Locating and Producing Bypassed Oil; A D.O.E Project Update
Authors: Walker Scott 
Published: December 2007

Tidelands Oil Production Company is conducting a Class III Near-Term Waterflood Project partially supported by the Department of Energy (DOE) titled "Increasing Waterflood Reserves in the Wilmington Oil Field Through Improved Reservoir Characterization and Reservoir Management." The project takes place across fault blocks IV & V of the Wilmington Field, Long Beach. CA. Using advanced reservoir characterization tools and reservoir management software, researchers identified bypassed oil. This oil was exploited by recompleting idle wells in danger of abandonment. Recompletion results were significantly better with a novel steam consolidation technique compared to a standard Wilmington recompletion technique.

Introduction

The objective of this DOE demonstration project is to increase waterflood reserves in fault blocks IV & V of the Wilmington Field and other slope and basin clastic reservoirs through improved methods of identifying sands containing oil bypassed by the waterflood and exploiting this oil by recompleting existing idle wells. Specific objectives include: identifying sands containing high remaining oil saturation using a multi-pole acoustic cased hole logging tool, determining geophysical parameters for interpretation of the acoustic data, demonstrating and gaining experience with a short radius lateral recompletion optimizing our standard and steam recompletion techniques, generating a three dimensional (3-d) geologic model, and transferring the technologies and methodologies developed to other operators of slope and basin clastic reservoirs.

The Wilmington Field is located within a NW-SE trending faulted anticline beneath and immediately offshore of Long Beach, CA. Reservoir sands are Pliocene and Upper Miocene-age turbidites. Targeted zones were the Tar, Ranger, Upper Terminal, and Lower Terminal which range from 2500' to 4000' in depth (Fig. 1).

Waterflood oil recovery in the Wilmington Field has been inefficient due to reservoir heterogeneities, poor vertical sweep efficiencies, high producing water cuts, poor water injection profiles, and unfavorable oil-water mobility ratios. Sands with bypassed oil are still present despite extensive waterflooding but locating these sands and quantifying the remaining oil reserves has been a formidable task.

The project was divided into seven activities as follows: reservoir characterization. reservoir engineering deterministic 3-d geologic modeling, multi-pole acoustic logging, recompletions tech transfer, and project management. Each activity consisted of several main tasks. This paper will cover each activity except project management.

Results and Data

The original strategy for this project was to identity areas of bypassed oil through reservoir characterization and reservoir engineering, verify its location behind pipe with the multi-pole acoustic sonic log, and produce the oil from recompleted idle wells. As the project advanced it became evident we had to modify this strategy as project activities evolved and progressed at differing rates. Rather than a series of activities. researchers pursued the activities in parallel.

Activity 1 Reservoir Characterization. Reservoir characterization in this project denotes not only defining gross geologic features such as structure, faults, and rock properties such as porosity and lithology, but also the distribution of remaining oil saturation in the reservoirs of interest. This requires complete integration of geologic and engineering data.

The first step in integrating the data for reservoir characterization was developing basic geologic and engineering representations of the data. This included revising geologic structure maps, isopach maps, and cross sections. Structure maps experienced the most changes and reinterpretations mainly due to the availability of new well data.

A key part of the characterization work involved developing and calibrating rock-log and fluid-log models from which to interpret the acoustic log data. Theoretical relationships, confirmed by laboratory and field data, suggest that hydrocarbon bearing rocks in situ can be differentiated from rocks containing brines using sonic velocity measurements.

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