Abstract

Production logs play a significant role in the implementation, evaluation and surveillance of enhanced recovery schemes. Maximizing scheme efficiency through the refinement of depletion strategies, improvements on completion effectiveness, and problem well diagnosis is based on a quantitative downhole look at production as well as injection profiles. However, production logging tools do have limitations and are only now evolving to a stage at which some of the more complex flow situations can be dealt with effectively.

The volumetric measurement and identification of low rate multiphase inflow is an area of production logging in which conventional tool response to fluid flow, can be confusing and rnisleading. Since many infill wells in secondary and tertiary recovery schemes traverse the reservoir at an angle, the difficulty in quantifying multiphase flow is compounded. Recent flow loop experiments have shown that as little as 2 degrees deviation can result in an apparent down flow of the heavy phase. even though the net flow is upward. Under these circumstances, tool response is not representative of actual flow rates or hold ups and results are easily misinterpreted.

Flow concentration devices are generally recommended for fluid velocity and fractional component measurements in wells of this type. The actual measurements are taken between productive intervals by channeling cumulative production through a small diameter metering section. However, the complex flow regimes must be disrupted and the measurements are not taken under what would be considered normal producing conditions. This technique may not always be representative of actual production as normal producing conditions include these complex flow regimes.

An alternative method of measuring inflow, without disturbing normal flow patterns, will be illustrated using field examples. The procedure includes the use of a flowmeter sensitive to radial rather than axial flow. The use of this instrument to detect and measure inflow directly at the entry points will be discussed as part of a detailed production evaluation of a typical deviated multiphase producer.

Introduction

The economic success of a secondary or tertiary recovery scheme is dependent on the efficient implementation of a sound depletion strategy. A quantitative understanding of the reservoir is critical to the development of that strategy. The reservoir characteristics, measured only at the wellbore, are the basis for prediction of oil recovery performance and projected profitability. The basic data required for the reservoir in question is obtained from several sources and utilized to make predictions of injection rates, production rates, producing GOR's and producing WOR's. The primary source of these data are core analysis, open hole logs and pressure transient tests.

Although open hole logs and pressure transsient tests are versatile tools, employing interpretive and diagnostic techniques to provide in place measurements of reservoir parameters, an evaluation of productivity is also necessary. When dealing with a system that cannot be seen, measured or tested in its entirety, our only communication with the reservoir is the individual well. After that well has been cased, perforated and stimulated, an evaluation of the well is required to determine production and completion performance.

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