Early Fluid Entry Determination; Key To Safe, Optimum Drill Stem Testing
Authors: Erdle J.C. , Upchurch J.M. , Warren D.A. 
Published: December 2007

Drill stem test results have been improved utilizing the closed chamber technique with an electronic surface pressure measurement system. Formation fluid type, instantaneous flow rates, average gas-liquid ratio and total liquid recovery are determined in the early moments after a test is initiated. Interpretive equations and test procedures are described for all commonly encountered procedures are described for all commonly encountered cushion conditions. Field examples are presented illustrating increased test safety, reduced wasted rig time, and refined engineering of the drill stem test.

Introduction

Any type of well test is designed, conducted and analyzed for the purpose of obtaining information pertaining to the reservoir and its contents. pertaining to the reservoir and its contents. Properly interpreted pressure transient well tests Properly interpreted pressure transient well tests are the most direct means of obtaining this information. Regardless of the competence of the well test analyst or the degree of sophistication of the analysis techniques employed, the utility of the test interpretation is limited by the quality of the measured data and the test procedure.

A significant portion of the recent pressure transient well test literature describes advanced data analysis techniques, whereas little improvement has been reported in test design and field practice. The logical approach to obtaining better well test results is to design and implement a test procedure which conforms to the most basic, yet comprehensive, mathematical model of fluid flow in the reservoir, rather than complicate the reservoir model and the associated analysis techniques to account for inadequate test design and inflexible field conduct.

Drill stem testing is a branch of pressure transient well testing in which the quality of the test results is dependent upon proper wellsite interpretation of ongoing test behavior. In many circumstances the critical wellsite decisions concerning flow and shut-in period duration are based on rigid, preset test plans or "rule-of-thumb" responses to highly subjective bubble bucket blow strength observations. A significant improvement in the utility of DST data can be attained by the universal application of sound design practices and improvement in wellsite test behavior monitoring and interpretation techniques.

In view of the importance of proper wellsite test procedures to obtaining analyzable data, the present work was initiated to improve or replace present work was initiated to improve or replace the bubble bucket observation DST monitoring method with a more objective, quantitative system. The closed chamber DST technique was selected for evaluation as the bubble bucket replacement system. The results of an extensive research effort involving (1) extension, refinement and verification of equations relating drill string pressure change to formation fluid type and flow rate, pressure change to formation fluid type and flow rate, (2) design, development and evaluation of field equipment required to conduct closed chamber tests, and (3) interpretation and evaluation of over one-hundred field tests of the closed chamber equipment, theory, and test procedures are presented. presented.

CONVENTIONAL VS. CLOSED CHAMBER DST

A conventional drill stem test consists of four phases:initial flow (i. e. preflow),initial shut-in,final flow, andfinal shut-in.