Abstract
The Formation Pressure While Drilling (FPWD) has been widely used in the industry in different downhole environments for formation evaluation purposes – pressure gradients, fluid identification and contacts, and reservoir pressure management. However, there is a niche application of this tool that no wireline formation tester could provide – real-time drilling optimization.
Drilling reservoirs with abnormal high pressure is a complex process. The overpressure can cause a well to blowout or become uncontrollable during drilling leading to catastrophic outcome if too low mud weight is selected. On the other hand, too high mud weight can lead to lost circulation, decrease in rate of penetration, stuck pipe and most importantly it can damage the formation hindering productivity of the well. The monitoring of actual pore pressures in real-time with FPWD tool is critical to make proper mud weight adjustments, rather than relying on inferred pore pressure from either predictive models or offset wells.
The paper discusses a case study of application of FPWD in a well drilled in a fault block never drilled before, where pore pressure data from wells located in nearby blocks indicated that there may be abnormal high-pressure zones. Pressure measurements were performed while drilling after every 100 m upon reaching a certain depth. Since downhole BHA included gamma ray and resistivity tools along with FPWD tool, the combination of this data was used to select the intervals to be tested.
The study shows how real-time pore pressure measurements helped to adjust mud weight from 1.45 to 1.80 sg to avoid the risk of formation fluid influx into the well, optimize drilling operations and, based on the acquired results, an operator decided on the total depth (TD) of the well. Since pretests were performed at targeted layers, formation pressure and mobility data also aided in reservoir characterization.
The paper presents the first successful application of FPWD technology in Russia and Caspian region for drilling optimization purposes in overpressured reservoirs. Real-time data availability allowed making quick operational decisions to safely drill the well until planned TD.
