Torbjørn Vrålstad

Experimental study on the synthesis and characterization of aplite rock-based geopolymers

This paper presents a new method for geopolymer synthesis of ground aplite rock. The resulting geopolymers were easy to manufacture and exhibited promising mechanical properties. Compressive strength testing, X-ray diffraction, and scanning electron microscope analyzes were performed. The results indicated that in manufacturing, the aplite-based geopolymers, potassium-containing systems gave noticeable improvements in comparison with sodium-containing systems. Rheological behavior of the geopolymeric slurry showed non-Newtonian behavior. The Bingham and Herschel–Bulkley models were selected to simulate the viscosities of the slurries. The Bingham model fitted to the measured data with an average deviation of 1.65 (lbf/100 ft2) while the Herschel–Bulkley model showed large deviations from the experimental data.

Cobalt functionalization of mesoporous silica by incipient wetness impregnation and co-precipitation

MCM‐41 and MCM‐48 were functionalized with cobalt by two methods, incipient wetness impregnation and co‐precipitation, and were characterized by XRD, N2‐sorption, and TPR. The incipient wetness impregnation method provides a high dispersion of small cobalt oxide particles, while the mesoporous structure and high surface areas are maintained. There seems to be a higher dispersion of cobalt oxide on the three‐dimensional MCM‐48 than on the one‐dimensional MCM‐41. The co‐precipitation method did not precipitate easily reducible cobalt oxide in any sizable amounts; instead, the cobalt was mainly bound as cobalt silicate.

Influence of Interfacial Tension on Seeded Calcium Carbonate Scale Precipitation: Effect of Adsorbed Asphaltenes

Clay particles with adsorbed asphaltenes, which are commonly found in produced water, have been used as seed particles during precipitation of calcium carbonate in order to determine whether such particles may influence the kinetics of precipitation. The results show that the presence of the adsorbed asphaltenes accelerates the precipitation, and there is also a significant difference between different types of adsorbed asphaltenes. The adsorption of asphaltenes at the seed surface leads to a significant increase in the interfacial tension between the seed surface and the aqueous solution, and calcium carbonate therefore precipitates at the seed surface in order to reduce this high interfacial tension.

A Direct Sol‐Gel Synthesis Method for Incorporation of Transition Metals into the Framework of Ordered Mesoporous Materials

A series of ordered mesoporous cobalt silicate molecular sieves with variable Si/Co molar ratios were hydrothermally synthesized. The materials were characterized by powder X‐ray diffraction (XRD), N2 adsorption, temperature programmed reduction (TPR), and transmission electron microscopy (TEM). TPR and TEM results indicate that Co introduced by this method is incorporated into the framework of the ordered mesoporous materials rather than residing as Co3O4 particles in the pore system. XRD and N2 adsorption experiments reveal that the interplanar Bragg spacing, surface area, and pore width of the materials are tunable as a function of the bulk Si/Co molar ratio. The surface areas of the materials range from ∼1300 m2/g (unmodified siliceous mesoporous ordered material) to ∼500 m2/g (maximum incorporation of Co before structural breakdown), with the Barrett‐Joyner‐Halenda (BJH) model pore widths varying from 2 to 3 nm, respectively. Vanadium was also introduced by the same method to demonstrate the applicability of the method.

Long-term durability of rock-based geopolymers aged at downhole conditions for oil well cementing operations

The long-term integrity of rock-based geopolymers was studied in corrosive environments. The geopolymers were cured for 7 days at ambient conditions. Afterwards, the geopolymers were exposed to crude oil, brine and H2S in brine at 100 °C and elevated pressures. The compressive strength, tensile strength, weight and volume changes were measured prior and after 3, 6 and 12 months of exposure. The measurements showed a turning point after 6 months of ageing. Whereas the compressive strength and tensile strength started to increase when the specimens were exposed to crude oil and brine, the specimens that were exposed to H2S experienced some degradation. Permeability of geopolymers before exposure and after 12 months of exposure to the crude oil and brine was very low. The permeability of the specimens which were exposed to H2S was not measureable. Substantial volume changes were observed for the geopolymers which were exposed to H2S and brine.

