Cementing is one of the most important steps in preparing a well for production. Critical parameters influencing the success of a cementing job are the concentration and the types of additives present in a mix fluid to prepare the cement slurry. However, it is extremely challenging to analyze water-soluble organics under oilfield operational conditions. In addition, with the complexity in chemistry of additives and mix fluids, it is also an analytical challenge to experimentally determine the quality of mix fluid and the slurry with standard analytical techniques such as high-pressure liquid chromatography (HPLC) or inductively coupled plasma spectroscopy (ICP). In addition to the general business need to verify chemical addition accuracy, in the field, the current practice to prepare mix fluid entails the addition of different additives either manually or using specialized liquid additive systems (LAS). Any human error in programming the LAS or manually adding the products yielding poor or no traceability for QA/QC could fail the cement job. This warrants the need for a reliable and field-robust method of quantifying additive concentrations in the mix fluid.
To address this challenge, we developed a workflow using electrophoresis to address this issue to support operations. Electrophoresis uses an electric field to separate and quantify the components of a single fluid or a mix-fluid additive system. More importantly, we can simultaneously detect and quantify multiple chemistries in a single run. We have developed methods to analyze and quantify all the ingredients in an aqueous fluid system. This includes organics such as surfactants, natural and synthetic polymers, organic acid, and the inorganic ions that are common in seawater and most base fluids in the additive system.
In the first step, we developed a method to analyze a single additive. This method addressed the issue of analyzing organics in aqueous fluid and demonstrated the applicability of this technology in determining the quality of the additives in terms of contamination. In later steps, the method was expanded to analyze and quantify dispersants, multicomponent retarders, and antifoaming agents individually as well together in a single run. Our study clearly demonstrated the electrophoresis technique can quantitatively differentiate multiple additives in a mix-fluid system while simultaneously estimating their respective ratios in the system. The developed method was applied to a mix-fluid system to identify a missing additive that led to the failure of a critical job.
Overall, a simple and reliable technique is introduced to determine the quality and composition of additives and the mix-fluid system composition to enhance the reliability of existing processes and thereby improve the success rate of cementing jobs. Examples from the field will be presented.
Nafikova, Svetlana (Schlumberger) | Bugrayev, Amanmmamet (Schlumberger) | Taoutaou, Salim (Schlumberger) | Baygeldiyev, Gaygysyz (Schlumberger) | Akhmetzianov, Ilshat (Schlumberger) | Gurbanov, Guvanch (Schlumberger) | Eliwa, Ihab (Dragon Oil)
A major operator on the Caspian Turkmen shelf has started to encounter sustained casing pressures (SCP) attributable to insufficient isolation across a hydrocarbon gas zone, due to downhole stresses and other contributing factors. Enhanced placement techniques of conventional cements failed to prevent SCP, confirming the requirement for an alternative cement system that can withstand anticipated stresses and resolve this challenge. An innovative and cost-effective solution was applied and successfully solved the SCP challenge due to its unique self-healing properties.
If cracks or microannuli occur and hydrocarbons reach the cement, the system has the capability to repair itself, restoring integrity of the cement sheath without external intervention. The cement system is placed conventionally in the annulus across or above the hydrocarbon-bearing formation. It then acts as a pressure seal, expanding to accommodate downhole changes and healing if any hydrocarbon reaches it. This technology has been used in four wells in the field with excellent results.
Two wells were used to demonstrate the capabilities of the self-healing cement as a lead cement slurry, which created a cap over the pay zones. The self-healing cement was designed with low Young's modulus for optimum flexibility. To minimize the risk of set cement integrity failure due to microannuli or microdebonding from chemical shrinkage after setting, linear expansion up to 1.2% was incorporated into the design. After cementing, the wells were intentionally exposed to a sequence of high-pressure tests, which induced annular pressures in the wells. However, because of the self-repair capability of this cement, isolation and integrity were effectively restored in the two wells within 1 to 2 weeks without external intervention. As a result, the self-healing cement technology has become the standard for the field for all future wells, and the operator plans to extend the self-healing cement technology to other fields with similar challenges.
This paper clearly demonstrates successful casing pressure remediation without intervention by engineering a flexible, self-healing cement system. The design strategy, execution, evaluation, and results for two wells are discussed in detail and will help to guide future engineering and operations around the world.
