A novel method for preventing technical challenge during drilled cuttings/produced water reinjection: An injection rate management tool

Abstract

Drilled cuttings reinjection (DCRI) is arguably the most cost-effective technique for disposing of drilling wastes, especially under the zero-discharge policy. However, there are many failed operations due to technical issues related to surface pumps and annular pressure. Currently, there is no sophisticated model for predicting an optimum injection rate that prevents technical failure during DCRI. The practice of using an arbitrary rate is not based on sound engineering principles and may be unable to prevent annular or pump failure. This is because operators do not relate the injection rate to the Maximum Allowable Surface Pressure (MASP) and/or the Maximum Allowable Annular Surface Pressure (MAASP). Due to these limitations, operators seek to find new methods to handle DCRI through the annulus. Thus, this study was carried out to derive a model systematically for the optimum injection rate to prevent technical challenges during DCRI. The components combined include the mechanical energy balance (MEB) and the model for hydraulic horsepower (HHP). The MEB between the wellhead and the annulus was used to derive a model for the annular pressure. Mechanical equilibrium between the STP and the MASP was used to generate another equation, based on the HHP. Then, the new expression was substituted into the annular pressure model. Lastly, the optimum rate was derived based on mathematical principles. The results applied to Well B of the Niger Delta showed a value (2.95 Bbl/min or 675.37 m3/day) that is consistent with the existing field database, and outperformed other related models for flow rate. Simulation results showed that the annular size (78.8%), rheological parameters (12.4%), and MASP (2.9%) were the main factors that affected the optimum injection rate. Thus, we can apply a higher injection rate in larger annuli compared to smaller ones, and to maintain annular pressure simply ensure uniform annulus devoid of erosion/thermal effects.