Cement Job Research Articles

Research and Application of Plugging Drilling and Completion Technology for Difficult Old Well in Changchun Gas Storage

Abstract Changchun Gas Storage has been included in the 14th Five-Year Plan for the development of petroleum and natural gas in Jilin Province. Its smooth construction and safe operation are crucial to ensure the stable supply of natural gas in Changchun. Well X106F located in the construction area was abandoned in 1988 due to drilling tool falling and multiple salvage failures. In order to ensure the sealing and integrity of the gas storage, it is necessary to effectively plug the drilling cover. In view of the problems of low well history accuracy, poor well wall stability and difficulty in cementing large boreholes, open hole drilling, trajectory design and control, film-forming and wall-fixing drilling fluid and prestressed cementing technologies are applied. By optimizing drilling tools, optimizing drilling parameters, designing the three-opening well structure and “five-section” profile, the plugging well construction requirements are met. The first and second open drilling along the old well borehole, 1313m deep on the first try to find top of the fish, after cementing plug, side tracking to 50m below the top of the fish and then cementing;for third spud control trajectory to accompanied the old well, according to the results of passive magnetic guidance, real-time adjustment of the trajectory scheme and construction plan, finally successfully collided with the old well at 1893m deep, after cementing the drilling plug, perforating and extruding cement, the cement job quality is good. The whole well construction period of 100 days, creating the fastest record of the old well plugging without trajectory of the fish type, providing technical support for the construction of Changchun gas storage, and providing experience for the same type of old well plugging and complex well treatment in China.

Application of Compressible Carbon in Cement to Mitigate Cement Pore Pressure Reduction and Improve Cement Bonding

Summary A quality cement job is essential to ensure long-term zonal isolation in oil/gas and carbon storage wells. This may be affected by the cement hydration process, during which water is consumed, causing pore pressure reduction and shrinkage, which increases the risk of fluid/gas invasion, formation of microannuli, and even the risk of shear bond strength reduction. In this paper, we present the application of compressible carbon (CC) particles as a cement additive to mitigate cement pore pressure reduction and improve zonal isolation. We designed cement formulations with CC and evaluated them using API standard tests and industry-wide recognized tests to ensure they met functional requirements for well cementing, such as mixability, thickening time, rheology, compressive strength development, fluid loss, and free water. The concept is as follows: When cement is pumped into an annulus, the CC particles will compress under hydrostatic pressure. When the cement is hydrating, the CC will expand to mitigate the pore pressure reduction. To validate the proof of concept, we developed a benchtop high-pressure, high-temperature setup and a pilot-scale test setup. A cement formulation with 9% CC by volume was found to be stable and have controllable performance properties such as thickening time, fluid loss, and free water. We also designed and tested a control slurry without CC for comparison. Both the benchtop and pilot-scale tests demonstrated that adding CC into the cement formulation mitigated the pore pressure reduction during cement hydration. This may reduce the risk of fluid/gas invasion that could result in migration in the set cement. Comparing the cement containing carbon with the control system without carbon, the gas permeability was reduced. The bond strength obtained from shear bond tests improved significantly, which may reduce the risk of debonding and be an indication of the reduction of shrinkage. In addition, a better hydraulic seal was found in one test, but further investigation is needed. Similar mechanical properties such as compressive strength were measured for both cements with and without CC. The data showed that adding CC does not have a negative impact on the hardened cement properties. In fact, adding CC decreased Poisson’s ratio slightly. In this paper, we present the results of proof-of-concept testing for the novel application of CC in cement to improve zonal isolation by mitigating pore pressure reduction. We also present new benchtop and pilot-scale experimental setups to measure pore pressure changes during cement hydration.

