Tight Hole and Closed Chamber Testing - A New Technique for Formation Evaluation

Abstract

The closed chamber and tight hole methods of well testing described in this paper are designed to overcome some special drill stem test problems existingat the surface. The primary purpose for conducting this type of drill stem testis to utilize a system that offers maximum secrecy and/or maximum control of fluid recovery; therefore, maximum safety. The problem of secrecy commonly occurs in Canada, and the tight hole technique was developed so that only authorized personnel would be able to determine the type of recovery and the pressure involved. The closed chamber method has application wherever a high degree of controlof the recovery is desired, such as in townsite and night-time testing, neither of which can be accomplished safely by the conventional drill stem test method.This method also permits a high degree of safety when testing high-pressure gassands. Experience with closed chamber testing has indicated that the fluid recovery data may be applicable for empirical analysis to determine reservoir fluid properties provided that certain problems are recognized. Static reservoir pressure can be determined by employing the initial shut-in-flow-period method described in the text of the paper. However, problems are encountered when attempting to utilize the pressure buildup curveto determine transmissibility and permeability with the degree of accuracy obtainable from a conventional drill stem test. Examples of pressure curves from tight hole and closed chamber systems are included and discussed. Introduction Tight hole testing was developed to provide maximum secrecy of drill stem test results in Canada. In order to maximize secrecy, it was necessary to provide a testing system that would not allow fluid recovery to be exposed to unauthorized personnel on or off the rig floor. The tight hole assembly consists of a closed chamber which allows the standsof drill pipe forming the chamber to be separated, drained and set aside in the derrick without revealing any recovery, even in the tool joints, to unauthorized personnel. Secrecy requires the elimination of surface indications during the test and the bringing of the recovery to the surface in such a manner that it will not flow freely from tool joints onto the floor or into the derrick. The recovery has to be removed from the chamber with maximum controlin order to provide secrecy. The conditions required for secrecy result in an increase in the safety of testing.