Plugging Materials Research Articles

Experimental study of the temporary plugging pattern of perforations by multi-particle size composites

In the process of temporary plugging and diverting fracturing of horizontal wells, the seating of large-size temporary plugging balls on the perforation is unstable and the plugging efficiency of irregular perforations is low, so a smaller-size composite temporary plugging agent is needed to improve the temporary plugging efficiency. In this study, based on the actual situation of Changqing oilfield, three kinds of temporary plugging materials with small particle sizes were used to plug the perforation. A simulated perforation plugging device with different permeability was built by artificial cores, and the plugging law and pressure-bearing capacity of the composite temporary plugging materials inside the perforation were studied. The results show that the temporary plugging materials with particle sizes smaller than the diameter of the perforation can form a plug inside the perforation, and the plugging zone formed inside the perforation is discontinuous. The plugging zone has good pressure-bearing performance, and the indoor blocking pressure is more than 15 MPa. The orthogonal experiments showed that the importance of three kinds of temporary plugging agents in the composite temporary plugging materials were 3-4 mm particles, 0.15 mm powder, and 1-2 mm particles, and the optimal ratio is 3:3:2. This study provides a technical basis for the design of the temporary plugging and diverting fracturing.

Study on the mechanism and performance of polymer gels byTEandPVAchemical cross‐linking

AbstractPolymer gels are widely used as drilling plugging materials. In this paper, titanium bis(triethanolamine)diisopropoxide (TE) and polyvinyl alcohol (PVA) solution were chemically cross‐linked to obtain a gel material. It shows that the OH on the PVA molecular chain are chemically cross‐linked with the Ti ion in TE crosslinking agent through complexation reaction, and the cross‐linked segment can inhibit the chain motion, resulting in a stable “crab structure” gel configuration. The gel materials synthesized under this configuration were characterized and analyzed by SEM, TG‐DSC, GPC, and contact angle measurement. It was demonstrated that the gel performance is optimal when the concentration of TE crosslinking agent is 2.2 wt%, considering the gel strength and gelation time. In addition, the simulated plugging experiment of the gel showed that the service life of the gel was about 72 days, and the sealing performance and tensile recovery performance were significantly improved compared with the previous ones, which would provide a new perspective for the novel plugging materials.

Physico-Chemical Peculiarities of Weighted Thermostable Plugging Materials Hydration

A new competitive class of plugging compositions (weighted non-shrink plugging materials) has been created using as components a fly ash from thermal power station, a weighting additive and a superplasticizer. X-ray phase analysis identified the composition of new materials formed in the hydration process of the developed plugging compositions. The kinetic curves of the plugging material expansion in a wide temperature range have been obtained. Rational temperature regimes of plugging materials hardening according to the criteria of strength and gas permeability of cement stone have been determined.

Basic Experimental Study of Plasticity Material for Coal Rock Fracture Grouting Based on RSM-PCA Technology

The internal fractures in coal and rock mass are important factors affecting the safety of underground engineering such as coalbed methane exploitation, so the comprehensive properties of materials used to seal the fractures are particularly critical. In this paper, firstly, the indexes of the main factors affecting the plugging material (viscosity, bleeding rate, setting time, and strength) were analyzed. Then, the sensitivity of the materials used to seal the fractures was studied and discussed using a principal component analysis and response surface analysis (RSM-PCA). The primary conclusions are as follows: (1) Bleed rate and setting time were the first principal components affecting the comprehensive properties of the plugging materials, and compressive strength was the second principal component. (2) The regression equation was established to characterize the comprehensive properties of the integrated plugging materials, and the optimal mix ratio was 34% of cement content, 11% of sand content, and 0.53 of the W/C. (3) The microscopic results showed that the silicate minerals in the consolidated body grow in a bridging manner and formed a mixed gel with cement hydration product to fill the pores and microcracks and improved the interface transition zone.

