Conceptual Model of FBIIA, Wilmington Field, from Field Performance Data
Authors: Akkutlu I.Y. , Handy L.L. , Ershaghi I. , Mondragon J.J. 
Published: December 2007

This paper presents calibration methodologies for representation of the Tar Zone in the FBIIA of the Wilmington Field using historical performance data.

The early history dating back to the 1940's includes the superimposed effect of compaction and mild aquifer influx. Because of the complex nature of compaction and considerable resultant changes in the storativity of the producing formation, an accurate conceptual model is required to describe the early history for simulation purposes. In the absence of comprehensive core data, pressure transient tests and other diagnostic field mapping databases, certain analytical reservoir engineering techniques are proposed to help in estimation of the influx and compaction.

The heterogeneous turbidite nature of the producing formation make the lateral extrapolation of local estimates quite uncertain. Localized estimation techniques employed, provide the foundation for a production-based data estimation.

Of particular interest are estimation methodologies required to reconcile initial fluid in place and in-situ variations in reservoir permeability and field based relative permeabilities. Signals imbedded in the production data and performance of individual wells as affected by the steam pilot were interpreted to arrive at first stage heterogeneity map of the fault block. Interpretations from injection surveys, were integrated to conceptualize the vertical permeability structure of layers.

Introduction

The Wilmington Oil Field, since 1940's, is known as one of the largest oil fields in the U.S. It's location and size relative to the other oil fields in Southern California area is shown in Fig. 1. A series of transverse normal faults divide the field into eight major operating units. The Fault Block IIA (FBIIA) is located in the central onshore section of the field between the Wilmington and the Ford Faults. FBIIA consists of seven producing zones within the Monterey (middle Miocene), Puente (upper Miocene), and the Repetto (Pliocene) formations ranging in depth from 2000 ft to 6500 ft. The Tar Zone, middle Reppetto formation (lower Pliocene), is the shallowest reservoir and is composed of four major soft and unconsolidated sand layers: T, DU, D1 and D2 with respect to increasing depth. The main characteristics of the Tar Zone are its highly porous shale impregnated sand structure containing relatively high viscosity oil. The block average rock and fluid properties based on earlier obtained core and well log data and laboratory test results are given in Table 1.

Primary production from the Tar Zone of the FBIIA started in 1937 and continued until pressure maintenance waterflooding in the early 1960. The production mechanisms during this period were solution gas drive, natural water drive and compaction drive. Because of adverse water-oil mobility ratios in the reservoir, waterflooding was deemed ineffective and uneconomic. Following a pilot in 1982 and a number of phases, today the oil recovery is mainly by field wide steam flooding. Figure 2 shows total daily production history of oil, water and gas in the Tar Zone FBIIA in yearly intervals. This paper presents a methodological approach to describe a conceptual reservoir model of FBIIA Tar Zone, using historical production and average static bottom hole pressure data. In many cases these data are the only available information for engineers and their application to certain estimation methods could offer invaluable information for numerical model construction.

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