Special Applications of Drill-Stem Test Pressure Data

Abstract

Published in Petroleum Transactions, AIME, Volume 210, 1957, pages 318–324. Abstract This paper discusses how the following formation characteristics can be determined mathematically from drill-stem test pressure charts: true formation pressures, effective permeability of the entire section tested, well productivities, wellbore damage and possible detection of barriers (faults, pinchouts, etc.). This paper also presents a practical method for immediate determination of effective permeability and wellbore damage from successful double shut-in pressure tests. A list of recommendations for improving the reliability of drill-stem test pressures is also presented. Introduction A drill-stem test is a temporary completion designed to sample the formation fluid and to establish the possibility of commercial production. Early pressure recording devices were used merely to verify proper operation of the testing tool. Until recently the accuracy of the pressure gauges has been insufficient for any reliable quantitative use of the recorded pressures. In view of the need for more reliable formation evaluation and as a result of the recent interest in exploration work employing the concept of hydrodynamic entrapment, better pressure recording gauges are now in use. These devices can record pressure within 1 per cent above 1,000 psig and can detect differential pressures as low as 1/2 psig. In addition to formation pressure, several other reservoir characteristics can be determined from DST charts; namely, well productivity, formation permeability, wellbore damage, and the possible existence of barriers (faults, pinchouts, changes in permeability, etc.). This paper presents a practical method to interpret DST pressure charts for formation pressures and many other reservoir properties, a method that has been developed in analyzing approximately 4,000 DST charts during the last five years. The techniques used are a composite of published articles on drill-stem testing together with well-known pressure build-up analysis methods.