Studies on the molecular interaction mechanisms of asphaltenes in organic solvent have not reached a widely accepted conclusion, mainly because of a poor definition of asphaltene molecules and lack of accurate information on the molecular structure. In this study, N-(1-hexylheptyl)-N 0 -(5-carboxylicpentyl) perylene-3,4,9,10-tetracarboxylic bisimide (C5Pe) of the polyaromatic core with a proper molecular weight and heteroatoms in its structure was used as a model compound of asphaltenes in an attempt to understand interaction mechanisms of molecular aggregation in organic solvents. A surface forces apparatus (SFA) was used to directly measure the molecular interactions of C5Pe in toluene and heptane. For the interactions between two model clay (mica) surfaces across a C5Pe-in-toluene solution, the repulsion observed between the adsorbed C5Pe molecules was shown to be of a steric origin. The forceÀdistance profiles at short separation distances under high compression force during approaching were well-fitted with the AlexanderÀde Gennes (AdG) scaling theory, while the weaker repulsive forces at lower compression force regime over longer separation distances can also be fitted with the AdG model using an independent set of fitting parameters, indicating the presence of possible secondary brush structures of the C5Pe molecules in toluene. For interactions of pre-adsorbed C5Pe films (C5Pe versus mica and C5Pe versus C5Pe), no significant adhesion was detected in toluene, while strong adhesion was measured in heptane. The comparison of the results obtained with the model compound C5Pe and native asphaltenes shows that C5Pe behaves quantitatively different from the real asphaltenes in the context of contact angle and interaction force profiles. However, there are qualitative similarities in terms of intermolecular forces, indicating that the polar components in real asphaltene molecules play an important role in determining their interfacial activities.

A method using low-field nuclear magnetic resonance (NMR) for measurement of water-in-crude oil emulsion stability has been optimized and compared to light transmission measurements. Two NMR sequences have been used; one of them applies a diffusion T 2 -weighted profile measurement sequence, which can return a water profile of an emulsion within 30 s. The stability of the emulsions was compared by studying emulsions in parallel in Turbiscan and NMR. Three different crude oils were used in the experiment. The emulsions prepared had water cut at 50%. The correlation between NMR and Turbiscan regarding the free water formation was good for the emulsions. The potential limitations and advantages of the technique are discussed.

The objective of primary cementing is to protect the casing and to ensure zonal isolation. It can be difficult to obtain a good cement job along the full length of a well, and casing centralization is one of the main factors that influence this. Even if the dependence of cement placement on casing centralization is well-known, little information is available on how the degree of casing centralization affects the well during its production phase. Well temperatures cycle up and down as a part of normal production operations – and well barrier materials, in particular steel, cement and rock, will consequently repeatedly expand and contract their volumes. Over time, this is likely to induce debonding and radial cracking of the cement sheath which threatens well integrity. This paper reports the results of an experimental study mapping how, where and when the annular cement loses its sealing ability upon temperature variations, and how this is dependent on casing centralization. The studied samples consisted of rock, cement and casing, and the temperature was cycled in a controlled and programmable manner. In-situ monitoring by Acoustic Emission (AE) sensors detected the development of cracking and debonding in the samples during thermal cycling. Initial and post-experiment computed tomography (CT) scans provided complementary three-dimensional (3D) information on the geometry and location of the induced cracks and debonding. Our study compared the thermal cycling resistance of two samples, one with centralized casing and one with a 50% casing stand-off. The AE monitoring results indicated that most of the cracking/debonding occurred during the actual heating and cooling, and not in between cycles when the temperature was held constant. The CT analyses showed that the thermal cycling caused considerable enlargement of cracks and voids initially present in the cement sheath, and this enlargement was significantly more severe when the casing was not centralized. The paper presents, for the first time, a 3D visualization of cracks and debonded volumes in the cement sheath, and it underlines the importance of obtaining a good initial cement job. Also, it is shown that it is important to obtain a good casing centralization during well construction – not only for optimal cement placement, but also for maintaining well integrity during production.

Petroleum activities in the sensitive Arctic environment require increased focus on well integrity, since even small leaks can affect production and surrounding ecosystems. It is therefore of the utmost importance that the sealing ability of the annular well cement can be maintained here. This is challenging in normal locations, and difficulties are intensified when moving north. Due to the harsh topside conditions in the Arctic, the operational windows are short -and production will necessarily be turned on/off repeatedly. The temperature of any unheated injected fluid will also be lower here. As a result, Arctic wells will be subjected to strong downhole temperature variations over their life cycles. These cause the volume of well construction materials, like casing steel and annular well cement, to repeatedly expand and contract, which might lead to loss of well integrity through debonding or cracking of the annular cement sheath.In the present paper we describe an experimental laboratory set-up that has been designed for studying the sealing ability of annular cement as a well is exposed to thermal cycling. The samples studied are small-scale well sections including casing, annular cement and rock formation. These are exposed to thermal cycles by using a computer controlled thermal platform, which heats up by means of electrical resistance and cools down through expansion of liquefied nitrogen. It has a temperature span from -50°C to +200°C, and adjustable heating/cooling rates and holding times. During the thermal cycling experiments, any cracking and debonding occurring in the system is continuously monitored in-situ by Acoustic Emission (AE). To demonstrate the functioning of the set-up we present some initial results obtained using ordinary Portland G cement as annular sealant. In this work, the AE events collected during cycling are compared with data from post-experiment computed tomography (CT) scans.The testing methodology presented in this paper is flexible, thus rock type, annular sealant type and casing type can be varied at will. Mud or filter cake effects can also be included. For all samples, the procedure will enable determination of when leakage paths appear (as a function of applied thermal cycles and time), where they appear (in the bulk cement or at its interfaces) and what their sizes, geometries and distributions are. This opens for improved material choices for Arctic well construction, and optimization of operational patterns and remediation strategies for the high north. Most of today's Arctic research and development (R&D) aims to overcome the many topside challenges associated with petroleum operations in the north. These are of obvious importance, comprising extremely cold Arctic temperatures, large temperature variations, harsh weather conditions, drifting ice and ice loads, strong ocean currents, long periods of darkness and remote locations. In fact, the strong focus on topside challenges has led to a down-prioritization of the many subsurface challenges in the Arctic -which stil...

Water-in-oil emulsions of a crude oil were prepared and destabilized by addition of demulsifiers. The goal of the study was to compare two different techniques used to evaluate demulsification effectiveness and to study the interfacial response of the demulsifiers. The stability of these emulsions was determined in an E Crit cell and low-field NMR, and the interfacial response of the demulsifiers was measured with the oscillating pendant drop method. The E Crit cell measures the electric field required to induce the formation of free water and the NMR monitors the vertical movement of dispersed water droplets. The stability measurements and the interfacial response gave different indications on the demulsifier effectiveness at different demulsifier concentrations. The difference could be attributed to the difference between how the stability is measured or by the effect of the electric field on the demulsifiers. The separation profiles obtained in the NMR illustrated that the demulsifiers increase the sedimentation velocity at increasing demulsifier concentration. The water recovery rates indicated that the demulsifiers had different properties. The interfacial study showed that low concentrations of demulsifiers decrease both the elastic and viscous modulus of waterÀcrude oil interface. At higher dosages both moduli increase. The different trends can be explained by considering the ratio between the total interfacial area and the demulsifier dosage. The demulsifier dosage was kept similar, but the amount of available area varied from the emulsion stability measurements and the interfacial study.