Transient Pressure Response of Horizontal Wells in Layered and Naturally Fractured Reservoirs With Dual-Porosity Behavior

Abstract

Over the last decade, extensive studies have been carried out on the behaviour of vertical well tests in dual porosity systems. Although some research has been done on the horizontal well counterpart [1-51, most of this work has just dealt with a specific situation. No systematic investigation has been yet reported on the behaviour of transient horizontal well tests in dual porosity systems. One of the major purposes of this study is to bridge this gap. An approximate analytic solution in real time space modelling the horizontal well test in a dual porosity reservoir is given. Responses for both pseudo-semi-steady-state (psss) and transient dual porosity models in linear flow are investigated. For homogeneous reservoirs the theory of pressure transient analysis for horizontal wells suggests that linear flow should be the dominant flow regime when Llh is large and the loglog derivative diagnostic would frequently exhibit a half slope. However field examples quoted in this paper do not show this feature nearly as often as one mifiht anticipate and unexpectedly quarter slopes have been observed in many cases. The paper particularly illustrates how a bilinear flow can arise in the case of a horizontal well in a transient dual porosity (fractured or layered) reservoir.

Bilinear Flow in Horizontal Wells in a Homogeneous Reservoir: Huntington Case Study

“…Briceño et al (2002), it was reported that a bilinear flow regime is observed in well tests for horizontal wells that are overlying or underlying formations with a shale barrier. This was attributed to the transient double porosity behavior as explained by Du and Stewart (1992) above.…”

“…Unless mentioned otherwise, all the following models are for a horizontal well length, L of 3000ft, an average horizontal permeability, k H of 50mD and a total reservoir thickness, h of 120ft. Du and Stewart (1992) claimed that a transient double-porosity behavior during intermediate-times can lead to a bilinear flow regime. For a horizontal well within a higher-permeability layer overlying a lowerpermeability layer, this is analogous to a dual-porosity system where two regions of different storativity and mobility exist.…”

“…Du and Stewart (1992) introduced the concept of bilinear flow due to transient double porosity behavior in a horizontal well. However, their derived equation results in the cancellation of the fracture permeability term:…”

“…This is recognized by a quarter-slope (¼) in a log-log plot of the pressure and derivative. Du and Stewart (1992) illustrated how bilinear flow in a horizontal well can arise in a transient dual-porosity multi-layered reservoir. It is explained that in the case of a horizontal well within a thin high-permeability layer overlying a low-permeability layer, linear horizontal flow in the high-permeability layer is being supported by linear vertical flow in the low-permeability layer during intermediate-time.…”

Pressure Transient Behavior of Horizontal Wells Intersecting Multiple Hydraulic Fractures in Naturally Fractured Reservoirs

“…In the first paper published on this subject, de Carvalho and Rosa (1988) used the pseudosteady-state flow conditions in matrix blocks with the s → s f (s) transformation to derive the pressure transient solution for a horizontal well in a naturally fractured reservoir. After the de Carvalho and Rosa (1988) solution, many more solutions have been published in the petroleum literature using the → s f (s) transformation, while varying the matrix block shape and matrix block flow condition, and adding the interporosity skin factor for the matrix (Aguilera and Ng 1991;Du and Stewart 1992;Williams and Kikani 1990), in addition to the more recent papers by Abdulal et al (2011), Brohi et al (2011), Guo et al (2012, Ketineni and Ertekin (2012), Lu et al (2009), Medeiros et al (2007, 2008, 2010, Nie et al (2012a, b), Torcuk et al (2013).…”