Investigating the Critical Velocity of Cement Slurry with Contamination and Applying the Results to Improve Primary Cementing Job Design

Investigating the Critical Velocity of Cement Slurry with Contamination and Applying the Results to Improve Primary Cementing Job Design

Evaluating the Mechanical and Rheological Behavior of Mud-contaminated Well Cements

Oil and gas well cementing is the process of filling the gap between wellbore and casing with cement to support casing and prevent communication between formations behind casing. A good and consistent cement slurry is critical for cement job success and, consequently, very important for well integrity and performance throughout the life of the well.When cement slurry is pumped down the casing in a cementing job, it comes in a direct contact with drilling fluids used to drill the uncased section. These fluids, if mixed with cement slurries, can act as contaminants causing an alteration in the properties of cement. It is, therefore, critical to evaluate the extent of cement properties alteration due to contamination by drilling and completion fluids.In this work, an experimental study was carried out to investigate the effect of contamination by drilling fluids; water based, oil based (50% Diesel, 50% water) and oil based (70% diesel, 30% water) on cement physical, mechanical and rheological properties.Cement slurries were prepared according to the API procedures and were mixed with different concentration of contaminants and cured at ambient temperature for 1, 2, 3 and 21 days. Physical, rheological, and mechanical properties were measured using API recommended practices and apparatus.It is observed and as expected that regardless of mud base fluid, as contaminant percentage increases, density of cement slurry decreases due to dilution of cement by water in contaminant. For oil-based invert emulations (50/50 and 70/30), as contamination percentage increased plastic viscosity increased, but yield stress decreased. It was also found that clean and less contaminated cement samples develop higher compressive strength in shorter times than mud contaminated samples.

Utilizing innovative nanolime-geopolymer as a cement for gas wells

This paper is to introduce the formulation of the innovative nanolime-geopolymer NLGP and its application in gas wells as a replacement for the traditional cement. The new mix is composed of nanolime NL, fly ash, sodium hydroxide, and sodium silicate. The compressive strengths of NLGP are measured using different molarities, and ratios of its components to compare and evaluate the results. After that, a detailed profit study in USD will show the profitability of NLGP compared to other types of current cement and the possibility of its manufacturing. Also, a separate comparison to cement fly ash CF was done. Finally, the “deep water horizon” incident will be used as a case study to indicate the applicability of NLGP in such cases for stopping gas channeling which occurs due to cement job failure.

MODELLING THE EFFECT OF CONTAMINATION ON THE RHEOLOGICAL PROPERTIES OF CEMENT SLURRY USING OIL-BASED MUD AS CONTAMINANT, TO IMPROVE CEMENTING JOB DESIGN AND EXECUTION IN THE OIL & GAS INDUSTRY

Cementing job failure often occurs due to cement slurry contamination with drilling mud during primary cementing and remedial cementing jobs in the oil & gas industry. The enormous consequences of cement slurry contamination with drilling mud include drastic reduction in the thickening time of cement slurry and increased rheological properties of the cement slurry due to the much more viscous resultant cement slurry/mud mixture often leading to incomplete cement job, poor mud removal, poor cement bond, gas channeling, gas kick, blow out, downtime, revenue loss and remedial cementing. The rheological properties of cement slurry and drilling mud are strongly dependent on temperature. There are also emergency situations in the oilfield where bottomhole temperature changes to a higher temperature requiring adjustments in the original cementing job design to include the new bottomhole temperature when Laboratory services are not immediately available. The aforesaid and the associated cost of remedial operations prompted this work to investigate the effect of temperature and contamination on the rheological properties of cement slurry using oil-based mud as contaminant to invent a process to better avoid cement slurry contamination and to improve cementing job designs and execution in the oil & gas industry. The methods applied include Laboratory testing and mathematical modeling. Mathematical models were developed using Microsoft Excel to predict the rheological properties of contaminated cement slurries as a function of temperature and contamination with oil-based mud as the contaminant. Results showed that the Plastic viscosity and yield stress of the contaminated cement slurries increased with temperature and extent of contamination with oil-based mud but the yield stress also decreased with extent of contamination at high temperatures. The very high regression coefficient obtained with each of the mathematical models showed that the mathematical models can be confidently applied to predict the rheological properties (Plastic viscosity and yield stress) of the contaminated cement slurries as a function of temperature and extent of contamination with the oil-based mud.

