Cement sheath is a critical barrier for maintaining well integrity. Formation of micro-annulus due to volume shrinkage and/or pressure/temperature changes is the major challenge in achieving good hydraulic seal. Expansion of cement after the placement is a promising solution to this problem. Expanding cement can potentially close micro-annulus and further achieve pre-stress condition because of the confinement. Primary aim of this paper is to investigate mechanical integrity of different pre-stressed cement system under loading condition.
To achieve the objectives, finite element modelling approach was employed. Three dimensional computer models consisting of liner, cement sheath, and casing were developed. Pre-stress condition was generated by modelling contact interference at the cement-casing interface. Three cement (ductile, moderately ductile, and brittle) were considered for simulation cases. Wellbore and annulus pressure were applied. Resultant, radial, hoop, and maximum shear stresses were investigated at the cement-pipe interface to assess mechanical integrity. For comparison purpose, similar simulations were conducted using cement sheath without pre-stress and cement system representing uniform volume shrinkage and presence micro-annulus.
For constant wellbore pressure, the radial stresses observed in all three types of cement system were practically similar and decreased as pre-stress was increased. Hoop stress also reduced with increase in compressive pre-load. However, their absolute values were distinct for different cement types. These results indicate that cement system with compressive pre-load can notably reduce the risk of radial crack failure by providing compensatory compressive stress. However, on the contrary, the maximum shear stress developed at cement-pipe interface, increased because of pre-load. This can compromise the mechanical integrity by reducing the safety margin on shear failure. Thus, the selection of expansive cement should be made after carefully weighing reduced risk of radial failure/debonding against the increased risks of shear failure.
This paper provides novel information on expanding cement from the perspective of mechanical stresses and integrity. Modelling approach discussed in this work, can be used to estimate amount of pre-stress required for a selected cement system under anticipated wellbore loads.
Cement is a key element for successful drilling and completing of a well. From oil and gas wells to geothermal applications, cement is a major material ensuring zonal isolation. With an increase in global energy needs and an expected uptick in drilling and plugging and abandonment activities, evaluating and understanding cement properties is crucial, since these properties are used in various engineering designs and calculations. The objective of this paper is to present how Nuclear Magnetic Resonance (NMR) can be used to understand the cement hydration process and the development of key properties such as strength and porosity. NMR applications for cement include determination of porosity, water interactions, identification of hydration stages and C-S-H gel development with curing time. Since water is present in all cement slurries, NMR can potentially help to understand microstructural changes in cement during curing. Data from more than 600 cement specimens cured for more than a year are compiled. Standard cement properties such as UCS (unconfined compressive strength) are compared with NMR responses. In this paper, we document cement hydration and porosity changes through NMR measurements in samples with five different recipes. Our study also confirms a strong correlation between NMR response and cement strength.
Primary cementing operations rank among the more important events that occur during a well's lifetime. The cement sheath plays a critical role in establishing and maintaining zonal isolation in the well, supporting the casing and preventing external casing corrosion.
For many years, the industry has employed strategies to promote optimal cement placement results. These strategies, collectively known in the industry as good cementing practices. Job execution is the key to insure success of the job based on the designed.
New technology that give us optimum execution evaluation (OEE) has been developed to enhance cement job execution by overlapping the design parameter over with the execution parameter real time. The OEE technology significantly improves cementing operations, enabling operators to monitor, control, and evaluate cement placement in real time. OEE combines job design data with acquisition data from both the rig and the cementing equipment to provide a more accurate representation of the job as it is being run.
In this paper, we present the process that we completed with detailed operational setup to allow us to monitor and record all parameters related to the cement job execution and the work flow implemented to be able to evaluate the cement job design and execution to achieve the required objectives. This study is also setting the basis to establish development of real time automated cementing advisory system.
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.
