Applied research has been undertaken to examine the potential of kaolinite combined with a kaolinite fixation agent to;Increase squeeze lifetime through alteration of near wellbore surface characteristics and mineralogy and,Provide water shut off control. With respect to enhancing squeeze lifetime, it is documented that kaolinite increases the quantity of inhibitor adsorbed. Conversely, clean sandstone with low clay content commonly provides a poor substrate for adsorption. Furthermore, in reservoirs that experience near wellbore formation damage due to kaolinite mobilisation, it has been shown that use of a fixation agent as part of a squeeze treatment can increase squeeze lifetime. Using these facts, research has assessed the feasibility of injecting microcrystalline kaolinite (average particle size 2 µm) combined with the fixation agent and scale inhibitor as a means of mechanically altering near wellbore mineralogy and surface property characteristics within clean, high permeability sandstones. The testing has been designed to mimic the squeeze procedure used in the field for performing such a job and involves no additional steps to that used in a normal squeeze, i.e. Pre-Flush ? Main Treatment ? Over-Flush. The paper presents the results of coreflood experiments that have been undertaken to demonstrate "proof of concept" for the above along with examples of potential field applications. A further concept, born from the initial idea, was the use of kaolinite and fixation agent for efficient, low cost, environmentally friendly water shutoff. There are several available products for water shutoff but the disadvantage of these is that they are not acceptable for use in Norway due to poor environmental characteristics. Hence, there was a need to fill this gap by developing water shutoff technology to meet country specific environmental legislation. The paper provides details of coreflood testing, where an excess of kaolinite has been used to form an internal and external filter cake that is attached to the wellbore face and within the near wellbore using the fixation agent. The paper draws on data from StatoilHydro operated fields in order to highlight the potential of this innovative approach to downhole scale management and water control.

Over the lifetime of a well it is possible that several squeeze operations will be performed depending on scaling severity. Downhole squeeze operations have been performed for many years and have on the whole been an effective scale management tool. However, the long term impact that successive squeezing has on treatment lifetime and well productivity has received little attention. This paper will address these issues by comparing the results from a unique sequence of long term corefloods that were designed to replicate five successive treatments on the kaolinite rich, Middle Tarbert core from the StatoilHydro operated field, Oseberg Sør. Relatively few squeeze treatments have been performed on this field, and the coreflood results have been up-scaled to provide a potential prediction of the effects of long term squeezing and well productivity on Oseberg Sør. Furthermore, the laboratory results have been cross-checked by comparing with the Heidrun field that has been squeezed for many years. Heidrun is an analog of Oseberg Sør with kaolinite rich producing intervals and similar productivity issues related to kaolinite mobilisation. Introduction In many respects the opening sentence of Vetter's article (Vetter, 1973), "There are a number of gaps in our knowledge of the principles involved in the squeezing process," is still valid 25 years after publication. This paper will address one of those identified knowledge gaps which is the effect that well lifetime squeezing has on treatment performance and productivity. Depending on the scaling severity, a well can require squeeze treatment as often as 10 days as is the case for the Miller field (Wylde et al, 2007) or after several months, e.g. Oseberg Sør field (Fleming et al, June 2007). With regards to the latter field, a study was initiated to determine the long term impact of squeeze treatment on well performance and this forms the basis for the paper. The laboratory results will also be compared to the StatoilHydro operated Heidrun field that has been squeezed over several years. The Oseberg Sør field is situated 130 km west of the Norwegian coast on the eastern flank of the Viking Graben structure (Fig. 1). It consists of fault bounded structural units of varying geological complexity. Within these units the reservoir intervals are of moderate to poor quality and can exhibit strong contrasts in permeability and formation water composition. Reservoir pressure support is provided by combined injection of gas and Utsira aquifer/produced water. The wells are a combination of platform and subsea and include extended reach horizontals with complex geometry and lesser numbers of vertical wells.