Lau, Chee Hen (Schlumberger) | Duong, Anh (Schlumberger) | Taoutaou, Salim (Schlumberger) | Kumar, Avinash Kishore (PETRONAS Carigali Sdn. Bhd.) | Ahmad, Khairunnisa Bt Abg (PETRONAS Carigali Sdn. Bhd.) | Jain, Pankaj (PETRONAS Carigali Sdn. Bhd.) | Amin, Remy Azrai M (PETRONAS Carigali Sdn. Bhd.) | Toha, Rozaidi (PETRONAS Carigali Sdn. Bhd.)
In 2018, an operator in Malaysia completed a sidetrack campaign consisting of injector wells. These wells were planned for maximum productivity via sustainable wellbore zonal isolation. The presence of Carbon Dioxide (CO2) in these wells elevated concern about the zonal isolation of cement across the interval. Moreover, for an injector well, the cement must exhibit resilient properties by design of enhanced mechanical properties to provide long-term isolation based on a cyclic wellbore. An advanced slurry system was designed that enabled the set cement to manifest superior properties in three parameters—corrosion resistance against CO2, flexibility against wellbore stress changes, and expansion to mitigate microannuli.
The design of the slag-based flexible cement system with expanding additive (slag-flex) considered all three parameters in the fit-for-purpose application of a resilient and flexible expansive cement system in a CO2-rich well. The system’s mechanical properties, such as Young’s Modulus, Poisson’s Ratio, and tensile strength, were verified with laboratory-scale testing and validation against stress analysis software to confirm on the resilient and flexible properties. The laboratory testing result demonstrated the improved properties of the system, including high tensile strength and low Young’s modulus. Furthermore, the reduced water content of the system decreases the permeability of set cement and thus increases resistance towards corrosive substance such as CO2.
For certain cases in the past, two separate slurry systems had to be designed—a lead slurry with CO2-resistant properties and a tail slurry with flexible and resilient properties. Often, several issues arose from this practice, including complex logistics due to cement silo blend arrangement and complexity during job execution. Hence, this new system presents a novel idea and methodology that will deliver value to the oilfield industry by integrating CO2 resistance, flexibility and expansion properties in a single slurry system.
The system was successfully pumped in wells in Malaysia; no sustained casing pressure has been recorded to date, and wells have been delivered to their intended zonal isolation requirements without compromising well design and overall integrity. This is an innovative application of this type of cement system in the region, and the long-term zonal isolation and well integrity assurance in these and future wells have the potential to save millions of dollars in remedial work. The cement system is currently recognized as the default technology for CO2-rich injector wells in Malaysia.
Gao, Fei (CNPC Xinjiang Oilfield Company) | Wang, Rui (Schlumberger) | Su, Hongsheng (CNPC Xibu Drilling Cementing Company) | Zhong, Shouming (CNPC Xinjiang Oilfield Company Research Institute of Engineering and Technology) | Guo, Yabin (Schlumberger) | Taoutaou, Salim (Schlumberger)
A design approach was developed to obtain an optimum annulus cement barrier during well construction of a 29-well underground gas storage (UGS) project to maximize the longevity of the UGS wells in the years that followed in production state. The effectiveness of this approach was verified by multi-year post-job surface and subsurface field data from all the wells from the time the wells were put into production in this project.
The UGS wells are adjacent to a residential area, making reliable well integrity of great significance. To facilitate this, the cementing design for an entire well was prepared to obtain good and durable zonal isolation. The design focused on long-term well integrity and longevity rather than short-term effectiveness. First, the cementing technique was reviewed so that best practice for a high-quality cementing operation was applied in this project. Second, an advanced third-interface pulse-echo cement evaluation logging tool was adopted for better understanding of the cementing job results and to use the indications for subsequent job improvement. The tool measures the state of annulus material and casing standoff, which considerably impacts the cementing quality. Third, a high-performance flexible/expandable (HPFE) cement system with engineered mechanical properties was introduced to the project. With a specialized cement stress simulation software, the mechanical properties of the cement were optimized to deal with the downhole varying pressures and temperatures the cement would see during completion and production. Temperature change was predicted to fluctuate between 69 and 81°C and pressure between 17 MPa and 34 MPa. From the 5 years of production of the UGS wells, downhole temperature and pressure were recorded. Pressure values were within the predicted range. The temperature was higher than expected, but the designed set cement was robust enough to deal with the higher temperature.
