Design Criteria And Selection of Downhole Tools For Conducting Interference Tests In Horizontal Wells
Authors: Osisanya S. , Tiab D. 
Published: March 2010

Abstract
Since horizontal drilling practices have become well established, operators are focusing on improving completion techniques as well as formation evaluation methods. Interference pressure testing is one method of formation evaluation that is a major step in understanding the fluid flow behaviour of horizontal wells. The measurement of transient pressure data during interference testing of horizontal wells presents specific design considerations that do not arise in the vertical wells. Multiple interference tests provide valuable information about reservoir characteristics such as areal average transmissibility, storage, and degree of communication between wells. The key to achieving a successful interference test is to take care of the horizontal wellbore from the beginning. This includes the design and selection of downhole tools as well as the development of planning and operational stages on a well-by-well basis. This is because no two horizontal wells are alike. This paper presents design criteria and selection of downhole tools, and planning and operational steps for conducting interference tests along the horizontal portion of the well. The paper also discusses some of the factors that must be considered before embarking on the job. Factors that must be considered include well geometry (lateral length), flow regimes, test duration, type of completion, and wellbore hardware. An example of simulated interference test design calculations in a horizontal well is given. The judicious design and utilization of downhole equipment will result in successful and meaningful interference pressure test data.

Introduction
As horizontal well technology continues to gain ground, the next major area of concern becomes that of obtaining meaningful transient pressure test data. One type of data is that for interference pressure tests. The term "interference test" is used to describe the test whereby a detectable pressure drop is measured at a point (in the same or adjacent well) because of production or injection at another point(l), that is, the test involves more than one point or well in the same reservoir. Generally, an active well is produced while the bottom hole pressure at a shut-in observation well is measured for several hours or days depending on the anticipated reservoir properties and well spacing. The measured pressure history is then analysed to estimate the interwell formation permeability and porosity. In the case of a horizontal well, the interference test will involve the production of one section of the horizontal part of the well while the bottom-hole shut-in pressure is measured on another part of the hole that is not contributing to flow.
This technique can be used to detect pressure drops at various points along the horizontal part of the well. The primary objective of an interference test is to establish the fact that two points in the reservoir are hydraulically connected. Thus, information on areal average transmissibility, storage, formation flow capacity (kh), isotropy and directional permeability and degree of communication between wells may be obtained after conclusively establishing that communication exists. The estimates from an interference test represent information over the horizontal part of the well.