Abstract

For more than a decade, several fields in China have produced heavy oil from cyclic steam thermal operations. High temperature (650F) steam has been injected into the reservoirs. One field operates cyclic steam wells completed at 1600 meters in depth. This paper describes an innovative system to measure continuously, from surface to downhole, the pressure, temperature, and spinner responses in these steam injectors. Compelling data is presented to evaluate wellbore heat loss, steam injection profiles, and reservoir properties. A unique wellbore heat-loss model applies the measured temperature data to quantify downhole steam quality. Steam injection profiles have been obtained by analyzing spinner data against perforation intervals. During the steam soaking period, downhole pressure and temperature fall-off behaviors have been observed. The analysis of pressure fall-off curves yields wellbore skin and reservoir permeability. A new model to analyze temperature fall-off curves, by applying the Marx-Langenheim theory and a new set of type curves, yields heat transfer coefficients and steam swept zone size in the reservoir.

Introduction

Due to operational difficulties, many steam injectors for the thermal recovery of heavy oil are not routinely monitored1,2,3. many wells associated with cyclic steam operations in China are under evaluation particularly when the oil/steam ratios are not satisfactory and a large amount of oil is left to be produced in the reservoirs4. The poor recovery factor of heavy oil from deeper reservoirs, in one field operating wells completed at 1600 meters, has added on the requirements for decent reservoir and well performance data. Other thermal recovery methods, such as steamflooding and in-situ combustion, have been tested and operated in the fields. Performance experience in steam cyclic operations has provided the basis for improving the recovery efficiency from heavy oil reservoirs.

This innovative system measures continuously, from wellhead to downhole, the temperature, pressure, and spinner responses during both steam injection and soaking periods. It consists of a special cable which transmits data to a monitor and a digital recorder. In order to evaluate wellbore heat loss, injection profiles, and key reservoir parameters, new interpretation models have been developed.

The system and the models were designed and manufactured in the United States. Four complete units were delivered to end users for the thermal recovery operations located at Liaohe, Shengli, Karamay, and Henan oil fields in China.

The Measuring System

A complete truck-mounted unit for high temperature logging and testing consists of downhole tools, a cable, a lubricator, a mast, a drum, and a surface operating system. There are no electronics used in downhole tools, which only include mechanical parts, such as a spinner tool, a thermocouple housing, and a pressure chamber.

The Cable

Fig. 1 shows a cross-sectional view of the cable. This 0.25" (0.194" ID) stainless steel tubing has tensile yield strength of 1950lbs. It includes two 0.094" tubes. One is filled with nitrogen for pressure transmission. The other houses two Type K thermocouple wires for temperature measurements and one copper wire for spinner signals. These three wires are coated with Kapton insulation material rated at 900F. This cable requires a larger diameter drum but is easily sealed going through the lubricator.

The Cable

Fig. 1 shows a cross-sectional view of the cable. This 0.25" (0.194" ID) stainless steel tubing has tensile yield strength of 1950lbs. It includes two 0.094" tubes. One is filled with nitrogen for pressure transmission. The other houses two Type K thermocouple wires for temperature measurements and one copper wire for spinner signals. These three wires are coated with Kapton insulation material rated at 900F. This cable requires a larger diameter drum but is easily sealed going through the lubricator.

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