Analysis And Repair of Production Problems Using Electrical Workover Systems
Authors: Chase A.E. 
Published: March 2010

The analysis and repair of many well problems are done more satisfactorily and usually at much less cost when downhole formation and well conditions are known. Such information can be obtained by use of logging tools, now available that are small enough to be lowered through commonly used sizes of tubing. Thus it is unnecessary to kill the well and pull the tubing, which would involve considerable expense and more important, would risk irreparable damage to the well.

These through-tubing- logging tools include the 1-11/16 inch Thermal Decay Time Log the 1-11/16-inch Cement Bond Log with variable-density and wave-train presentations, the 1-11/16-inch Gamma Ray – Neutron Log and the Production Logging tools (e.g., Flowmeter, Gradiomanometer, Densimeter, Thermometer, Radioactive Tracer, Thru-Tubing Caliper and Production Fluid Sampler).

The Thermal Neutron Decay Time Log is useful for evaluating water saturations behind casing. Comparison of the Thermal Neutron Decay Time Log run through tubing with the open-hole logs run before casing was set is an effect the method or locating h:rdrocarbon-bearingzones and fluid contacts and monitoring contact migration in the reservoir. When the necessary parameters have been evaluated, quantitative determination of saturations with the Thermal Decay Time Log is possible with the help of porosity information from the open-hole logs. If necessary, porosity can be estimated from the 1-11/16-inch Neutron Log in the cased hole.

Comparison of the Variable Density Log run in casing with the variable Density Log run in open hole provides invaluable information on the existence of fractures and evaluation of the cement job. Interpretation techniques have been developed for both carbonate reservoirs and sand reservoirs.

The production Jogs provide information, in producing or injection wells, on the fluids and flow conditions in the well bore and the points of fluid entry or exit (e. g. thief zones).

Applications of the through-tubing logs are illustrated by examples from Western Canada, with emphasis on medium-to-low porosities.

These applications of cased-hole logs extend the scope of log analysis. Although the log analyst's previous experience may have been confined to open-hole logs, it is apparent that he can play a valuable role here. After the well problems have been analyzed, they can often be remedied without pulling the tubing by use of the 1-11/16-inch Thru-Tubing Bridge Plug.

INTRODUCTION

MANY WELL PROBLEMS, such as low production rates, production of undesired fluids (e.g. gas or water) and the establishment of optimum production rates, are more easily and more definitely analyzed when formation and downhole well conditions are known. Without this information the cost of well repairs can be unnecessarily high.

To kill the well and pull the tubing in order. In obtain the downhole data with larger-size devices is often extremely expensive, Even more important, this procedure may result in damage to the well. This is particularly true in Western Canada where many of the major reservoirs are non-uniform carbonaceous formations with porosities of about 10 percent or less.