Reservoir Characterization of the Tulare Formation Sands at the South Belridge Field Using a Team Approach
Authors: Holman M.L. 
Published: December 2007

Abstract
Current surveillance efforts in the South Belridge Tulare Formation rely heavily on the integration of marker data with other sources of data such as production rates, temperature logs, and net pay counts. Examination of the marker system in place at South Belridge and relevant core data during 1993-94 revealed serious flaws in the geologic data used in surveillance processes. Early in 1995, team restructuring created a core group of staff to modify and correct the marker system as well as design new surveillance tools. Approximately eight members (one-half) of the Tulare engineering group were involved full-time in this effort. The results exceeded expectations, with surveillance process cycle-time reductions of 70%, steam cuts of 40,000 bspd, and the identification of several new horizontal well locations in 1995.

Introduction
One of surveillance's key products is an understanding of individual sand performance in a given field. With the availability of easy to use databases, surveillance data can be loaded and simple queries written to create sand-specific maps. Implicit in the creation of those queries, however, is the assumption that all of the data components (geological, petrophysical, production, operational, and others) in the database are accurate.
Unfortunately, that assumption was not valid at CalResources' acreage at the South Belridge field before 1995, particularly with respect to the geological data. Please note that hereafter, references to South Belridge will apply only to the northern (CalResources operated) half of the field. Close examination of the marker system in place prior to 1995 showed that the stratigraphic and structural relations between markers were no longer reliable and that the markers were unsuitable for use in geology-dependent applications. During this period, surveillance was conducted by a team composed of three reservoir engineers, seven production engineers, and three support technicians. Geological and petrophysical engineering staff were in a "consulted as needed" position on this team.
Several possible solutions to the poor geologic data integrity issue were proposed by the surveillance team, including: delete and stop using the geologic data; understand the errors and take no further action; fix the geologic data in a short (and therefore high-level) effort; and reorganize and completely fix all geologic and relevant surveillance data. Ultimately, the last solution was chosen, and the result was the dissolution of the old surveillance team, and the creation of a new reservoir characterization team.
The team's composition was one geological engineer, one petrophysical engineer, four production engineers, three reservoir engineers, and nine support technicians. The focus of this team was to first select an area of interest, verify and correct all available surveillance data, and ultimately make and implement operating strategy decisions. The team's products were steam cuts, definition of vertical and horizontal well opportunities, and financial performance optimization.

History
The South Belridge Field is located in northwestern Kern County, California, USA, approximately 40 miles west of Bakersfield. The Pleistocene Tulare Formation at South Belridge is the shallowest producing horizon, and is currently under extensive steam flood. CalResources' Tulare production is currently 35,000 bopd from approximately 1,600 active producers.
P. 913