Formation Testing and Stimulation Using Modern Generation Test Tools - The Test-Acidize-Test Technique
Authors: Crockett R.K. , Cooper R.E. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the SPE-European Spring Meeting 1976 of the Society of Petroleum Engineers of AIME, held in Amsterdam, The Netherlands, April 8–9, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal, provided agreement to give proper credit is made.
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Abstract
With the rapidly rising costs of offshore exploration the need to quickly but effectively evaluate potential production zones has become necessary. One of the conventional formation evaluation tools has been Drill Stem Testing. A formation testing procedure has been developed which allows an operator to test a zone, evaluate the test results, acidize the zone and re-test without removing the tools from the hole. The operator is able to obtain all data normally associated with formation testing including bottom hole samples and indications of future sand production problems. production problems. Several test-stimulate-test series were performed without removing the tools from performed without removing the tools from the well.
Data is presented showing North Sea Drill Stem Tests which flowed more than 8,500 BOPD, Appendix, A. Other North Sea data is presented where pressure drop across perforations presented where pressure drop across perforations and various internal tool restrictions can be seen, and results of acidizing, sometimes detrimental, before and after testing is seen using the McKinley method of test interpretation.
The purpose of this paper is to describe the development of the T.A.T. technique and report on some results of actual field useage.

Introduction
Somewhat unique and necessary to the north Sea, but an approach which will become more and more common as exploration costs increase, is the practice of development platform commitment based on the results of very few exploration wells. Because of this, formation and fluid data obtained from Drill Stem Testing is very important in making this commitment.
Particularly in exploration wells, zones of Particularly in exploration wells, zones of interest are sometimes damaged by mud losses or mud and cement filtrate. Subsequent Drill Stem Testing may be inconclusive in regards to fluid production due to this damage.
Previous to the development of the Previous to the development of the Test-Acidize-Test technique of T.A.T., operators would face several time consuming or undesirable possibilities.Acidize with a separate bottom hole assembly, then pull out of the hole and run, drill stem test tools in the well. This procedure could potentially redamage the zone after acidizing and before testing.Test the well, pull the drill stem test tools out of the hole and acidize and then rerun the test.Run the drill stem test, calculate the Estimated Damage Ratio, Appendix C, and estimate the undamaged production potential. This is undesirable since the true nature of produced fluids is usually not accurately known; possible depletion (limited reservoir) cannot usually be seen and the calculated production potential is often incorrect.