled to inject prop-pants, and displacement begins after the end of proppant injection. Finally, a series of tasks, including well shut-in for soaking and flowback, is carried out successively.

Technology Focus: Cementing and Zonal Isolation (May 2021)

Wow! What a year it has been! We have experienced enormous upheavals in our professional and social circles and wholescale changes in the way that we interact with each other. As engineers, though, we recognize that in every challenge there is an opportunity. I have been lucky to attend SPE online events, including a happy hour and a webinar on geothermal energy. As we witness a shift to renewable energy, I note that 2020 SPE President Shauna Noonan highlighted that our SPE professional expertise in the subsurface will be needed to both maintain existing energy production and develop new sources of energy. Cementing, zonal isolation, and well integrity continue to be an important piece of the puzzle. This year, in the presence of enormous challenges, the selected papers demonstrate step changes both in efficiency and in the results of cementing operations. Managed-pressure cementing extends the benefits of managed-pressure drilling, and a successful case is described in paper OTC 30481. Last year, we read about offline cementing in North America. Offline cementing continues to increase rig efficiency, and wellhead equipment that enables offline cementing is described in paper SPE 202439. Improving cementing results by enabling casing rotation with rotating cement heads is discussed in paper SPE 198970. Research that will enable future successful changes also continues. Although not summarized in this edition, extra reading is recommended for interesting discussions on proving shale as a barrier (SPE 200755), cement properties and initial state of stress in confined pressure conditions (SPE 201770), and the evaluation of neutron logging as a possible cement evaluation tool (SPE 202973). As an industry, we also continue to investigate materials that will provide effective isolation in the annulus. Papers about self-healing systems (SPE 203174), epoxy (SPE 202648), and expanding metal sealing systems (SPE 203354) are also recommended as extra reading. Although it has been a challenging year, operational improvements, research, and material investigation continue to provide engineering opportunities in cementing and zonal isolation. Recommended additional reading at OnePetro: www.onepetro.org. SPE 200755 - Innovative One-Trip System Helps Qualify Creeping Shale as Permanent Barrier for Plug and Abandonment of Wells on the Gyda Field by Thore Andre Stokkeland, Archer, et al. SPE 201770 - Laboratory Measurement of Cement Stress Before, During, and After Curing Under Undrained Condition With Constant Hydrostatic Pressure by Meng Meng, Los Alamos National Laboratory, et al. SPE 202973 - Potential Usage of Neutron Logging Technology for Casing Cement Evaluation—Feasibility Study by Espen Dommersnes, University of Stavanger, et al. SPE 203174 - A Game-Changing Technology for Cementing in Highly Deviated and Horizontal Wells Using Interactive Mud-Sealing Cement System by Choosak Orprasert, Mubadala Petroleum, et al. SPE 202648 - Primary Cementing Using Epoxy Resins as Additive: Experimental and Application by Khawlah Abdulaziz Alanqari, Saudi Aramco, et al.