Summary Applied research has been undertaken to examine the potential of kaolinite combined with a kaolinite-fixation agent to increase squeeze lifetime through alteration of near-wellbore surface characteristics and mineralogy, and to provide water-shutoff control. With respect to enhancing squeeze lifetime, it is documented that kaolinite increases the quantity of inhibitor adsorbed. Conversely, clean sandstone with low clay content commonly provides a poor substrate for adsorption. Furthermore, in reservoirs that experience near-wellbore formation damage because of kaolinite mobilization, it has been shown that the use of a fixation agent as part of a squeeze treatment can increase squeeze lifetime. Using these facts, research has assessed the feasibility of injecting microcrystalline kaolinite (average particle size 2 µm) combined with the fixation agent and scale inhibitor as a means of mechanically altering near-wellbore mineralogy and surface-property characteristics within clean, high-permeability sandstones. The testing has been designed to mimic the squeeze procedure used in the field for performing such a job and involves no additional steps to those used in a normal squeeze (i.e., Preflush, Main Treatment, Over-Flush). The paper presents the results of coreflood experiments that demonstrate "proof of concept," along with examples of potential field applications. A further concept, born from the initial idea, was the use of kaolinite and fixation agent for efficient, low-cost, environmentally friendly water shutoff. There are several available products for water shutoff, but the disadvantage of these is that they are not acceptable for use in Norway because of poor environmental characteristics. Hence, there was a need to fill this gap by developing water-shutoff technology to meet country-specific environmental legislation. The paper provides details of coreflood testing where an excess of kaolinite has been used to form an internal and external filter cake that is attached to the wellbore face and within the near-wellbore region using the fixation agent. The paper draws on data from StatoilHydro-operated fields in order to highlight the potential of this innovative approach to downhole scale management and water control.

Summary Over the lifetime of a well, it is possible that several squeeze operations will be performed, depending on scaling severity. Downhole-squeeze operations have been performed for many years and have been an effective scale-management tool on the whole. However, the long-term impact successive squeezing has on treatment lifetime and well productivity has received little attention. This paper will address these issues by comparing the results from a unique sequence of long-term corefloods designed to replicate five successive treatments on the kaolinite-rich, Middle Tarbert core from the StatoilHydro-operated field Oseberg Sør. Relatively few squeeze treatments have been performed on this field, and the coreflood results have been upscaled to provide a potential prediction of the effects of long-term squeezing on well productivity on Oseberg Sør. Furthermore, the laboratory results have been cross checked by comparing them with the Heidrun field, which has been squeezed for many years. Heidrun is an analog of Oseberg Sør, with kaolinite-rich producing intervals, and has similar productivity issues related to kaolinite mobilization. Introduction In many respects, the opening sentence of Vetter (1973) is still valid 35 years after publication: "There are a number of gaps in our knowledge of the principles involved in the squeezing process." This paper will address one of those identified knowledge gaps, which is the effect well lifetime squeezing has on treatment performance and productivity. Depending on the scaling severity, a well can require squeeze treatment as often as every 10 days, as is the case for the Miller field (Wylde et al. 2007), or after several months [e.g., Oseberg Sør field (Fleming et al. 2007a)]. With regard to the latter field, a study was initiated to determine the long-term impact of squeeze treatment on well performance. This forms the basis for the paper. The laboratory results will also be compared to the StatoilHydro-operated Heidrun field that has been squeezed over several years.

This paper presents a case history of scale treatments performed in a well producing in the North Sea. Kvitebjørn is a gas and condensate producer with high reservoir pressure (480bar) and high temperature (152°C). Well A-7 T2 started production in January 2014 and has a history of a carbonate scale precipitation.A few months after start-up, formation water breakthrough was observed in addition to a reduction in Production Index. Due to challenges with removing scale by wireline, interventions using scale dissolver were performed in late 2017 and early 2018. The second dissolver treatment was followed by a scale squeeze to protect the well from further scaling. The chemicals used were qualified according to the Operator’s technical specifications. Due to high reservoir temperature, thermal stability was vital in the qualification process. The formation permeability was moderate, which was important to consider when evaluating the risk of formation damage. The environmental category for the chemicals versus their performance was an important factor in the qualification process. Modelling programs were used to assess placement distribution under various bullhead pumping conditions. For the scale squeeze, a modelling program was used to simulate treatment lifetime using isotherms derived from laboratory core flood testing. Water samples were taken from the well and analysed onshore in the supplier’s laboratory. Following the scale squeeze, water samples were taken from the well during the entire treatment lifetime. Ion concentrations and residual inhibitor concentrations were monitored together with production parameters to assess the scale situation in the well. Following the treatments, the well showed an increased gas production. The well produced 1.2MSm3 at 40% choke before the treatments and 1.2MSm3 at 6-7% choke after. Laboratory work combined with field experience from this first well that was treated, forms the basis for possible future treatments. Being able to treat wells through pro-active and efficient scale inhibitor squeeze treatments will allow for continued production of wells exposed to scale risk, avoiding the cost and risks associated with mechanical scale removal and avoiding production deferral associated with potential dissolver jobs.