Abstract

A multiphase flow meter was used in addition to conventional surface well test equipment during five deep offshore exploration drill stem tests. Several immediate benefits were derived. The clean-up phase was monitored, which improved control of the formation drawdown as well as the prediction of well eruption. The flow history was better quantified, which improved the pressure transient analysis. The instantaneous flow rate measurements shortened flow periods and accelerated the decision process, which reduced the overall test duration. In general, the multiphase flow meter enhanced the operation flexibility, the confidence in the information acquired and the accuracy of the results.

Introduction

There are three distinct processes occurring in a surface well test. Well fluids must be controlled, measured and disposed. The objective of a well test is the measurements. The operational requirements to obtain those measurements are the fluid control and disposal. A successful well test requires an effective interaction of the measurement with the fluid control and disposal.

In exploration well testing, little is known in advance about how a well will perform. Exploration well testing procedures and equipment, therefore, are designed to handle a broad spectrum of eventualities. Nevertheless, there are uncertainties that must be resolved during the well test to effectively control the well, obtain representative well test data and efficiently dispose of the fluid.

Deciding how and when to proceed in the well test program requires information about how the well is performing relative to the conditions. For example, the main flow period might not be commenced until nearly all of the non-reservoir fluid is removed from the well and formation test interval. This requires a complete record of oil and water recovery volumes. Using conventional well testing methods, this information is not complete. Thus, in the absence of some information, a successful test can rely considerably on the judgement of an experienced well test operator.

Conventional Well Testing.

In a conventional well test, determining sufficiently accurate gas, oil and water flow rates can be a challenge. Some common problems are poor fluid separation, flow instability and poor meter calibration. Furthermore, by using a large vessel to separate the fluid phases, flow measurements lack the resolution to identify small flow events or transient behavior. Fluid level instability caused by control valve oscillation or floating vessel heave can also distort the measurement. With all the process equipment needed to separate the phases, the maximum well potential cannot be obtained sometimes because of excessive back pressure imposed on the well.

Critical to exploration testing, well production is not even measured before the well stream is "cleaned-up." Among the numerous challenges this causes, the build-up analysis of an early shut-in can be affected by the assumptions made for the flow rate history.

The sum of these challenges can cause a mis-interpretation of the well performance and a flawed execution of the well test. At the end of the test, the reliability of the results may be in question. The analysis of the test may be misleading.

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