Permeability enhancement , which is due to the sand produced from disturbed zone around wellbore, is the key mechanisms to improve the oil production rate in CHOPS.
This has lead to the demand for the accurate predicting methodology to the amount of sand production. In this paper, a new integrated spread-erosion numerical model was developed, in which sand is produced from disturbed zone, and its dynamic performance depends on the spreading of wormhole which is determined by the pressure gradient between wormhole tips and reservoir. Also sand is fallen off from sand wall which is depends on the erosion parameter. Mechanisms case study shows that sanding will continue for a while even when the spread of disturbed zone is pause, as sand wall erosion is another source of sanding. Compare with wormhole lab testing data and sanding well monitoring data, sanding dynamic performance which is simulated by this new model is more reasonable and more reliable.
CHOPS is often associated with high drawdown and solid production. Understanding of its mechanisms and affect factors is very important to the field operations to make sure the oil production could be enhanced. There are three types of mathematical model: skin factor, mobile permeability and wormhole spreading, which are applied in most commercial simulators to describe the dynamic performance of sanding and oil production in CHOPS.
Production enhancement from sanding is substituted by a negative skin factor. It's simple and runs fast. However, the performance of sanding and wormhole spreading in the disturbed zone cannot be study through this model. Furthermore, it is difficult to determine a reasonable skin factor to match the real sanding case.
Theoretically, there is a relationship between porosity and permeability. Assume a distance from the disturbed zone boundary to the wellbore sand wall, and then the change of porosity and enhancement of permeability from sanding is evaluated. Finally, the production rate could be predicted. However, the behavior of spreading in disturbed zone is not shown in this model and the production rate is estimated incorrectly either.
Based on the fractional and geomechanical theories, the wormhole network simulator, in which the dynamic spreading performance is involved, is developed. Sanding behavior is corresponding with the spreading of disturbed zone, and oil is produced from wellbore and wormhole network. In this model, sanding is happened only at the tips of wormhole. However, it is verified by core experimental data that sand is also produced from sand wall in wormhole. Erosion is ignored in this wormhole spreading model.
More complicated methods are developed and presented by researchers and sanding experts in recent years. Rock geomechanics and reservoir seepage mechanisms are fully coupled, in which the spreading of disturbed zone, dynamic sanding performance and oil production rate are predicted quantitatively. However, these simulators are not flexible enough during applied in field as their highly complex with low running efficient. Furthermore, some geomechanical input data, which are required in these models, are not available in field. As a result, forecasting of sanding behavior and production performance through these models are affect by lots of uncertain factors.
Based on the analysis of sanding experiment and field monitoring data, sand is produced from 2 sources, one is the spreading of wormhole tip due the pressure gradients exceed the residual cohesion of rock; another is the erosion from sand wall in wormhole.