Study of dispersed-reinforced expanding plugging materials to improve the quality of well cementing

The most common complications during the construction and operation of wells, such as gas and water showings and interstratal crossflows, in most cases result from seal failure of the annular space caused by cracking and destruction of the cement ring. The main way to improve the stability and tightness of well support is a rational cementing technology using high-quality plugging materials. Recently, due to the toughening of environmental requirements for a number of chemical reagents used for the treatment of plugging solutions, the most expedient in terms of increasing the fracture strength of a stone has become a method for developing plugging materials from several components with different physicochemical and physicomechanical properties. These are dispersed-reinforced materials, which are a mixture of backfill cement and mineral or artificial fibers, as well as organic fibrous additives from cellulose, jute, cotton, etc. The article discusses the results of studies of expanding reinforced plugging solutions in order to study their main technological and strength characteristics.

METHODS OF PREPARATION AND PLUGGING MATERIALS APPLICATION TECHNOLOGY WHEN WATERPROOFING WORKS ON OIL WELLS PERFORMING

It is well known that many oil wells in the Volga-Ural Region have a high water cut degree. For the fields of PJSC TATNEFT, the average water cut is 70 %. Sometimes this value reaches 98 %! There are many reasons for this water cut level, including depreciation of the entire underground part of the well, non-compliance with technologies and the low-quality materials application in the well construction, operating rules violation. The resulting water flow between the aquifers and oil well horizons leads to a high water cut in the produced product and very often constitutes the greater amount in the produced fluid composition. To eliminate such crossflows, waterproofing works are carried out to separate the layers, which must be performed as efficiently as possible. Despite the large plugging compounds assortment and the variety application technologies, the success of waterproofing works remains low in many cases. The materials composing the plugging solutions do not always turn out to be of the required quality, and the work technologies, as a rule, are of a recommendatory nature and require amendments taking into account specific conditions. In this regard, a number of new materials, structure-forming agents and injection techniques have been proposed, which increase the waterproofing screen resistance to the formation waters breakthrough.

Long term assessment of the geochemical integrity of offshore wellbore cement– results from numerical modeling

Oil and gas wells across different offshore fields are currently experiencing plugging and abandonment. With this comes the risk associated with leakage of fluids from wellbores. One area of the long-term integrity of oil and gas wells that has received less attention is the geochemical assessments of cement and cement-rock integrity. This study investigates rock-fluid-cement interactions over long time scales using numerical models of coupled heat and fluid flow and reactive solute transport. Four different kinds of brine compositions from the Gulf of Mexico formations are used to simulate chemical interactions in wellbore plug, cement, and adjacent rock. Porosity changes are used as indicators of the geochemical integrity of the plugging and cement materials. Results demonstrate the impact of temperature, pH, and depth of cement placement in integrity predictions. At greater depths, higher temperatures and pressure will be encountered leading to the precipitation of gypsum and the dissolution of ettringite, calcite, and portlandite which adversely affects the integrity of the wells. The cement-rock interface is a zone of vulnerability and subject to greater loss of integrity. Other modeling parameters from our study which influenced integrity include reactive areas, diffusion coefficients, flux rates, boundary conditions, and the presence of mechanical damage. This study highlights the importance of brine specific geochemical assessments as well as the importance of thermodynamic properties when investigating geochemical wellbore integrity, and the approach used can be applied by practitioners for predictive analysis of geochemical longevity of cement and plugs in subsurface conditions.

Development of responsive well plugging material in carbonate reservoir

One of the most critical problems limiting the exploration and development of the Central Asia and Middle East Areas is lost circulation caused by the natural fracture propagating in carbonate reservoir. Traditional plugging materials had limited performance due to poor adaptability to carbonate formation. This paper investigated the mechanism of lost circulation in Central Asia and Middle East Areas, and a new responsive fracture plugging materials was developed. After implementation, the complexities treatment time was shortened and drilling efficiency was increased. The main types of lost circulation mechanism are summarized and analysed by studied the reservoir characteristics of Central Asia and Middle East Areas. A physical model of horizontal V funnel leakage channel in the target block was established to simulate the migration and plugging process of plugging particles in natural fractures. Based on the analysis of the flow and accumulation pattern of the plugging fluid in the leakage channel with different aperture ratio, a statistical model of the particle flow in the plugging material was established. A response controllable solidification plugging material was developed. The application results show that, the responsive solidification controllable well plugging material could rapidly accumulate in the 1mm and 3mm fractures in the upper sealing formation. The mud cake has good toughness with compressive strength of 3.4-9.5MPa, which achieves a rapid and high-strength plugging for the fracture formation. The acid soluble consolidation plugging material, mainly composed of curing agent, retarder, suspending agent, etc., is developed for long open hole section. The dissolution rate could reach up to 91%, the plugging strength of the solidified plug is up to 10MPa and which could be stable for 15d under 150°C. This innovative anti-lost circulation materials for carbonate reservoirs can effectively solve the problem of serious loss of production due to sever lost circulation problem in the Mishrif reservoirs of Central Asia and the Middle East and enhance the drilling of complex carbonate oil and gas fields. The implementation of this plugging material improves the technical level of drilling and completion of complex carbonate oil and gas fields and provides strong support for exploration and development in Central Asia and the Middle East.