Investigation of carbon black nanoparticles on effectiveness of cementation in oil and gas well

Drilling is expensive in the oil and gas sector, from exploration through drilling and production to enhanced oil recovery. As a result, it is critical to keep the well intact until the end of completion phase. Understanding the conditions of wellbore and cement quality is very important for achieving efficient cement job. The characteristics of cement can be adjusted dependent on the addition of certain nanomaterials to the cement. Use of nanotechnology in the cement slurry can aid in attaining answers to numerous difficulties that concern to oil well cementation. The present study aimed at investigating the effects of nanoparticles on the properties of prepared cement slurry (Class G Cement and carbon black nanoparticle (CBN) mixed). The effectiveness of cement slurry is analysed through compressive strength test and porosity test for all different carbon black nanoparticle composition. The experimental results indicate that the addition of carbon black nanoparticles has shown a very high increase in compressive strength and lower porosity at the dosage of 0.1% of carbon black nanoparticles by weight of cement compared to 0.25% of carbon black nanoparticles.

Cement Placement Modeling—A Review

SummaryEnsuring cement sheath placement is of paramount importance for the success of a primary cementing operation. Poor mud displacement and fluid contamination can lead to cement isolation failure, loss of production, and even well abandonment. Over time, many cement placement computerized models have been developed, leading to a significant number of theoretical and case history papers. However, using these to design a cement job is difficult because their physical and mathematical assumptions are most of the time unclear, and because their application requires balancing precision with computation time. Models that are too precise may lead to very long runs, while oversimplified models could result in nonpredictive simulations. To the authors’ knowledge, nothing has been published to explain how to perform efficient predictions with a cement placement computerized model. Such is the object of this paper. It presents an extensive analysis of all the available cement placement computerized models, highlighting their advantages and disadvantages and listing their assumptions. This analysis indicates that (1) the actual methods used to estimate the equivalent circulating density window are not rigorous enough; (2) there still exist a lot of uncertainties when predicting the tubular standoff; (3) modeling fluid contamination, especially when the fluids are not compatible, remains very cumbersome, if not impossible, because the true interfaces’ physics is not completely considered; (4) a local contamination observed at an intermediate time can disappear at the end of the simulation due to numerical diffusion, meaning that just looking at the concentration maps at the end of placement is not sufficient to judge the efficiency of a displacement scenario; and (5) changes in geometries along the cement sheath are not considered with precision. This work allows establishing guidelines to help understanding how to manage simulation inputs and analyzing and communicating the produced results.

Unconventional Bradenhead Cementing in the Delaware Basin Case History

SummaryThis Delaware Basin case history describes a bradenhead cementing method that improves zonal isolation and top of cement (TOC). Common solutions for cementing depleted formations include stage tools, low-density slurries, and reverse circulation. For this bradenhead method, cement is pumped through the wellhead valves and down the annulus to a target loss zone. Field data, laboratory data, and the engineering model support the improvement bradenhead cementing provided across depleted formations.The depleted Brushy Canyon Formation serves as an injection interval for a two-stage bradenhead cement job. This approach isolates formations below the Brushy Canyon with a conventional first stage, while achieving TOC with the second stage pumped down the annulus. Fracture gradients of the injection interval and casing shoe constrain the cement design. To achieve adequate cement placement, the design phase includes the pressure calculations required to start flow and injection for the bradenhead stage. Reactive spacers are utilized to prevent annulus fluid level drop in extreme cases. A benchmarked cement bond log (CBL) quantifies the results and validates this unconventional cementing method.More than 50 two-stage bradenhead cement jobs were executed with a TOC success rate of 100% in intermediate and production hole applications. CBL data obtained after cementing the intermediate casing confirm the two-stage bradenhead as a placement method. In areas constrained by casing shoe pressures, CBL data identified potential areas of shallow injection. These data resulted in a modification of the fluids pumped. Use of these re-engineered fluids reduced injection initiation pressures and improved cement bonding across salt and anhydrite formations. Cementing costs were reduced by eliminating stage tools, annular casing packers, and low-density cement slurries. Pumping the bradenhead job offline (off the rig’s critical path) reduces cost further. These features support bradenhead cementing as an effective solution for wellbore sections with a potential injection zone.The regulatory requirement to place cement above depleted formations resulted in many innovative cementing methods. Stage tools, low-density slurries, and reverse circulation are attempts to avoid formation breakdown, but these methods increase cost and have limited reliability and integrity. Bradenhead cementing takes advantage of the depleted interval to aid in cement placement. Although counterintuitive, bradenhead cementing has proved to be a cost-effective solution that improves zonal isolation and eliminates integrity risks associated with stage tool failures.

