Pressure Transient Behavior of Horizontal and Slant Wells Intersecting a High-Permeability Layer

Abstract

This paper describes numerical simulation studies designed to investigate the behavior of horizontal wells that intersect high permeability layers sandwiched between two lower permeability layers. The paper investigates the pressure transient behavior of 1) purely horizontal wells drilled in the middle layer and 2) slant horizontal wells that intersect all three layers, as the permeability of the high permeability layer is varied. A previous paper1 (SPE 88704) focused on late time interference effects and radial composite behavior caused by a limited high permeability Super-K layer. This study focuses on the early time dual permeability effect and its impact on recognition of conventional horizontal well diagnostic derivative slopes. The horizontal well simulations show a dual permeability effect as the contrast between the high permeability layer and the adjacent layers is increased. The vertical radial flow regime is seldom visible and masked by wellbore storage effects. Interestingly, what is observed however, is a plateau (or sometimes valley) caused by the dual permeability effect followed by a transition to horizontal radial flow regime. This may be explained as a combined effect of recharge and linear flow in the lower permeability layers. The plateau (or a valley) caused by the dual permeability effect, can easily be confused as representing the vertical radial regime. Similarly, the transitional data prior to horizontal radial flow, which includes the dual permeability effects, can be incorrectly analyzed and lead to misleading results. This paper will demonstrate the increased complexity of the pressure transient behavior when the well is slanted through all layers while intersecting the high permeability layer. Introduction The ability of horizontal wells to provide large areas of contact with the reservoir makes horizontal wells more suitable for the efficient recovery of oil, especially from thin reservoirs. Thus, horizontal wells have become the norm, rather than the exception, for the exploitation of oil and gas reservoirs, especially when the reservoir is underlain by an acquifer21. Pressure transient testing has become the standard means of evaluating the effectiveness of horizontal wells, as well as characterizing the reservoir being drained by the horizontal well. Several studies have proposed analytical solutions and also methodologies for analyzing horizontal well tests3 2–65. Some of these analysis techniques use sequential straight line methods based on the identified flow regimes, to estimate reservoir and well parameters from the tests. For automatic parameter estimation using the whole test data, non-linear regression techniques are used. Mattar and Santo7 have proposed an analysis technique based on a combination of the two methods6.

Analysis of Gas Flow Behavior for Highly Deviated Wells in Naturally Fractured‐Vuggy Carbonate Gas Reservoirs

“…Ozkan and Raghavan presented a solution for a deviated limited-entry well in an infinite reservoir with no-flow top and bottom boundaries by employing the Laplace transformation [24]. Harmohan et al introduced a method of numerical simulation to analyze the pressure transient behavior of deviated wells that intersect high permeability layers between two low permeability layers [25]. Based on rigorous derivation, Wang et al presented a transient pressure solution for deviated wells, which reduced the amount of computation and significantly improved the computational efficiency [26].…”

Dual Porosity and Dual Permeability Modeling of Horizontal Well in Naturally Fractured Reservoir

“…These models considered the fracture and matrix systems as the flow pathway directly connected with wellbore, in addition, considered the inter-porosity flow between matrix and fracture systems. (3) Flow models of horizontal well production in a single medium, such as analytical models (Frick et al 1996; Goode and Thambynayagam 1987;Kuchuk et al 1991;Ozkan et al 1989;Sheng 2008), semi-analytical models (Duan et al 1998;Kuchuk and Hbashy 1996;Ozkan and Raghavan 1991a,b) and numerical models (Hashemi et al 2006;Gill and Issaka 2007). In these models, there have various complex boundaries for different porous medium, such as homogeneous media, anisotropic media; (4) Flow models of horizontal well in naturally fractured reservoirs, such as analytical model (Du and Stewart 1992) and semi-analytical models (Ng and Aguilera 1999;Ozkan and Raghavan 1991a,b).…”