OptimizatioBl of a Mature Steam Flood Utilizing Horizontal Well?, Midway Sunset Fiend
Authors: Kuhach J.D. , Myhill N.A. 
Published: March 2010

Three short radius horizontal wells drilled in the steeply dipping Sub-Hoyt "E" sands of the Midway Sunset Field showed encouraging performance. These successes prompted a three-dimensional thermal simulation study to evaluate additional horizontal well potential and to optimize the remaining steam flood development. During this study, four medium radius horizontal wells were also drilled with very encouraging initial performance, All seven wells seem to perform within simulation and analytical expectations.

This study improved the understanding of reservoir dynamics leading to a revised operating and development policy. Key conclusions are to place horizontal wells close to the oil-water contact, drill long horizontal laterals, and heat the oil in proximity to the horizontal wells. These give an optimum recovery, a more stable oil-water contact, and minimize water coning problems. Simulation results and additional field surveillance led to a revised field development plan currently underway in this mature steam flood.

Introduction

Historically, California's heavy oil fields have been developed with steam soaking and steam flooding of reservoirs developed with conventional, vertical wellbore. In 1990–1991, three short radius horizontal wells were drilled in the heavy of E sands of the Midway Sunset field to test their potential in mature thermal recovery projects. The success of these wells, described in detail in the literature(1), prompted a stimulation study to determine the potential long-term impact of horizontal wells on E sand reservoir management. Since the start of this study, four medium radius horizontal wells have been successfully drilled and produced in the E sands. Based on study recommendations and current success, horizontal wells should play a key role in the optimization of remaining E sand oil recovery as well as similar Midway Sunset reservoir.

Geological Setting/Reservoir Description

The Midway Sunset field is located in the southwest portion of the San Joaqun Basin in Southern California (Figure I). It is classified as a "super giant," with ultimate reserves of 440 million cubic metres. The majority of the field's production and reserves comes from Upper Miocene turbidite sand reservoirs. These sands were deposited in a series of interfingering submarine fans, and in some areas accumulated up to 460 m in thickness. As one of these fans. the Sub-Hoyt sands consist of massive to thin bedded unconsolidated sands and sandy conglomerates, interbedded with diatomaceous clays and siltstones.

The E sands consist of amalgamated very fine to coarse grained sands which dip at 35 to 50 ° to the northeast (Figure 2). They have an average vertical thickness of 120 m, with a very high total net sand thickness to gross interval thickness ratio (N/G) of 0.85. The oil sands overlie an inactive aquifer.

Production History

The Sub-Hoyt E sands have produced 12 - 13 ° API crude since the early 1900's. Wells produced on primary until steam soaks were introduced in [ate 1966. Steam soaking was expanded through the mid 1970's to enhance the gravity drainage recovery mechanism. Steam flood pilots began on the L&H and Anchor leases in the late 1970's.