Well and Reservoir Analysis and Simulation

Chapter 4

Abstract

useful applications.

1. Introduction

is worth mentioning.

59

fracture conductivity, hydraulic fracturing

Well Test Analysis for

Freddy Humberto Escobar

Hydraulically-Fractured Wells

This chapter focuses on the application of Tiab's direct synthesis (TDS) technique for practical and accurate interpretation of pressure tests on vertical wells in conventional reservoirs, so bilinear, linear, and elliptical flow regimes can be used for fracture characterization. Most fractured well interpretation tests are conducted using nonlinear regression analysis if the pressure model is available. This method has some drawbacks associated with the nonuniqueness of the solution. Also, the conventional straight-line method requires one plot for each individual flow regime observed in the pressure tests, and the estimated parameters cannot be verified. Tiab's direct synthesis (TDS) methodology, which uses specific lines and intersection points found on the pressure and pressure derivative plot, is used in some direct equations which are obtained from the solution of the diffusivity equation for a given flow regime. It has been proven to provide accurate results, and its power allows verification of most results which is not possible from any other technique. The methodology has been successfully explained and tested by its application in two examples, although there exists more than a hundred articles that provide many

Keywords: bilinear flow, linear flow, elliptical flow, half-length fracture,

Throughout their history, well test analyses for fractured wells have received many contributions. For practical purposes, let us name the most important ones for this chapter. A good place to start is by mentioning the work in [1], which described the pressure behavior for infinite-conductivity and uniform-flux fractured wells, so people started conducting interpretation tests on such wells by using type-curve matching. Later, [2] introduced the concept of finite-conductivity fractures and established the onset value of dimensionless conductivity as 300. Values lower than that are considered finite-conductivity values, and those above 300 are classified as infinite conductivity. In [2], a fine semi-analytical solution was introduced for describing the well-pressure behavior in hydraulically fractured wells. This solution was then applied in [3] to provide a well interpretation method using type-curve matching. Since then, other mathematical solutions have been presented for finite-conductivity fractures. Among them, the work in [4] using fractal theory

The way of conducting well test interpretation was changed by the introduction of Tiab's direct synthesis (TDS) technique by [5]. This revolutionary and modern