Cement logs evaluation Ghadames Basin, (Al Wafa Gas field), case study, Libya

The acoustic logging method is the most commonly used to qualify a cement job. It can be run several hours or several days after the cement placement and evaluates the quality of the bond (acoustic coupling) between the casing, the cement and the formation. It measures the attenuation of the sound signal as it propagates through the casing, cement and formation and returns to the sensor. This technique and will help spot free pipe, partially bonded or fully bonded pipe. The aim of this paper is analyses and evaluates cement logs data in two wells within Al Wafa Gas field, the cement logs analysis results of two wells shown variables cement condition behind the casing. The well A24-NC169A, analysis showing a good cement condition for both casing and formation as the signature of cement logs showing very low amplitude reading due to high attenuation of waves in cement bound log because the cement was good behind casing. The well A56-NC169A, showing variable results, as good cement condition behind the casing bond to casing, formation, micro- annual and channeling condition. The gamma- ray ranging from 40 to 150, as sand to shaly sand sediments, transit-time was normal, cement bound log recorded variables from low, medium to high amplitude (18 to 56) due to different wave attenuated depending on cement condition (good to partially cement). Variable density log showing variable results (Formation arrive, casing arrive, no casing arrive and no formation arrive, all depending on cement behind the casing. In general, the results revealed good cement condition.

Experimental investigation of the effects of temperature on the morphological characteristics of geopolymer binders

Since the beginning of this century, assessment of the environmental impacts and the global warming potential of industrial practices and technologies are on the top agenda. Therefore, many construction materials such as cement systems are being designed for reducing the environmental impacts and greenhouse gas emissions. For that purpose, the petroleum industry is also striving for developing environmentally friendly cementing systems for oil well application; for example, a better alternative to the class-G cement, which is consumed in a tremendous amount worldwide. In finding the greener alternative to class-G cement, geopolymer binders are being researched for possible applications for oil-well cementing jobs. This paper presents the experimental investigation of the effects of temperature on the morphological characteristics of geopolymer binders. For that purpose, sodium silicate and sodium hydroxide were used as the alkaline activator with fly ash as the precursor. Fifteen samples were prepared with a density of 10, 11, 13, 15 and 17 ppg (3 samples for each value of density). The samples were subjected to a temperature of 30, 60, and 90 °C and cured in a water bath for 24 h. Morphological and microstructural characteristics were analyzed using XRD and FESEM. In an overview, increases in temperature significantly impact the geopolymerization process where the microstructure in geopolymer cement produces more reacted particles, which results in excellent mechanical strength. Generally, the strength of geopolymers is associated with the fly ash dissolution FESEM image for 17 ppg mixture cured at 90 °C clearly shows that it underwent extensive geopolymerization with the formation of continuous alumino-silicate gel and almost entirely reacted fly ash particles, resulting in relatively dense geopolymer matrix.

Modeling, Planning Allow Successful Implementation of South Texas U-Turn Lateral

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208801, “Successful Planning and Implementation of First South Texas U-Turn Lateral,” by Riley Schultz and Joe Kiefner, Chesapeake Energy. The paper has not been peer reviewed. Legacy fields require innovative solutions for developing capitally efficient projects within highly developed acreage blocks. As another tool to improve well economics, a U-turn lateral strategy was implemented in the Eagle Ford Shale. This wellbore trajectory resulted in capturing a 9,200-ft equivalent lateral length well in a 5,000-ft-wide lease space. This successful U-turn trajectory test has created new economic project opportunities for the company and has increased optionality within challenged lease spaces across the field. Well Overview In a single U-turn well, the horizontal wellbore turns 180° to create two parallel laterals in a map-view U shape. The successful U-turn project detailed in the complete paper was the first drilled in south Texas (Fig. 1). This resulted in significantly improved economics by using a horizontal turn as a hydrocarbon pathway, rather than an additional vertical section from a new well to gain the equivalent treatable lateral length. This well followed operator standards for south Texas Eagle Ford two-casing-string well design. A 9⅝-in. casing was set to protect shallow water zones, and an 8¾-in. production section was drilled for the remainder of the well (using 5½-in. drillpipe). 5½-in. production casing was then run to total depth (TD). 8¼-in. centralizers were placed on each joint of the casing, freely floating between the collars. The production section was drilled with oil-based mud, and a standard cement job was pumped. Conventional directional tools were used for the entirety of the drilling phase. The decision was made early in the planning phase of the well to forgo fracturing the turn portion of the wellbore and instead drill into the adjacent unit to conduct the turn to maximize the amount of optimally oriented lateral footage in the unit to be produced.

