Remedial cementing requires as much technical, engineering, and operational experience, as primary cementing but is often done when wellbore conditions are unknown or out of control, and when wasted rig time and escalating costs force poor decisions and high risk. Squeeze cementing is a "correction" process that is usually only necessary to correct a problem in the wellbore. Before using a squeeze application, a series of decisions must be made to determine (1) if a problem exists, (2) the magnitude of the problem, (3) if squeeze cementing will correct it, (4) the risk factors present, and (5) if economics will support it. Most squeeze applications are unnecessary because they result from poor primary-cement-job evaluations or job diagnostics. Squeeze cementing is a dehydration process.
Rollins, Brandon (Whiting Petroleum Corporation) | Lauer, Travis (Whiting Petroleum Corporation) | Jordan, Andrew (BJ Services) | Albrighton, Lucas (BJ Services) | Spirek, Matthew (BJ Services) | Pernites, Roderick (BJ Services)
Frequently exposed weak formations require the use of lighter slurries, and with increased wellbore pressures encountered during fracture stimulations, stronger cements are essential. Lighter, stronger cementing technologies are the key to ensuring well integrity and enabling simple, cost-effective well construction designs.
This paper describes the benefits and features of newly developed, lightweight cementing materials available for operations in the Williston Basin. Applications of these materials are supported by case histories and extensive laboratory test data.
Regionally, materials have been identified that can be used to produce innovative, bulk lightweight cementing systems. These materials can be inter-ground with the cement during manufacturing or blended with bulk cement. Both methods create cost-effective, high-strength cement systems that can easily be formulated into slurries with densities as low as 10.5 ppg.
Comprehensive laboratory test data was generated to support well simulations and field trials of the new materials. Field trial data is then analyzed to illustrate the benefits of cement systems.
Economical lightweight cements are commonly produced with fly ash extended systems, however, these systems have low strength at low densities. Lightweight, high-strength, fit-for-purpose cement materials are common in southern oil and gas basins, but transporting these materials to northern states is cost prohibitive. Exotic solutions to create lightweight cements (nitrogen foams or hollow glass micro-beads) are available but expensive, adding considerable operational complexity.
Laboratory data demonstrates mechanical properties of the cement systems, slurry properties and set characteristics. The new, low-density cement systems show far greater compressive strengths than conventional blends. Conventional slurry provides a compressive strength of 500 psi, whereas the new low-density 12 ppg blends provide compressive strengths greater than 1,000 psi.
Additional practical benefits of these systems are illustrated by varying water content to improve slurry density from 11 to 13.5 ppg without additional cementing additives.
Multiple case histories illustrate the results of the applications of these materials at downhole temperatures ranging from 140°F to 220°F and well depths up to 11,000 ft TVD in the Dakota, Mowry and Charles Salt formations.
The limitations associated with traditional cementing materials will no longer restrict the creation of efficient well designs in northern states with the implementation of new, low-density cement systems necessary to exploit these oil and gas basins. Using lighter, stronger cement technologies will provide simple, cost-effective designs that are needed to ensure wellbore integrity in the Williston Basin.
Bagheri, Mohammadreza (Research Centre for Fluid and Complex Systems, Coventry University) | Shariatipour, Seyed M. (Research Centre for Fluid and Complex Systems, Coventry University) | Ganjian, Eshmaiel (School of Energy, Construction and Environment, Built & Natural Environment Research Centre, Coventry University)
The fluid pressure, the stress due to the column of the cement in the annulus of oil and gas wells, and the radial pressure exerted on the cement sheath from the surrounding geological layers all affect the integrity of the cement sheath. This paper studies the impact of CO2-bearing fluids, coupled with the geomechanical alterations within the cement matrix on its integrity. These geochemical and geomechanical alterations within the cement matrix have been coupled to determine the cement lifespan. Two main scenarios including radial cracking and radial compaction, were assumed in order to investigate the behaviour of the cement matrix exposed to CO2-bearing fluids over long periods. If the radial pressure from the surrounding rocks on the cement matrix overcomes the strength of the degraded layers within the cement matrix, cement failure can be postponed, while on the other hand, high vertical stress on the cement matrix in the absence of a proper radial pressure can lead to a reduction in the cement lifespan. The radial cracking process generates local areas of high permeability around the outer face of the cement sheath. Our simulation results show at the shallower depths the cement matrices resist CO2-bearing fluids more and this delays exponentially the travel time of CO2-bearing fluids towards the Earth's surface. This is based on the evolution of CO2 gas from the aqueous phase due to the reduction in the fluid pressure at shallower depths, and consumption of CO2 in the reactions which occur at the deeper locations.
