Take Another Look at Those Gas Shows-An Update on Infill Drilling and Workover Activities in the Greater Willows and Grimes Field, Northern Sacramento Basin, California

L. K. Morrato¹ and R. J. Suchsland^2
1Venoco, Inc., Denver, CO, [email protected]
²Venoco, Inc., Yorba Linda, CA, [email protected]

The Willows and Grimes fields are two of California’s largest gas fields and are located in the northern Sacramento Basin. Lenticular deltaic sandstones within the Upper Cretaceous Kione Formation produce gas from faulted structural traps in the Willows field area. Production from the Upper Cretaceous Forbes Formation is present in both fields and is found in a variety of facies deposited within this deep-water marine turbidite system. Traps can be either stratigraphic or fault related.

In 1996 Venoco, Inc. acquired Mobil Oil’s assets in these two fields and took over operations. The following year Venoco commenced workover operations on existing wellbores and drilled 5 new wells. Results specific to the Forbes Formation supported additional infill drilling locations and the need to re-evaluate the economic potential of all zones within the Forbes that had mud log gas shows. The majority of these intervals were interpreted using open hole log data and classified as levee, overbank, and distal facies within stacked deep-water marine turbidite systems. These intervals are not the classic “multiple BCF channel type” sandstone reservoirs which have historically been the primary target of companies involved in this play.

To date Venoco has drilled 330 new well bores with a 70% completion success rate and performed over 500 workovers. The greater part of this activity has occurred during the last 4 years and each one of these new wells contains multiple behind pipe zones with workover potential. The acquisition of additional gas producing assets in and around the greater Willows and Grimes fields continues to increase development drilling and workover opportunities and has made Venoco the #1 gas producer in the Sacramento Basin.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009