The goal was to search for a replacement of CaCl2 which presents the most widely used accelerator for oil well cement used in cold and arctic environments and sometimes in deepwater drilling. For this purpose, novel calcium silicate hydrate (C-S-H) nanoparticles were synthesized and tested. The C-S-H was synthesized by the precipitation method in an aqueous solution of polycarboxylate (PCE) comb polymer which is widely used as concrete superplasticizer. The resulting C-S-H-PCE suspension was tested in the UCA instrument as seeding material to initiate the crystallization of cement and thus accelerate cement hydration as well as shorten the thickening time at low temperature. It was found that in PCE solution, C-S-H precipitates first as nano-sized droplets (Ø ~20 - 50 nm) exhibiting a PCE shell. Following a rare, non-classical nucleation mechanism, the globules convert slowly to nanofoils (HR TEM images: l ~ 50 nm, d ~ 5 nm) which present excellent seeding materials for the formation of C-S-H from the silicate phases C3S/C2S present in cement. Thickening time tests performed at + 4 °C in an atmospheric consistometer revealed stronger acceleration than from CaCl2 while very low slurry viscosity was maintained, as was evidenced from rheological measurements. Accelerated strength development was checked on UCA cured at + 4 °C and under pressure, especially the wait on cement time was significantly reduced. Furthermore, combinations of C-S-H-PCE and HEC as well as an ATBS-based sulfonated fluid loss polymer were tested. It was found that this C-S-H- based nanocomposite is fully compatible with these additives. The novel accelerator based on a C-S-H-PCE nanocomposite solves the problems generally associated with CaCl2, namely undesired viscosity increase, poor compatibility with other additives and corrosiveness against steel pipes and casing.
With the current applications of CO2 in oil wells for enhanced oil recovery (EOR) and sequestration purposes, the dissolution of CO2 in the formation brine and the formation of carbonic acid is a major cause of cement damage. This degradation can lead to non-compliance with the functions of the cement as it changes compressive and shear bond strengths and porosity and permeability of cement. It becomes imperative to understand the degradation mechanism of cement and methods to reduce the damage such as the addition of special additives to improve the resistance of cement against acid attack. Hence, the primary objective of this study is to investigate the effects of hydroxyapatite on cement degradation.
To investigate the impacts of hydroxyapatite additive on oil well cement performance, two Class H cement slurry formulations (baseline/HS and hydroxyapatite containing cement/HHO) were compared after exposure to acidic environments. To evaluate the performance of the formulations, samples were prepared and aged in high-pressure high-temperature (HPHT) autoclave containing 2% brine saturated with mixed gas containing methane and carbon dioxide. Tests were performed at different temperatures (38 to 221°C), pressures (21 to 63 MPa) and CO2 concentrations (10 to 100%). After aging for 14 days at constant pressure and temperature, the samples were recovered and their bond and compressive strength, porosity and permeability were measured and compared with those of unaged samples.
The results demonstrated that adding hydroxyapatite limits carbonation. Baseline samples that do not contain hydroxyapatite carbonated and consequently their compressive strength, porosity, permeability, and shear bond strength significantly changed after aging while hydroxyapatite-containing samples displayed a limited change in their properties. However, hydroxyapatite-containing samples exhibit high permeability due to the formation of microcracks after exposure to carbonic acid at high temperature (221°C). The formation of microcracks could be attributed to thermal retrogression or other phenomena that cause the expansion of the cement.
This article sheds light on the application of hydroxyapatite as a cement additive to improve the carbonic acid resistance of oil well cement. It presents hydroxyapatite containing cement formulation that has acceptable slurry properties for field applications and better carbonic acid resistance compared to conventional cement.
Several polymer technologies are commonly used as fluid loss control additives. Working mechanisms were studied by Plank et al. (
The scope of this paper is to investigate the impact of several types of fluid loss polymers on cement slurry stability. Then, an effort is made to correlate the working mechanism of the fluid loss additive with cement slurry rheological behavior and its ability to prevent segregation or settling.
