Pressure Transient Testing and Interpretation for Horizontal Wells: Field Examples
Authors: Kuchuk Fikri J. 
Published: December 2007

The use of transient well testing for determining the productivity of horizontal wells has become a common practice because of the upsurge in horizontal well drilling. In this paper, we first investigate certain conditions of the formation and wellbore that affect transient pressure tests for horizontal wells. The formation pressure variation along the horizontal wellbore just after drilling is very important measurements. It gives the true dynamic condition and information about depletion characteristics of the reservoir. The wellbore condition during production, obtained by an integrated production logging toolstring, is crucial for well testing as well as for the determination of the flow profiles and effective well length. Second, we present a horizontal well test interpretation methodology by analyzing two buildup tests from the same well conducted at different times. In addition, two more buildup tests are presented as examples of inadequately designed and conducted tests. It is shown that uniquely determining the reservoir parameters from short buildup tests is impossible. It is also shown that minimizing the well bore storage effect is crucial for system identification as well as for parameter estimation.

Introduction

Because they are dynamic and direct, pressure measurements and pressure transient testing provide essential information for well productivity and dynamic reservoir description and holds critical importance for exploration as well as production and reservoir engineering. For exploration, pressure measurements may give information about formation fluid density and contacts. Pressure-testing may also show that the formation can flow, permit sampling of the formation fluid and provide productivity index, reservoir pressure, permeability, and heterogenity.

For producing fields, testing objectives might have to answer questions such as:what is wrong with poorly performing wells?does the well need stimulation? andare faults open or closed?

For horizontal wells, transient testing is the key to determine the well productivity and formation parameters, because the observed horizontal well productivity is often lower than the theoretical predictions. The low productivity can usually be related to one or more of the following issues:Non-uniform reservoir pressure distribution along the wellbore because most horizontal wells have been drilled in producing fields;Lateral heterogenity in the reservoir, particularly along very long wells;Formation damage along the wellbore during drilling processes;A long, snakelike completed wellbore, which makes the cleanup process difficult, particularly tovards the tip of the well;Local water pumps and gas traps along the wellbore; andUnsuitable and/or poor completion practices.

Of course, one can list a number of other parameters that can also be critical for the well performance.

With the increasing number of horizontal wells, transient pressure tests have been conducted in many wells with different geological settings and wellbore conditions. In this paper, we present the use of local pressure measurements for the near-wellbore condition before just after drilling and an intergated production logging toolstring for the wellbore condition. Determining both of these condtions are essential before conducting a transient pressure test for a horizontal well.

The purpose of this paper is to provide a methodology for the interpretation of well tests from horizontal wells and is to present interpretations for the field example.