Formation Evaluation from a Drill-Stem Test - an Aid to Stimulation Design
Authors: Murphy W.C. 
Published: December 2007

This paper was prepared for the 41st Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Dallas, Tex., Oct. 2–5, 1966. 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 PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

The purpose of this paper is to show that data from a drill-stem test may be effectively used to aid in the design of production stimulation treatments. Formation characteristics determined from the pressure behavior on a tests are compared to simulated characteristics by propping or etching a core sample to indicate the type and size of treatment necessary. The formation characteristics considered that may be used in stimulation design are production rate, permeability, flow capacity, and reservoir pressure and its stability. Formation conditions are investigated to show how they may affect the stimulation treatment. These conditions are existing fracture system, permeability discontinuities, and formation damage. These formation conditions and characteristics are used to show an estimated production increase wider certain conditions. Field results are used to illustrate the method.

Introduction

Well stimulation is the source of a good part of the oil industry's domestic production. There is a constant search for methods and supporting formation characteristics to help design stimulation treatments to give optimum results. To get the best possible results, a stimulation treatment should be designed utilizing all pertinent data available. The most reliable single piece of information available is a pressure analysis of the drill-stem test. This is the first evidence of the performance of the well. The pressure performance of a drill-stem test may provide natural or matrix production, flow capacity, permeability, formation damage, formation anomalies, and reservoir pressure and its stability. These data may be evaluated and compared to an improved or stimulated condition to determine the need for and the type of treatment necessary, and the production increase that may be expected, In addition, this comparison may indicate the size and rate of treatment to accomplish a certain condition. However, the design of the stimulation treatment is beyond the scope of this paper.

BACKGROUND DEVELOPMENT

There are two primary classifications of a reservoir in pressure analysis those in an infinite system and those in a finite system. An infinite system is one in which the outer boundary is an infinite distance from the wellbore and has not been reached on the test. Therefore, constant pressure is maintained at the extremities of the pressure disturbance. This condition exists in most cases during a test; therefore, only the infinite system is considered in this paper. Frequently, a boundary is reached; however, the pressure behavior before this disturbance may be used to determine formation characteristics.