In all, 29 UGS wells were cemented from 2011 to 2016 in this campaign. Due to the continuous effort of improving the cementing quality through the iterations of optimizing job program, the cement bond log result was better in the later 4 years of the project compared to the first 2 years. In June 2013, some of the wells were put into production and gas injection initiated. In the following 5 years, the whole storage block was gradually put into production up to its full capacity. We conducted a post-job numerical cement integrity study based on the acquired field data from the last 5 years with the measured set-cement mechanical properties. The result indicates the cement barrier can remain intact under the varying downhole conditions. This is evidenced by the post-job production behavior, which was being monitored during the gas injection and withdrawal cycles and no sustained casing pressure (SCP) problem was ever reported during the process.
The design for the cementing program focused on the well barrier quality from the beginning with the goal of maximizing well longevity by means of a durable well integrity. The design iterations based on a job-by-job design-execute-evaluate cycle helps improve the cement job quality throughout the whole project. The combination of best practice implementation, reliable cement bond evaluation tool, and the engineered HPFE cement system realized a robust well integrity for the wells. This lasting well integrity is evidenced by continuous post-job downhole and surface data acquisition. The acquisition also fine-tuned the model for predicting downhole dynamics for future UGS wells in the same block, facilitating a more realistic start for the engineered HPFE cement system design.
Zonal isolation is reliant on successful cement placement. Part of the key criteria to achieve zonal isolation includes effective mud removal and fluid displacement efficiencies. To meet the mud removal requirements, a spacer system promoting physical or mechanical scrubbing appears to increase the efficiency of filter cake removal. The spacer has been deployed in Saudi Arabian wells containing water- and oil-based mud systems. For any given application, this paper discusses advanced laboratory testing to obtain performance properties such spacer stability and spacer integrity while managing the downhole plugging risks. This paper will document examples demonstrating results the spacer performance including cement evaluation logs supporting the use for achieving similar cement placement objectives.
Due to pressure and temperature changes during the life of the well (from drilling to production); globally many Casing-Casing Annular (CCA) leaks are observed in the annuli between surface and intermediate casings. A new approach to well cementing had to be developed, and advanced cement technologies considered, taking into account both short and long term design parameters.
To assess the effect of pressure and temperature cycling on the long-term well integrity, finite element modeling of sections of interest was performed to analyze the stresses applied on the cement sheath throughout the life of the well. Such modeling requires detailed knowledge of the pressure and temperature cycles, as well as the mechanical properties of the formations, casings and cement.
The output is a failure analysis of the cement sheath in terms of compression, tension and micro annulus development. Once the failure mechanisms are well understood, further sensitivity analyses permit to select the most adequate cement system for the application, based on target windows of compressive and tensile strengths, Young's modulus, Poisson's Ratio, and expansion capacity.
The paper will discuss a case study where a fit-for-purpose durable cement system was designed to meet the required mechanical properties as suggested by the stress modeling performed on a candidate well. It was placed as a Tail slurry on the 9 5/8" Tieback casing to provide 1000 ft. of long-term hydraulic isolation in the cased annulus should the liner top packer fail to seal the high-pressure water formation below. A post-job analysis using job data and cement evaluation logs showed that placement was executed as per design and that the durable cement system provided excellent bonding and annular coverage. The well was later drilled to total depth, completed, fractured and delivered to production without CCA pressure at the wellhead.
The new approach consists of performing finite elements stress modeling during the well planning phase to custom design cement systems that will withstand the anticipated loads.
A recurring challenge in cementing concerns the effectiveness and the quality of cement blending and handling procedures. Some recent technologies involve dry-blending operations and cement-blend handling of specifically tuned blends that mix particles of different characteristics in terms of density, shape, size, and chemistry, including mineral and/or organic components. All blends are usually transported pneumatically, loaded to the rig, and then transferred to the rig silos. During the multiple transfers, depending on its characteristics, the blend may become difficult to flow and prone to segregation. This causes the blend to lose its homogeneity, and, consequently, it becomes difficult to use or even unusable.