A Study of Possible Solutions for Cost Efficient Subsea Well Abandonment

There is a large number of subsea production wells offshore Norway approaching the end of their lifetime. Considering high spread rate of semisubmersible rigs, abandonment operations of these wells will be quite expensive. Moreover, Plug and abandonment (P&A) can easily contribute with 25% of the total costs of drilling for exploration wells offshore Norway. Hence it is of great importance to seek approaches and solutions to reduce the P&A cost. This paper reviews some possible new ways and also alternative technologies as the solutions to cut down the P&A expenses. Some of these technologies are now being used offshore Norway.In the first section of this paper, challenges of performing P&A operations offshore Norway together with the main cost drivers are discussed. It is then briefly argued how to consider issues such as barriers setting depth, cementing depth and logging in the design and well construction phases to ease or avoid future P&A challenges. For hydrocarbon exploitation in the Barents Sea and Arctic regions it is important to take into account the P&A phase in the early stage of planning and development.Light well intervention vessels as alternatives to semisubmersible rigs are recognized of being the largest contributor to cost saving. It will then be discussed to what extent vessel technologies can cut down the expenses for subsea abandonment. New ways of performing P&A can be another contributor to cost saving. It is shown how research and testing can assure the operators of new ways for performing P&A. Retrieval of production tubing is a challenging suboperation such that it imposes significant cost to subsea well abandonment. There have been performed studies on how P&A could be performed with tubing left in hole and it is of interest to pursue this further. We will investigate how the abandonment operations can be simplified and be more cost efficient if the production tubing can be left inside the well where the basic assumptions for being able to do it is accounted for.In addition, some complexities in abandonment operations can cause additional cost. An example of such complexities can be the need to establish two permanent barriers for potential permeable zones in overburden. It will be demonstrated how much can be saved with respect to cost if the regulations allow to ease some parts of abandonment operations.In this study, a probabilistic approach as a systematic tool to produce unbiased results is applied to quantify cost savings of new alternatives compared to the traditional ones.© 2015 ASME

Improved Laboratory Set-Up for Pressurized and Confined Cement Sheath Integrity Tests

The annular cement sheath is one of the most important well barrier elements, both during production and after well abandonment. It is however well-known that repeated pressure and temperature variations in the wellbore during production and injection can have a detrimental effect on the integrity of the cement sheath. Degradation of cement sheaths result in formation of cracks and microannuli, which leads to loss of zonal isolation and subsequent pressure build-up in the annulus.A unique laboratory set-up with downscaled samples of rock, cement and pipe has been constructed to study cement sheath failure mechanisms such as debonding and crack formation during thermal cycling. Cement integrity before and after thermal cycling is visualized in 3D by X-ray computed tomography (CT). However, this previous set-up had some significant limitations such as lack of direct physical confinement around the rock. This lack of direct confinement created unrealistic outer boundary conditions around the rocks during experiments as opposed to field conditions, which influenced the obtained experimental results.This paper describes in detail an improved version of this laboratory set-up, where the set-up has been redesigned to include direct physical confinement around the rock as well as improved cement placement, while retaining all the advantages of the previous set-up.Copyright

Cement Sheath Integrity Implications of Scaled-Down Wellbore Casing-Cement-Formation Sections

Many offshore petroleum wells have serious cement sheath integrity issues that imply costly repairs, limitations with respect to short- and long-term use of planned or converted production and injection wells, and safety issues. The annular cement sheath is exposed to a wide variation of thermal and pressure loads that potentiality may result in zonal isolation failure throughout its lifecycle.While several experimental and numerical work manage to map highly loaded scenarios that leads to radial cracks and micro-annulus generation, little effort has been taken to investigate and quantify the impact of moderate pressure and thermal loads on cement sheath stresses. This paper presents a 2D finite element assessment of impacts of numerous material properties, geometric parameters, pressure and thermal loading variables contributing to cement sheath stresses. A centralized wellbore section of casing-cement-formation is considered, representing a production casing string. This work is conducted as a preliminary effort in order to develop a down-scaled laboratory set-up, that represents realistically the impact of thermal and pressure loads on cement sheath stresses.This paper introduces a discussion about the capabilities of a down-scaled well section to characterize the stress distribution around the annular cement sheath of a conventional 9 5/8″ production casing. Results indicate that a down-scaled configuration exposed to comparable internal pressure and temperature profile resembles the stress distribution associated with completion and production operations of wells. It is shown that a proper characterization of the cement stress regimes requires the combined effect of pressure and thermal variations.Sensitivity studies conducted on cement sheath stresses, for both wellbore and down-scaled configurations, have assessed the relative influence of mechanical and thermal properties as drivers of cement stresses. For well operations with substantial wellbore temperature variations such as production and frac job, particularly uncertain parameters such as cement-formation-Young’s modulus and thermal expansion coefficient of cement have shown significant impact on annular cement sheath stresses. In terms of combined pressure and thermal loading, cement stresses have proved to be more sensitive to temperature differential than pressure differential variations.Copyright