A coupled single well geomechanical- gas/sand flow simulator is developed to study sand production in gas producing wells. In the gas flow model, gas flow can be either Darcy or non-Darcy flow, porosity and permeability can vary during sand production. Sand particles are assumed to have the same velocity as gas, and they are generated in the failure region. In the geomechanical model, the formation rock is assumed to obey Mohr-Coulomb failure criterion and once the formation around wellbore is yielded, sand may be produced from the failure region. The gas/sand flow model and geomechanical model are coupled and solved implicitly through iteration. Sensitivity analysis is performed to study the effects of various factors on sand production and strategies for managing sand production are indicated through the analysis.
Gas well sand production is of primary concern in certain formation because of the erosion damage to downhole tubular goods, surface facilities and the disposal of the produced sand. Controlling of sand production using gravel-pack, frac-pack and some other methods are particularly expensive.
In order to make decisions, it is necessary to use some models to predict when sand production may occur and then adjust the well production rate or bottomhole pressure. If sand production cannot be controlled by adjusting those parameters, then it is necessary to use some sand control techniques such as gravel-pack, fracpack. In order to model sand production, we should first know when sand production may occur and then how much sand may be produced without sand control.
Two types of sanding prediction models were published so far. The first type includes those studying perforation tunnel stability and predicting when sand production may occur. Those models can only be used to predict the onset of sand production but not its time behavior. The other type includes those considering coupled fluid flow and reservoir elasto-plastic deformation. The following is a brief review of the literature and sand production modeling:
Morita et al provided both analytical method [1] and numerical method [2] to simulate the perforation tunnel stability and the effect of perforation geometry on tunnel stability and hence sand production. There are three types of perforation instability: a shear failure, a tensile failure during loading, and a tensile failure for unloaded rock. The shear failure type sand problems occur for a weak formation if the effective in-situ stress is high or the well pressure is low. The tensile failure during loading occurs for an abnormally high pressure gradient around a cavity due to highly damaged permeability or a sudden increase in flow rate. A tensile failure for an unloaded zone occurs with a relatively low flow rate if the previous drawdown before a well shut-in exceeds the critical drawdown. Tronvoll [3] proposed a 3D numerical model based on non-linear continuum theory to predict elastic deformation and the onset of non-linear surface deformation of a model perforation cavity. It is said the onset of sand production is mainly controlled by the formation strength and the magnitude of the in-situ stresses. Later, he also studied the effect of perforation damage on sand production [4] and sand production in ultra-weak sandstones [5]. Hilding et al [6] also used the perforation tunnel stability analysis to avoid potential sand production. Santarelli et al [7] used a 3D Finite Element Code to model the near wellbore region of a perforated well. The stress concentration around perforations is computed and related to the possibility of reservoir rock failure and hence to sand p