Optimizing selection method of continuous particle size distribution for lost circulation by dynamic fracture width evaluation device

The increase in the pressure bearing capacity is critical for mitigation of lost circulation, and to do so the strength of the plugging zone should be increased via picking an effective evaluation method and choosing the proper particle size distribution (PSD). Therefore, in order to successfully investigate this process, the traditional evaluation device of lost circulation should be improved for dynamic variation of fracture width to find the optimized plugging materials. This means, a new testing apparatus device capable of testing dynamic fracture width should be developed. Additionally, commonly used selection criteria of PSD are incapable of providing us with a continuous PSD curve since they only fulfill discrete PSDs. To overcome these two obstacles, a variety of continuous PSD models based on a new testing device and method are examined. Likewise, the impact of governing parameters and an optimized PSD selection criterion were studied with a specific lost circulation material (calcium carbonate) and concentration in a water-based drilling fluid. The experimental results demonstrate that the normal distribution model provides the best selection result while the sensitive analysis indicate that the factors influencing pressure bearing capacity in a sequential order are: minimum particle size, standard deviation, maximum particle size and average value. Besides, the optimized experiments illustrated that the maximum particle size should be 1.3 times of the maximum fracture width and the minimum particle size should be 0.8 times of the average fracture width. Moreover, the average value should be equal to the optimal particle average size and the standard deviation should be 0.3 times of the particle average size. It was found that the optimized selection method results in the highest plugging efficiency compared to conventional selection criteria. Collectively, the new device and optimal assessing approach would improve the prediction accuracy of pressure bearing capacity to select an appropriate PSD with varying of fracture width in field operations.

Development and Application of TL-1 New High Temperature and High Pressure Plugging Instrument

In view of the fact that most of the filter media of existing plugging evaluation instruments use steel plates or steel balls, which cannot truly simulate the characteristics of the formation, a new type of TL-1 high temperature and high pressure plugging instrument has been developed. The filter medium of the instrument is the natural stone with different cracks and quartz sand beds with different particle sizes, which can better simulate the adsorption and hang-up effect of the formation on the plugging agent. It is possible to evaluate the plugging effect, pressure-bearing capacity and return pressure of the plugging slurry for different cracks and sand beds of different sizes under different temperatures and pressures. Using new and old instruments to evaluate the plugging effect of the same plugging slurry, it is found that the plugging effect is different from the distribution of the plugging material on the crack surface, the plugging effect and the pressure bearing capacity. The instrument is stable and reliable in operation and simple in operation. It is a new instrument for conducting research on anti-leakage plugging materials and anti-leakage plugging drilling fluid systems.

Synthesis and Evaluation of a Water-Swelling Polymer Plugging Agent SWL-1

In this paper, to solve the problems of low water absorption and weak pressure bearing capacity of current plugging materials, acrylic acid (AA), acrylamide (AM), and sodium allyl sulfonate (SAS) are used as monomers, and soluble starch is used as grafting. Material, the use of free radical aqueous solution method to synthesize the plugging agent SWL-1 with good water absorption and strong salt resistance. The monomer ratio is set as n (AA):n (AM):n (SAS) = 5:2:1, the experimental synthesis temperature is 70°C, and the orthogonal experiment is used to determine the experimental synthesis conditions as AA neutralization degree 80%, The amount of initiator is 0.60%, the amount of crosslinking agent is 0.50%, the ratio of monomer to starch is 7:1, and the amount of calcium carbonate is 13%. The comprehensive evaluation of the performance of the plugging agent SWL-1 shows that the water absorption performance at 60°C is the best 268.78 g/g, and the water absorption performance in 8% NaCl, 0.9% CaCl2 and composite brine is 21.5 g/g, 12.5 g/g and 24.9 g/g, indicating good resistance to sodium and calcium, the water retention rate is still higher than 30% after 15 days at 160°C. The sand bed plugging test found that the maximum pressure of SWL-1 was 7 MPa, and the crack plugging test found that when the crack width was 1 mm, 2 mm, and 3 mm, the maximum compressive strength of SWL-1 was 10 MPa. The acid solubility test showed that the maximum pressure was 10 MPa. The highest rate is 86.38%.

