Title: Pressure transient behaviours of vertical wells in low permeability reservoirs with threshold pressure gradient

Authors: Wenshu Zha; Daolun Li; Yishan Zeng; Detang Lu

Addresses: Hefei University of Technology, No. 193, Tunxi Road, Hefei, Anhui, 230009, China ' Hefei University of Technology, No. 193, Tunxi Road, Hefei, Anhui, 230009, China ' Hefei University of Technology, No. 193, Tunxi Road, Hefei, Anhui, 230009, China ' University of Science and Technology of China, No. 96, Jinzhai Road, Hefei, Anhui, 230026, China

Abstract: Many studies show that the threshold pressure gradient (TPG) is physics behind the upwarp of pressure derivative curves in intermediate and later time by using superposition principle to solve mathematics model with TPG, which misleads us to a dilemma: although TPG can match the measured build-up data, the interpreted TPG does not accord with reservoir development. Our research shows that this dilemma is caused by wrongly applying superposition principle to non-homogeneous equation. In this paper, a fully implicit numerical scheme is developed to solve the flow model incorporating TPG and is used to study the error caused by wrongly using the superposition principle. The error is so big that the results based on superposition principle are totally wrong and lead to dilemma. Therefore, the main contribution of this paper is that the physics behind upwarp of derivative curves is not TPG, and we should go further to find out the true flow mechanism in the low permeability reservoirs. [Received: May 24, 2017; Accepted: September 30, 2017]

Keywords: threshold pressure gradient; TPG; low permeability reservoir; superposition principle; numerical solution; homogeneous equation.

DOI: 10.1504/IJOGCT.2018.093131

International Journal of Oil, Gas and Coal Technology, 2018 Vol.18 No.3/4, pp.279 - 304

Received: 24 May 2017
Accepted: 30 Sep 2017
Published online: 10 Jul 2018 *

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