Abstract

The Kern River Field is a large, shallow, heavy oil reservoir located five miles northeast of Bakersfield, California. Both reservoir and fluid characteristics are very favorable for thermal recovery methods. The unconsolidated oil sands exhibit high permeabilities of 1–5 darcies (1–5 μm2) and porosities of 28–33%. Reservoir pressure is low, averaging 100 psig (690 kPa). Oil viscosities average 4000 cp (4 Pa ·s) at reservoir temperature and drastically reduce at elevated temperatures.

Previous articles1,2,3,4 have been published concerning steamflood pilot design and behavior in the Kern River Field. This paper updates previous articles with a review of 263 steamflood patterns started in 1970 and 1971. The effects of sand thickness, completion interval and heat injection rates on steamflood recovery will be analyzed. Effective project evaluation through the use of temperature observation wells, coring, casingblow measurement and production from wells completed solely in the steamflood interval is emphasized. Problems of evaluating steamflood performance in amulti-zone reservoir are discussed and two field tests for improvement of steamflood sweep efficiency are also presented.

Introduction

Getty Oil Company attempted the first steamflood pilot in the Kern River Field in 1964 with four inverted 5-spot patterns on the Kern property in the center of the field, as shown in Figure 1. The design and results of this pilot proved successful as reported by Bursell.2,3 In 1968 and 1969, eight additional steamflood pilots were installed in the Kern River Field to evaluate the steamflood response of other oil sands in different locations within the field. The successful response of these nine to twelve pattern pilots led to the first major expansions in 1970 (189 patterns) and 1971 (325 patterns). The initial steamflood is now complete or is approaching completion in these early expansions, and results of these projects will be analyzed within this paper. Through the use of coring, temperature observation wells, production from wells completed solely in the steamflood interval, and casing blow measurement anaccurate evaluation of actual steamflood performance is attempted.

Post displacement coring in the pilot steamflood projects revealed poor vertical sweep efficiency which led to two different field tests to improve sweep efficiency within the 1971 expansion projects. A review of the two field tests is presented.

Field Description1

The Kern River Field reservoir is comprised of the Kern River Series sands. The Kern River Series consists of an alternating sequence of unconsolidated sands with considerable interbedded silts and clays. A typical cross-section of the various sands is shown in Figure 2. The four main oil sand intervals are defined (C, G, K and R) and can be correlated across the entire field. The sub-divisions of the main intervals comprise the steam displaceable zones which range in thickness from 25 to 125 feet (7.6 to 38.1 m). These sands characteristically exhibit 30% porosity and 1–5 darcies (1–5 μm2)permeability.

Structure of the Kern River Field is a simple homocline dipping at 3–6 ° to the southwest. The updip oil sands pinch out and the productive downdip area isbound by an oil-water contact. Oil sands are present at depths of 400–1,400 feet (122–427 m).

Produced oil gravity varies across the field from 9 ° to 16 ° API. Corresponding viscosities also vary greatly from 10,000 to 600 cp (10.0 to 0.6Pa ·s) at 100 °F (38 °C). Heat very effectively reduces the viscosity of the Kern River crudes. Typically there is a 100 to 500 fold decrease in viscosity at 250 °F (121 °C) which is the reason of the success of thermal operations in heavy oil.

Field Description1

The Kern River Field reservoir is comprised of the Kern River Series sands. The Kern River Series consists of an alternating sequence of unconsolidated sands with considerable interbedded silts and clays. A typical cross-section of the various sands is shown in Figure 2. The four main oil sand intervals are defined (C, G, K and R) and can be correlated across the entire field. The sub-divisions of the main intervals comprise the steam displaceable zones which range in thickness from 25 to 125 feet (7.6 to 38.1 m). These sands characteristically exhibit 30% porosity and 1–5 darcies (1–5 μm2)permeability.

Structure of the Kern River Field is a simple homocline dipping at 3–6 ° to the southwest. The updip oil sands pinch out and the productive downdip area isbound by an oil-water contact. Oil sands are present at depths of 400–1,400feet (122–427 m).

Produced oil gravity varies across the field from 9 ° to 16 ° API. Corresponding viscosities also vary greatly from 10,000 to 600 cp (10.0 to 0.6Pa ·s) at 100 °F (38 °C). Heat very effectively reduces the viscosity of the Kern River crudes. Typically there is a 100 to 500 fold decrease in viscosity at 250 °F (121 °C) which is the reason of the success of thermal operations in heavy oil.

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