On top of conventional tests on fluid loss and flow rheology, refined evaluations of the rheological behavior are performed in oscillatory rheometry at very-low strain. This technique allows some insight into the microscopic interactions at stake in cement slurries. In particular a "yield stress model" is applied to formulated oil well cement slurries at 90°C providing additional insight on the impact of adsorbing or non-adsorbing polymers.
From this study it can be confirmed that adsorbing polymers have a strong impact on rheological properties with a surprisingly lower yield stress combined with improved slurry stability. On the other hand non adsorbing polymers of either linear or μgel form have a very limited impact on slurry yield stress and a variable impact on slurry stability through either viscosification of the interstitial fluid for linear polymers or enhanced settling hindrance from μgels.
Contreras, Elizabeth Q. (Aramco Services Company: Aramco Research Center – Houston) | Johnson, Kenneth D. (Aramco Services Company: Aramco Research Center – Houston) | Rasner, Diana (Aramco Services Company: Aramco Research Center – Houston) | Thaemlitz, Carl J. (Aramco Services Company: Aramco Research Center – Houston)
Encapsulation-based systems are of interest in the oil and gas industry in applications such as chemical additive preservation, small molecule release, particle delivery, and self-sealing materials. Many methods are used to encapsulate relevant chemical additives for the controlled release of contents like polymeric vesicles, inorganic shells, and mesoporous materials. Here a novel system for the controlled release of encapsulated cargo that utilizes engineered features of permeable polymeric shell walls is shown.
When placing cement, a multitude of additives in large quantities are needed to meet a variety of functional needs that are suitable for the many diverse wellbore conditions. However, using large amounts of certain additives could have adverse effects which can destabilize the slurry at surface conditions. Using vesicles, cement additives are delivered without requiring modification. In this way, the possibilities of formulations comprised of a number of vesicles with various encapsulants lends to significant advancements in cementing. Applications in cement design is demonstrated from measurements obtained using the consistometer as well as testing from oilfield equipment.
Experimental results show that a basic cement slurry design responds to the release of an encapsulant by the measure of change in viscosity and thickening times at two different temperatures at 3,000 psi. For example, the thickening time of a slurry can be controlled with the delayed release of an accelerant, at ambient pressure. With an increase in temperature up to 100 °F and 300 °F, the encapsulated additive is squeezed at a higher diffusion rate, resulting in a faster thickening time. In all cases, the vesicles are observed to remain intact within the set cement and contribute significantly to the mechanical properties of set cement. Vesicle dual performance stems from unique characteristics, such as an aqueous core, wall thickness and permeability, chemical composition, and mechanical integrity of the shell wall. Here, the shell walls are engineered with high molecular weight polymeric material that upon release of the encapsulated chemical additives, the emptied vesicles continue to impart beneficial mechanical properties to the set cement, such as compression strength.
Partch, Ilia (Fritz Industries, Inc.) | Ferrell, James (Fritz Industries, Inc.) | Morrison, Donald (Fritz Industries, Inc.) | Salinas, Elexander (Fritz Industries, Inc., Wika Group) | Franks, Stacy (Fritz Industries, Inc., QMax)
In cementing applications, the release of gas is used to prevent shrinkage of the set cement in an annulus. With a significant decrease of volume of the wellbore, long term annular isolation may result in microfractures of the cement system; therefore, a failure of the cement bond (
Traditionally, a known rudimentary technique in measuring gas expansion in cement slurries is to use a glass beaker and to record the observations. Under static and atmospheric conditions, a graduated cylinder has been used to quantitatively measure the displacement of gas release within the annulus at ambient conditions. The new method developed in this paper will demonstrate that gas was being expelled into the atmosphere when the cement slurry containing gas generating additives was tested under ambient conditions. The procedure developed here will demonstrate that gas was entrained within the cement matrix.
