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.

Summary Squeezing of clean, high-permeability reservoirs frequently results in relatively short treatment lifetimes because of the low inhibitoradsorption rates achieved. One of the main controls on inhibitor retention is near-wellbore mineralogy. Clay-rich reservoirs that contain abundant kaolinite, for example, often have long squeeze lifetimes because enhanced inhibitor adsorption can occur on the clay surface. The occurrence of calcium carbonate (CaCO3) cement in the near-wellbore region can also enhance inhibitor retention by forming a Ca2+/inhibitor complex. Previously published research (Fleming et al. 2009a) demonstrated the potential to mechanically alter the near-wellbore region through incorporation of low concentrations of kaolinite and organosilane. The data presented in the present work show that the additional incorporation of calcium carbonate provides a step change in the potential squeeze lifetimes achieved. This paper will present the results of using low, nondamaging concentrations of kaolinite and calcium carbonate particles in the preflush followed by scale inhibitor and organosilane in the main treatment. The kaolinite particles are retained in the near-wellbore region by the organosilane and enhance the number of potential sites for inhibitor adorption. At the same time, dissolution of the calcium carbonate particles by the acidic scale inhibitor forms a Ca2+/inhibitor complex that further enhances inhibitor retention. A review of the technology performance envelope has been made through coreflooding that includes optimizing the concentration of injection particles vs. permeability, the ratio of injected kaolinite to carbonate particles, and performance at elevated temperature (175°C) along with an assessment of how often a well would require retreatment with particles. The latter has involved successive coreflooding of the same plug with the full treatment package followed by brine flowback and retreatment with scale inhibitor alone or with organosilane. This information can be used by the assets in their evaluation on potential use of the technology.

Scale control during Alkaline Surfactant Polymer flooding can be challenging1,2,3 The effective performance of scale inhibitors is a problem, given the high oversaturation expected due to mixing of injected alkali and formation water. Moreover, ASP creates a high pH condition in the reservoir and at production wells. Selecting an effective inhibitor and achieving a long return profile following scale inhibitor squeeze treatment under these conditions can be difficult. This paper describes the studies performed to address the scale management issues for a field where ASP flooding is planned. Scale prediction was carried out and a list of scale inhibitors was screened through performance testing. A number of ASP-specific factors were taken into account for the modeling and testing, including the injected and expected produced chemical concentration, salinity change and chemical compatibility. The results have shown that under these particular field conditions, a conventional penta-phosphonate can provide effective scale control in this field during ASP flooding. Initial core floods indicated that long squeeze life time can be achieved, but the application of the inhibitor in a typical acid form resulted in severe formation damage. A non-damaging formulation was designed by adjusting the inhibitor concentration and partially neutralizing the inhibitor package. The final testing results of the designed inhibitor package show that an effective scale inhibitor squeeze can be attained in the production wells during ASP flooding. More significantly the work demonstrated that the composition of the produced water (% of ASP injection water) producing from a particular zone has a dramatic impact on the potential squeeze lifetimes.

Scale control during Alkaline Surfactant Polymer (ASP) flooding is a recognised challenge especially following ASP breakthrough at the production wells, due to continual mixing of the high pH ASP waters with reservoir brine. The effective performance of scale inhibitors (SIs) is a problem, given the high oversaturation expected due to mixing of injected alkali and formation water. Previous work (SPE 141551) described this challenge for a conventional system whereby ASP was injected into a reservoir containing low salinity / low divalent ion Formation Water (FW). This work showed that chemical performance (SI/ brine compatibility and performance) could be achieved using conventional inhibitors and that treatment of the production wells via downhole squeeze treatments was achievable. It also demonstrated that the production of high pH ASP fluids had a considerable impact on the retention and release properties of the chemicals. This paper progresses significantly from the previous work by examining a field case study. Although the formation water is a low salinity / low divalent cation brine similar to that in the earlier example, this field represents a considerably more severe scaling challenge since it has already been flooded with Sea Water (SW). The SW contains considerably higher divalent cation concentrations (c.f. Ca2+ ~ 450mg/l vs. ~40 mg/l for the formation water) and results in a considerably more severe challenge in terms of SI/Brine compatibility and chemical performance when examining a range of conventional SI's. The paper describes extensive modeling of the in situ conditions for this field following ASP flooding, extensive scale inhibitor performance tests across a wide range of conditions and mixtures of ASP/FW/SW together with a series of core flood tests to assess the potential for squeeze treatments in this new pilot ASP system. For the pilot, reservoir modelling was essential to simulate the expected mixture of ASP/FW/SW which would be produced, such that chemicals could be targeted for the expected produced mixtures (Note: increased FW:SW ratio results in more achievable inhibition) allowing chemical selection for squeeze. The pilot ASP flood in this field is now planned for 2014.

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.