Geological Factors on the Design and Surveillance Of Waterfloods in the Thick Structurally Complex Reservoirs in the Ventura Field, California
Authors: Schneider John J. 
Published: December 2007

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Abstract
The nucleus of an operationally sound waterflood is a geologic framework that defines reservoir continuity relative to its capacity to transmit fluids as well as restrict fluid movement. The structural complexity, thick oil column, long producing intervals, and highly deviated wells of the Ventura field, located on a tightly folded and faulted anticline, have necessitated the development of new geologic techniques to adequately describe the boundaries and internal continuity of the sandstone reservoirs. Contour maps on multiple horizons and pattern recognition are used to delineate pattern recognition are used to delineate contour anomalies that often indicate faults with small apparent displacements. To aid the reservoir engineer during the planning phase, the modified palinspastic map has been designed to show the spatial relationships between oil accumulation, fluid barriers, and well bores.
Geologic surveillance is maintained over Ventura waterfloods because a well's water injection capacity and profile are often related to the effects of geologic processes. Thief zones frequently occur in injection wells that penetrate high permeability sands in close penetrate high permeability sands in close proximity to cross faults, while impairment of proximity to cross faults, while impairment of reservoir properties has been documented in wells adjacent to major thrust faults.
Computer techniques are utilized in preparing studies and in updating maps of preparing studies and in updating maps of operational waterfloods.

Introduction
While preparing for supplemental recovery activities in the Ventura field in the mid-1950's, the Shell Oil Company concluded that previous geologic studies, although adequate previous geologic studies, although adequate for primary development, lacked the detail required for sound waterflood planning. To date, nine geologic studies have been completed specifically for waterflooding.
The magnitude of each study as well as many of the interpretive techniques and methods of illustration have changed but the purpose has remained the same. The initial purpose has remained the same. The initial geologic framework must define reservoir continuity in terms of its capacity to transmit fluids as well as restrict fluid movement. All known and suspected fluid barriers must be documented to achieve proper balance between production and injection wells. Sand quality production and injection wells. Sand quality and continuity, structure, and fluid distribution, as well as mechanical factors such as the existing primary well spacing and completion interval must be considered.