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.
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.
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.
Prabhakar, Abhinav (National University of Singapore) | Lee, Namkon (Korea Institute of Civil Engineering and Building Technology) | Ong, Khim Chye Gary (National University of Singapore) | Zhang, Minhong (National University of Singapore) | Moon, Juhyuk (Seoul National University) | Cheng, Arthur (National University of Singapore) | Kong, Kian Hau (National University of Singapore)
This study aims to design and evaluate a well cement slurry as an alternative to the standard API ‘G’ slurry for utilization in plugging and abandonment (P&A) of oil and gas wells. OWC slurries are formulated with Portland API ‘G’ cement as the base material, along with calcium sulfoaluminate (CSA) cement, gypsum and chemical additives. The slurries are experimentally tested using API standard procedures to determine gel transition time and right-angle-set (RAS) tendency at a temperature of 50 °C and pressures up to 34.5 MPa (5000 psi). The hydration characteristics of CSA cement can be utilized to control the gel development behaviour of a well cement slurry in order to minimize fluid or gas migration. Formation of ettringite greatly influences early age gelation. The potential to enhance gel strength development of an OWC slurry with CSA cement is presented whereby the gel transition time decreases with higher dosages of CSA cement. Thickening time studies to investigate the RAS tendency of the designed cement slurries are presented.
Ahdaya, Mohamed Saad (Missouri University of Science and Technology) | Imqam, Abdulmohsin (Missouri University of Science and Technology) | Jani, Priyesh (Missouri University of Science and Technology) | Fakher, Sherif (Missouri University of Science and Technology) | ElGawady, Mohamed (Missouri University of Science and Technology)
One of the most important steps in drilling and operation completion is oil well cementing to provide wellbore integrity. Cementing is usually performed in the oil industry using conventional Portland cement. Even though Portland cement has been used for many years, it has several drawbacks, including operational failures and severe environmental impacts. Fly ash based geopolymer cement has been recently investigated as a low-cost, environmentally friendly alternative to Portland cement. This research develops a novel formulation of Class C fly ash based geopolymer and investigates its applicability as an alternative to Portland cement in hydrocarbon well cementing. Twenty-four variations of fly ash Class C based geopolymers were prepared, and by comparing several of their properties using API standard tests, the optimum geopolymer formulation was determined. The ratios of alkaline activator to fly ash that were used are 0.2, 0.4, and 0.8, along with different ratios of sodium silicate to sodium hydroxide, including 0.25, 0.5, 1, and 2. Multiple sodium hydroxide concentrations were used, including 5, 10, and 15 molarity. The selection of the optimum formulation was based on five different tests, including rheology, density, compressive strength, fluid loss test, and stability tests (sedimentation test and free fluid test). Then, a comparison between the optimum mix design and Portland cement was conducted using the same tests. Based on our results, increasing sodium hydroxide concentration resulted in an increase in compressive strength and showed a slight decrease in the plastic viscosity. However, increasing in the alkaline activator to fly ash ratios increased plastic viscosity, and thus the pumpability of the slurry was reduced. Increasing the sodium silicate to sodium hydroxide ratio significantly decreased the fluid loss. The optimum design of geopolymer, which had lower fluid loss, 93 ml after 30 minutes, sufficient compressive strength, 1195 psi, and an acceptable density, 14.7 lb/gal, and viscosity, 50 cp, was selected. Compressive strength of the optimum design showed better results than neat Portland cement. Unlike neat Portland cement, which needs fluid loss additives, the new formulation of geopolymer investigated in this study showed fluid losses lower than 100 ml after 30 min when tested using a low-pressure, low-temperature filtrate loss tester. The higher mechanical strength of geopolymer using fly ash Class C compared to Portland cement is very promising for achieving long-term wellbore integrity goals and meeting regulatory criteria for zonal isolation. The rheological behavior, compressive strength, and fluid loss tests results indicate that fly ash Class C based geopolymer has the potential to be an environmentally friendly alternative to Portland cement when cementing oil wells.