Horizontal Well Production Optimization Using Production Logs Run on Coiled Tubing in the 26R Sand Reservoir, Stevens Zone, Elk Hills Field, California
Authors: Walker Charles W. , Garcia Steven A. , Querin E. Mark , Moore David M. 
Published: December 2007

Elk Hills Naval Petroleum Reserve has drilled 19 horizontal wells to date. Some of these wells are now producing at high water cuts and/or high gas-oil ratios. The standard procedure to correct this situation in a vertical well would be to ruin production logging tools to determine the fluid entries and then isolate the offending zone(s). In horizontal wells the procedure is more complicated. Logging tools must be run on coiled tubing with integral wireline Wellbore flowing conditions and vertical segregation of fluids play a significant role in interpretation of water entry and other logs and determination of actual production rates and flow profiles.

Several horizontal wells have been logged using a variety of production logging tools run on coiled tubing. Of the wells logged, two have been reworked. In one well water cut was changed from 80% to 13% by isolating two sand layers. In another well a significant reduction in gas production was achieved by isolating several excessively high gas producing intervals. Methods used to analyze logs to identify fluids and the remedial work to isolate water and gas are discussed.

Introduction

The 26R Sand Reservoir is part of the Elk Hills Naval Petroleum Reserve #1 located in the southern San Joaquin Valley of central California, about 20 miles southwest of Bakersfield and 10 miles north of Taft. In late 1988 a horizontal well drilling program was initiated in the 26R Sand to increase recovery from the steeply dipping, layered, pressure-supported, gravity drainage reservoir. Since then 19 wells have been drilled and completed. Initial production from the earlier completed wells was characterized by high oil rates, low water cuts and solution gas-oil ratios of about 500 scf/bbl. As infill drilling continued, initial production from some wells was characterized by increased water production due to penetration of the convoluted oil-water contact. Further production of the pool and gas migration through high permeability stringers led to free gas production in some other horizontal wells. As this occurred it became necessary to attempt to optimize production by isolating the undesired water and free gas. The first step was to run production logs in these wells to identity the source of the water and/or gas production and then use the information to plan and execute remedial isolation work. These tasks were successfully undertaken in two wells. The production logging technique, the log analysis, and the resulting remedial work are discussed.

General Geology. The 26R Sand Reservoir is an Upper Miocene turbidite channel deposit that formed between three developing en echelon anticlines: The 31S, The 29R, and the Northwest Stevens structure. Continuing structural growth during and alter the deposition of the channel-fill sand resulted in what is now a steeply dipping structural/stratigraphic turbidite reservoir with dips increasing from 10 degrees near the crest to more than 60 degrees on the flanks. The pool is located on the southwestern limb of the 31S anticline and contained within the productive N and A shales.

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