One of the major challenges in reservoir engineering is the accurate description of the reservoir. This description is essential in all aspects of petroleum engineering, and is typically achieved through reservoir characterization by integrating various kinds of information obtained from the reservoir. One reliable source of reservoir information is well testing. Analysis of well tests, especially interference tests in horizontal wells could be very complex but effective in that rock matrix intersected by pressure response cover wider area of the reservoir. This study extends previous studies on horizontal-well interference testing by applying a modified function for the dimensionless pressure at the horizontal observation well. The work investigates the effects of well lengths, directional permeabilities, and separation distances between active and observation wells on the pressure response at the horizontal observation well. Multiple active horizontal wells have been studied using the superposition principle by considering the influence of the number of active wells, locations and timing of activities of active wells on the pressure responses at a horizontal observation well. Field data have been used to validate the findings of this study and to estimate the equivalent observation points using known correlations. The results obtained from this work can be applied in well placement decisions during field development as well as in understanding the distortions caused by nearby wells during well tests.
CHAPTER ONE INTRODUCTION 1.1 Overview of Well Testing
Well test analysis or pressure transient testing involves generating and measuring pressure variations with time in the well in order to estimate rock, fluid and well properties. Information that can be estimated from well testing include wellbore volume, damage and improvement; reservoir pressure (initial and average); permeability; porosity; reserves; reservoir and fluid discontinuities; and other related data1. These pieces of information are important in analyzing, improving, and forecasting reservoir performance. Well testing is considered essential in many phases of petroleum engineering. Information from this test helps reservoir engineers analyze performance and predict future production under different operational mechanisms. Production engineers also utilize well test information to effectively combine injection and production wells in order to optimize reservoir performance. There are different well testing techniques such as pressure buildup, pressure drawdown, injectivity, falloff, interference and pulse tests. A single well can be used to perform well tests as well as multiple wells; these can be vertical wells, horizontal wells or a combination of both. This work focuses on interference testing in horizontal wells.
1.1.1 Interference Tests
When one well is shut-in and its pressure is measured while other wells in the reservoir are produced, the test is termed an interference test. The name comes from the fact that the pressure drop caused by the producing well(s) at the shut-in observation well “interferes with” the pressure at the observation well2. For this test, long duration rate modification in one well creates pressure interference in an observation well which can be analyzed for required reservoir properties.
1.1.2 Pulse Tests
Pulse Testing belongs to the family of multi-well testing methods. It requires the introduction of flow disturbances into a reservoir by alternately increasing and decreasing the flow rate at an active or pulsing well3. The effects of these shorter-rate pulses are investigated at the observation well. Each pulse can be an alternating period of production (or injection) and shut-in, with the same rate during each production or injection period.
1.2 Horizontal Well Testing
Previously, well testing was performed in the ‘then common’ vertical wells but when horizontal well drilling became a commonplace, it became pertinent to perform well tests in reservoirs penetrated by only horizontal wells. Horizontal wells are inclined at near 0o to the horizontal plane. Horizontal wells are becoming increasingly useful in modern reservoirs, and in some oil fields, old reservoirs are being redeveloped with horizontal wells. Well tests in horizontal wells are significantly more complex to interpret than vertical well analysis.4 Figure 1.1 indicates how a horizontal well is represented in reservoir systems for analysis…….