Testing and Evaluation Method Investigates Cement Expansion in Cased-Hole Wells

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 208679, “Cement Expansion in Cased-Hole Environments: A Novel Laboratory Testing and Evaluation Method With Successful Field Implementation,” by Vasilii Sukhachev, Amir Salehpour, SPE, and Ilshat Akhmetzianov, SPE, Schlumberger, et al. The paper has not been peer reviewed. Preventing bulk shrinkage of cement in cased-hole wells is important when dealing with the risk of sustained casing pressure (SCP). Current studies based on membrane tests suggest that, even with a high-percentage content of expanding agents, cement systems show little or no expansion in dry media. An alternative laboratory method for measuring cement expansion, followed by a successful field application, was used to evaluate the total bulk volume change of the cement based on curing in a dry environment and in water. Optimal cement-slurry properties were obtained. The developed cement system, which was successfully implemented in the field, provided long-term zonal isolation with no indication of SCP to date. Introduction For a major operator in the Caspian region, drilling development wells required passing through shallow overpressured permeable zones containing water and biogenic gas. The optimal casing design used to minimize the likelihood and severity of SCP consisted of isolating the shallow-soil zone by use of a cemented 24-in. liner followed by a 20-in. surface casing cemented using a two-stage method (Fig. 1). During the first stage, the cement was pumped inside of the 24-in. liner. Then, an external casing packer placed in the 20-in. casing was inflated against the 24-in. liner before performing the second-stage cement job. The second-stage cementing operation brought the cement above the top of 24-in. liner and provided sufficient length to isolate against the shallowest distinct permeable zone. Cement is considered a primary wellbore barrier element. However, the cement placed between the 24-in. liner and the 20-in. casing and in the annulus of the 30-in. conductor and 20-in. casing is subject to shrinkage. This shrinkage leaves a potential leak path all the way to the wellhead on an offshore platform. The cement systems chosen consisted of the 1.92-SG (16-lbm/gal) slurry for the second stage cementing of the 20-in. casing because this stage was the system most susceptible to shrinkage. This slurry was placed in the annular space of the 20-in. casing and both the 24-in. liner and the 30-in. conductor. The curing temperatures and pressures in the field are 32°C and 6.74 MPa at the bottom of the well and 28°C and 2.48 MPa at the top of the cement. The top of the cement will be in direct contact with the spacer, a fluid with 89% water content; however, the remainder of the cement column will not have access to excess water during curing. If acceptable results could be achieved with the 1.92-SG cement system, then the same blend could be used for the 24-in. liner tail and the first-stage tail slurry of the 20-in. casing. This method is a possible solution to obtain a more-robust system that prevents the risk of SCP.

