Numerous papers have been published on the influence that kaolinite mobilization has on well productivity. However, less attention has been directed toward identifying methods to minimize the detrimental impact of this mobilization. This paper will detail the pro-active approach that the authors took in engineering solutions to enhance oil productivity by reducing kaolinite mobilization. Specifically the paper will focus on the experiences from Oseberg Sør (North Sea). Significant formation damage has been attributed to kaolinite mobilization in this field. This damage can occur at any stage within the well lifetime from initial drilling and through the production lifecycle. SPE 107758 provided details of a unique chemical that can be incorporated into scale inhibitor squeeze treatments to reduce kaolinite mobilization while a well is in production. This paper will focus on the development of smart mud filtrate technology that incorporates kaolinite fixation agents that minimize clay mobilization within the near wellbore during drilling.
Introduction
There are countless ways to cause formation damage; however the most difficult mechanisms to prevent are those which are caused by a combination of the nature of the reservoir and production from that reservoir. These mechanisms can be considered "natural" and affect productivity whether the drilling and completion fluids are present or not. Examples of "natural formation damage" are organic and inorganic precipitation resulting from a reduction of pressure in the near-wellbore region1 or the migration of native fines towards the wellbore and subsequent plugging of pores. Fines migration and in particular the issue of kaolinite fines migration, causing formation damage, is described extensively in the literature.2,3,4 In answer to the problem highlighted here and in the 2007 paper by Fleming et al.,5 we have extensively researched the issue of formation damage created by kaolinite fines and have designed an advanced drilling fluid filtrate to combat this problem. The filtrate is designed to treat the near-wellbore area even before and during the penetration of the specific depth by the drill bit. This early treatment of the formation is intended to stabilize the fines in the near-wellbore area before they have a chance to migrate. The treatments are designed to prevent the migration of kaolinite during production. A significant development in the study of treating kaolinite migration in the Oseberg Sør formations was the realisation that it is oil flow causing the most significant migration in these formations. The reason for this is that the fines range from mixed wettability to oil-wet.
Theory
A number of return-permeability tests have previously been performed on Oseberg Sør core material from the Ness, Middle & Upper Tarbert and Upper Jurassic formations in a number of different laboratories. A common damage mechanism was noted throughout the core floods. The mechanism was migration and plugging of pores by kaolinite clay particles even at very low flow rates. Evidence for fines migration was observed both in the increasing differential pressure during steady state dead crude oil flooding of the core plugs @ Swi and in post-test geological analysis (SEM, Cryogenic SEM and thin section). An indication of the mechanism was also highlighted in SPE 107758 where a squeeze treatment provides a marked increase in production which then declines with continued oil production. Semi-quantitative mineral analysis in the form of X-Ray Diffraction (XRD) was performed on the core material and displayed approximately 15% kaolinite. Muecke15 explained that fine particles tend to remain in phases that wet them. This was taken into account when the cores were found not to display fines migration during water flooding, as the flowing water could not migrate the oil coated fines, but crude oil did during oil flooding.
