A new generation Reservoir Drill-in Fluid (RDF) has been developed to mitigate the potential of damage to the producing formation and eliminate the need for post-completion cleanup.This RDF system was developed to perform synergistically where openhole gravel-packing or expandable screen completion styles are utilized. This new RDF system generates an active filter cake which is impermeable to aqueous fluids, thus reducing fluid loss into the producing formation. Concurrently, the now residual filter cake is permeable to formation hydrocarbons. This system utilizes organophilic components which generate preferential oil channels in the residual filter cake, thereby, eliminating the need for stimulation/cleanup from either internal or external chemical breakers. The preferential channels also help reduce the influx of aqueous formation and/or injection fluids. This paper details the development of the RDF system and the engineering of it on two openhole gravel-pack completions in the East Wilmington Field off the coast of Long Beach, California. It discusses the development of the system and the field trials. A maintenance schedule used by the fluid engineers for anticipated potential problems is also discussed. The field performance is discussed and lessons learned are contrasted with conceptual design. Comparative data from earlier horizontal wells are included and contrasted with respect to the RDF system design, drilling parameters and well start-up. Finally, the initial well-test data are presented. Introduction In wells that are completed with open gravel packs, particular attention and study has been given to effects of the filter cake deposited on the sandstone reservoir. Depending on the chemical and physical nature of the filter cake, there can be detrimental impairment to both the producing reservoir and to the devised completion.[1–6] One of the primary functions of a Reservoir Drill-In Fluid (RDF) filter cake is to minimize both the invasion of the fluid's filtrate and drill solids into the intended producing zone. The deposition of an impermeable filter cake is critical in various reservoirs that have openhole completions where damage to the formation cannot be by-passed by perforating. The reservoir drilling fluid filter cake should be strong enough to prevent losses and premature screen out during the gravel pack process. After the gravel packing of the well is completed, the removal of the filter cake is desired to prevent plugging of the gravel pack and the completion screen. In low pressure reservoirs, filtercake removal could be especially necessary to prevent completion blockage. The preferred method employed to clean up the drilling fluid filter cake has been the use of chemical breakers such as oxidizers, acid, enzymes, a chelating agent solution or a combination of the latter two. Placement techniques for chemical breakers have included both post-gravel-pack and during the gravel pack. When post-gravel-pack placement occurs, sometimes there may be difficulty in treating the entire filter cake causing only localize treatment. If the chemical breaker is added during the gravel-pack operation, there may be a risk of premature filtercake breakthrough which could prevent the well from being completely packed with sand. External filtercake stimulation may not effectively contact all of the filter cake resulting in patchy filtercake dissolution. Breakthrough of aggressive chemical treatments may cause the migration of fines and chemicals into the formation under high differential pressure conditions. It is against this background that a new type of Reservoir Drill-In Fluid was designed utilizing the concept of an active filter cake whereby cleanup is initiated by the oil produced out of the reservoir instead of an external means. This Active Filtercake System still deposits a protective barrier across the formation; but instead of using a conventional starch fluid-loss-control agent and conventional calcium carbonate bridging material, it uses hydrophobic components that produce an organophilic filter cake. This organophilic filter cake provides channels through which hydrocarbons are travel through the gravel and then through the completion hardware into the production tubulars. The overall objective of the Active Filtercake System is to be non-damaging to both the reservoir and the completion.

This paper is a case study calibrating well log derived lithology indicators with productivity attributes from modern production logs. More than thirty wells drilled thirty years ago into the South Ellwood Field were completed based on limited understanding of the well log responses in the complex Monterey Formation. From a retrospective study of well productivity, Wylie, Ershaghi and Christensen1 presented a pattern recognition technique for identifying productive intervals. Availability of recently obtained state-of-the-art production logs has provided invaluable information about the relevance of the well log derived potential zones to positively tested productive and undamaged intervals. This paper includes an analysis of the information processing from the Flow View and Gas Holdup Sensor Tool. A calibration of production log data and well log lithology pattern studies is the basis of designing a re-development strategy for untapped intervals not perforated in the initial completion work. Furthermore, the calibration methodology is extended to a nearby field with similar geology for reassessment of reserves potential. Introduction With the limitation imposed by regulatory agencies, the prospects of obtaining permits for re-completion rather than new drills are becoming of significant interest to California offshore producers. A major geological horizon with substantial potential in productivity is the extensive Miocene Monterey Formation. The geologic characteristics of this formation have been discussed by researchers such as Issacs2, MacKinnon3 and Belfield4. Recent reservoir studies by our team and others have pointed out the compartmentalization of Monterey horizons separated by major and minor faults. The compact laminations of various lithologies leaves very little communication path along the bedding planes. It is recognized that regional stresses are the main cause for creating a series of highly permeable brecciated and faulted intervals. As such, wells completed with course direction parallel to the brecciated intervals would turn out to be poor producers. A re-drill of such wells into the neighboring fractured intervals can change the productivity characteristics of the well. The Monterey Formation has provided substantive oil production for the State of California since its discovery in the 1970's. Its complex geological fabric consists of a mixed lithology characterized by folds, faults and fractures. Well completion in fractured intervals accounts for a large share of the oil produced from the Monterey. Identification of lithology intervals with production potential (IWPP) in the formation would serve not only to increase production, but also extend reservoir life. The major problem in deciding to re-drill or re-complete an existing well is the unavailability of complete suite of logs. From an earlier study by Wylie, Ershaghi and Christensen1, a procedure was devised where IWPP could be mapped along the well course from radar diagrams incorporating signals from seven logs. This methodology was substantiated from the correlation data observed between the historical cumulative productivity of the wells and the density of the occurrence of IWPP. With the advent of a new production logging tool (GHOST®), an opportunity developed to test the concept of proposed zonal detection method vs. the information obtained from such a modern approach to interval testing. This paper includes an analysis of the IWPP detector as calibrated vs. the GHOST® tool with the potential extrapolated to detect untapped zones behind the pipe.

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