Appraisal Well Design in "X" Oil Field

The selection of casing depths and casing design are considered one of the most critical steps in the well construction process. Inaccurate selection of casing setting depths and casing design can result in many challenges, long time and hence high well costs.
 "X" oil field was taken as a case study. There is only the exploration well X-1 drilled up to date. The 20˝ surface casing was relatively long because it was set at the top of Dammam Formation. That means deep surface hole, long trip time, large amount of mud, long surface casing, large amount of cement and hence high cost. Also, Hartha Formation was not evaluated because it is isolated with the 13 3/8" & 9 5/8" casing and the perforation through two casing was not available. Another problem, the 9 5/8˝ production casing damaged at the depth 32 m due to failure of tolerating the axial forces before or after the cement job.
 All data was inputted into the Landmark software to simulate the well. It was found that the surface casing can be set at the top of Lower Faris Formation instead of Dammam Formation. Also, The Hartha Formation can be drilled in the 12 ¼ ˝ hole and isolated by 9 5/8˝ casing instead of drilling it in the 17 ½ ˝ hole and isolating it by the 13 3/8˝ casing. It was also found that the 9 5/8˝ production casing can withstand all loads by selecting casing with higher weight.
 The cost of the modified design was also checked to study the feasibility of the modified design. It was concluded that the modified design can save around 300,000 USD for each well comparing with the design of well X-1.
 It is recommended to apply this design on the appraisal well to be drilled. If the design shows no problems, it can be considered the optimum design of appraisal and development wells to be drilled in the future. Also, the slim-hole design can be studied and an economic feasibility comparison can be made with the current and the proposed design in this study.

Distributed fiber-optic sensing transforms an abandoned well into a permanent geophysical monitoring array: A case study from Australian South West

Distributed temperature sensing (DTS) and distributed acoustic sensing (DAS) data recorded by a fiber-optic array installed during the decommissioning operations of the 1550 m Harvey 3 well in Western Australia reveal an abundance of valuable information about the course of the decommissioning process and the quality of the cement job. The DAS monitoring has detected vibrational disturbances during the cement's setting up, while DTS was used to assess setting up of the cement and curing times as well as uniformity of cementation from the distribution of temperature along the borehole. A weeklong trial acquisition of passive seismic data with the same array a year later shows an abundance of seismic events in a wide frequency range from below 1 mHz to above 200 Hz. The downhole DAS array provides traveltimes and amplitudes of these events, which include earthquakes, mine blasts, ocean microseisms, and local human activity. The amplitudes of waves from distant seismic events can be used to estimate and monitor physical properties of the media along the extent of the well. When used in combination with information from active vertical seismic profiling, these events can help obtain independent estimates of velocities and densities. Spectral analysis of low-frequency microseisms shows a strong correlation between passively recorded DAS and local weather observations. This shows that the ability to continuously record oceanic microseisms at low frequencies opens opportunities to employ such arrays for wave climate studies. In addition, the data contain peculiar in-hole reverberations likely caused by crossflow of groundwater behind the intermediate casing, which may indicate imperfections of the cement job. The results demonstrate that a downhole fiber-optic array installed in an abandoned well represents an opportunity to establish a permanent facility for continuous recording of passive and active geophysical data and for exploring various applications.

A critical analysis on role of nanoparticles in oil-well cementation

The main objectives of oil-well cementing are to restrict the movement of fluids from one zone to another and to provide a stable position for the casing string. Achieving greater compressive strength, tensile strength, and lower permeability are the main features for increasing the effectiveness of cement jobs. The conventional cementing job lacks the ability to attain these properties even with the usage of advanced materials like self-healing agents, fibers, and polymeric materials in cement slurry. However, a scope of improvement is required in providing better zonal isolation. According to studies, the inclusion of nanoparticles would improve cement efficiency by achieving sufficient compressive strength and durability, reducing potential maintenance costs and environmental effects. With the addition of nanoparticles to cement, slurry increases compressive strength, decreases settling time, and increases density by reducing the porosity and permeability of the cement sheath. This study provides an explanation of the alterations in oil-well cement properties with the addition of nanaparticles at different temperatures and incubation periods.

Polyaramide Vesicles Prove Effective for Wellbore Integrity and CO2 Sequestration

