Abstract

Previous researches on sand production prediction were focusing on when sand will be produced during depletion basing on some mechanics analyses but the amount of sand production was ignored. Recently more and more researches are focusing on the simulation of heavy oil sand production processes. For unconsolidated heavy oil reservoir which employs sand production to enhance production, the amount of sand production is of great importance because too much sand production may cause formation collapse while too less sand production may not maximize well productivity. In view of this, based on both fluid flow modeling and reservoir mechanics concepts, a coupled heavy oil / sand particulate flow/reservoir elasto-plastic deformation model is used to simulate sand production, oil production and reservoir deformation. With this model, we can determine an optimum flow rate which will not cause formation collapse while maximizing well productivity.

Introduction

Heavy oil sand production as an important production enhancement measure has been used in the primary development of heavy oil reservoirs in Canada for a long time.

Because the production of sand may leads to the change of formation flow parameters such as permeability and porosity and mechanical parameters such as cohesion. It also causes near wellbore stress redistribution. So, sand production is a very complicated process involving both fluid flow and geomechanical problems. In order to simulate the effect of sand production and productivity enhancement, simulation of the physical process needs to be done. Because of the long history of cold production, the simulation of cold production is becoming mature and a lot of excellent work has been done by experts in Canada and elsewhere around the world.

Wang [1] first developed a model to predict sand production in heavy-oil reservoir in Frog Lake and Lloydminster, Canada. It is believed that reservoir depletion induces stress concentration around the wellbore and large drawdown causes foamy oil zone, in which large drawdown and seepage force are created and causes sand production. A fully coupled geomechanical, foamy oil now model was developed. Sand production is assumed to start when the effective radial stress is equal to the tensile strength. Later Wang [2] also developed a coupled reservoir-geomechanical model to simulate the enhanced production phenomena in both heavy oil reservoirs (Northwestern Canada) and conventional oil reservoirs (North Sea). It is believed that the production enhancement is contributed (I) by the reservoir porosity and permeability improvement after a large amount of sand is produced, and (2) by higher mobility of the nuid due to the movement of the sand particles. Once the reservoir formations yield plastically, loose sand particles can be generated. Sand production has been postulated as a critical condition when the effective radial stress reaches the tensile strength or when the plastic strain reaches the critical plastic strain. Recently, Papamichos et al [3] and Stavropoulou et al [4] also provided similar models to simulate sand production. Later Papamichos et al [5] applied this model to interpret sand production from a North Sea reservoir.

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