Inflow Performance Analysis of a Horizontal Well Coupling Stress Sensitivity and Reservoir Pressure Change in a Fractured-Porous Reservoir

Mingxian Wang,Weiqiang Li,Ruiqing Ming,Wenqi Zhao,Zifei Fan,Lun Zhao,Chengqian Tan,Juan Zhang,Zhongwei Wu

doi:10.2113/2021/7024023

Abstract

Abstract Stress sensitivity has always been a research hotspot in fractured-porous reservoirs and shows huge impacts on well productivity during the depletion development. Due to the continuous reservoir pressure change, accurate evaluation of stress sensitivity and its influence on well productivity is of great significance to optimize well working system. Taking horizontal well trajectory as the research object, the principal focus of this work is on the analysis of inflow performance for a horizontal well coupling stress sensitivity and reservoir pressure change in a fractured-porous reservoir. Firstly, a relationship between permeability damage rate and stress sensitivity coefficient was established to quantitatively evaluate the influence of reservoir pressure and stress sensitivity on reservoir permeability. Secondly, considering stress sensitivity and reservoir pressure drop, a set of practical productivity equations were derived for a horizontal well in a fractured-porous reservoir by adopting the equivalent seepage resistance method. Finally, the influence of relevant important factors on the inflow performance of horizontal wells was discussed in depth. Results show that a positive correlation exists between stress sensitivity coefficient and maximum permeability damage rate. At the same maximum permeability damage rate, high initial reservoir pressure corresponds to low stress sensitivity coefficient. In general, stress sensitivity coefficient mainly ranges from 0 to 0.2. Reservoir pressure change drastically affects the production dynamic characteristics of horizontal wells, and both the inflow performance curve and the production index curve decline and shrink as reservoir pressure decreases. Stress sensitivity is negatively correlated with horizontal well productivity, and the inflow performance/production index curve bends closer to bottom-hole pressure axis, and an inflection point can be observed with the aggravation of stress sensitivity. In addition, horizontal wellbore length and initial reservoir permeability also show significant effects on the inflow performance and are positively correlated with well productivity. For water cut, it has little effect on the well production when bottom-hole pressure drawdown is low, but its effect gets stronger as the drawdown becomes higher. Meaningfully, depending on these newly established productivity equations, a reasonable production system can be quantitatively optimized and achieved for the horizontal wells in fractured-porous reservoirs.

Highlights

Under the influence of tectonism and diagenesis, natural fractures are often developed in various reservoirs, which are referred to as fractured-porous reservoirs, including sandstone fractured reservoirs, glacier fractured reservoirs, carbonate fractured reservoirs, and igneous fractured reservoirs [1, 2]
Depending on the above productivity equations established in fractured-porous reservoirs, various inflow performance relationship curves can be drawn out to investigate the productivity change of horizontal wells incorporating stress sensitivity and reservoir pressure change
The influences of stress sensitivity and reservoir pressure change on inflow performance and production index were discussed in detail

Summary

Introduction

Under the influence of tectonism and diagenesis, natural fractures are often developed in various reservoirs, which are referred to as fractured-porous reservoirs, including sandstone fractured reservoirs, glacier fractured reservoirs, carbonate fractured reservoirs, and igneous fractured reservoirs [1, 2]. Fractured-porous reservoirs often show a degree of stress sensitivity during depletion development, leading to a decrease in reservoir permeability and well productivity [3,4,5]. Many laboratory tests show that for fractured-porous reservoirs, porosity and permeability of matrix and natural fracture decrease with the increase of overburden pressure and effective stress, and the permeability damage of fracture system is more serious than matrix system under the same effective stress increment [12,13,14]; (2) rigorous theoretical derivation by defining stress sensitivity coefficient to establish seepage theory of deformable medium reservoirs. Nur and Yilmaz [15] first defined stress sensitivity coefficient to quantify permeability variation Depending on this newly defined parameter, Kikani and Pedrosa [16] derived a permeability formula with respect to pressure change in the form of exponential function:

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Results

Conclusion