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 204385, “Wellbore Integrity and CO2 Sequestration Using Polyaramide Vesicles,” by Elizabeth Q. Contreras, SPE, Saudi Aramco. The paper has not been peer reviewed. The complete paper describes a cementing additive chemically engineered to react with formation fluids that act antagonistically toward cement. Engineered polymer capsules house encapsulants to react with antagonistic gases downhole, such as carbon dioxide (CO2), to form a more benign and beneficial material. Embedded in cement, the polymer capsules with semipermeable shells allow fluids to permeate and react with encapsulants to produce beneficial byproducts, such as calcite and water from CO2. Reactivity between the encapsulant and antagonist gas CO2 is demonstrated using thermal gravimetric analysis (TGA) and other tests from oilfield equipment. Cementing Applications for Polyaramide Vesicles The study presents the third and final technology for polyaramide vesicles, a novel polymeric material for cement enhancement and for multifaceted cement applications. In oil and gas wells, polyaramide vesicles have applications as a cement additive with delivery capabilities. This family of polymers also is chemically inert and stable enough to serve in various applications under extreme downhole conditions during the construction of an oil well. When incorporated into cement, the high thermomechanical stability of these vesicles serves to enhance mechanical properties of Portland cement such as elasticity while maintaining the full strength of the cement. The unique vesicular design of the polymer also serves as a delivery system for relevant cement additives and is applied in the development of right-angle-set cements. Thereafter, the robustness of the shell remains intact after chemical delivery to impart strength and flexibility to set cement for the lifetime of the well. In this study, the vesicles housing reagents are used for the sequestration of antagonistic gases, to neutralize and to produce mineral precipitate for the applicatory repairs of microannuli in the cement sheath, and for self-healing cements. During the construction process, a good cement job serves the purpose of providing a reliable infrastructure during production and for zonal isolation of the casing string from subterranean environments. Zonal isolation by cementing is important to prevent the loss of hydrocarbons during production and to prevent the influx of unwanted formation fluids into the wellbore, such as sweet and sour gases. Maintaining cement-sheath integrity helps keep the production of hydrocarbons cost-efficient and safe. However, numerous factors may cause cement to fail. Oil and gas wells generally go through stress and thermal cycles during production. Changes in downhole conditions, in terms of temperature and pressure, can induce enough destructive stress to affect the integrity of the cement sheath. Any producing oil and gas well can suffer sudden thermomechanical fatigue failure, leading to microannuli and fractures in cement sheaths. Elastomeric materials such as polyaramide vesicles can be added to make cement less brittle and reduce the development of microannuli. However, in the event of gas migration by casing/casing annulus (CCA) events, mitigation requires a solution for complete remediation and recovery of the well.

Sensitivity analysis of factors controlling the cement hot spot temperature and the corresponding well depth using a combined CFD simulation and machine learning approach

Designing a suitable cement system has been a challenging task in high pressure-high temperature wells (e.g., deep oil and gas wells, geothermal wells). Bottom hole circulating temperature (BHCT) is commonly used as the key operating variable in the cement design. However, it has been shown that cement formulations based on the BHCT failed to meet field requirements in many cases (especially in deep wells or geothermal wells). In reality, the temperature of the hot spot, where the highest temperature occurs in a well during the circulation, should be used as the setting temperature criteria for proper cement slurry formulation. However, as there are multiple factors affecting the hot spot temperature and its corresponding depth, it is not a simple task to determine these design parameters. To overcome these design challenges and facilitate optimization of the cement system formulation for the deep, hot wells, a new systematic approach has been developed by coupling a machine learning and a computational fluid dynamics (CFD) simulation technique. In this study, we investigated the effects of the five common design variables (i.e., wellbore depth, geothermal gradient, casing size, hole size and flow rate) on the hot spot temperature and the corresponding depth. Data extracted from the simulation study results were used to train multiple linear regression models, which were developed as part of using machine learning approach for comparing the influences of these five factors on the hot spot temperature and the corresponding depth. The results indicate that increasing casing size (OD), geothermal gradient and the well depth also increased the hot spot temperature and its corresponding depth, while the increasing flow rate and the wellbore size caused reduction in the hot spot temperature and its corresponding depth. Casing size and the cement circulation rate seemed to have the greatest impact. Results also indicated that the effects of these factors on the hot spot temperature and its corresponding depth were synchronized. With the increasing wellbore to casing diameter (i.e., do/di) ratio, both the hot spot temperature and its corresponding depth decreased (i.e., lower maximum cement temperature was observed at the shallower depth). The new numerical method is proven to be a realistic and reliable approach for comparing the influences of different factors on the hot spot temperature and the corresponding depth. Practical guidelines developed from the results of this study can be used for improved cement job design in field applications.