An initial assessment of varying particle sizes of coated aluminum granules in a caustic solution showed that a consistent volume of gas was released. This working hypothesis was substantiated by measuring the volume of gas released within a closed system using a data logger. To ensure validation of this procedure, in-situ gas producing cement slurries were measured utilizing this method. With this experimental setup, quantifying the measurement of released gas from the cement matrix confirmed that variation of particle size does not affect performance.
Gas volume displacement measurement using an inverted graduated cylinder was set up to quantitatively determine the volume of the released gas within the cement matrix with the utilization of a stir plate. The system utilized polytetrafluorethylene tubing to transport the released gas that was produced from the matrix to the inverted graduated cylinder that was filled with deionized water. The released gas volume was assessed by displacement.
The enclosed dynamic apparatus with an inverted graduated cylinder was fitted with a paddle. This experimental setup enabled a homogenous blend and prevented void formation as the matrix was continuously agitated. This enclosed dynamic apparatus prevented the release of gas to be consumed by the atmosphere and gas entrainment. With the utilization of this procedure, the functionality of the gas expansion additive was fully attained without hindering performance and the gas release profile was controlled. This technique exhibited reproducibility and the theoretical gas release volumes were as calculated.
After placement, the cement systems must preserve their integrity and provide zonal isolation during the life of the well. It has been possible to accommodate a wide range of conditions through the development of cementing additives that modify different Portland cements for their individual well requirements. During the hardening phase of a standard proportional cement to water content, the cement system becomes solid with low permeability. As a result of the cement matrix, the release of gas cannot migrate at a quantifiable rate with the partially water saturated pores. Low density cement systems with high water to cement ratios can exhibit high permeabilities. Therefore, it is possible for gas to flow and eventually reach the surface though at low rates. Additives are uniquely manufactured for gas expansion to prevent annulus shrinkage and high permeability; thereby preserving the integrity of the well isolation.
Murtaza, Mobeen (King Fahd University of Petroleum & Minerals) | Mahmoud, Mohamed (King Fahd University of Petroleum & Minerals) | Elkatatny, Salaheldin (King Fahd University of Petroleum & Minerals) | Majed, Abdulaziz Al (King Fahd University of Petroleum & Minerals) | Chen, Weiqing (King Fahd University of Petroleum & Minerals) | Jamaluddin, Abul (King Fahd University of Petroleum & Minerals)
In cementing operations of deep oil and gas wells, long term integrity of the well is highly dependent on the cement sheath. Obtaining success rate in cementing operations has been subjected to a myriad of challenges, as drilling into deeper, high pressure/high temperature horizons is done. To gain long term integrity of cement sheath, a successful placement of cement slurry plays a pivotal role. So, the design of suitable rheological properties helps characterize the cement pumpability, mixability, and displacement rates for adequate removal of mud. So, the design of cement slurry for HPHT and deviated wells has become a complex task. Recently employing nano-materials in improved oil recovery, designing of drilling fluids as well as hydrocarbon well cementing has been the focus of many studies. The intrinsic characteristics of being smaller in size, while at the same time providing a larger surface area, nanomaterials can prove to be a game-changer for the challenges faced in HPHT cementing. This paper reproduces the outcomes of an investigational study conducted to determine the effect of nanoclay as an additive on rheological properties of Type-G cement slurry under various temperature conditions. Nano-clay with Class G cement in two different concentrations 1% and 2% by weight of cement, mixed and tested under different temperature conditions (37°C, 50°C, 60°C & 80 °C). Additionally, nano-clay based cement mixtures were prepared by substituting cement with 1%, 2% and 3% of nano-clay by weight of cement(BWOC), and admixed with silica flour, along with various chemical admixtures. American Petroleum Institute (API) standard-10B was followed to condition the slurry at predetermined temperature, while the slurry was under atmospheric pressure. This conditioning was followed by the measurement of rheological properties. Results of this investigation demonstrate that incorporation of nano-clay advances the rheology of prepared cement slurry that could aid in mud-displacement and anti-settling as per the requirements.