Planning the First Horizontal Well for the Shallow Oil Zone of Elk Hills Field, Kern County, California

Abstract

Abstract A horizontal well was successfully drilled and completed in the Shallow Oil Zone (SOZ) of the Elk Hills field (Naval Petroleum Reserve #1), Kern Co., California. The reservoir formation is Pliocene age, low pressured, unconsolidated sands separated by thin, impermeable shales. The well was drilled to a TVD of 3,998 feet and an MD of 5,648 feet. A 1,111 ft lateral was drilled at 900 and 580 ft of that was completed in two sands. Adjacent wet sands, faults and a thin pay zone were some of the challenges faced in planning and drilling this well. This paper addresses the reservoir characteristics of the pay zone, planning of the well, and drilling and completion methods that were used. Results of drilling operations, completion operations, production performance and costs are provided, and some comparisons are made to offset vertical wells. Introduction Horizontal drilling has proven itself in recent history as a highly profitable alternative to conventional vertical drilling. In a paradigm shift, horizontal wells have become common in some applications, displacing vertical wells. The Shallow Oil Zone at the Elk Hills field was originally developed through vertical drilling as a strategic reserve under the management of the Department of the Navy (now under the U.S. Department of Energy). Of the estimated 1.6 billion barrels of oil in place in the SOZ, approximately 450 million barrels have been produced since the early 1900s. The SS-1 (Sub Scalez One) is the most significant oil producing sand within the interval referred to at Elk Hills as the SOZ. Gravity drainage and low reservoir pressure in the SS-1 sand have led to a low reservoir decline rate and long productive well lives. This is especially true along the southern flank of the anticlinal structure which comprises the primary trap for oil and gas in the SS-1 sand. Realizing this, recent planning for the SOZ has focused on accelerating recovery and increasing recoverable reserves. The SS-1 sand at Elk Hills has reservoir characteristics similar to other reservoirs that have been exploited successfully by horizontal well technology. Initial evaluation suggested that horizontal wells could economically accelerate and increase recovered reserves if several challenging obstacles could be overcome. Reservoir Characteristics The SS-1 is a member of the Pliocene San Joaquin Formation and has been divided into twelve sublayers within the eastern portion of the field. These sublayers are separated by thin shales which serve as vertical seals through most of the productive area. Gas/oil and oil/water contacts vary between sublayers. Individual sublayers vary considerably in thickness across the field and pinch out locally, and to the west entirely, along trends easily defined by well logs. P. 185