Numerical Study on the Impact of Spiral Tortuous Hole on Cuttings Removal in Horizontal Wells

SummaryHorizontal wells are designed to have smooth (straight), curved, and lateral sections. However, the actual drilled path usually suffers from unwanted undulations from the planned well trajectory known as wellbore tortuosity. Wellbore tortuosity can slow the drilling penetration rate, aggravate drillstring vibration and buckling, complicate the casing and cement job, and lead to inaccurate wellbore position. This paper presents a validated computational fluid dynamics (CFD) model to investigate the impact of wellbore tortuosity on hole cleaning. The Eulerian-Eulerian approach is used to simulate solid-liquid laminar flow in annular geometry using polyhedral mesh. Then, the impact of wellbore tortuosity on cuttings accumulation, annular pressure loss, and fluid velocity was investigated and compared with the flow behavior in a straight horizontal well. A parametric analysis of spiral period length, spiral amplitude, drillstring rotation, flow rate, annular eccentricity, drilling rate of penetration (ROP), and cuttings size was conducted to assess their influence on cuttings transport in spiral tortuous holes and their relative magnitude to other design or operating factors.Simulation results show that polyhedral mesh is an optimum meshing technique for spiral profile geometry. Wellbore tortuosity aggravates hole cleaning in lateral sections based on the length of the spiral period and/or the spiral amplitude. Reduction in cuttings velocity was observed in the top part of the spiral geometry (crest), causing large deposition of cuttings in this area compared to the spiral lower part (trough). Drillstring rotation from 0 to 200 rev/min is the critical range for efficient hole cleaning in spiral geometry. Cuttings size can improve cuttings accumulation if the particle size is larger than the viscous layer located near the bed velocity profile. The drilling ROP and annular eccentricity aggravate cuttings accumulation and bed deposition in a spiral hole, similar to what is normally observed in straight horizontal wells.

Rotating Cement Heads Improve Results of Zonal Isolation in Colombia

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 198970, “Casing Rotating Cement Heads: A Custom-Fit Solution To Improve Zonal Isolation Results In Colombia—A Field-Proven Case,” by Jose Vela, SPE, Henry Arias, and Edwin Sanchez, Ecopetrol, prepared for the 2020 SPE Latin American and Caribbean Petroleum Engineering Conference, held virtually 27–31 July. The paper has not been peer reviewed. In the current challenging drilling environment, effective annular zonal isolation is required for long-term integrity. Among proven cementing practices, casing rotation has been widely applied to liners but not as commonly to full casing strings. The complete paper describes the use of custom-fit rotating cement heads (RCH) to improve cementing results. Cementing Practices in Colombia The following methods of cementing, described in detail in the complete paper, are applied currently in Colombia: - Preflushes and spacers - Slurry design - Casing standoff - Borehole conditioning - Mud circulation and conditioning - Casing movement during the cement job - Monitor job parameters compared with design - Pressure testing and surface-equipment installation Most of these best cementing practices have been followed on a daily basis for all production and intermediate casing. Rotation practice has been widely applied to liners but not for casing strings. This observation led to the introduction of RCH, a technology that arose as the most- appropriate link to connect the top drive or rig prime mover with the casing so that rotation for a full string of casing could be achieved. RCH Use and Implementation Before the implementation of RCH, cement evaluation logs did not show the expected response. Evidence of fluid channeling and fluid contamination was very common, and fair casing to cement bonds was a concern, particularly in washed-out sections and very long cement columns. RCH provides a technical solution for the need to rotate the casing strings while maintaining best practices common to all cement jobs. Rotation has shown to be mandatory for intermediate and production casing to obtain a better log response by enhancing displacement fluid efficiency and mud removal. Well-design and cement objectives vary according to regional sedimentary basins around the country. In the Llanos Basin, the intermediate casing shoe integrity and the isolation of the T1 sand unit are primary objectives; the most-common wellbore problems are the presence of very washed-out sections in front of the E3 and E4 shale formations. The T1 sand unit is located between them and is prone to water or gas influx. Next, the production section is drilled with a lighter mud so that a high negative differential pressure is induced around the casing shoe once the shoe track is drilled. If shoe integrity is not suitable, an influx can be promoted when drilling the productive zone.