An On-Line Method for Troubleshooting Wells Without Wireline Tools
Authors: Wellington S.L. , Simmons J.F. , Richardson E.A. 
Published: December 2007

A tracer method is provided for troubleshooting gas-lift wells, to identify whether gas-lift valves on the production tubing are open or closed, without the use of wireline tools. The method may also be used to detect leaks in the production tubing or in the well casing.

INTRODUCTION

Conventional methods of detecting casing leaks in gas-lifted wells have involved the use of wireline tools including mechanical calipers and production logs. The depth of gas entry for the purpose of lift is usually determined by flowing pressure gradient survey. Noise and temperature logs or caliper surveys are often used to locate casing leaks. These wireline methods have several disadvantages for the well operator. It is usually necessary to shut down operations on the well, at least during insertion and removal of the tools. Specialty tools are used and interpretation of the results often requires expert analysis. There is also some risk associated with inserting tools into a well, since if the tool is irretrievably lost in the well, it may be necessary to implement expensive remedial operations or abandon the well.

The tracer method1 described in this paper allows detection of production tubing and casing leaks and to determine whether gas-lift valves on the production tubing string are open or closed. The method is performed while the well is in operation and without the use of wireline tools. The method is simple, and easy for field personnel to perform with minimal equipment. The test is inexpensive, and the results obtained are usually easy to analyze and should in most cases allow interpretation at the well site.

DESCRIPTION AND APPLICATION OF THE METHOD

Figure 1, a schematic diagram of a gas-lift well system, is used to describe the method. A pulse of tracer fluid sufficient for detection in the produced fluids is injected into the lift-gas supply line near the wellhead. The lift-gas, containing the tracer fluid, travels down the annulus between the well casing and the production tubing, entering any openings along the production tubing. An analyzer is attached to the produced fluid line. A small separator attached to the wellhead may be associated with the analyzer to segregate a particular produced fluid for analysis. The analyzer is used to detect the presence of the tracer in produced fluids as a function of time. The analyzer may be connected to a digital or analogue hard copy recorder to provide a graphical representation of the data.

Many fluids are available for use as the tracer. The tracer fluid must be injectable in a sufficient quantity and over a short time period such that it, or any tracer it generates, may be detected in and distinguished from fluids produced from the well. Gases are preferred for their ease of use and miscibility with the lift-gas. Examples of such gases include carbon dioxide, nitric oxide, ammonia, sulfur dioxide and halogenated hydrocarbons such as Freon®. Radioactively tagged versions of such inert gases may also be used.

It is preferable to inject a pulse of the tracer fluid, i.e., a concentrated amount of tracer in a short period of time, rather than using continuous tracer injection. This allows the use of peak tracer analysis to determine the entry points of the injected fluid, and thereby the lift-gas entry into the production tubing. Continuous tracer injection can require more tracer and presents a somewhat more difficult response for analysis.