Flowability and robustness to segregation are essential blend properties for the handling process. Overall, the differences between particles in chemical nature, density, size, and shape will influence the flowability and the tendency to segregate. Dealing with blends is, therefore, complex since they contain small, medium, and coarse particles, all of them in various proportions depending on the targeted cementing-fluid density and set cement properties.
To counter this challenge, an innovative methodology and equipment were systematically used in field cases to characterize the blend flowability and robustness to segregation.
This new approach is used during the cement-job design as a preventive measure to validate the design and quality control of the dry-blending operations and transportation to the rig. This process helped in designing robust homogeneous blends, thus reducing the likelihood of blend transfer problems.
Three case histories illustrate our new process. In the first case, we evaluated the blend selection between two designs that had good slurry performance for a critical job at a field location. We measured the shear under consolidation, the aerability, and the proneness to segregation of the two blends. Because both blends have good and equivalent flowing properties, we selected the blend that was less prone to segregation. In the second case, the field location designed four complex blends for lead and tail slurries having good slurry performance. We evaluated the shear under consolidation of the four blends, which were classified according to their flowability. Next, we measured the aerability of the blends as a second parameter to discriminate the blends, and then we considered segregation as the last screening parameter. In the last case, we used our flowability criteria to select the maximum acceptable concentration of an additive, which increased cement fluid performance but degraded blend handling.
The outcome of this multidisciplinary approach of blend characterization helps the oil and gas industry anticipate blend-handling issues and continuously improve quality and field handling of engineered complex blends with high confidence and consistency.
Oil and gas well integrity is obtained by placing a steel casing in the well and a cement sheath in the resulting casing/formation annulus. To provide zonal isolation, a large portfolio of cementing technology is available to meet various well conditions. Some of these technologies involve dry-blending operations and cement-blend handling of specific-tuned-blends mixing together particles of different characteristics in terms of density, shape, size, and chemistry including mineral and/or organic components. These blends are usually transported pneumatically and loaded to the rig then transferred to the rig silos. During the different transfers, the blend may be prone to segregation, thereby losing its homogeneity, which makes it difficult to use or even unusable.
Flowability is an important blend property for the blend-handling process. Segregation can be viewed as a mechanism leading to a nonrandom degree of uniformity of the different blend components at the scale at which end-use properties are required. Overall, the differences between particles in chemical nature, density, size, and shape will influence the flowability and, above all, the tendency to segregate. Dealing with blends is, therefore complex since they contain small, medium, and coarse particles in various proportions depending on the targeted slurry density and set material properties.
To counter this challenge, an innovative methodology and equipment to characterize the blend flowability and robustness to segregation were developed and implemented.
The laboratory results were validated with those obtained in the large-scale results using a pneumatic conveying flow-loop.
The implementation of the new methodology during the design phase of the cement job was used as a preventive measure to validate the design and quality control of the blend before the blend is prepared and sent to the rig. This helped in designing robust homogeneous blends and reducing the likelihood of blend transfer problems, thus ensuring the placement of the right quality cement slurry and assuring downhole well integrity.
The new methodology described in this paper was applied to tune several field blends known or identified to have problems and to develop of new generation of cementing technologies.
The outcome of this multidisciplinary approach of blend characterization helps the oil and gas industry to anticipate blend-handling issues and to continuously improve quality and field handling of engineered complex blends with high confidence and consistency.
