Quartz arenites are very clean quartz sandstones with unusually high permeabilities for any given porosity. This is attributed to the presence of large, clean pores which are often well connected. These large pores are susceptible to drilling damage, mainly from the invasion of solids. This paper presents both laboratory and field data on the development of drilling fluids to minimise damage in quartz arenites. The required changes in field mud engineering practices, to achieve improved well performance, are discussed. Field experiences are presented, including the impact of the modified mud systems and engineering practices on the resulting skin factors. Introduction Quartz arenites are very clean quartz sandstones with unusual poro-perm properties. Significant permeability is retained at low porosities and as the porosity increases the observed permeabilities are much higher than would normally be predicted. This unusually high permeability is attributed to the presence of large, clean pores which are often well connected. Despite these favourable characteristics, many wells drilled in quartz arenite reservoirs have not been as productive as expected, and have had high skin factors. In the absence of reactive clays, many recognised damage mechanisms are not applicable in quartz arenites, yet drilling damage is still seen to occur. Laboratory data shows that conventionally designed drilling fluids can cause high levels of damage, but that mud filtrates alone do not cause significant damage. The main damage mechanism is solids invasion into the large pores, and it is shown that changes in drilling fluid design can minimise this damage. These modifications to the drilling fluid require changes in field mud engineering practices, in order to achieve improved well performance. Field experiences are presented, including the impact of the modified mud systems and engineering practices on the resulting skin factors. The Mirador Formation Quartz arenites are clean quartz sandstones, which contain more than 95% quartz. The Mirador formation in the Cusiana field in Colombia is a quartz arenite, with a very low clay content. The typical mineralogy is 78% quartz grains, 14% quartz cement and 8% porosity. Despite low porosity, permeabilities are high. For example, 8% porosity corresponds to about 100mD and 10% porosity to about 4o0mD, although permeability is dramatically affected by grain size. The permeability of the very coarse grained sand is about 800mD at 10% porosity, whereas the permeability of the fine grained sand is about 90mD at the same porosity. The completed intervals have a wide range of permeability, sometimes from less than 10mD to more than 5000mD (the >1000mD sands generally have low thickness). The Mirador has very low vertical permeability, compared to horizontal (Kv/Kh = 0.1 or less, dependent on formation permeability). Reservoir pressure is approximately 5300psi and reservoir temperature is 127 F. Pore Size Distribution. The high permeability at low porosities is a result of large pore size and good interconnectivity. The median (D50) pore size in the lower Mirador is usually about 60, although in the high permeability streaks the D50 pore size has been measured as high as 110. More importantly, typical pore size distributions show the D95 to be substantially higher than the Dso (Fig. 1). As an example, a core with Dso pore size of 60 will have a D95 of 350-400. By converting a typical pore size distribution to a predicted permeability distribution (Fig. 2) it is apparent that the large pores dominate the permeability. In the example presented, the largest 30% of the pores account for about 85% of the permeability. Consequently, the large pores need to be protected in order to minimise damage. Compressive Strength. As a result of the secondary quartz cementation, which produced the low porosities, the Mirador sands also have high unconfined compressive strengths. P. 147

This paper describes properties that are desirable in a water-based filter cake and test methods that can be used to measure these properties. One method uses a dynamic filtrate-loss apparatus that stirs the fluid mechanically during filtration. Test results show that the initial dynamic filter-cake formation is very important in controlling all future filtration properties and cake quality. The various factors affecting filter-cake quality and how they can be controlled to give better field performance are discussed.

The E&P industry is a highly technical and complex world which is inhabited by skilled professionals of many different specializations and backgrounds working all over the globe. In order for an organization to perform effectively, it is very helpful to have a shared view of that world and a common vocabulary to describe its artifacts, processes and challenges. Over the past two years, we have developed a multi-faceted taxonomy that describes the realm of technical services in the upstream E&P domain. It comprises the areas of E&P disciplines, application methods and environments, technical services, and problem diagnoses. This taxonomy is finding wide use within our technical communities and has been embodied into computer-based applications in the areas of collaboration (workspaces and wikis), knowledge capture, expertise identification, field technical support and "smart" enterprise search. This paper discusses our methodology in establishing and reviewing the E&P taxonomy within a large technical community and how we are applying it to solve real-world business problems.

Today's oil and gas industry relies increasingly on integrated multi-disciplinary services to provide effective risk management, wellbore and reservoir delivery while minimizing operating costs, cost of failure and non-productive time (NPT). New collaboration technologies enable the rapid storage, transfer and consumption of information and require robust but flexible knowledge management techniques to fulfill the requirements of a global learning organization. New tools need to be developed and successfully implemented tools need to be expanded to enable cross-disciplinary teams and communities the ability to capture, share and reuse validated knowledge efficiently. This paper presents how a single-domain lessons-learned system was extended to represent the entire spectrum of the upstream industry; assuring interdisciplinary information is reusable in multiple communities and market segments. The paper presents the challenges inherent in leveraging a common classification scheme; lessons-learned framework, enterprise platform, and search-and-retrieval systems with the goal of connecting people and making the collective knowledge seamlessly accessible across different business units, time zones and geographies. Also discussed is how building a common framework and incorporating the lessons-learned system into communities of practice, training and certification programs helps drive acceptance/implementation of the program. Finally, we showcase how the system has been used to deliver game-changing performance in time savings to locate relevant information and how re-use of stored knowledge enables performance improvements in wellbore delivery.