Estimation of sand production volume for weak to moderate strength sandstone reservoir using finite element method

Abstract

The aim of this research work is to develop a new non-liner constitutive model and novel technique to estimate sand production volume for weak to moderate strength sandstone reservoir rocks. Sand production due to rock failure can have a severe impact on the economics of an oil or gas field where the downhole or surface components erosion due to sand production can lead to loss of well integrity and hydrocarbon leakage. Furthermore, if the drawdown increases, sand production volume is becoming more prevalent. To facilitate best sand management over the life of a field, an accurate prediction of sand production volume is required to increase productivity of the well at low operating cost. The current method is unable to fully cater the industry’s need as most of the work related to sand production models are developed for onset failure but little on sand production volume estimation. This research work was initiated to fill this industry gap by developing a new technique for sand production volume estimation. The selection of failure criteria has a big impact on accurate predictability on sandstone failure and sand production volume prediction, thus an investigation on the needs for a new non-linear constitutive model has been performed. A new constitutive model has been developed and validated to assist numerical model validation. A new workflow and method have been developed for accurate sand production volume prediction. A novel approach has been developed in this study to enable continuum Finite Element Method (FEM) model to replicate as discontinuum model. This was achieved by creating a new computer code to communicate with FEM solver to remove all failed grid cells (mesh) and allow stress stabilisation around perforation cavity. This technique is known as progressive perforation cavity failure and stabilisation (PPCFS). The invented technique was tested on both laboratory test and field data. A 3D FEM model developed using actual well and field data was used to validate and evaluate the robustness of the developed workflow and method. The outcome of this study shows that the new constitutive model has better predictive capability on both the sandstone failure and sand production volume. The combination of the newly developed Assef-Surej-Ariffin (ASA) constitutive model and the PPCFS FEM method is able to predict onset failure of sandstone and sand production volume accurately within 2.5% and 5% error margin respectively when compared to actual laboratory testing. Meanwhile, field data yields an excellent match with actual observed sand production volume in the field within 3% error margin. The parametric analysis concluded that rock strength has proportional impact on sand production volume. Meanwhile the combination of borehole deviation, smaller perforation diameter, and oriented perforation could reduce the sand production volume. This method also can be used to optimize the controllable parameters (well and perforation design) to eliminate sand production completely provided that the compressive strength and far field stresses of the reservoir permit. Therein, it can be concluded that the developed model is novel and able to assist the oil and gas industry to estimate the possible producible sand volume for their planned drawdown for sandstone reservoirs using the geomechanical properties.