Study on the Plugging System of the Lower Ancient High Loss Zone in Changqing Gas Field

At present, in the workover operations of old gas wells in the Changqing Gas Field, due to years of exploitation in the production layer, pressure deficits, and general leakage during the well killing, the well must be plugged before the well can be killed. In particular, the fracture-cavity type fractures of the lower paleocarbonate reservoirs have serious leakage. Traditional plugging materials and traditional plugging materials and methods have some limitations in dealing with leakage problems. Therefore, a composite plugging system using polymer solution as the base carrier fluid, multi-particle size rigid particles, expandable particles and modified fibers is developed. Its formula is: water + 2% polyacrylamide + 0.1% N, N-methylene bisacrylamide polymer gel is the base carrier fluid; the formulation of the particle plugging agent was continuously optimized through the CDL-II high temperature and high pressure dynamic and static plugging ability to plug the core. The final formulation of the plugging agent is: 1) 20% rigid particles (5 mm, 1 mm, 0.5 mm CCP-3 ratio 4:2:1) + 1% 3 mm expanded particles SMK-1 + 1% 1 - 2 mm fiber SRXW-10; 2) 20% rigid particles (3 mm, 0.1 mm, 0.05 mm CCP-3 ratio 3:2:1) + 1% 3 mm expanded particles SMK-1 + 1% 1 - 2 mm fiber SRXW-10. The water swelling multiples of the granular plugging agent in salt water are all above 7 times, which meets the requirements of leak-proof plugging operations under high salinity; 3% HCl is selected as the gel breaker, and the plugging system has a gel breaking rate of 95%; through the water plugging and profile control experimental system, the sand-filled pipe is used to simulate the plugging effect under high temperature and high pressure, and the plugging system can be sealed for 5 days at a high temperature of 110°C and a high pressure of 20 MPa to achieve a good plugging of the formation. It is expected that the developed plugging system has a good application prospect in future workover operations.

Unplugging Standalone Sand-Control Screens Using High-Power Shock Waves

SummaryPrevious studies showed that different parameters influence the plugging of completion tools. These parameters include rock mineralogy, reservoir-fluid properties, and type of completion tools. Although different methods have been used for unplugging these tools, there is still debate regarding the performance of these methods on damage removal. In this study, we assessed the performance of high-power shock waves generated from an electrohydraulic-stimulation (EHS) tool on cleaning completion tools plugged during oil production. These devices were extracted from different wells in Canada, Europe, and the US. First, we quantified the extent of cleaning for the plugged slotted liners using the EHS tool at the laboratory scale. Next, we analyzed the mineral composition of the plugging materials removed after the treatment by conducting scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma mass spectroscopy (ICP-MS), colorimetric, and dry-combustion analyses. Finally, we reviewed the pulsing-stimulation-treatment results applied to several field case studies. The results of unplugging slotted liners at the laboratory scale showed that up to 28.5% of the plugged slots are cleaned after 120 pulses of shock waves. The mineral-characterization results showed that the main plugging materials are calcite, silicates, and iron-based components (corrosion products). The cleaning performance (CP) of the EHS tool increases by increasing the number of pulses and the output energy (OE) applied to the tool. The CP parameter is high at (i) high concentrations of carbonates, barium (Ba)-based components, and organic matter, and (ii) low concentrations of corrosion products and sulfates. The results of field case studies showed that the cleaning of the EHS tool is not limited to the sand-control devices and it can clean other tools that are less accessible for other techniques, such as subsurface safety valves. This paper provides a better understanding of the performance of shock waves on damage removal from plugged completion tools. The results could open new insight into the applications of shock waves for cleaning the completion tools.