Contreras, Jose (Schlumberger) | Bogaerts, Martijn (Schlumberger) | Griffin, Dave (Schlumberger) | Rodriguez, Faiber (Schlumberger) | Sianipar, Sakti (Schlumberger) | Villar, Vitor (Schlumberger) | Taoutaou, Salim (Schlumberger)
AbstractThe updates in the US code of federal regulations 30 CFR Part 250 Oil and Gas and Sulphur Operations in the Outer Continental Shelf, released in 2016, relate to, among other things, real-time well monitoring on critical well operations including cementing. The regulations do not assume that onshore-based staff would assume operational control, but rather that onshore expertise can assist the offshore location in determining anomalies before they become critical issues. Currently, cement job monitoring is often limited to the acquisition of pressure, rate, and density measurements. Based on those measurements, a basic evaluation is performed during the job. A new software tool has been developed to improve the ability to interpret and diagnose critical job parameters while the cement job is in progress.The real-time cement monitoring (RTCM) simulator combines data from the cement job design with acquisition data from the cement unit and rig to provide a detailed picture of the operation by comparing acquired values with predictions computed in real time. Data acquired during the cement placement are processed by a hydraulics simulator incorporated into the software to provide key information about the fluids' position in the annulus, comparative trends of acquired versus simulated surface pressures, density quality assurance and quality control, and real-time visualization of dynamic well security. Based on the real-time estimation of the fluids' position in the annulus and other key parameters measured during the job execution, a contingency plan can be followed, thus avoiding the need to wait on a detailed post-job analysis of the raw acquisition data.This paper describes the methodology of the software and how it helps to diagnose the cement barrier placement in deepwater wells. The real-time monitoring of the cement job starts with the evaluation of the pre-job circulation and ends with the final displacement. With the real-time capabilities, experts can remotely view operations and provide recommendations during the cementing operations and immediately advise on post-cementing rig activities. Through case studies from the Gulf of Mexico and Atlantic Canada, the process and benefits will be shown to improve barrier verification as early as possible in the well construction phase.The novelty of the software is that it can be used to diagnose the quality of cement jobs during the execution stage. Synchronized visualization of wellbore schematics showing fluids position, equivalent circulating density (ECD) progression, and combined measured versus simulated surface pressures are critical to help determine the position of fluids in the annulus and provide early verification of a barrier.
Guo, Yabin (Schlumberger) | Li, Xiaochun (PetroChina Tarim Oilfield Company) | Feng, Shaobo (PetroChina Tarim Oilfield Company) | Zhang, Changduo (PetroChina Tarim Oilfield Company) | Liu, Rui (PetroChina Tarim Oilfield Company) | Zhang, Zhi (PetroChina Tarim Oilfield Company) | Li, Tan (Schlumberger) | Guo, Peng (Schlumberger) | Wang, Rui (Schlumberger) | Taoutaou, Salim (Schlumberger) | Lee, Junn Shyong (Schlumberger)
Ultra-deep wells (maximum measured depth of 8000 m) located in the Tarim Kuqa foreland oil field in western China pose significant challenges to well integrity because of the high temperature (maximum bottom hole static temperature of 180°C), high pressure (maximum 145 MPa), and a deeply buried, thick, salt-gypsum formation (maximum measured depth of 7800 m). An engineering cementing approach with continuous improvements has been applied in the cementing operations in over 200 wells from 2008 to 2015.
The ultra-deep casing program was designed to meet the complex drilling and high-pressure completion requirements. Meanwhile, fit-for-purpose cement systems have been developed to seal the long, high-pressure interval of the salt-gypsum formation. In addition, a procedure on spacer optimization and evaluation has been established to optimize target zone cementing in oil-base mud. Tailored cementing procedures from well preparation to post-job remedial work were developed to meet the severe lost circulation challenge caused by the narrow pore-fracture pressure window in the reservoir.
Since 2008, various problems related to well integrity have been encountered in the field, including casing leaks, incomplete zonal isolation post cementing and sustained casing pressure (SCP) during the exploration and development activities. Substantial local operational practices have been accumulated to solve these intractable problems through the 1200 primary and remedial cementing operations undertaken to the present. A comprehensive pool of cement slurry formulations has been established with optimized properties including extreme high density with good pump-ability, saturated salinity resistance, and cement setting under an extended temperature difference to meet the various cementing requirements resulting from complex and extreme downhole conditions. A design-execution-evaluation (DEE) cycle of cementing operation has been implemented to achieve continuous improvements and shorten the learning curve in the face of the new challenges continuously encountered during the extended exploration activity of this region. The annual average percentage of qualified cementing jobs has been enhanced steadily from an initial 55% in 2008 to the present 73%.
The nature of this ultra-deep reservoir limited the application of lessons learned from other oil fields. A series of cementing practices developed empirically to address the challenges of this field have been documented and optimized over the years. They have proven to be successful in the field and form the foundation of designs going forward.