Numerical simulation of formation damage by drilling fluid in low permeability sandstone reservoirs

Weiwei He,Zhiqiang Liu

doi:10.1007/s13202-021-01137-x

Abstract

Understanding the formation damage surrounding the well during the drilling operation is the key to predict damage degree and protect the formation in oil/gas reserviors. Based on the core drainage results, we obtained an empirical relationship between the invasion volume of drilling fluid and permeability reduction of formation. Furthermore, the equation is incorporated into a commercial reservior numerical simulation simulator to characterize the behaviors of drilling fluid invasion process. The results show that, although the invasion depth in low permeability reservoirs is short with the range of 1.7–2.5 m, the effect on recovery factor is significant due to the narrow seepage area in the near fracture region. When considering the formation damage, the pressure in the near-fracture damage region drops sharply, leading to a three-stage shape in pressure distribution curve. In addition, we found that high viscosity and low density oil-based slurry and shorter soaking period are conducive to decrease the formation damage during drilling operation. This work reveals the fundamental mechanisms of formation damage in low permeability reservoirs, which is a theoretical basis in formulation drilling fluids and optimization operation parameters.

Highlights

The oil/gas in low permeability reservoir, as one of the important fossil fuels, has a great deal of resources in worldwide (Xu et al 2016)
The formation damage by drilling fluid in low permeability reservoirs can be classified into three types:
Because the matrix in the near-well region is fully saturated with drilling fluid, the formation damage is severe and the permeability reduces to the lowest limit, in which the permeability of high permeable layer reduced to 14.6 mD and the permeability of low permeable layer reduced to 5.2 mD

Summary

Introduction

The oil/gas in low permeability reservoir, as one of the important fossil fuels, has a great deal of resources in worldwide (Xu et al 2016). The reservoir formation can be severely damaged due to the invasion of drilling fluid during the drilling operation (Coskuner 2004). The formation damage by drilling fluid in low permeability reservoirs can be classified into three types:. In this work, based on the results of core drainage experiments, an empirical equation between the permeability reduction and the invasion volume of drilling fluid is obtained. The equation is incorporated into a commercial simulator to numerically characterize the invasion behaviors of drilling fluid in low permeability reservoirs. We quantified the effects of formation permeability, properties of drilling fluid (viscosity, density, etc.), and the soaking period on the damage radius, invasion volume, skin factor, and reduction degrees of recovery factor. Our investigation is conducive to predict the formation damage degrees and propose the corresponding strategies to mitigate the formation damage during drilling operation

Simulation methodology

Results and discussion

Conclusion