Retracted] Influence of Al Content on Degradation Behavior of Cu‐Doped Mg‐Al Alloys for Drill‐Free Plugging Applications

Herein, we report low‐cost and rare‐earth‐free Cu‐doped Mg‐Al alloys for drill‐free plugging applications and present the influence of Al content on degradation behavior. The phase composition and microstructure of fabricated alloys were characterized by using a scanning electron microscope (SEM) and X‐ray diffractometer (XRD). Also, degradation properties were investigated using hydrogen evolution tests and the electrochemical measurements. The results reveal that the Al content is directly related to the proportion of secondary phases, such as Mg2Cu, Mg17Al12, and MgAlCu. Moreover, the Mg17Al12 and MgAlCu phases are distributed at α‐Mg grain boundaries, whereas the MgAlCu phase is distributed within the Mg matrix. Acceleration of degradation rate is found due to microgalvanic corrosion in Mg‐xAl‐2Cu (in wt.%, named as ACx2, x = 0, 3, 5, and 9) alloys. In this regard, Mg2Cu, Mg17Al12, and MgAlCu phases act as a microgalvanic cathode against anodic magnesium matrixes. As such, the degradation rate of ACx2 alloys in 3.5% NaCl solution is ranked from AC02, AC32, AC52, to AC92. In this context, the AC02 alloy shows the fastest degradation rate, 46 times higher than the AC92 alloy. This may provide a practical solution to develop good alternatives for drill‐free plugging materials.

Revision surgery after triple semicircular canal plugging and morphologic changes of vestibular organ

This study aims to investigate the causes of vertigo relapse in patients with Meniere’s disease (MD) who had undergone triple semicircular canal plugging (TSCP) and explore the morphologic changes of vestibular organ through revision surgery. Eleven intractable MD patients who underwent TSCP initially and experienced episodic vertigo recurrence later, were enrolled. All patients accepted revision surgery, including seven cases who underwent labyrinthectomy and four cases who underwent repeat TSCP. Pure tone test, caloric test and video-head impulse test (v-HIT) were used to evaluate audiological and vestibular functions. Specimens of canal plugging materials and vestibular end organs were collected from patients who underwent labyrinthectomy during revision surgery. Mineralization and other histological characteristics of canal plugging materials were evaluated by von Kossa staining. Incomplete occlusion or ossification was observed in the semicircular canals (SCs) of all eleven patients, with all three SCs affected in three, the superior SC in five patients, the horizontal SC in two and the posterior SC in one. The results of v-HIT were in accordance with findings discovered intraoperatively. Few mineralized nodules and multiple cavities were found in the von Kossa-stained canal plugging materials. Incomplete occlusion or ossification of SCs was the principal cause of vertigo recurrence in MD patients who underwent TSCP. v-HIT was helpful in determining the responsible SCs.

Selection of suitable acid chemicals for matrix stimulation: A Malaysian Brown field scenario

Matrix acidizing in sandstone reservoirs require a series of chemicals to dissolve the plugging materials around the wellbore. The selection of suitable chemicals is important because it is one of the key factors to ensure success in acidizing due to the complex mineralogy of sandstone reservoirs. Furthermore, limited studies have been done to compare the chemical selections between industry guidelines and the success rate from historical field execution, worldwide. In view of the current low oil prices and increasing treatment costs, the selection of the chemicals is important to maximize oil gain. Hence, this project was embarked to develop a database of the historical acid matrix stimulation chemicals used in a Malaysian brown field. This paper also includes recommendations of the suitable acid chemicals for matrix stimulation for future applications. The selection of chemicals can be enhanced by using the combination of historical experience, recommendations from industry guidelines and simulation results to model the estimated potential economic oil gain of future matrix stimulation candidates. The comparison on skin reduction and oil gain between the three chemicals short-listed from historical analysis and industry guidelines has been conducted using nodal analysis and acid placement software namely; Prosper and Stimpro, which enabled the selection of the most suitable chemicals. Where the selection of chemicals (Main flush chemicals are; 10% HCl - 1.5% HF, 12% HCl - 2% HF and 12% HCl - 3% HF) can be enhanced by using the combination of historical experience, recommendations from industry guidelines and simulation results to provide potential estimation in achieving economic in achieving economic oil gain for future matrix stimulation candidates. From the project, a database has been established to review the chemicals that have been applied in the selected Malaysia brown field and the oil gain formula has been identified as the success rate indicator. The comparison on skin reduction and oil gain between the three chemicals shortlisted from historical analysis and industry guidelines has been conducted using nodal analysis and acid placement software, which enabled the selection of the most suitable chemicals. The most suitable chemicals were selected based on the highest average oil gain.

