Pressure-Transient Analysis for Horizontal Wells

Abstract

Summary In recent years, pressure-transient behavior of horizontalpressure-transient behavior of horizontal wells has received considerableattention because of the increase in horizontal drilling. This paper presentsan interpretation method for presents an interpretation method forhorizontal-well pressure-transient testing that is applied to a buildup testfrom a horizontal well in the Prudhoe Bay field. The complex flow Prudhoe Bayfield. The complex flow geometry associated with horizontal wells makeswell-test interpretation difficult. Unique determination of the systemparameters from pressure data with a short testing time (typical test times forvertical wells) and/or production time is not possible. We production time isnot possible. We must run drawdown and buildup tests and acquire the downholeflow rate with pressure to estimate the reservoir parameters accurately. Introduction Interpretation of well tests from horizontal wells is much more difficultthan interpretation of those from vertical wells because of a considerablewellbore storage effect, the 3D nature of the flow geometry and lack of radialsymmetry, and strong correlations between certain parameters. Also, zonalvariations of vertical permeability and shale distribution complicateinterpretation. A well-defined flow period, comparable to that of the infinite-acting radialflow period (free from storage and boundary effects) period (free from storageand boundary effects) of a vertical well, is not apparent for horizontal wells, largely because most horizontal wells exhibit partial penetration effects evenwhen they are hilly perforated. Specific methods have been perforated. Specificmethods have been proposed to identify flow regimes and their proposed toidentify flow regimes and their durations under ideal conditions. AlthoughReiss and Sherrard et al. presented performance and production data fromperformance and production data from several horizontal wells and mentionedinterpretation of well-test data, they did not show how to extend theidentification and usage of flow regimes to the interpretation of realpressure-transient tests. This paper presents a method for the interpretation of wells data fromhorizontal wells and analyses of pseudosynthetic and real well-test data. Solutions With and Without Gas Cap or Aquifer In a horizontal well, there is usually considerable wellbore volume (50 to100 bbl) below the measurement point, even if the downhole flow rate ismeasured or a downhole shut-in device is used. The storage effect with thisadditional volume typically lasts longer than that in a vertical well in thesame formation because the anisotropy reduces the effective permeability atearly times to root of kHkV.