NUMERICAL MODELLING OF MULTIPHASE FLOW IN POORLY CONSOLIDATED SANDSTONE RESERVOIRS

Abstract

The oil and gas production from reservoirs of weakly-consolidated or non-consolidated strata is often accompanied by sand production. The sand production phenomenon is encountered in many oil fields of Kazakhstan, such as Karazhanbas, North Buzachi, Kalamkas, Zhalgiztobe, and Kenkiyak. It can dramatically affect production flowrate, damage downhole and surface equipment, raise critical failure probability. Understanding and predicting the sand production process are one of the main challenges for safe and profitable hydrocarbon production in Kazakhstan and worldwide. The technical and operating procedures as drilling, perforations and hydrocarbon production, the stresses around the rock materials increase and fulfil the failure criterion and material can change from elastic to the plastic state. The plastic zone is an important part of the sand production models and is still not understood. In this research, the plastic zone properties during the perforation process of the material were investigated by the Discrete Element Method (DEM) approach. The contact model for weak sandstone developed by (Rakhimzhanova et al., 2018) was used to mimic cement material behaviour. The perforation process created a damage zone of about 3𝑟 to 4𝑟 thickness of the unbonded particles with nearly complete bond breakage in this zone, where 𝑟 is the radius of the perforation tunnel. A compacted lower porosity zona 2𝑟 to 4𝑟 (minimal porosity is 30.5%) was embedded inside the perforation damage zone. The reservoir and fluid properties can significantly impact sand production. The effects of fluid type and fluid-phase composition on sand production was investigated using coupled Computational Fluid Dynamics and Discrete Element Method (CFD–DEM) approach. The coupled CFD-DEM multi-scale models, where fluid is considered single-phase or multi-phase, are implemented to investigate the bond breakage behaviour during sand production. It was found that very different microstructural changes for light and heavy oils inside the sandstone samples. Light oil facilitated more significant particle movement and porosity change within the damage zone around the central perforation tunnel. The heavy oil outflow mobilized a more significant proportion of the sample’s particles and would lead to more severe sand production. The CFD-DEM simulations with Karazhanbas oil field properties (reservoir pressure 4.5 𝑀𝑃𝑎 and overburden stress 5.9 𝑀𝑃𝑎) were conducted. It was found that sand production with heavy oil provides a high bond breakage rate, and this behaviour is changed only after gas/water breakthrough. The fingering effect and formation of new channels due to injection of more mobile fluid were observed. The CFD-DEM models have been compared qualitatively with the semi-analytical model results and laboratory data.