Research of technological properties of cement slurries based on cements with expanding additives, portland and magnesia cement

The boring log in the Eastern Siberia regions is characterized by the presence of frozen rocks, which causes a number of specific drilling problems. In such conditions, magnesia materials characterized by high expanding capacity are widely used for cementing wells. These materials improve well cementing quality by increasing the areas of complete contact at the rock-cement and cement-casing boundaries. For their effective use, it is important to evaluate the cementing parameters in comparison with the traditionally used Portland cement-based plugging materials. The high quality of the magnesia cement compositions in comparison with Portland cement was justified based on the data obtained from laboratory analysis.

Challenges and their remedies while cementing production casing in high-temperature wells

The development of the global oil industry is closely related to the exploration of new oil and gas fields through the drilling new deep and ultra-deep wells, as well as the application of modern methods of hydrocarbon production. Usage of new methods of production, increasing the depth of the wells, bottomhole temperatures and pressures sets strict requirements and restrictions for the applied plugging materials. Oil well cements must have a long time of thickening to successfully complete the cementing process, grouting stone must have high strength characteristics, heat-resistant properties at high temperatures and provide reliable isolation of the annulus, also have corrosion resistance, ensure durability of the well lining.

Experimental study of a degradable polymer drilling fluid system for coalbed methane well

Drilling along the coal seam is an effective way to improve gas recovery. Due to complex coal body structure and natural fractures, there are many difficulties, including a low abilities of cutting carrying, leakage while crossing the fracture zone and reservoir damage. In this work, a low density degradable polymer drilling fluid system is developed to solve these difficulties to enhance coalbed methane (CBM) production. In the laboratory, the properties of the polymer drilling fluid were evaluated using the coal cuttings suspension experiment, borehole stability simulation test, viscosity attenuation method, laser particle size analysis, polymer removal and core permeability recovery method. The experimental result indicates that the developed drilling fluid has good rheology and filtration, a high yield point and a strong inhibition, thereby meeting conventional drilling requirements and carrying coal cuttings effectively. Under the bio-enzymes, the viscosity of degradable drilling fluid can be initially reduced to 16%. The optimum temperature and pH for the enzyme activity is obtained, and enzymes with small weight fraction of 0.01% can dramatically alter rheological properties of drilling fluid and thereby the high biological activity. After degradation, the particle size in drilling fluid decreases greatly. During immersion test, the polymer film on the surface of the lump coal and thin sections is almost removed by enzyme solution. The reservoir's permeability damage rate may be reduced from 50% to 25% via the functionality of the enzymes, and it is noticeable that the relationships between effective stress and gas permeability treated by the drilling fluid and enzyme still obey the exponential function. Field applications show that the drilling fluid has a good coal fines resistance and compatibility with conventional plugging materials, which ensures the long horizontal footage of 901 m with the short construction period. The later decreased viscosity of the drilling fluid by the enzymes is conducive to reduce the damage to the coal reservoirs.

Application of Dynamic Multi-stage Temporary Plugging Fracturing Technology in Directional Wells

At present, the mainstream technology for the stimulation of tight reservoir which exists a large number of interlayer is perforation concentrated & large-scale fracturing. But the fracture simulation and monitoring result indicates that the vertical zone of the reservoir actually isn't stimulated fully. To increase the degree of the reservoir stimulated, the stimulation mechanism of dynamic multistage temporary plugging fracturing, temporary plugging agent and technological parameter have been studied. By optimizing the combination of temporary plugging materials, dosage, construction parameters and adding speed, the temporary plugging material has stable performance, has played a good role in temporary plugging and boosting pressure in field tests. The critical technique which is characterized by multi-cluster perforation, temporary plugging near wellbore and multistage is developed, and the design concept of dynamic multi-stage temporary plugging fracturing pump injection is defined. The production of the test well is twice as the neighboring well, in addition, it can realize multistage fracturing in single operation to decrease the fracturing cost, which makes the technique a promising future.